2seater

Lower fuel pressure now makes sense for the injector size. That would make them about 29.5# injectors @ 3 bar, about the same as used in a GN. Is it possible Philips plugs are simply wet? On some of the older GM ignitions, like the HEI, it won't fire into a shorted or wet plug.

Did you lay a straight edge across both the upper and lower to check for flatness? I think the seals you are talking about are the throttle body heating passages? It appears to be a pretty good design that shouldn't require any help from sealants. I agree with the other post that the Permatex or whatever was used on the manifold may have prevented them from being "squashed" properly? I would doubt this would cause the bogging problem, as you didn't seem a have vacuum leak, and if the coolant leak went external only, it won't do any real harm. If it leaks into the engine, that isn't a good thing. Watch you oil carefully for contamination.

That part number is a Bosch injector. The information I have indicates that is a 28#/hr injector and comes from a Pontiac 3800. The one thing I could not find is the pressure where the flow rate was determined. Usually the default is 43.5 psi if not listed. That should be about right, a little more than 50% larger than stock. No problem there.

The tables would seem to be back asswards I don't remember exactly where the break points were for the L67 engines but I think the initial ones were like 205hp, then they went to 225hp before the later Series II with 240hp. Two things come to mind. GM is treating the output signal differently from one year to the next, meaning the gm/sec reading is a reference, not a real number, or the signal is modified from the MAF (I found this can be manipulated easily), again making the signal a reference number only? It doesn't make sense since they have the ability to change everything to make the signal reasonably accurate and the computing power to use it? The later model L67 should definitely run beyond that limited MAF table, no matter what conversion I use for the mass of air. Once I corrected some errors in my flow bench and Excel formulas, I find the four 3800 MAF sensors I have (including the TPI L27), max out (10.4kHz) between 300 - 318 cfm, converted to 171-183 gm/sec (34.4 grams/cu.ft) at my test conditions). My numbers are close enough to seem to indicate the MAF readings "should" be real numbers. There is probably some manufacturing tolerance, and the MAF signal isn't entirely stable, it floats around a bit, no matter what the inlet tract looks like, so I am relying on averaging several sensors to get decent numbers. Did I just luck out getting mine to run reasonably well using essentially the same platform? The only difference between Philip's car and mine are the balancer/CPS and the MAF, aside from the way the boost is made. Greg and Don have running S/C's, although they were complete engine swaps. Strange behavior.

I don't know what Philip's MAF scale might be, but it looks like a dead ringer for the L27 one I have. If it is the same, my testing indicates it is almost exactly the same as the stock LN3 flow rate vs frequency. It looks like you guys have narrowed the problem area to a timimg issue. Low timing without boost to speed the flame front would certainly cause what seems to be happening. The one thing lacking in the Reatta diagnostics is the LV8 reading. It would be nice to have a scantool connected to see what cell the ECM is reading. I would guess GM spaced the rings on the balancer differently to prevent them being switched, but the reason baffles me? The internal construction of the engine indicates the only difference is that some of the s/c engines used a floating piston pin. Maybe something else?

I don't think the balancer moving is what is suspected, I think it is the phasing of the windows to the keyway. I don't know why GM would have changed it from the N/A engine, since the operating system is the same, but it is simply an avenue to look into. Fuel or timing could cause the problems you are experiencing, so we are looking for a way to narrow the search. We don't have conventional timing marks, and with a stock system they aren't really needed, but you aren't stock anymore. The cam sensor isn't used for timing, only the reference from the crank sensor. If it is off, nothing downstream will be right. If the regulator is the one I think it is, it can be taken apart. There is a snap ring on the top. Remove it. I grabbed the top of the vacuum can with a channel lock pliers and rocked it back and forth while pulling straight up. It is sealed internally with 0-rings and it didn't want to come out. Once out, the inside of the can can be viewed for contamination. The fuel enters the side of the can, travels upwards through the screen, which is removable, into the area below the vacuum diaphragm. The operating mechanism is pretty well protected above the screen, but there could be old deposits from stale fuel out of sight. The fuel regulator pintle is out of sight but you can spray carb. cleaner up the central return passage and through the outer passages the screen normally covers.The can where the regulator sits can be cleaned out, pretty much a manual operation. The central passage in the can connects to the return line to the fuel tank. Disconnect the fuel line and spray carb cleaner through that central passage, which should flush out anything that may be blocking it. As for what it should be doing when the vacuum is disconnected is exactly nothing. It should give you a static fuel pressure reading, neither rising or falling when the engine is running at any speed. Personally I don't like the small diameter, construction and long length of that fuel rail, but apparently it works okay. It may cause a small change in fuel pressure just from change in demand, but that should only be momentary and should return to the base reading, that same as what it would be with the key on and engine off. If the injector is a Bosch, the part number should start with 280, likely followed by 150 followed by another three digits. It might be a Rochester or possibly Motec injector. Any numbers would be helpful.

I think you may be on to something. The windows in the shutter wheels wouldn't have to be off by much to radically change the timing, at least confuse the ECM. The timing is way retarded, for a light load situation, but that may not be valid either if the signal itself is offset? The timing mark idea sounds like a good one, although it will take some figuring. The light will flash twice normal speed with the type of ignition we have, but it should still be valid. The good thing is it won't matter if the piston is on compression or exhaust, just as high as it will get. A timing light with a built in advance/retard would allow reading the timing advance directly without offset marks. The ECM is certainly capable of running a low boost engine, mine has run over 20k miles, and economy is as you say. High loads are still a problem (knock), but below 5# of boost or so is handled just fine. My tuning with Ryan's help continues soon. It sounds like the fuel is connected correctly, but I am still wondering why the fuel pressure acts the same with or without vacuum, it shouldn't do that. I am almost positive the fuel rail is the same as the L27 n/a engine. It does look like it would be impossible to force fuel backwards through the regulator, the return passage from the regulator is quite small, around 3/16" and it would require a bunch of pressure on that small area to force it open, unless of course it is stuck open? The one I have is marked 3 bar on the outside of the little vacuum can part, so base fuel pressure should be around 43.5 psi if it is the same one. The one I have is from a junkyard manifold (TPI), and I pulled the regulator guts from the housing. It was full of crud, but it also contains a filter element to keep contamination from the actual internal workings, and that was clean. The odd thing when I tested it is the vacuum port will sometimes hold vacuum and sometimes not? Granted it is a junkyard part, but I wonder if there are possibly two problems in Philip's case? Philip, can you get the part number from the injectors? If it is a Bosch, it will be marked on the side of the body where the electrical connection is. I just hope to confirm the injectors are what we think they are.

The injector pulse width seems very high for idle? Granted the fueling numbers look much better, but the fuel pressure change, or lack of it, when disconnecting the vacuum is definitely not right. Did you leave the vacuum line disconnected (plugged) and try the "rev test"? The pressure should not change, or change very little as the demand changes. The glowing manifolds are either retarded timing or dead lean, as suggested by others. The timing seems a bit low for idle, that is more like the timing for full load and boost, but it isn't retarded enough to account for the glowing pipes. If the O2 locked around .67 that's awfully lean for a high load, but I don't think your are loading the engine much unless it is in gear? Is it possible that the fuel rail is plugged or something? If the pump is new, and the filter clean, the pressure appears to be acting oddly. The pressure tap is right on the lower part of the regulator, right? If that is the case the fuel would have to pressurize the entire rail first and if the pressure remains constant with the vacuum disconnected, idle and revved, the rail "should" be flowing okay. I know you said you had the lines backwards once and reversed them. Is it possible they are connected backwards? The return line should be connected to the regulator. The rail pressure is regulated on the outlet end, not the inlet. Please disconnect both lines and place them in a small container to catch the fluid and momentarily make the pump run. Be careful of sparks and the force of the fuel flow. The pressure line must be connected to the non-regulator end of the rail. Ryan knows plenty when it comes to the tuning of the chip and it shouldn't be far enough off to cause these problems, and even though other problems may exist, like a massive vacuum leak, or plugged exhaust, it still sounds like a fuel delivery problem. The big bog sounds just like mine when the filter plugged. Do you have a vacuum gauge? A plugged exhaust will show up as a gradual decline in the vacuum reading at a steady elevated rpm, like below where the bog occurs.

I agree with Ryan 100% that you shouldn't use the LN3 MAF sensor, the construction is completely different, as can be seen, although my testing indicates the calibration is essentially identical to the LN3. The location of the O-ring being different will cause a vacuum leak as well as the sensor wires not being inside a symetrical opening. What are the two rows of numbers on the L67 MAF sensor? I don't suspect the MAF at this time, it appears to be the correct type, unless it is bad. I think you are working with a 1990 engine and ECM and this one will go into closed loop operation at 130* F, observed many times. Your fuel pressure reading still seems funky? Unless that regulator is damped somehow, the pressure should snap up and down when you blip the throttle. It will slowly change with a slow change in throttle, but I would think the pressure should actually do down at a constant engine speed of say 2000 rpm vs idle, since the engine vacuum at essentially no load should be higher. The only caveat is the s/c itself and the comment that it picks up the vacuum signal from below the blower. I think I remember you said the boost bypass is blocked in the closed position. Maybe there is a slight boost pressure, or a reduction in vacuum from the blower spinning? Tee a vacuum gauge into that line to see what it is seeing? Actually, just disconnect the vacuum from the regulator and plug the line. The fuel pressure should now be at a fixed value of around 3 bar, 43.5 psi, if the regulator is calibrated the same as the LN3, and it should not vary with engine rpm or whatever you do with the throttle. If it changes, something odd is going on. If it drops when you mash the throttle, fuel delivery is inadequate, for whatever reason. The higher fuel pressure should gradually move the BLM lower since the pressure and fuel delivery will be higher than normal. The O2 must be connected and up to temperature for this adjustment process to work and it will take a little while. The TV (throttle valve) cable controls the shift point on these transaxles. The modulator controls line pressure and shift firmness. They are apparently a little different than most mechanical transmissions in that the two functions are pretty much divorced from each other. On most systems the two items interact more with each other. With the cable disconnected I would expect the trans. to upshift earlier than normal. In theory it shouldn't do any harm, at least short term, but the s/c engine produces a lot more torque and early shift points will tend to place more strain on the system, and load the engine more than normal. Best bet would be to get it connected and adjusted properly. For your testing in park/neutral, it won't matter. For the record, I run Autolite 103 plugs gapped @ .048" with the stock Magnavox ignition. This is a cold plug, two ranges below stock. A 104 would be better choice, one range colder than stock as a good starting point. Just my opinion, but platinum plugs don't perform well in a boosted engine, especially Bosch, but there are a lot of different opinions on this.

Congratulations! Knew you were smart, just by what you have accomplished sort of "seat o' the pants". I think the TV cable connection you are looking for might just unbolt from the original LN3 throttle and could be transferred to the L67 t/b? The TPI throttle body I have looks to have the same linkage and connections as the LN3, including the little arm for the TV cable. It appears to be retained by a single nut and appears to be a discrete part that can be removed. The reason I say this is the '91 Buick would likely have the "E" transmission, but this t/b came from a Pontiac and they retained the mechanical transaxle for a couple of years beyond some Buicks. I would doubt GM used a dedicated throttle body for each of them.

I agree with Padgett that it is pointing more and more like the ECM is going south. There is a diagnostic "tree" in the manual to help sort it out, and if you cannot find a physical problem with the harness or connections, I would suspect the ECM. Since it seems to run for a while, and then acts up, you might try pulling the ECM and let it lay on the floor where it will stay cooler to see if the behaviour changes. Not the best but mine has been like that for two years to make it easier to change chips and I generally don't have a passenger The fuel pump won't set a code, but it is possible it has enough fuel for low speed and cannot supply enough for greater load. The only way to know for sure is to be able to watch the pressure while driving. The harness on the front of the engine is very common in the 'yards. You can wiggle the harness or connections if you are taking voltage readings with the engine off but unfortunately it would be very dangerous or impossible with it running. I do not know what the timing advance would read in diagnostics if the EST circuit fails? If it is something like 10 degrees or so while idling it is no doubt not working, but I do not know where the diagnostic will pick up the reading when in failure mode?

E042 is the spark timing circuit (EST). ECM, maybe, or possibly a harness problem? You tried a different ICM, one of the items the diagnostic tree leads to, the other is the ECM itself. Make certain you press on the ends of the connection at the ICM when you tighten the screw. The EST circuit is near one end of the plug (white wire on pin A)and it is quite long so the screw doesn't necessarily tighten it fully. The harness runs across the front of the engine and connects to the cam and crank sensors as well. There is another large connection near the right rear corner of the engine where it connects to the harness that goes to the firewall. The problem does sound like a possible crank sensor, but it is acting oddly for that to be the case. If one of the signals from the crank sensor is lost while running, it will continue to run but in the limp home mode. Usually if that is the case it will not restart, it must have both signals to start the engine. It may be temperature sensitive, causing loss of signal when hot and making the connection again when cooled? I do not believe that will set the code 42, it is either an open or short to ground on the EST wire.

I would bet the sensor in the S/C MAF is the same style as the TPI one I mentioned. I looked at the photos you have provided and the inlet to the S/C with the throttle body removed looks exactly like the inlet to the TPI manifold. That about 1/2" diameter hole to the rear of the throttle passage is the air inlet hole to the PCV system. All six of the MAF sensors I have are marked AFH50M, but they have three different suffix's -02A, -02C and -02E. All have different four digit numbers below. The TPI sensor is included in the six I have and it is one of the -02C sensors. The only external difference in the markings is the set of lower numbers is A1304 on the TPI sensor. My guess is the electronics is the same but the "A" prefix indicates a different internal construction for sealing and around the wires as I mentioned before. The only way to know for sure is to pull the sensor and see if it has the same consruction as the LN3. If it is the same, either the MAF passage is different than the TPI style I think it is, or, the sensor is the wrong one. I have included an attachment of the two sensors, the LN3 sensor on the left.

I think I remember you said the MAF sensor is the same on the S/C as on the LN3 engine parts you removed, right? In other words, this is the same two piece assembly as the LN3? The reason I ask, is I noticed something during the MAF flow testing I have been doing. I mentioned I have a TPI manifold from a '91 engine. The MAF and throttle body are in a single integrated housing. There are two differences internally and that is why I ask. There is a passage inside that appears to allow air into the engine for the PCV system, and I don't know where that passage could exist with the stock style LN3 MAF/throttle body, there doesn't appear to be room for it. The s/c manifold has the same integrated PCV system as the TPI manifold does. I know you used the correct gaskets for the s/c manifold, so that passage should be blocked off, and not cause a problem. If the MAF is the same style that is a single piece with the throttle body, the sensor itself is different. If the donor engine did not come with the actual sensor, the LN3 sensor will bolt on fine, but it will not seal correctly. The sensor wires will be in the correct location inside the passage, but the passage is not a true round tube like the LN3 MAF housing. It has a larger cross section in part of it and the correct sensor has a tubular surround over the sensor wires so when it is inserted it completes the circular cross section passage. The location of the O-ring, and the size are also different, so it will leak vacuum also. I know this may not be a problem and everything is as it should be, but a bad MAF signal will cause all sorts of driveabilty problems. It may even run better with it disconnected, although not as it should. One last thing, I noted during the air flow testing of the various style MAF's that the MAF/throttle body from the TPI manifold flows no more air than the stock LN3 setup. It looks more efficient, but the frequency response is the same, the flow rates are the same at the same frequency and it causes exactly the same amount of resistance to flow (depression). If the flow and sensor readings are placed side by side with the other five 3800 and 3300 sensors I tested, you couldn't pick it out.

The drop in fuel pressure seems a bit rapid. It will decrease over time, part of the reason for the two second pump run with the key on, it will not hold indefinitely. It is possible there may be a small leak in an injector or possibly the regulator is allowing the pressure to drop, for the same reason. It could be these items need to be cleaned? Injectors rarely fail, and if they do it will probably just not open. Professional cleaning can be done for a reasonable fee, but you can try this for almost no money: get a good carb cleaner, Berryman is cheap and works very well (a lot of others are junk IMHO). Remove the injectors, cycle them open and closed by applying 12 volts and ground to the connection and spray the carb cleaner backwards through the injector. This is messy and you need to protect yourself from the spray. You might make an adapter of some sort to sort of seal the spray tube to the end of the injector. Do not hold the injector open for long or it will get hot. You only need hold it open for a few seconds to get a couple of squirts through it. This is crude but it will help if there are deposits holding it open. Actually you can flow through it in both directions when open but there are different types of injectors and it may now want to flow backwards too easily. You can do the same for the fuel pressure regulator, just apply some vacuum to the nipple to open the regulator fuel passage and spray carb cleaner into the inlet and outlet for the fuel. I do not know what the base fuel pressure should be for that particular engine. Back around the time of our cars, the most common pressure was generally around 3 bar, or 43.5 psi, and it is still a common pressure where injector flow is rated, but, the manufacturer can manipulate fuel delivery by simply changing the fuel pressure within a small range. This allows a single injector to cover a wider range of engine sizes and demand by changing the fuel pressure. Later model engines tend to run higher pressures, in the 50-55 psi range or so. This is not so much for greater delivery, but the higher pressure aids atomization of the fuel (up to a point). High base fuel pressure does not work well on a forced induction engine as the fuel pressure should increase with boost and there is an upper limit where the injector flow becomes unstable at too high a pressure, usually around 65-70 psi for common injectors.

I think (Padgett can speak for himself of course) he means if the fuel pressure is too low, the ECM must compensate by increasing the injector pulse width to get the mixture where it should be. The adjustments show up in the long term fuel trim, or BLM. The injector is designed to flow a certain amount of fuel at a specific pressure. If the pressure is low, the injector will flow less than expected. The injector cannot adjust itself, it is either open or closed, controlled by the ECM. The ECM simply holds the injector open longer to get more fuel, but there are limits as to the amount it can compensate. Two things work against you at higher rpm, the fuel demand increases and the time to get the fuel into the engine decreases (two complete revolutions). At 5000 rpm there is only 20% of the time available to get the fuel into the engine as at 1000 rpm, plus there will generally be a greater demand, especially if accelerating, where the fuel mix will need to be richer than for cruise. Even if it can be made to run at low speed, the demand caused by accelerating will probably outpace the delivery capability. In short form, it appears you O2 sensor is working pretty much normally, your cross counts were decent, but if lack of fuel is the real cause, the O2 sensor can't do anything about it. The cross counts will slow down or possibly stop since it cannot get the engine to cycle rich and lean as it should. The money will be better spent buying a diagnostic tool like the fuel pressure gauge.

The only thing I can say about the fuel pump is I am using a Walbo 242, a 190 liter per hour pump, and it is plenty for your needs. The Walbro 307 (255 lph)has a higher flow but also a higher amp draw, especially if you go for the high pressure 307. I cannot find the website where I found mine but it was around $88. If you use the large pump, upgrade the feed wire to a larger gauge. The only other concern would be the large pump may have enough flow to overpower the size of that small fuel rail causing pressure to run high. Probably not a problem, but I think it is more pump than you need. The 190 liter pump will supply enough fuel for around 50 lb/hr injectors, way larger than what you will be running. I am curious about the fuel pressure reading? 30 psi at idle is somewhat low, you said when throttle is applied it jumps to 40? Is this when you blip the throttle or is this a steady elevated speed? The simplest is to simply pull the vacuum line from the regulator and plug it. This will be the zero vacuum setting, or the base spring pressure in the regulator. I confess I am not certain how the S/C pressure regulator is made, but if it is similar to the N/A engine, it is a simple diaphragm and spring. Vacuum pulls against the spring and boost pressure adds to it. A 10 psi change in the pressure roughly corresponds to a change of 20" of Hg vacuum. If the engine is generating 20" of vacuum at idle, it is very tight, I usually see about 18" of vacuum at warm idle. With the engine idling, and you pull the vacuum line from the regulator, the pressure should rise approx. 1 psi for every 2" of Hg vacuum. I looked at the small regulator from the TPI manifold, which looks like the same fuel rail as the S/C, and the regulator does appear to be asymetrical, the diameter of the fuel side is larger than the vacuum side, so the ratio may be different? It is the opposite of what I would expect for a rising rate regulator, where it increases fuel pressure at a faster rate than the increase in boost? As for the fuel filter, I agree to change it again even if low miles. It is easier and cheaper than the pump, and will be a good idea if you change the pump in any case.

I love the look under your hood Greg Mine is much "busier". As for the fuel rail; from the comparison of the N/A vin C, and the S/C fuel rail, the vin C rail is smoother and larger, IMHO it is superior. I have that same fuel rail as on the S/C engine from the TPI manifold I picked up, and the design looks restrictive? I hope to use the TPI lower manifold with a custom upper plenum and adapt the standard N/A fuel rail to it. The other situation regarding fuel delivery is the regulator. I do not know what the factory setting is for the S/C engine, and it is a different design from the vin C. The stock vin C regulator is a Bosch 237, base setting around 43.5 psi. I am using a Bosch 233 from a GN which has a lower base setting, in the upper 30's, and it is modified to allow adjustment above or below the factory setting. I suspect either style of regulator will do the same thing, normally it sees vacuum and reduces fuel pressure and will rise above base spring pressure in relation to boost pressure, in a 1:1 ratio. I do not have a clue where the S/C engine picks up the boost sensing. It would have to be from below the blower or it will not increase the pressure as it should under boost.

Uh, yes, fuel is critical, especially on a forced induction engine. A fuel pressure test set isn't too expensive, and can be used on other cars too. It is possible to make a substitute with a #4 JIC swivel fitting (for 1/4 hydraulic flare fittings) which will screw right on the fuel rail pressure tap, however, the core must be removed from the pressure tap. An inexpensive gauge, can be connected to the swivel with fuel injection rated hose. It can be made long enough to tape to the mirror or windshield. 100 psi gauges are available inexpensively or even a tire pressure gauge can be substituted, as long as the bourdon tube inside is brass or stainless. You must be very careful and it should be connected or disconnected when the engine is cool, it will dribble fuel. This isn't the best solution, but it will allow for watching the pressure while driving. The best and safest is a remote fuel pressure gauge with an isolator in between the gauge and the engine.

It looks fairly normal except for the integrator and BLM. As the rpm goes up and starts the erratic operation it could be at the top of the range for the amount of fuel it can add? The BLM should gradually increase with the integrator that high. The BLM shouldn't dance around at a fairly constant speed, although you could be at the border between two cells and the erratic engine behaviour is cycling between them, but I wouldn't think they should be that far apart in adjacent cells? I would guess that Ryan adjusted the range of the BLM for the L67 injectors, we did so several times to get mine close to the desired 128. If operating normally and it needs more fuel, the integrator will rise until it gets to a point where it will cause the BLM to move in the same direction and the process will start over. This process should happen over and over until the BLM has risen far enough to allow the integrator to cycle around the 128 number. It certainly looks like a fueling problem, there just isn't enough to allow for much acceleration, but you can sneak up on the speed with very light throttle.

I don't think intially reversing the fuel lines would kill the regulator, it's a pretty simple mechanism, just a spring and diaphragm, but it is certainly a good idea to check fuel pressure, even better if you can watch it while driving. I found a partially plugged fuel filter that only showed up under a good load (high demand). The pressure test after turning the key off may help to tell if an injector is stuck open but not if stuck closed or restricted. It is normal for the pressure to bleed down over a period of time. If it holds reasonable pressure for an hour or so there probably aren't any large faults. As for a scan tool, it only helps you record for a period of time but isn't any more capable than the onboard stuff. If the lack of performance is consistant, you will have plenty of time to watch different sensors while it is acting up. Greg is right that the O2 reading will fluctuate, but you can see if it is consistantly low, like staying below .5 volts. You could also watch the cross counts to see if it is going rich/lean as it should. The BLM and integrator will give you a good idea if it thinks it is rich or lean too. A simple vacuum gauge connected while the engine is at warm idle may help detect a vacuum leak. I usually see 18-19" of vacuum at idle. Just gather as much data as you can to help narrow the search. Crossed plug wires can make a difference and also crossed injector connections, but the injectors firing out of sequence will tend to get better as speed increases. It sure sounds like lack of fuel, mine would nose over pretty hard with the bad filter, but it could be timing as well. Just getting it running and somewhat driveable is a victory of sorts.

Considering the hybrid you created, you are doing pretty well up to now. There is no doubt it will require tuning. Do you have a scan tool to record all sensors? Hard to diagnose without more data. You could pick a few different sensors to watch and toggle between them in diagnostics to maybe get a handle on what the engine is asking for. Severe knock will make the engine lay over from reduced timing or more likely it wants more fuel. Does the TPS operate over the entire range it should? It may not be getting enough PE or power enrichment. While it won't make much difference, set the TPS as high as you can, like .42 for idle if possible. It may also require some run time to get the ECM programming to adjust to the new air flows and such. Watch the O2 reading if possible and see if it goes lean while trying to accelerate, a very low reading. If I remember right, you don't have EGR at this time. If it is disconnected, the E026 may show up (quad driver). You cound just connect the EGR solenoid assembly and tie it out of harms way. The EGR won't work but the ECM should be happier. Keep at it, but be careful about knock and running lean. Look at the simple and obvious stuff too. Make sure the spark plugs are on the correct coil outputs, vacuum leaks of course and check the fuel pressure. I assume you are using the injectors for the S/C engine. Do they all operate correctly? None are stuck or restricted from sitting?

Maybe my terminology is confusing, but what I mean is the main air passage through the LN3 MAF has no wires in it, but the secondary passage, about 3/8" diameter, houses the actual sensor, kind of an indirect sensing method. That is what I mean by the bypass theory. If the amount of air flowing through the sensor passage is modified, it will change the frequency response at the same total air flow. From the little investigation I have done, it appears the frequency range used for the L67 is the same as the LN3, but it has to flow more air. Apparently GM did use a larger 255 gm/sec table in only a few years of the initial L67 production and then changed the table back to similar to the LN3, even a little less. They even changed the ECM values assigned to different frequencies on seemingly identical MAF's. It seems very confusing. It looked like the MAF used on F14's s/c engine is the same style as the LN3. I don't think it is the same integrated MAF/throttle body as used on the L27 TPI manifold, at least it didn't look like one. That construction is different, also made by Hitachi. I have not flow tested the one I have yet. Initially I though the throttle bore was larger but I found it is the same as the separate throttle body for the LN3. The sensor itself appears very similar, although the sensor does sit in the center of the MAF passage in a sub passage. If it was a carburetor, the sensor would reside in the booster venturi with the main air flow around it.

I found my previous statement about the size of the MAF passages being the only variable,(aside from the sensor itself), is not correct . I found the frequency output vs the actual air flow can be manipulated by changing the size of slot from the sensor passage where it connects to the main passage. Decreasing the length of the slot (with foil tape for testing) lowered the frequency output at the same volume of flow. For example; in stock form, the MAF flows 151 cfm @ 8kHz. By covering approx. 1/2 of the slot, the air flow rate is 210 cfm @ 8 kHz. The bypass rate can be changed fairly easily, although calibration would be needed to match the new flow rate to the ECM. It appears the stock slot length is about 4 cm, maybe the L67 MAF slot length is different?

Trofeo, I think I understand the point you are trying to get across. The only way I can see the bypass theory would be true is if the main straight through passage is larger, and it may be. The Hitachi MAF passage for the actual sensor is tied into the main passage and all air must pass through the throttle body. From the flow bench testing I am doing, the throttle body itself make essentially zero difference in the air flow through the MAF. I have tested it by itself, attached to the throttle body and with and without the screen. The screen does decrease total flow by 3%-5% in the upper flow range. It would make a difference if the T/B was smaller. I am curious as to the internal passage sizes for the L67 MAF. If they are the same as the LN3, the air flow vs frequency has to be the same, unless the sensor itself is different. I will see if I can find the frequency response is supposed to be for the L67 MAF.