2seater

Could try disconnecting O2 sensor, or almost any single sensor for that matter, but it should be inactive when engine is cold? Bad information from a sensor is worse than no signal at all. The preprogrammed ECM info takes over when a sensor fails. Might try cycling through the various sensors and record the information they are reporting. I think Daniel is suggesting the O2 is telling the ECM to run leaner than it should, and that is possible. Same for water temp. sensor and intake air temp. sensor. All have an effect on the program in the ECM. EGR malfunction can cause operational problems but if one or more pintles is stuck open, it will usually do serious harm to the idle and low speed operation and get better as the rpms overide the leak (similar to vacuum leak). Cheapest fuel pressure gauge I have made is a $6, 60 or 100psi gauge from the local farm store, a length of fuel injection hose, a -4 female 45 deg AN or hydraulic fitting and two hose barbs to connect them together. You do have to pull the valve stem from the test port on the engine (same as used in a tire valve stem), since the AN fitting lacks the insert to open the test port. A dial type tire pressure gauge will work too but still must convert to the threads on the test port.

I would certainly get a fuel pressure gauge on it right now. It sounds dead lean despite what spraying stuff in the intake did. It only takes a couple of minutes to rule that out. A vacuum gauge on the engine will tell you something about the condition of the upper end too. There was an case just in the last couple of months where there was similar parts replacement but the fuel system was the problem.

Thanks for the offer. I will see what it costs for a "start over" system recharge to get a baseline for the expected system performance. It still works almost perfectly but I know age will eventually catch up with even a sound system. The temptation is to try adding R12 until the system cycles in the pressure range desired but I may have a specialist give it a once over for issues as mentioned previously. I didn't intend to hijack this thread as I thought my symptoms were somewhat similar to the original post. Thanks to all.

Mc, very informative. I have been considering having my original system evacuated and recharged due to similar circumstances. I have owned my '90 for over 17 years and am pretty certain it is untouched. The system will work normally at temperatures above about 70* ambiant or so, but will trip out at lower temperatures, like for defrost operation. I don't remember the exact code but I remember it said something like "low side pulls down too rapidly". I have attached my gauges and the system has about 90psi static and I watched it cycle for several minutes, (compressor on-off) and the numbers were similar but slightly lower than when last checked about five years ago. Once tripped out, it will only reset by battery disconnect and then may work normally for weeks or longer as long as temperatures are relatively warm. Am I wasting my time looking at a recharge or maybe just a top off? I can't find my numbers right now but I am pretty certain the low side pulled down into the 20's for psi.

I imagine you have checked for an actual leak but another possibility is one or more of the rubber hangers for the exhaust has failed allowing the piping to contact the undercarriage at some point. The engine rotates slightly when under tension while in gear so it is also possible there may be a leak or contact only evident when in gear. I would suspect the round seal where the exhaust connects to the rear manifold. They get hard over time and that is where the engine movement is taken up.

The fans do have a small drag/free/drag type of feel to them. I imagine it is when the segments inside the motor line up with the magnetized portion. The two fans on a '90 operate in series for low speed and parallel for high speed and the relays are what do the switching between the two modes. The relays are common five terminal 20/30 amp and could be switched with almost any others to test operation. Does the fan in question operate on straight 12v?

F14 Crazy had an extensive writeup on doing the conversion of an LN3 to the supercharged configuration a few years ago. He did as you described, essentially melding the two engines together. He also had the ECM tuning done by GM Tuners (Ryan Gick). The 170 gm/sec limit in the MAF/ECM signal will be marginal if not exceeded. That flow capacity is about 225 hp.

'96 and later is OBD II so it probably is not appropriate for our OBD I system. That said, if the battery is disconnected it does take the ECM a little while to relearn its normal operating characteristics. Checking fuel pressure should be done to eliminate it as a cause of your issues. Simple check that takes only a couple of minutes (if you have or borrow a gauge). It may be coincidence that the problem seems to be worse or one of the replaced parts is not up to snuff.

I haven't done so lately on a fully assembled engine but The clearance is tight at the power steering pump and if I remember correctly, the valve cover can be rotated rearward and it will clear, however you will need to remove the EGR valve and pipe to make this easier. You will need to disconnect the rear plug wires and swing out of the wayThere are no connections to the rear cover, so that isn't a problem. The front one is relatively easy except the pcv grommet may be hard so removing the pipe may resist a bit. Also the spark plug routing raceway is connected to the valve cover and it covers a couple of the holdown bolts, so it will need to be at least partially disassembled. The assembly slides on vertical rails on the valve cover and the front cover on the raceway slides sideways and clips together with the base. One other thing. I have removed my stock engine lift brackets from my engines, so I am not certain, but I believe they may also cause a little interference.

The lack of cam sensor signal shouldn't really have much effect on the actual fueling of the engine. The only thing that happens is the fuel sits on the intake valve for a split second before the valve opens. The sequential part of the fuel injection is only really effective at low speeds and at higher rpms the injector is actually open longer than the intake valve event and many makes of cars get along just fine using batch fired injectors rather than timed. The O2 sensor should take care of the air fuel ratio when in closed loop and the engine warm. Have you checked the actual fuel pressure and/or the Fuel Integrator and Block Learn in the diagnostics? Is the O2 sensor good and active? Check cross counts in diagnostics. A sticking EGR valve can cause rough idle and off idle stumble also. I believe the MAF was mentioned in previous posts and will cause poor operation from off idle if it does not respond immediately when the throttle is opened. From you original post, it sounds like the stumble is only a problem after the engine warms and goes into closed loop? Vacuum leaks are also a source of low speed misbehavior. I know this is a large grab bag of items but most sensors can be checked for proper operation in diagnostics, with the engine warmed up, to see if anything is out of whack. If a sensor is operating, but giving bogus information, it will not necessarily set a code.

The magnet shouldn't be a problem. As a matter of fact, I tried removing the magnet from an old one I had and it appears to be made of magnetic powder and pressed together inside the plastic holder. I suspect the magnet actually dissolves into small pieces or powder? Many of these have failed in the past and I have never heard of any additional damage aside from the Code 041. The engine will start and run fine without the cam sensor although injector sequence may be incorrect. This may cause a somewhat rougher idle and low speed operation, but is otherwise not harmful.

Hmmm, I don't believe the timing chain should do much for fueling but it will have some effect on engine efficiency. When I changed cams on my original engine, I found the chain with 92k miles on it retarded the cam a couple of degrees. It would probably be a greater difference if it didn't have the integral tensioner. As for vacuum leaks, the pcv valve, and also the grommets, are an easily overlooked source of leaks. What sort of idle vacuum reading do you have? I usually see a good solid 18"Hg or more at hot idle. What is the fuel pressure? Low pressure will cause the ECM to increase injector fueling to compensate. Likewise, a partially clogged injector(s) will need an increase in fueling to compensate. You can listen to each injector with a probe to see if they sound alike, look at the spark plugs to see if there may be cylinder that indicates a substantial difference in operation or try an injector balance test using the diagnostics. None of these tests will be conclusive but may indicate they could use servicing. If the O2 sensor NEVER indicates more than single digits for cross counts, it sounds like it is not as active as it should be. I will re-look at the action of my O2 sensor on a couple of recordings I did before the winter sleep, but I do know the O2 is very active only under certain conditions, like steady cruise if memory serves, and is less active during engine transitions like accelerating. A malfunctioning EGR can cause a rough idle if stuck open and will definitely affect fuel mileage (lower) if stuck closed or reduced flow. Will also increase knock sensitivity if inoperative. I found 10% ethanol fuels decreased my mileage by 3% or so (will also call for slightly more fuel in the BLM). A basic compression test will also help determine the general health of the engine. Lastly, how stable is you MAF reading at a steady cruise speed? I had a previous thread on a similar problem (although for a different reason), and I noticed if the MAF reading bounces around like 2 or 3 grams/second @ 60 mph, the BLM will tend to ramp up to the upper limit. When I relocated the MAF, the readings stabilized to .2 or .3 gr/sec and the BLM came right back close to normal.

Sure sounds like the CPS as mentioned by Ronnie. I suspect the oil pressure light came on because the engine quit, not the other way around.

Is it possible you are concerned about the water neck not inserting fully so the flange for the bolt sits all the way down? As long as the o-ring is inside the manifold itself, it should not leak. The rubber ring that sits on top of the thermostat is generally thick enough that the neck won't go all the way down, especially a new, unsquashed one. I've never had a problem with a leak, even though the neck sits a little crooked. It does look funky and usually you will find the old lower ring over the t'stat is squashed at an angle.

I never thought to apologize for hijacking the the O.P.'s thread, but I do so now. As long as I ran so far off topic, can anyone tell me what their MAF readings do at a steady highway cruise speed? Does it move around and by what amount? Maybe my operation is "normal"?

Padgett: Ahh so! That does make sense and maybe helps explain why I seem to need bigger injectors on an otherwise stock engine. I never did figure out why the MAF bounces around 2-3 gr/sec at a steady 60mph cruise but if I locate the MAF further upstream (away from the plenum) the same cruise speed shows a variation of .2-.3 gr/sec, about 1/10 the variation? I conjectured the ECM saw that large variation as a call for more power and tried to richen things up? I appreciate the insight.

Not sure I understand completely either, but my conjecture was the greater volume would pressurize a little slower. Maybe a little easier on the transaxle? It looks different too. Probably about the same volume as a tuned port manifold but those take up a lot of the room with long curved runners inside. Sort of a strange design with a slanted entry into the runner rather than a squared off runner with a bellmouth like a conventional ram style manifold. Probably broadens the area where it is tuned, rather than a specific rpm?

That's another experiment. I desired to soften the throttle response when turbocharged so I increased the size of the intake plenum. I cut the top off of the stock manifold at the top of the runners and welded on a sheet aluminum enclosure with a removeable top. Approximately doubled the plenum volume. The other possibility is to add intercooler coils inside the plenum for the turbo. Works just fine in n/a form as it is at this time. That small red hose behind the alternator connects both valve covers together and the air inlet tube for the pcv system is now a wye connection welded together from stock pieces.

I imagined this was a question about swapping a Buick engine into the Chebbies, but if just about switching one 2.8 for the other one, I defer to the last post. It would seem that switching oil pans and oil pickup wouldn't be a big trick if required.

Sweet, that sounds like the larger s/c. Should be a nice performer.

Are the fuel injectors in the head or the intake manifold? The larger supercharger required them to be moved the cylinder head. L36 is the naturally aspirated engine, L79 is the s/c. If it is a 1995 engine, it should be a Series I and OBD1. I believe the Series II arrived in 1996.

You may have some issues with the motor mounts if using the fwd engine. The Series II was also used in Camaro's and I would doubt they had a special engine block for that application only, but anything is possible. There are several sites for 3800 swaps.

The 3800 uses the same bellhousing pattern as the 60* Chevy V6 so it will physically bolt up to the existing transmission. Now how well the transmission will perform is an unknown, but I understand it is a fairly common swap in those vehicles as well as Fiero's.

Yeah, I know. The coil pack is actually supposedly an upgrade unit sold to the GN guys, but no way to prove if anything special or not? I have never found a need for anything more. I can't say the later model Delco units aren't better and even though I plan to give it a try, I just never got around to it. Too durned cold to do the junkyard thing now and the car is sleeping awaiting a different style turbo installation, similar to the Volvo V6 setup from the late '90's thru early '00's.

Are you asking about the K&N cone filter I use? I have had that for years in several different configurations, including ahead of the turbo, and the one in the pic is just slapped on when I reinstalled the original engine. Surprizingly, the filter actual picks up little heat from under the hood, at least when the ambiant was about 50*. It does rise to around 12* above ambiant at slow cruise, like 25-30 mph in traffic, but actually dropped to only one or two over ambiant when at highway speed. My engines have not been completely stock for many, many years, so I really can't comment on mileage or performance attributes. It is simply a convenient filter to install as I fiddle with things.