Decel Fuel Cut Malfunction - L67 Conversion

[Guest GPGTX2000]

New to the forum, but as I'd mentioned in response to hndblt88's post regarding the L67 Series I swap, I've experienced a 'decel fuel-cut' problem with my '89 since the conversion. I purchased it on Ebay in 2005 with a cooked 4T440 and brought her home on the dolly. Clean unit for Philly with 235k. VIN# 1G4EC11C6JB902729 Silver/Gray, no roof, no 16-way.

Already had an '88 in my possession that was originally my 'resto' project, but after close examination aborted that idea as it was a lifelong upstate NY salt-belt cancer pile that ended up demoted to parts car. For those viewing this, I still possess this unit and anything I haven't robbed or cannibalized from it is up for grabs as I'll be relocating to NC in the very near future with no plans of transporting the carcass. Red/Tan, 16-way no suede, Roof (rotted worse than most) .. Cleaned, seats would still be fair with no tears. PM for any needs and I'll check inventory. For those keeping track of wounded soldiers and thier eventual demise VIN# 1G4EC11C6JB902729.

Pardon the brief sideline, but some of it does pertain to the issue at hand as I have my suspicions about possible transmission electronic differences between '88 and '89 as I had the 4T440 from the '88 overhauled for use in the '89.

3800 Series I L67 was donated by my old friend, the 1995 Riviera, retired in '05 w/227k on her. Engine was in perfect condition with no electronic or mechanical malfunctions at time of cannibalizing (short of guide seals getting a lil weak, but still minimal oil use between changes). Did all the necessary modifications (I thought) to drop directly in place of 'C' engine in the '89 including using all sensors/senders/switches that were different between 95 G body and '89 E body. Bolted to the freshened up 4T440 donated by the '88 and all was good .. electronics seemed happy, transmission was happy .. until closed throttle coast. Experiencing a 1.5 second interval injector pulse flat-line at any speed that results in a 'burp' thru the exhaust and a surge that can be felt. Vehicle speed bears no relevance until 70 mph is exceeded, at which point the decel fuel-cut programming functions as expected .. no injector pulse to conserve fuel and provide dynamic braking. Allow it to coast below 70 and it starts in with the burping again. Low resistance cruising (slight down-hill, low/no headwind .. HEAVY little car) can also induce the burp but significantly more irritating as there's still enough TPS signal to keep converter in lock-up resulting a violent jerk of the powertrain.

I've tried everything I can possibly think of in my arsenal of 23 yrs of automotive experience and still have yet to conquer this one. PCMs, sensors, switches, PROMs .. at a loss at this point and hoping there's someone here with more knowledge and understanding of the correlation of electronics. Maybe what parameters PCM uses for decel fuel-cut function. :confused:

[Ronnie]

Do you still get the burp if you ease the throttle closed or does it only happen when the throttle is snapped shut?

[Guest GPGTX2000]

Always there at closed throttle whether it's snapped closed or backed off gently, will begin just prior to fully closed with minimal TPS signal.

[Ronnie]

Have you tried unplugging the TPS to see if the problem goes away?

[Guest GPGTX2000]

Haven't attempted that one, but will do it as soon as I'm done typing and keep you informed as to the result.

Thanks for the quick reply!

[Guest GPGTX2000]

Angered the PCM and aborted converter lock-up but no change in symptom.

[Ronnie]

I'm out of ideas for now. Are you using the PCM fro the 95 or the ECM from the 89?

[Guest GPGTX2000]

ECM from the 89 to keep the remainder of the electronics happy. Curious about the possibility of it being attributable to the 2 different MAFs listed for both model years. The current MAF is from the '88 as the original was damaged on the '89 engine. Neither had an OEM # that even looked like the #'s listed by aftermarket parts suppliers, and I long ago discarded the damaged '89 sensor and didn't have the piece of mind at the time to write the # down. I've gone yard scavenging and grabbed them by the handful and it never seems as I've come across the same # twice.

[2seater]

Curious about the MAF sensor? Did the MAF come with the 1995 engine? Isn't the intake to the L67 an integrated MAF and throttle body (one piece)? If so, the actual MAF sensor is a different configuration. The LN3 sensor will bolt right in place, but the L67 won't fit the LN3 . If it is what I think it is, the L67 has a plastic extension that wraps around the sensor wires and forms part of the passageway through the MAF. Externally, the flat black plastic exterior is identical. The frequency range for both style sensors is the same, so the ECM should be able to read the L67 just fine.

[D-a-n-i-e-l]

So did you piggyback an other ecm or reprogram the original?

[Guest GPGTX2000]

Understand the physical differences in the MAF body design. I had to make a flat gasket for the LN3 MAF when I installed it on the L67 TB. That was actually one of the 1st things I tried as a remedy was going back to the original L67 MAF post re-assembly and discovery of the malfunction. That made the ECM extremely unhappy to be looking at the input from the MAF from the 95. In watching both CRT ECM data and having my MTG2500 taking a graph of MAF input, I have to disagree on the 'same frequency' principle. Using the original L67 MAF induced numerous driveability issues .. poor, loping idle (almost had that out of time, labored sound - like the days of a distributor retarded by a tooth) but most noteable was the lean under load condition that would bring on the death rattle from hell. I've never experienced spark knock in that extreme. I only took it for a 2 mile test using that MAF due to that fact, but was able to watch the O2 readings all but disappear under load. Returning to the LN3 MAF (from donor '88, original from '89 had cracked housing), all was good .. but for the 'burp'.

As for the ECM/PCM questions .. original 89 ECM is in play, with no reprogram or piggybacking. Only output I could see was missing from the equation was the lack of boost solenoid, which I omitted with the idea that the bypass valve would operate strictly on vacuum, albeit with a lil bit of delay, much like the wastegate actuator on a turbocharger without it. I'm relatively proficient with electronics, but the Reatta's 'primative' CAN system is over my head by just a lil bit. I wouldn't have the first clue in terms of piggybacking another ECM/PCM into this system without aggravating all other controllers and inducing codes, if they'd even communicate. Daniel, I understand your need for ECM/PCM modification due to the need to communicate with the 4T60E-HD you're using. You're well above my level of ability to have made it work with BCM, IPC, CRT and all other components in the network. If you have a free tender moment, I'd love a tutorial .. maybe I could wrap my head around the concept. I took the simpler approach and figured most if not all sensor inputs would remain relatively identical between LN3 and L67, but for the boost under load, which I'd hoped would be compensated for by MAF and O2 inputs. Greater volume of intake air seen by MAF would in turn increase injector pulsewidth. O2 input would further regulate and fine tune fuel delivery. Am I grossly mistaken in taking this approach? All seems to function in harmony except for the fuel-cut issue. I have a 60 mile/day commute round trip to work and am averaging mid 30s for fuel economy. Plugs have a nice tan burn. Nothing really seems too unhappy with the L67 .. I've just beat my brains out on this fuel cut problem. Having seen so many others like yourself with this modification successfully completed, I was hoping someone could lead me in the right direction.

Appreciate all the input I've been receiving from everyone. With the help of many, I'm confident I'll be able to conquer this once and for all.

[Ronnie]

I would get in touch with the folks at Sinister Performance. They are experts at this type of thing.

[Guest GPGTX2000]

Thanks Ronnie .. just fired off an email to them. I'll keep ya posted.

[2seater]

Thanks Ronnie .. just fired off an email to them. I'll keep ya posted.

X2 on dealing with Ryan @ Sinister Performance. As to the MAF, did you record what sort of airflow the L67 was indicatiing? I was surmising that the LN3 MAF sensor was not reading consistantly due to the passageway not being a smooth tube for the air flow. I have only tested the LN3 and L27 style MAF sensor on my flowbench, which is the style on the right of my poor photo, and the frequency vs airflow range is exactly the same as the LN3. Your 1995 L67 may be different due to the higher arflow potential of the S/C engine? Isn't that the 225hp version? I would be very appreciative if you could let me know what the maximum airflow indication is when you get everything operating. Your ECM should limit out @ 170 gm/sec, and that engine should be very close, or over that reading.

Thanks

[Guest GPGTX2000]

I'll be glad to keep everyone in the loop as to what transpires in the near future with this. I put this thing together 5 yrs ago as a toy .. finally registered it this year (clicked quite a few on it using boss' dealer plate prior) for the summer months and easier transport for the relocation (to an area of the country I hope to enjoy it more, with less winter to protect it from). Now is the time to start working out the quirks .. this being the biggest. Also to replace the failing accumulator before I have to aim for something hard to stop. I'm eager to have it right, once and for all.

I'll get the WOT and closed throttle MAF readings with the current LN3 MAF and also reinstall the L67 MAF for a point of reference. I've got a drawer full of em in the one end cabinet .. maybe get readings for many variations. Anyone possess normal MAF range charts? Be interested to know what one should expect to see in different circumstances.

[2seater]

I know the maximum reading of 170 gm/sec is a frequency of 10.4kHz output from the MAF. I have a chart somewhere but I can't seem to lay my hands on it right now. Many years ago I requested air flow readings from stock Reatta's and the few I received were in the 125-130 gm/sec maximum, although I believe Padgett reported a bit higher at around 140. I posted a little while ago about the '88 camshaft which is a little more robust than the '89-'90 and I believe Padgetts test car at the time was an '88. I did not record the years for the others that responded. Is it possible the MAF from the L67 is bad? I will PM the MAF chart if I can find it.

Edit: An approximate horsepower figure is 1.32hp per gram/second. It works as a point of reference for modifications.

Edited April 12, 2010 by 2seater (see edit history)

[D-a-n-i-e-l]

GPGTX2000,

Use Ryan, he knows what he is doing and is alot cheaper than going to a full tune shop. He only cost me like $100 vs $500+ at a tune shop. I am happy with the job he did on mine. Alos if you are not using the injector off the L67 switch to them, befor the tunning.

With the access to all the ifo threw the touch screen you do not even have to have a high end diagnostic machine.

[Guest GPGTX2000]

Injectors are about the only thing I left alone between the LN3 and the L67 .. are you using the balance of the L67 sensors on yours, or did you revert to the LN3 MAF, etc? In all my research I've found very little difference in part #'s other than the obvious point of discussion (MAF) and crank and cam sensors .. both of which are providing the same input, just adjustable air gap on LN3 versus fixed position on the L67.

[2seater]

The stock LN3 injectors are only about 19# per hour and are not large enough for the L67. Even if the fuel pressure on the L67 is higher, I don't think you will have enough fuel for high power runs. I would think your fuel trim (BLM and INT) should indicate higher than the target of 128. Daniel can probably give better info as to what to expect for program changes in the ECM. I am running 30# injectors on my turbo application and the EPROM had to be adjusted to bring the fuel trims back in line with the target values. I did try my initial running of the engine with the stock injectors, and it did operate reasonably well at around town speeds, but when pushed a little harder, the engine would lay down due to lack of fuel. I learned some things the hard way.

[Guest GPGTX2000]

BLM values are on the higher end, memory serves somewhere in the low to mid 140s .. suspicious of fuel pump volume. Has equivalent pressure to S/C L67 Series I engine, but I'm not sure it has the volume to keep up with additional fuel requirements and larger injectors of L67 engine.

[jonlabree]

I have tried several different injectors, including GN injectors 27.9#. At the moment I have 36# injectors, running 50lbs fuel pressure, and they seem to be doing the job. But I should add I also have a Water/methanol injection system

[2seater]

I have tried several different injectors, including GN injectors 27.9#. At the moment I have 36# injectors, running 50lbs fuel pressure, and they seem to be doing the job. But I should add I also have a Water/methanol injection system

Do you happen to know the brand and part number for the 36# injectors? Pushed to 50psi would be just shy of 39#, about what I need to run E85.

[jonlabree]

The injectors are "Bosh" part# 0-280-155-811. They are from a late model S/C Pontiac. They were also used in Fords and other S/C GM cars. I have shut off my Water/Methanol injection system and run on just gas and they seem to perform very well.

[D-a-n-i-e-l]

Injectors are about the only thing I left alone between the LN3 and the L67 .. are you using the balance of the L67 sensors on yours, or did you revert to the LN3 MAF, etc? In all my research I've found very little difference in part #'s other than the obvious point of discussion (MAF) and crank and cam sensors .. both of which are providing the same input, just adjustable air gap on LN3 versus fixed position on the L67.

As I remember the things I used off the reatta engine were oil presure sensor and got rid of the EGR valve (still passes emissions, thanks to being 3700 lbs).

[2seater]

The injectors are "Bosh" part# 0-280-155-811. They are from a late model S/C Pontiac. They were also used in Fords and other S/C GM cars. I have shut off my Water/Methanol injection system and run on just gas and they seem to perform very well.

Do those have our style of electrical connector (EV1) or do they require an adapter? I have been looking for a photo of them but haven't found them yet. Are they the new style "skinny" injector and possibly white in color? I "thought" the stock injectors for the late model Series 1 L67 injectors were about 36#? I am looking for something affordable around 39# for E85 use, even used ones, that is why I inquired about the part number. Thanks for the help.

[jonlabree]

They are plug and play. a perfect fit. I think the 36# injectors are as big as you want to go otherwise you will be putting the fire out a WOT. One other thing, Check for knock:).

[D-a-n-i-e-l]

also the ones off a typhoon, syclone, or sc thunderbird fit. They may be the ones that Jon is refffering to. I do not recall the specs any longer.

[padgett]

Just a side note but the EGR only functions at cruise so unless your inspection involves rollers it may never get tested.

[Guest Richard D]

Just a side note but the EGR only functions at cruise so unless your inspection involves rollers it may never get tested.

Hi Padgett, As far as emissions tests go I liked the Florida system. Build inspection station stations all over the state, top end models with rollers for cruise testing. make everybody get inspected once a year, decide that about 99% of cars pass the inspection so you close them all and sell the buildings and property for about one fifth of what the tax payers paid five years prior.

Don't get me wrong, I was very happy to see the program go away, I just wonder how much it cost us Fl. residents.

[padgett]

Ended in '72 for most of the state, six problem counties (Dade was one) kept into the 80's. Dunno about the "99%" though if failed once, you could fix and retry.

One of the best parts was that every car had to show proof of insurance along with the registration.

[Guest Richard D]

Once again you are correct, I had forgotten about the early inspections that were for more mechcanical things like parking brake, lights, horn, tires, etc. I was thinking of the emissions testing in Dade, I thought it was state wide. I should put brain in gear before posting. Thank's

Richard

[D-a-n-i-e-l]

any progress?

[Guest GPGTX2000]

Got boned on a used ECM on ebay .. figures. Paid w/no product. Waiting for the ECM I had from my 88 parts car to get here from PA so I don't suffer any downtime while EPROM is in transit to Ryan for the reflash. I'll keep ya in the loop as to any progress.

[Guest GPGTX2000]

The 'back-up' ECM has arrived! I'll pull OEM PROM in the AM and get it shipped to Sinister Performance and see what Ryan can do with it.

On a side note, the Solid State Headlamp Door Module packed up on me the other night (left quit out of no where) and after researching some with my local GM parts room discovered that the original number supersedes to the module used in 93-02 Trash Ams! Alas we have another outlet for some of the fragile and ageing electronics on these beasts .. hope this lil tid-bit does someone some good. Should you need, the superseded part is Delco # 16525685. List is $236.54 (ooofa) but they're readily available used in the aftermarket.

Edited April 29, 2010 by GPGTX2000
mis-spellings and omitions (see edit history)

[Ronnie]

Could you please tell us the symptoms that led you to conclude the headlight module was bad? It might be helpful to others in the future troubleshooting their headlight problems.

Thanks.

[padgett]

87-88 Fiero module is also a substitute.

[Guest GPGTX2000]

The left side wouldn't retract with the switch .. figured the motor finally bit it (the one that previous owner gutted and never reassembled .. cover half missing, screws drilled) but when energized with the PowerProbe, it functioned as expected. In turn tested leads from the module (other half of plug to motor, normally both hot w/ignition on) for alternating ground in up/down using both headlight switch and retract switch and had nothing from the module. Tossed used module from parts car in and all was well and good. Furthered the research as far as part numbers and availability with the parts room and without giving them the application (anyone else seem to notice 'Reatta' frightens most parts room employees) just the original module part number, they went thru the multiple supersessions to the latest part number. I followed that up by a quick search of the final superseded number to find it's the module used in the Firebird/TA of 93-02. Glad Padgett has pointed out the Fiero interchange, but I like the idea of newer (i.e. late as 02) electronics for replacements. Hopefully the latest part number I've come up with will also be a viable replacement subject for the Fiero in the future.

[padgett]

Just get them while you can. Since the 84-86 switch & brush set for the Fiero motor has been discontinued, retrofitting an early Fiero with the later system has become popular.