1992 - Stall After Surge / Slow Cycling

[jack.rupert]

I have a 1992 Beretta with around 70,000 miles which I bought new. My mechanic is having some difficulty with and issue that popped up in the last month - mostly because it never seems to happen for him. Periodically, when no gas is being applied it will stall. Usually, this is preceded be the engine surging and slowing, maybe on a 2-3 second on/off cycle. Most of the time it will start right back up, although sometimes is wants to complain. Stop and go traffic, especially high-traffic side streets is the worst. It does not seem to be dependent on the engine being warm or cold. It can happen within a mile or two of starting up or 10-15 minutes down the road. Most of the time, once it restarts after a stall, it's good for the rest of the drive, but periodically it will get finicky and keep doing it for the next 4-5 stops and then finally work. If gas is applied and going fast, its' good - generally, the problem is at 30 mph or below. Maybe also a rougher than normal idle (in drive, not neutral) and a bad gas smell.

We have already replace the ignition control module (it actually did fail), along with the crank shaft sensor, ignition coil and lockout torque converter solenoid.

What's next other than new car shopping?

Thanks!

[Rettax3]

2.2 or 3.1? No MIL (Check Engine Light)?
Starting at the basics, when was the last time the spark-plugs were changed? Especially since the ignition module went bad, the plugs could be causing some issues not perceptible at higher RPMs -unlikely, but a good tune-up is the best place to start since it should be done periodically anyway, I call it 'clearing the dust off, to see what is underneath'. Dito for your ignition wires.

This does not sound like a fuel supply problem, but with smelling fuel, I would check for leaks. The main thing to look for is the FPR (Fuel Pressure Regulator). Sometimes, the diaphragm inside splits, and allows fuel to be sucked into in intake through the vacuum-line. This causes two problems; Loss of fuel pressure at the injectors and raw unmetered fuel entering the intake. A very small crack in the FPR's diaphragm could cause this minor issue and be intermittent too.

A worn, dirty, or sticky fuel injector could do this too, allowing too much fuel in, or poorly atomized fuel that doesn't burn as well. Run a can of BG 44k through the system -expensive fuel treatment, but if you want a cleaner that works, cheap doesn't do it in my experience.

A bad O2 sensor could be sending poor mixture data to the computer, causing a surge in fuel flow, gas smell and stall from over-rich. As your engine sits idling, even if warm, it can lose enough heat to switch in and out of closed-loop mode (where the computer reads data from the sensor, instead of supplying fuel strictly based on initial programming). A borderline sensor can cause the exact problems you have -even though not necessarily the most likely of your problems, I get the feeling this is the culprit. A $25 part -eliminate this possibility and move on.

Getting a new ICM (Ignition Module) doesn't mean that fixed the problem -hang around long enough and eventually you will get a defective ICM out of the box. Unlikely the issue, but if it misses a few ignition cycles here or there, it will be felt more at idle, and could cause a stall. Same goes for one of your coils.

How about your IAC? This is the Idle Control Valve -the part that regulates the idle speed and the most likely cause of your problem. If it gums up or wears out, it may not respond properly or fast enough.

A vacuum leak is your next place to look. Check all vacuum lines, have your mechanic 'smoke test' it if necessary -this is where they pump a mineral-oil smoke into the intake, and look for it coming out from places it shouldn't. A smart mechanic will also cycle emissions devices, like the EVAP solenoid, to make sure a leak in a controlled vacuum circuit isn't causing the intermittent problem. Your engine is MAP or 'Speed Density' operated, meaning that it doesn't use a Mass Airflow Sensor, so unmetered air is most likely to cause the engine to idle-up rather than stall, but if the IAC tries to compensate and lower the RPM and the leak stops at the same time, surge-and-stall, especially with a worn or dirty IAC.

Lastly, these computers are nearly bullet-proof, and it used to be that every time someone couldn't figure out a problem, they screamed bad ECM. It (almost) never was. But, they are getting old now, so the failure-rate has gone from one in a million to one in 100,000, and one in 10,000.
Eventually it will be one in ten. This could be the problem you have now, though I doubt it.

Good luck, welcome to the site.

[jack.rupert]

Thanks for the suggestions! I really appreciate it. It's a 3.1 and no Check Engine Light comes on (at least until after it dies when the whole dashboard lights up). The spark plugs and wires were done in October, 2017, so I don't think that's the issue. Now I've got a few things to check into. Thanks again.

[whiteretta]

Any updates on the issue?

Sent from my VS501 using Tapatalk

[jack.rupert]

That's a good question. I was going to give it week before writing an update and that would have been today (since I got it back from the mechanic). I gave him the list, and he checked and cleaned everything, but didn't see anything bad. One thing he mentioned was he wasn't there for the last repair (the torque converter). The guy who did it, didn't disconnect the battery, so he thought that the ECM might be working off of bad data. After doing that, he thought it ran better. So, I've been driving it for a week and hadn't noticed anything, although, I still think it run rough at stop lights. Then today going to work, something felt slightly squirrelly approaching the last stop light and as I pulled into the parking space at next to zero speed, it felt like somebody touched the accelerator. (Since I was getting ready to brake, it wasn't me). Not fast, that the car was going to run away (or hit the wall), but just enough. However, because of my location, there wasn't much i could do for testing. It went home ok at the end of the day. We'll see what happens tomorrow.

[jack.rupert]

Sorry for the late response. Still need to get my 5 posts so the don't need approval.

Back to square one. After about 5 miles of normal operation it started running real rough at stop signs, to the extent I felt the need to pop it into neutral in order to keep it running. Then, it decided to stall before I even got to the light – still going about 20 mph or so and was able to coast to the parking lane. It had some trouble restarting. I was getting ready to call a tow when it caught. After that the first light needed neutral to keep going and after that it worked fine again.

Does this give anybody any more ideas? Thanks.

[heavywoody]

Try unplugging the TCC on the transmission. Should be a plug on the front of the trans, near where the ground wires go from the harness to one of the bolts connecting the trans to the engine block.

[jack.rupert]

Thanks heavywoody. I'll pass that on to the mechanic. I assume that TCC is the torque converter that was replaced as part of this situation. It's back in the shop today after rolling into the parking lot at work. (Stalled at the gate and didn't want to restart right away, so I had to pop it into neutral and let gravity help). It had a little trouble restarting at noon when I headed home, but then it was ok for the rest of the drive. I went home first to drop off my work stuff before heading over to the mechanic, but I was wondering if I was going to make it out of the driveway - rough with varying speed. First time I ever had that in reverse.

[Rettax3]

TCC won't cause a hard re-start, and would cause a dragging and chugging prior to stall -definitely sounds like a different set of symptoms. When your mechanic disconnected the computer, he reset the idle calibration. It usually takes a little while to come back around unless he went through the relearn process himself -doubtful. Most likely, the ECM relearned the idle settings when everything was going okay in the engine, rather than hunting for a good setting and reacting more to unusual conditions. In other words, it usually runs worse while relearning, but it might respond faster to an unexpected problem because it doesn't know yet what to expect.

A defective catalytic converter that is partially plugged could also cause your symptoms. Extremely hard to diagnose on an OBD-1 car, it can cause a wide range of problems that look like other issues. Less likely to cause intermittent problems though, unless there is literally something stuck in it or it is disintegrating inside. Get under the car and lightly bang on the converter, listen for rattling. I actually saw a Toyota where the monolithic block inside the cat had broken apart, and would rotate around alternately allowing exhaust flow then blocking it. The owner finally brought it in when he heard an exhaust leak -caused by the monolithic block finally grinding through the casing -pretty entertaining watching it spin around in there...

Another possible culprit could be your EGR valve. If it leaks or sticks partially open, your engine is sucking in unburnable exhaust gasses instead of fresh air. It will still match fuel to what it thinks it is getting, which can cause a rich condition (plug fouling, fuel smell) as well as power loss and an inability to idle correctly. If EVERYTHING else has been checked, this is a good place to go next. I delete them on my cars: by the time you run 80,000 miles on an engine, they have caused more harm than good. Do cold-air intakes work? Do you use an air filter on your intake? Then why allow hot, dirty exhaust gasses into your intake? (Rhetorical question, BTW...)

[jack.rupert]

Today’s update…. It’s been in the shop since my last post. Unfortunately, it never seems to fail when he’s driving, so while he doesn’t think it’s possible, I’m wondering if the gauges he puts on changes the response making it work. This time I’m getting a remanufactured computer. He is also going to electrically test the fuel pump without removing it. The catalytic converter was changed in 2013, but I asked about it anyway. He thinks I would be having more power problems during normal driving, which it doesn’t seem to be experiencing. I had mentioned the EGR valve awhile ago due to a problem on my parents’ car back in the 80s. During one of the investigations, it was taken apart and cleaned, but I was told it wasn’t in bad shape. The saga continues….

[woody90gtz]

I had the same issue with a Bosch o2 sensor. I read a few others also had issues with Bosch sensors. I replaced it with a Denso and have never had issues since. Sounds strange, I know, but that's my experience.

[Rettax3]

A bad O2 sensor could be sending poor mixture data to the computer, causing a surge in fuel flow, gas smell and stall from over-rich. As your engine sits idling, even if warm, it can lose enough heat to switch in and out of closed-loop mode (where the computer reads data from the sensor, instead of supplying fuel strictly based on initial programming). A borderline sensor can cause the exact problems you have -even though not necessarily the most likely of your problems, I get the feeling this is the culprit. A $25 part -eliminate this possibility and move on.

I had the same issue with a Bosch o2 sensor. I read a few others also had issues with Bosch sensors. I replaced it with a Denso and have never had issues since. Sounds strange, I know, but that's my experience.

I do like Bosch O2s, they essentially invented this generation of Lambda feedback technology, so it is hard to call foul on them, but yeah, I have had a couple of new Bosch O2 sensors act strangely out of the box over the years -nothing recent though. I don't like Denso, but for a completely irrelevant reason, and I know my bias isn't helpful here. NGK also makes these sensors though, and I do like them a lot. Either way, if this hasn't been ruled-out yet, this is still the first direction I would have gone...

[jack.rupert]

Time for an update.... I've had the car back from the mechanic for two weeks now and put on around 300 miles with no stalls or motor speed fluctuations that I've been complaining about. This time they put in a remanufactured computer. The owner of the shop said that the one I had was known bad. It's number ended in 3377 and back in the day they were told to just replace them first thing if anybody's car was acting up. Apparently, that series started to warp after they got warm. We're surprised it lasted 27 years.

It still seems a bit rough at full stop in Drive after it warms up a bit, but that might be due to stiffer engine mounts or other changes. It's not like the engine feels like it's going to shoot through the hood or anything. Once in a while, it does seem like a slight delay in response when I put on the gas, but the computer might still be in learning mode. I did notice that I'm driving slightly differently because of all the time trying to keep it from acting up. Now I find my foot is usually on either the gas or the brake and not doing much "coasting".

Thanks for all your suggstions!

[Rettax3]

Lastly, these computers are nearly bullet-proof, and it used to be that every time someone couldn't figure out a problem, they screamed bad ECM. It (almost) never was. This could be the problem you have now, though I doubt it.

I am glad you seem to have it figured out. I have noticed a lot of the time when replacing the ECM with a reman, it acts a little differently, a little rougher, maybe because of slight differences in electrolytic capacitors or other minor components that might be changed during the reman process. Replacing with a factory original used ECM, I don't see that so much. Hence, when (if) there is a choice, I am not a fan of the reman...

But, in all honesty, that line about the 3377s (that SHOULD actually be a 7730...) all being bad sounds like BS to me, they were used in nearly everything GM had with a V-6 for years, and if they were so bad back in the day, why didn't your shop swap that out for you months ago? Also, ECMs don't 'warp' from heat, and inside the cabin, the physical temperature of the ECM should be relatively consistent, so if he means the 'heat' from operation, that would tend to be a more consistent failure, as the component would heat up quickly with a problem, and fail out. With electronic though, anything can and does happen, so it easily could be an internal heat issue -nearly everything expands with higher temperature.

Anyway, how ever it was he explained it, it does look like you found the problem, so that is all good. Thanks for sharing the experience.

[woody90gtz]

I've talked to an old GM "calibration tech" and he did say those computers can and will fatigue the solder connections over time and cause some strange things to happen.

Of course he did also say OEM computers are better than the remans as well.