Engine idles rough for 2 seconds and dies

[Jess W]

I've been doing a lot of work on my '89 coupe recently, and getting it to start has been a pain. The engine will crank and start running a but rough for about two seconds before sputtering out.

 

We know there's fuel pressure at the engine, the compression is good, the air flow should be fine, and there are no vacuum leaks anymore to the best of my knowledge.

 

The engine was able to idle smoothly just one time for about 20 seconds the other day - then it eventually died again, and a new light on the dash came on saying 'electrical problem'. That was also the first time I've ever seen any part of the IPC come on, and that light is persisting.

 

I have no idea what other problem this engine could have, especially considering it worked just fine once. After that one time it blew a vacuum leak again but I fixed that again immediately. Hasn't idled for more than 2 seconds since. Thoughts?

[2seater]

Is the check engine light on? Do you know how to access the built-in diagnostic system to check for trouble codes and read the various sensors?

 

Do you know what the actual fuel pressure is at the test port? If it is less than 30psi it will be difficult to start. With the key on and engine off, it should be greater than 40psi.

 

You mentioned a vacuum leak and that it was repaired. What was leaking? A large vacuum leak will also make it difficult to start. One often overlooked place for a vacuum leak is the pcv system on the rear passengers side of the intake plenum. It is sort of buried under spark plug wiring and other harnesses. 

 

Was the error message on the IPC (instrument panel) or the CRT in the center of the dash?

[60FlatTop]

I have an '86 Park Avenue that has the same ALDL computer system. There are OTC 4000 readers available for servicing the cars. There are always a few on Ebay. I bought mine about 10 years ago. Ebay also has early Computerized Engine control college level textbooks for around $10-$20.  They are a great investment and way less expensive than when the cars were new.

 

Here is a 1994 edition on Ebay for $8 right now.

 

I have a stack of the texts and have been upgrading my diagnostic tools on a regular basis as my old cars get newer.

[Jess W]

Thanks for the reply! 

 

The "Service Engine Soon" light is on, yes. I believe I know how to read diagnostic codes via the touchscreen climate menu, but there's one problem: I can't navigate to any other screen but the radio. I've managed to open the climate screen for a split second by pressing the button as I turned the key, but it switched back to radio instantly. So... not sure how to overcome that part.

 

I don't know what the exact fuel pressure is but I will be testing that soon with a gauge - I'll get back to you on what that reads.

 

The vacuum leak came from the vacuum manifold on the top of the engine. Of the four lines connected to it, the small one facing the rear of the car was severed (the plastic nozzle had broken off in the rubber hose) and has since been reattached. It's entirely possible that another one has sprung somewhere considering the age and brittleness of the vacuum lines. I'll look for the PCV line and check if there's a problem there too.

 

The error message that said "electrical problem" was a light on the IPC. Since I can't read engine codes from the CRT, I don't know what issue it found. I've heard there may be a way to read codes from the ALDL port, but I'm not sure how.

 

 

[60FlatTop]

One more thing, learn the part numbers of your engine control devices. My rough idle was due to  faulty MAF sensor. They are out there for $250. I got one new in the box for $15 on Ebay. I think the seller dealt in lawn mower parts and had bought the obsolete parts from a garage that went out of business.

[Jess W]

Responding to 60FlatTop - I'll definitely have to invest in an ALDL reader, thanks for pointing me in that direction. This car will probably have every error code in the book, but I'm determined to get it running.

 

And about the MAF sensor - after removing it and trying to run it again, it seemed to do the same thing either way. It may be faulty, so I'll look for another one if only for peace of mind.

Edited October 19, 2023 by Jess W (see edit history)

[60FlatTop]

Just reading the codes gives you a fuse for the "parts cannon". Reading the operating parameters with help you pinpoint the problem. studying the books means a lot.

 

I actually pay monthly to follow this Youtube site. It is like $3.50 per month.  https://schrodingersboxqm.com/ I watch that, read the books, put my scanners on the car when I don't have a problem, and think deep thoughts. The worst problems I have are when one of the old cranks at coffee says "All those young kids do is plug in a computer it it tells them what to do." Depending on my mood it's a crap shoot how that will go. But it's always fun.

 

Edited October 20, 2023 by 60FlatTop (see edit history)

[Bloo]

The thing to pay attention to in these old scan tools is the software included. Software is in a plastic thing like an old video game cartridge that plugs into the scan tool. It goes in the bottom of an OTC. There are four of them in the lower left of @60FlatTop's picture. Early on there were separate ones for GM, Ford, Chrysler, Imports, etc. Later on, the "big three" American makers were all in the same cartridge. Every year a new one came out so MAKE SURE that one you buy has a GM (or a "big three") cartridge that goes new enough to cover your car. Yes, you had to buy a new cartridge or cartridges every year if you wanted to work on brand new cars.

 

There is also the OTC monitor 2000. It is older and less desirable than the monitor 4000 in @60FlatTop's picture. The 4000 added some little capability, I forget what, but the main thing is the bigger display. With a scan tool on a computer controlled pre-OBD-II GM car you get live sensor data, not just codes. On a 2000 you can only see 2 things at a time. I doubt there's much difference in value today so get a 4000 if you get OTC, but on the other hand if you saw a 2000 at a near giveaway price, it does the trick in almost all cases. I never updated to a 4000 before OBD-II came along and changed everything, and this is what I did for a living. I figured I would get a Snap-On Scanner instead. It has an even bigger display than a 4000. Once in a great while only seeing 2 things at a time on my old 2000 was inconvenient, but usually not a big deal. **Having a new enough GM cartridge is the main thing**. I believe the 2000 and 4000 take the same series of cartridges. Snap-on and any other brands would take different ones.

 

Also, make sure the GM ALDL connector is with the scan tool. It is a pigtail that unplugs, because there are different connectors for Ford, Chrysler, etc. If there's a GM cartridge with the tool the ALDL connector should be there, but it unplugs and people do lose things....

 

Hey @60FlatTop, is there any reason he can't use the paper clip trick to get the codes on a Reatta?

 

@Jess W, don't fall into the old trap, once you get a code, into thinking that the code tells you what is wrong. It's almost true on newer models, but back in those days. The code just told you what to look at and test. Today cars have systems with many sensors that interact, and often just replacing whatever the code says happens to work. It usually didn't work back then. Those cars had only enough sensors to tell the computer what it needed to know to run the engine, and a code just meant that the computer got some reading that it should not ever see. For instance, if a code is something like "oxygen sensor stuck rich". it the sensor might be "stuck rich" because it failed, but it also might be that the engine is running extremely rich. Once you have codes, get out the manual, check the circuit, and see if the sensor is telling the computer the truth. Maybe the sensor is bad, maybe it isn't, but if it isn't bad you still have a clue where to look next.

 

Edited November 5, 2023 by Bloo (see edit history)

[Ronnie]

1 hour ago, Jess W said:

I can't navigate to any other screen but the radio. I've managed to open the climate screen for a split second by pressing the button as I turned the key, but it switched back to radio instantly. So... not sure how to overcome that part.

Sounds like you have a R.A.P. problem keeping the CRT from displaying properly. You should get to know the how-to guides on my website. Lots of good Reatta information there.

 

Reatta Owners Journal - CRT Doesn't Light Up But Radio Plays

[EmTee]

11 hours ago, Bloo said:

is there any reason he can't use the paper clip trick to get the codes on a Reatta?

That's what I was thinking -- I believe that trick should work on all pre-OBD2 GM cars.  The SES is illuminated, so at least that indicator appears to be working.  Bear in mind that there are issues that can cause the engine to not run that don't necessarily set a code (e.g., crankshaft position sensor).

 

https://f01.justanswer.com/nmwagschal/c2dc1097-6a35-4b83-8844-813a806098ce_p30_checking_codes.pdf

[60FlatTop]

12 hours ago, Bloo said:

Hey @60FlatTop, is there any reason he can't use the paper clip trick to get the codes on a Reatta?

I remember sticking a paper clip across the terminals on something years ago. It never developed into a habit. Prior to buying my '86 Buick my computer controlled cars were relatively new and never really needed much in the way of diagnostics. I bought the '86 in 2011 and it needed work. I had a good idea I would need the proper tools so that was the beginning of my of my computerized engine control education.

 

I went from this:

 

To this:

 

And can still spend an enjoyable evening reading either.

[DAVES89]

21 hours ago, Ronnie said:

Sounds like you have a R.A.P. problem keeping the CRT from displaying properly. You should get to know the how-to guides on my website. Lots of good Reatta information there.

 

Reatta Owners Journal - CRT Doesn't Light Up But Radio Plays

I agree with Ronniw. The car believes it's in "accessories"  which is why it defaults to the radio page. The radio page is the only page you can read when the car is in accessory. You might have an ignition switch problem as well.

[60FlatTop]

On that original starting problem, one of the common fuel pump sequences is to run the pump for 3 to 5 seconds on startup and the pull in the pump run relay when a set RPM is sensed by the crankshaft sensor. The problem could be a bad relay, crankshaft sensor, or PCM.

[EmTee]

3800 V6 crankshaft position sensors were notorious for failing during that era.  I had one quit on my '90 Bonneville.  I don't think there's a good way to test it without using one of those scan tools shown above.

[Jess W]

Here's an update on what we're checking.

 

On 10/19/2023 at 1:26 PM, 2seater said:

Do you know what the actual fuel pressure is at the test port? If it is less than 30psi it will be difficult to start. With the key on and engine off, it should be greater than 40 psi.

I've read the pressure at the test port and it's exactly 40psi, and its 45psi when the fuel pump is active, so it seems this is fine.

 

On 10/19/2023 at 1:26 PM, 2seater said:

Do you know how to access the built-in diagnostic system to check for trouble codes and read the various sensors?

I've checked the codes and it's showing us two: 12 (just telling me we're in diagnostic mode) and 23. 23 looks like it could be a number of things: MAT sensor voltage issue,  throttle position sensor problem, mixture control solenoid is shorted or open, or the air intake temperature sensor is low.

 

It would make sense that the mixture control is off, considering it runs rough and won't idle. I don't know where that is or how to check it however.

Edited October 22, 2023 by Jess W (see edit history)

[EmTee]

From what I have read, Code 23 is a Manifold Air Temperature (MAT) issue.  Specifically, 23 says the PCM is getting a temp value pegged at the low value (-32° F).  This is apparently caused by the PCM seeing the full 5V bias signal.  You can try unplugging the MAT sensor and short the two pins on the connector together.  If the wiring is OK, that would cause a code 25 to be set (MAT will be pegged at highest value).

 

I'm not sure how this would cause the symptoms you're seeing unless the PCM is setting the mixture extremely rich to compensate for the cold air temperature.  Before the engine dies is it belching black smoke from the exhaust?

[Bloo]

1 hour ago, Jess W said:

It would make sense that the mixture control is off, considering it runs rough and won't idle. I don't know where that is or how to check it however.

It's automatic based on the real world numbers the ECM (ECU in modern terms) gets from the sensors. @EmTee is on the right track here.

[Ronnie]

2 hours ago, Jess W said:

It would make sense that the mixture control is off,

Interesting theory. Will be interesting to see how this plays out. Keep us posted.  

[2seater]

From the way the codes are mentioned here, they are from an ALDL connection of some kind? The built in diagnostics would be displayed differently on the CRT and it would also contain specific text. I have used the ALDL to display ABS codes, but they aren't relevant here, and I haven't tried the old school pin shorting for ECM data. There is no PCM on a Reatta, they are discrete ECM and BCM modules.

 

One common way to narrow the search for a bad part is to disconnect it to see if behavior improves or stabilizes. Default values are then used by the ECM to keep the engine running. EO23, low MAT temperature can cause bad behavior with the mixture combined with the MAF. The MAF uses a heated wire and thermistor to try to maintain a target temperature and I THINK(?) it needs an accurate inlet temperature as part of the calculation. Essentially, bad sensor data may not be far enough out to set a code.

[Jess W]

Sorry for the long pause here, but I haven't had a lot of time to work on the car. I unplugged and re-plugged the MAT sensor that was supposedly causing code 23 to flash.

 

That really shouldn't have fixed anything, but code 23 no longer flashes.

 

Instead, we are getting a new error: 42. I believe that means something is wrong with the ICM, but my guide isn't very specific on what this means. Any thoughts? The same issue is happening - engine runs rough for a second or two and stalls.

Edited October 29, 2023 by Jess W (see edit history)

[2seater]

Yes, E042 is communication between the ECM and ICM. The engine starts on commands from the ICM and the ECM takes over spark timing after the engine starts. You might try unplugging and reconnecting the ECM, contact cleaner optional. If the onboard screen would work perhaps a clearer picture of the errors would emerge plus you could read spark timing directly. 

I am guessing that holding the throttle open a little to keep it running has already been tried already. This is the information the onboard system can provide: Reatta Owners Journal - ECM Diagnostic Codes

[Barney Eaton]

Another easy exercise is to unplug, clean and replug the connectors at the BCM and ECM 

30+ year old cars also have 30 year old electronics and a bad connection can give your fits in tracking down a problem

[EmTee]

On 10/29/2023 at 1:11 PM, Barney Eaton said:

Another easy exercise is to unplug, clean and replug the connectors...

This ^^^ did work before on my father's '84 Corvette, so it's definitely worth a try.

[Jess W]

Alright, we're under the dash checking out the wiring, unplugging, cleaning, and re-plugging plugs as we go.

 

We did find this though, a very thick pink wire with a black stripe that doesn't seem to be plugged in to anything. I've seen a few things in the wiring diagrams saying that the injectors are wired to pink/black wires, but I'm not certain this is the same. I also don't see a slot this can plug into, so I figured I'd ask - Can someone identify this?

 

I'll keep y'all updated as we finish troubleshooting.

 

Edit - sorry about the blur. I should also mention there's a cap that goes on the end of this wire too.

Edited November 5, 2023 by Jess W (see edit history)

[Jess W]

I put the battery back in and went through the motions again. When I shorted the pins for the diagnostics codes, I got the same 12 and 42.

 

Interestingly, when I put the car in accessory, there's a slow clicking coming from under the hood. Trying to locate it, it seems to be coming from an injector. Unplugging the injector seems to make the click only happen once when I put the car in accessory afterwards. No significant changes to any lights or diagnostics thus far.

[Bloo]

12 is normal and means the engine is not running. 42 may be the interesting code to look at. Write it down, clear it by disconnecting the battery for a couple of minutes, and see if it comes back after the car fails to stay running.

 

Is it losing spark?

 

Generally speaking, GM V6s of this period could have Magnavox or Delco ignition. I'm not sure if this applies to Reattas. Which system do you have? Magnavox was known to be problematic as the cars got older. Delco has 3 separate removable coils. If I am remembering this correctly, Magnavox does not. If something in a Magnavox system is bad, a whole Delco assembly may interchange, at least in some cases.

 

[2seater]

I don't know specifically what that pink/black wire is, but it is likely for an option you don't have, especially if it was capped. The constant hot wire to the injectors is brown if my memory serves and the six ground wires from the ECM will be in a group, not hanging loose. You have a communication problem from the ECM to the ICM. I don't have a manual handy, so I cannot specify which plugs or wires, but the wiring from the ECM to the ICM is all in one of the plugs on the ECM. The 13 pins at the ICM are mostly connected to the cam and crank sensor plus power and ground. There are just a couple of wires that direct connect the ECM-ICM and the color codes are the same at both ends. You need to check those wires for continuity, crosstalk or short to ground. A helper will make that easier.

[EmTee]

1 hour ago, 2seater said:

You have a communication problem from the ECM to the ICM.

Do you have a shop manual, or at least the wiring diagram?  If so, check the grounds for the ECM and ICM.  A longshot, but I can at least imagine a ground potential differential possibly causing intermittent communication.

[Ronnie]

The pink wire with black stripe (Pink/Blk) is used to power virtually anything to do with the fuel injection and ignition system that has power anytime the key it turned to the RUN position. ECM, BCM, fuel pump, MAF, you name it, it's powered with a Pink/Blk wire.

 

The brown wire 2seater mentioned to supply power to the fuel injectors branches off a Pink/Blk wire. Since the Pink/Blk wire in the photo had a cap, I'll bet it was used to power something in a Riviera that was not used in a Reatta.

 

As far as what happens when you turn the key to the Accessory position...  I wouldn't worry about that until you get the engine to start and run properly with the key in the RUN position.

 

You should get back to basic troubleshooting. Do all the fuel pressure tests in the How-to guides on my website. Check for spark at the plugs. Check for the injectors firing with a Noid light. Once you know all that stuff is good you can move on to the hard stuff.

[DAVES89]

That strange wire is used to run the Boze system found on a Riv. Did a dash swap and used the wrong plug. Stereo didn't like that much...