ow85

We’re so close to getting Humpty Dumpty back together again. Now we’re back to facing this old foe. Here’s what she does:
at extended idle, everything running fine, then suddenly she goes stupid. A/F vacuum goes nuts and she stalls. Cranks back up, runs fine. Does not throw a code. Runs beautifully when driving.
She just had engine/transmission rebuilt. NewECM. South Bay injectors. New fuel regulator. IAC 6 months old. Fuel pressure tested and was fine.
My mechanic installed new MAF for ***** and giggles and she hated it. Chugged and sputtered and then shut down. He unplugged and she cranked right up, ran fine. Plugged back in and the SECOND time she ran fine, until she idled 5 or so minutes and then died again.
This was a problem that was never resolved many years ago before I sold her. I can’t believe it’s still going on after everything that’s been checked and replaced!!
My mechanic was leaning towards something amiss with the MAF connection?
Fingers crossed that somebody has the magic fix for this!!!!
(Hi Orange! &#128513

ow85

2.8 automatic, forgot to say

GeneralDisorder

iTrader: (1)

What does live data say for the MAF data prior to shutdown? What are the BLM and INT doing? O2 cycling? Fuel pressure? We need to know what the ECU is seeing.............

GD

ow85

I’m sorry that I don’t know these details. He did say that everything runs perfect until that second just before shutdown, and that the air fuel mix went “stupid”. He didn’t say anything about the O2.
He said a buddy of his was going to use a different scanner on her that would hopefully show more information. The one he used was The Brick.

GeneralDisorder

iTrader: (1)

It could be any of dozens of problems. Without consulting the computer you have little chance of fixing anything. You need a scan tool and you need to understand how to use it.

GD

ow85

My mechanic is doing the work on her and is using his scanner, but it didn’t point definitively to any one thing. He’s going to try a better scanner this week to see if he can get more details.
When he told me about this issue, he didn’t give me the numbers/values, he just tried to explain what she was doing when she gets stupid. I will see if he can send them to me and I’ll update, if so.

dan5

If you have chronic, seemingly unsolvable intermittents in an ECM system, it is often a wiring fault. You may need to go through the system and check the connector pins. The scan data might help you narrow it down to a particular circuit. It is very common to have a pin in one of the low voltage controller circuits that doesn't make good connection. All it takes is one bad pin and it doesn't need to be an open, just an intermittent high resistance. Get a set of correct bare pins for the connectors of interest, then use the bare pins to test each connector pin and socket in the suspect connectors. You are looking to see that each connector pin has consistent drag and that none are loose. It's a test by "feel." If you find a loose or really low drag pin, it should be replaced. Be sure none of the connector pins has backed out and that they are latched in the connector body. It could also be a bad crimp between a pin and the harness. These are harder to track down. If you can isolate it to a particular suspect connector, you may need to "repin" the entire connector. The diagnostics in these OBD1 cars were not as sophisticated as the new OBD2 cars and you can have a bad intermittent that doesn't trigger the logic to set a check engine light.

Jeremy Brown

throttle positioning sensor

Jeremy Brown

I wonder if you have a Camaro that has the self check in the obd plug I would check and see because if I remember correctly all you have to do is run a jumper wire and the cars check engine will flash a certain amount of times for you to get the code. Hope that stuff helps good luck

Jeremy Brown

yea I agree with this too. If just one wire comes out of its little home it will give you all sorts of problems. But hey it can be fixed I mean it’s not a mustang so luck is on your side lmao

Jeremy Brown

you want to keep the key off and on the A and B connector use a paper clip to put in there. Turn your key on and the check engine will start it’s diagnostic. It will flash a number twice like 1 and then 7 continuously before it flashes the code you want so expect a same type of pattern at first it will be like 1 flash then 7 flashes then 1 flash then 7 flashes then it will flash the code you want

ow85

Still trying to get the numbers from my mechanic from the scanner.
Meanwhile...he checked the TCC solenoid, but she still cut off with it unplugged. Also, he said the MAF connector is perfect.
We’re wondering about the MAF relay, and also wondering if this could be in the ignition switch somehow?

dan5

Perhaps there is a different way to look at it. I will start by stating the obvious, but sometimes you need to step back and look at the big picture, then consider a process of elimination. You need fuel, spark and air. This is an ECM controlled system, with a number of sensors. Let's start with sensors- most sensors for the ECM have a backup strategy. If the sensor fails, the backup should allow the engine to continue to run. If it sputters and continues to run, that's different than stalling, and your description is stalling. The system usually is designed not to stall with a bad sensor. Try to disconnect the sensors and verify that the engine will continue to run. If IAC fails, you should have base idle air. If O2 fails, it should go open loop, and so forth. Even MAF, if it will run with no MAF then that ought to eliminate that as a cause of stalling. Since you have new injectors and new ECM with new injector drivers, you can monitor the fuel rail pressure to see if it drops when the engine stalls. That would rule out fuel pump and plumbing, with the exception that you could have a wiring fault between the ECM and a bank of injectors. If this checks out, then that leaves ignition (coil, cap, rotor or module?) or 12V feeds to the ignition or ECM. You could have a fault in the fuse block or feed wiring crimps or connections. You could have a bad ignition switch. I would get a logging voltmeter and pick up the 12v feeds at various points and see if you can catch a voltage drop when it goes bad. My sense is still that it is likely you have a wiring fault.

Just for example: I had a car where I installed an aftermarket ignition module. After a few weeks it began stalling intermittently at idle or driving. It would immediately restart. I blamed the module and it was replaced under warranty. A few weeks later it began the same trick- so not the module. The car had run for years without issue before this. At one point it became very persistent. I went under hood with the engine off and with an ohmmeter and checked all the wires I had added. It turned out that one of the jumper wires in the kit that went from module to coil had a bad crimp at a ring terminal. It looked great on the outside, but by slowly moving the wire, you could see the connection go open. When I replaced the warranty module, I didn't change these wires. The fault would occur from engine vibration, but either the engine shake from the stall or when you hit the starter to re-crank, it would vibrate enough to make contact again.

ow85

Thank you! I might be going to visit her tomorrow and I will read this to my mechanic.
It’s just so weird that she ONLY does this nonsense at extended idle, never stalls when driving or even moving without throttle. I looked back in her history, and she’s been doing this since late 2006! You would think this gremlin would’ve made itself obvious by now.
The ignition module...wouldn’t that cause her to cut off at random, and not just at idle?

dan5

Yes, that is a good thought. Although in all of these cases, including the ignition module, it does seem that you should notice some sign of trouble while driving above idle. Not a stall, but a short bobble in the power flow. TPS ought to be the only sensor that knows the difference between idle and off idle.

The only other thought that I had was an EGR solenoid fault. EGR will kill an engine quickly at idle and be much more resistant when off idle. However, I checked the book and it should be fed by a ported vacuum signal that (if true) should be zero vacuum at idle.

I agree this is a tough one.

ow85

Can’t wait to talk to my mechanic and tell him all this! Thanks again, and I’ll update after my visit with him, hopefully tomorrow!

dan5

Sorry to overload you, but I am going to add one more possibility. I am still trying to address your comment about idle vs driving. Have you replaced the ignition coil? I have seen a case where a weak coil would cause idle stalls, yet you could restart it and if you could get away from a stop, it would run. If this particular case, the coil would break down with heat. If you had the car running down the road with air flow under the hood, it would stay cool enough to perform normally. If you stopped and idled for 5 or 10 minutes, it would start to break down and idle rough and stall. It took me weeks, but I was able to track that one with an IR gun. When the coil case temperature exceeded 160-170, it would start to fail and when the temperature came below that it would be normal.