Hi, I am trying to diagnose an occasional no-start condition on my 89 IROC. I have also been getting rough idling/misfiring as well. I just had my mechanic change out the 20 year old fuel pump but the problem persists. He is telling me that I have one bad injector and that is causing the ECM to shut down all the injectors so it won't start. This is the first I have ever heard of this. Can anyone confirm? I know a bad injector can cause the misfiring, but I would think that the car could still start with that condition.

 

Not exactly, but if you have some bad injectors it can overload the injector driver and even burn it out. Had exactly that happen to my 89.

My advice is take any remaining Multec injectors in that car and throw them away and replace them with a new set of Bosch III and if it still does not run right replace the ecm.

 

So is the guy at the auto repair shop feeding me BS just so I might be convinced to plop down ONE GRAND for them to change the injectors? I was planning to do it myself anyway, but I want to know if I can trust these guys.

 

If you can do it yourself, save a lot of money and do it yourself. You can get some injectors for a couple hundred tops, a gasket set, and a reman ecm is about 80.

 

I had one bad injector. When it would get hot it would short out and the ECM would shut down all of them. The stock injectors are prone to failure, replace them.

 

Hmmm....that seems to be the problem I am having. It will start up when cold in the mornings, but won't start when hot and I have to disconnect the bad injector to get it to start, although one time it didn't start EVEN WITH the bad injector disconnected. Maybe some of the other injectors are not functioning well either. I am going to replace all of them as you guys (and others) recommend. I am just surprised to learn that the ECM will shut down all of them. Thanks for the info!

 

If you have some tools, you can do this yourself. It's actually fairly easy, just take your time.

It's a batch fire system and all the injectors are fired in parallel. One shorted injector brings down the house.

 

With the information in this thread I was (I think) able to fix a vexing problem in my '89 Buick Regal 3.1L. After a hot soak it would intermittently lose almost all power. Usually it would immediately restart and I could limp, but not always.

I test the injector resistances and one read 3 ohms so I replaced it and the car has run great, so far. This also fixed a long-standing problem with the computer always having to lean out the mixture. I have a real-time diagnostic monitor and it previously showed INT values less than 100 and the ECM struggling to maintain the correct mixture at idle. It would sometimes throw a code 45 at idle, which I could prevent by running the AC. With the new injector the INT value is around 128 and it idles and runs much more smoothly now.

Outside of the car I heated the bad injector with a heat gun, but the resistance rose slightly instead of shorting as I expected it would. I'm suspecting, therefore, that it was not the injector that was causing the intermittent loss of power after hot soak, but instead maybe it was the ECM. For at least several years the injector driver circuit must have been subject to higher current load than it was designed to handle. Maybe the ECM finally developed a heat-sensitive fault. Now that it's no longer subject to the higher current load maybe it'll be okay, maybe not. Does anyone have any experience with this issue?

On a slightly separate note I don't understand the injector driver circuit. All 6 injectors are wired in such a way that they'll fire simultaneously, but surely they should fire sequentially? How is fuel delivery managed at the appropriate point in the combustion cycle when all 6 injectors are being fired simultaneously?

 

I blew an injector last year,, the car would start but ran like **** it was really bad I didn't drive it like that and had the injector replaced by a professional mechanic and it cost me $336.00.... The car ran great after that... also, it never threw a code......

 

Thanks for your note.

It surprises me that my car ran as well as it did with the bad injector and I'm sure it was bad for >2 years. Maybe because it was because the bad injector was 3 ohms, and not a dead short, that it sort of ran okay. With the replaced injector the car runs noticeably better, but I'm not convinced replacing the bad injector fixed the intermittent loss of power problem.

Driving it around this afternoon, it suddenly felt as though it lost power. The exhaust note deepened (dropped in frequency) and the diagnostic monitor showed it was running rich again. Then it suddenly cleared up and I drove it home no problem. No code.

I'm still leaning toward the theory that the higher than normal current flowing through the injector (and the ECM) for such a long time (>2 years) has created a heat-sensitive intermittent fault in the ECM.

I already replaced the oxygen and MAP sensors and (before I replaced the injector) found the car had an ignition spark on all cylinders even when it wouldn't start so I'm still assuming it's a fuel problem. The fuel pressure tests okay too.

The only code has been a 45.

 

Replacing the injector fixed a problem, for sure, but it didn't fix the problem that started me out on this trouble-shooting odyssey.

I just returned home from a short jaunt down the freeway. The car ran fine on the first leg, 15~20 minutes. After sitting (engine off) for about half an hour it started acting up again, on the freeway, within 5 minutes.

All of a sudden the engine (exhaust) tone dropped, the oxygen sensor reading shot up and the INT value dropped to about 100 to compensate. The injector pulse width increased to about 5 (from about 2 when it was behaving normally). I took an exit off the freeway, turned around to head back home and the car ran fine all the way back home even though I never shut off the engine.

This problem was definitely compounded by the bad injector, but I guess this doesn't indicate that it's necessarily a fuel problem. However, I swapped in a known good ignition module and checked the ignition coils (which all tested fine) when this problem first arose. I also installed new plugs and ignition wires.

I'm going to try a replacement ECM next unless anyone has any other ideas.

Eeargh!

 

I just discovered that I never posted the resolution of this problem. It was a bad crank sensor, not the ECM, that caused a no-start after hot soak and caused the intermittent loss of power.

 

No crank sensor on tbi or tpi engines in IROC