86TpiTransAm

About 3 months ago my 91 (3.1L V6) started stumbling and hesitating and eventually wouldn't start at all. I replaced the ignition module thinking that was the problem but it didn't fix it so I had it taken to the shop. The check engine light never came on so there was no codes. The shop tested the ECM and said the injector controller in the ECM was bad. They couldn't find anything else wrong so they replaced the ECM with a new one from GM. Everything seemed fine for the last 3 months or so and then about 2 weeks ago it did the exact same thing. I had it towed to the shop again and they said that one bank of injectors wasn't getting a ground from the ECM. They said it was just like before but when they put the test light to the ground on the ECM, the engine fired right up and stayed running. So they shut it off and it kept restarting every time they tried. They went ahead and replaced the ECM again but the problem returned while they still had the car. They pulled the wiring harness apart and checked all of the wires for broken or loose wires but found nothing. They again put the test light to the ground on the ECM and got the engine to fire up. Then, for the next week and a half, they started and stopped the car about once an hour and it fired every time. 3 days ago they put the wiring harness back together and bolted the panels up and it still started. The next morning they started it again and called me to come pick the car up since they couldn't figure anything else out. (They didn't charge me for anything) So I picked up the car and drove it home and didn't have any problem. Didn't drive it for two days and then went out today and it wouldn't start again.

What would cause just one bank of injectors not to ground? I understand that the pickup coil/ignition module sends a signal to the ECM to ground the injectors right? If it were the ignition module (which has been replaced) or the pickup coil, I would assume that none of the injectors would be getting a ground from the ECM right and not just half of the injectors?

Anybody that has had this problem before or anyone that has any suggestions at all, any input would be greatly appreciated. This is really baffling myself and the guys at the shop.

Thanks in advance!

RBob

iTrader: (1)

Odds are the issue is that the injectors are shorting out. The '91s (among other years) came with Multec injectors. The coils in these injectors have the insulation breaking down over time. This leads to the coils shorting and a no run condition.

On some others notes: the ECM has one (1) injector driver in it. This drive splits to 2 traces inside of the ECM and exits on 2 separate pins.

Each bank of injectors has its own fuse. So a fuse may have also popped.


To check the injectors measure the resistance across the injector pins. It needs to be above 14 ohms. Best if checked while they are hot.

RBob.

86TpiTransAm

Thanks for the reply. When I picked the car up from the shop he did tell me that one other possibility was that the injectors were shorting out and causing this problem.

Should I go with Bosch aftermarket injectors instead of getting factory replacements? What's the best way to go there?

I considered the fuse as well and haven't checked yet but the shop was able to get the car started by manually grounding the pin out at the ECM. Would they be able to do that if one of the fuses was bad? I'll go out tomorrow and check them anyway just to be on the safe side.

RBob

iTrader: (1)

I wouldn't put new GM injectors back in, too expensive and failure prone again. See the current thread titled "Ditch your stock injectors!" for some ideas.

My preference is to use Bosch injectors. The issue is finding ones that flow the same as the stock ones. Otherwise calibration changes in the ECM is required.

The only place that I know of that carries a direct replacement in Bosch is Lindertech (www.lindertech.com):

Bosch DRI
(Lifetime Warranty MULTEC Replacement)
fits most GM 2.8, 3.1("T" engines only), & 3.3 liters

Price isn't too bad either. Linder has been around for quite a while, and in the business I've done with him he was straight forward & honest.

RBob.

86TpiTransAm

Thanks for the advice. I'll probably call Linder tomorrow since they're closed today. $200 isn't a bad price for lifetime warranty injectors. Do you know if those are new or rebuilt? It was hard to tell from looking at the website.

I checked with OReilly Auto Parts (my employer) and it's $350 for new Borg Warners and they only have a 1 year warranty. Autozone is the same price for new GP Sorensons and they only have a 1 year warranty.