I am new to this site, but I have had my 91 firebird 3.1 for 10 years now w/134k miles. So I get in the car to come home from the store and it dies buy the time I get to the other side of the parking lot. I started it back up and it ran fine for about 3 miles and i'm stoped at a light the cars idleing fine them it just died. I couldn't get it started again towed it home. Checked for codes got a code 34, so I changed the MAP sensor. Then I started it up and it chuged for 30 seconds and then ran great for three days no problems. Got in to go home and it wouldn't start. Towed it home checked for codes got a code 34. So I took the sensor back and excanged it for a new one, still won't start. Checked the MAP circut, every thing checked out good. Also checked the TPS its good. It tries to start when you crank it sometimes.

Did GM still use ignition moduals with ECM's?
Sorry so long winded. Thanks

 

Yes, GM still used the Ignition Control Module on the computer controlled cars, it just got a little fancier in electronics.

Since the car doesn't start, there are 2 questions I have to ask and a third since you have stored codes...

1: Are you getting spark to the plugs?

2: Are you getting good fuel pressure? Spitting out the schrader doesn't matter, get a guage on it and make sure you have at least 40PSI.

3: After you "fixed" the code 34, did you reset the ECM? The easiest way is to pull the fuse located on the right side fender.

 

Yeah, I cleared the codes. The spark is good and strong. I couldn't get a fuel presure reading my gauge doesn't go high enough. Today when I checked the spark it fired right up and ran smoth for 30 seconds or so and then is started running rough. I reved it up and it smoothed out for a few seconds and then the check engine light started flickering and it was reving up and down with the check engine light untill it died. With the key on the check engine light flashes with a steady 3 secnods on/off. Also the cooling fan relay tweeks out and turns the fan on/off irraticly. I'm begging to think the ECM has took a dump. Thanks

 

I'd get a fuel gauge on the car and I'd check all the sensors.

 

I checked all the sensors @ 68*f
IAT - 3.053 k ohms
CTS- 3.216 k ohms
TPS- .73 v (closed) 4.43 v (open)
MAP- 4.83 v key on engine off
coil- 8.17 k ohms
Do these numbers look okay? Did GM use crank sensors with distributors? I can't seem to find one.

Thanks

 

no I dont think theres a crank sensor. the numbers look good. but you should check the voltage of the map at idle, 1/2 throttle and WOT to see if it varys. especially since you keep getting a code for it.

 

Thanks for the input, but there's one small problem it won't stay running when it does decides to start.

 

I'd put money on the ignition module, or the fuel pump.

 

My first genuine GM ignition module died at 103,000 miles. Aftermarket ones seem to last less from auto parts houses. I know Advanced has a tester you can use but that's still no guarantee.

It used to be with a GM you always had to keep a module in your glove box. It got better with 80's cars but they still fail often due to heat. It's a good bet that all of your dielectric grease finally dried up and the module has overheated. You will get weird codes when it dies because the ECM thinks that the car is still running when the module is failing.

When you replace the module make sure that you use lots of dielectric grease when you install it.

 

Yeah, the ignition module was my first thought after the MAP sensor didn't fix it, but I didn't know if they were still used with an ECM. Thanks I will try the module.

 

Today I checked the fuel presure and I got 42 psi so its good. I also changed the ignition module and it's doing the same thing. I wants to start but something just wont let it. It's getting the nesesities air, fuel, spark. Every once in a while it will start but it won't stay running. How can you tell if the ECM is shot?

 

Your ECM is not shot. Unless you hit it with a hammer it should be okay. I've only lost one and that was when a Pep Boys lifetime guarantee alternator shorted out 2 days after it was installed. It sent a voltage spike through the system and damaged my ECM (but not the prom) and my injectors.

I had the same thing happen to my car as what you first described twice; first it was the module and the second time it was the coil. The coil actually started shorting out through the insulation and grounding itself to the bracket that it's bolted to. It would give a weak spark so I kept seeing spark during my testing. I put a new coil and "voila!" it ran again!

 

check the resistance of the ignition coil and see if your results are within specs

 

I pulled a spark plug wire and let the spark jump to the plug it jumped about an inch, that seams good to me.

How much resistance should I get from the coil at each terminal?

 

I'm about to go insane. I thinking of taking this POS to a shop. I went back to square one today and tried to check the codes again. I had trouble getting it to spit out the codes and when it finaly did I got a code 12 and after the the last set the check light started tweakin' flashin' like crazy and the EGR valve was cliking on/off as well as the purg canister and the cooling fan relay and you could hear the IAC growling. The only thing I don't know how to check is the ECM, I think a tech II scaner is required. What now? Thanks

 

Help me please. I will take it to the shop next week if I can't figure it out.

Thanks

 

It's VERY hard for any of us to fix your car accross a modem. We are giving you what we have been through but that doesn't fix everything. Sorry...

Please let us know what your results are so that we all can benefit. This is how we all become wiser...

 

I was hopeing that someone would have been through this situation before, as there are so many of these cars out there with much more miles than mine. Out of all the people that I've ran into over the years with a third gen, my car has always been on the low side for miles and hasnt given me an ounce of trouble. This is the first big problem this car has ever given me. (starters, bateries and alternators don't count in my book)

Thanks for the help I will post an update when it gets out of the shop.

 

my 91 just did that running barely or not at all to find out had an injector dead short.

 

So? Did you replace just one injector to fix the problem? Are you running now? Please give us the details...

 

is this turning into a common problem?? my friends 3.1 just stoped running and my 2.8 blew the fuel pump i replaced that its gettign 42psi and still not running i pulled the plugs out and the 1and 3 cyclender are dry and the rest are wet so iam thinking i got a spark problem, also some one told me if the oil sencer is dead itll cut the fuel off and not let it run cause the car with think it has low oil presser so idk its something to look into

 

If you have a dry cylinder I would think you're not getting fuel...

These cars are getting old now so I would suspect that we will all be experiencing these problems sooner or later...

 

This isn't going to help solve your problem, but I thought it would be helpful to clear something up that was mentioned earlier in the thread. Dielectric grease isn't used between the ignition module and the distributor body. KrisW was correct in mentioning that the grease used there conducts heat away from the module, but dielectric grease is used to conduct electricity not heat.

New ignition modules will come with a small pack of silicon heat sink grease. However, if you want to replace it on your existing module your best bet is to head to the nearest Radioshack and pick up a tube of thermal conductive heat sink grease. It's pricey, but usefule to have on-hand. A small tube is about $2.99.

I'm not trying to step on anyone's toes. Just wanted to make sure everyone reading this gets the correct information before working on their own vehicles. Good luck with your problem GearheadNate!

 

I did replace one at first it did run (was drivable), but not as well as i thought it should. so i went ahead and replaced the rest when i got payed. it has 140000 miles on it. i dont know the exact specs on the ohms for the injectors. i think its like 13 to 17 dont quote my on that. but mine ranged from dead short to 15 ohms. 4 of them below 10 ohms. hope that helps

 

Would anybody know the proper ohm range on an injector?

 

Well, I just want to finally give an update. Last week I just went with my gut and purchased a new ECM for my bird, pluged it in and it fired right up. Been runnin' like a top all week.