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1993 Grand Prix won't start after new ECM installed


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IrJoWo
User

Jan 27, 2013, 1:28 PM

Post #1 of 13 (2692 views)
1993 Grand Prix won't start after new ECM installed Sign In

Hello all,

After unsuccessfully spending some time on Google, I have decided to venture into the forums.

I have a 1993 Pontiac Grand Prix 3.1 Liter LE with 67,200 miles (yeah I know it's my Grandma's old car.) My original problem was that every once in awhile the engine would start running very rough, my acceleration would decrease, and the car would shake noticeably; a strong rich smell came along with all of this. Usually, after maybe 10 or 20 miles, everything would return to normal.

My trusted mechanics suggested that I replace the computer because it was reading out with junk codes. I ordered a new computer from the dealer; when they assured me that the car would start if my friend installed it, I asked him to do so.

Unfortunately, the car now starts and then dies immediately. I am not sure where in the process it is stopping, but the whole engine shakes and you can smell the fuel. Also, we put the old computer back in and it does the same thing. We did transfer the memory-chip.

I would really appreciate any ideas. My friend is a fairly knowledgeable mechanic although that is not his job; he has a lot of tools and I'm sure we could run at least some tests if you have any to suggest.

Thank you very much,
IrJoWo in Seattle


nickwarner
Veteran / Moderator
nickwarner profile image

Jan 27, 2013, 2:32 PM

Post #2 of 13 (2669 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

You need to know what you are losing when this happens. Do you have good spark, injector pulse, fuel pressure? Do you have a scan tool that can read the datastream info? Its OBD-1 so its a limited one in the first place, but this ECM has likely been unfairly condemned. Just needs to get the proper testing to find the issue. Thats some very low mileage but still 20 years old for everything. Have you looked at vacuum leaks? The intake gaskets, air ducting and all the vacuum hoses are suspect. Personally I'd toss every piece of vacuum hose for new on this. You can buy it in bulk for dirt cheap. Change each on one at a time, cutting a new section based of the length of the old one. Have a razor blade with you and slit the side of the old hose at the connector to make it easier to take off.

Would be interested in knowing the codes that it did have before and the ones it does have now, which you can find even without a scanner by getting the blink codes with a paper clip.


Sidom
Veteran / Moderator
Sidom profile image

Jan 27, 2013, 3:12 PM

Post #3 of 13 (2658 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

Is the security light flashing?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 27, 2013, 3:30 PM

Post #4 of 13 (2649 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

You have all the classic symptoms of a Passlock code lost which would be normal except from what I see, this car didn't have Passlock. Are you sure about the year?
Either way, I'm giving you the relearn procedure.



You have to do a security relearn before it will run.

PASSLOCK 30 MINUTE RELEARN

Disconnect the battery and hold the cables together for about 30 seconds then reconnect the cables before performing the procedure.Read it carefully if done incorrectly it won't work.
Turn ON the ignition, with the engine OFF.
Attempt to start the engine, then release the key to ON (vehicle will not start).
Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
Turn OFF the ignition, and wait 5 seconds.
Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock™ Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).
Important
The vehicle learns the Passlock™ Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
Start the engine (the vehicle has now learned the Passlock™ Sensor Data Code and/or password).
With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jan 27, 2013, 3:37 PM)


IrJoWo
User

Jan 27, 2013, 3:45 PM

Post #5 of 13 (2642 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

Ok, so the car is actually at my friends house where he was doing the work on it. I have to go over there first.

It is definitely a 1993.

I'm not sure I understand about holding the cables together--which cables?

Also, what/where is the security telltale?

Thanks.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 27, 2013, 4:02 PM

Post #6 of 13 (2634 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

The battery cables. Remove one and touch it to the other one to discharge all the capacitors in the system.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



IrJoWo
User

Jan 27, 2013, 5:04 PM

Post #7 of 13 (2619 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

OK, for some reason I thought the cables touching would be a short circuit but then I realized that without a power source it would be fine.

All right, the car starts and runs now without me doing anything but turn the key. It is running really rough right now, however, and has been for 30 or 40 miles.

My friend's theory is that the computer just needed time to figure out what it needed to do (it's been about 22 hours since we reinstalled the old computer.)

His suggestion is that I drive it as normal and hopefully the computer will be reset. However, I know that my mechanics checked the codes, got a bunch that seemed like too many, reset the computer and drove it around, then scanned again and got new codes. The dealer I took it to later also scanned and got Codes 65, 12, 14, 15, 22, 23, 24, 32, 46, 66. They wrote: "cleared codes and some codes reset. Found numerous engine sensor show reading incorrectly through ecm. Recommend to repace ecm and then recheck systems..."

Thanks much for your help, and curious to hear any new thoughts.

P.S. I can provide the VIN if that helps verify the make/year of vehicle.

Incidentally, it has started almost always without trouble until we messed around with the computers yesterday afternoon, so it seems unlikely to me that us switching the computers around coincided with a new problem in some other system; of course I am not a mechanic...


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 27, 2013, 5:27 PM

Post #8 of 13 (2613 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In


Quote
My friend's theory is that the computer just needed time to figure out what it needed to do


He would be very wrong about that.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



IrJoWo
User

Jan 27, 2013, 7:25 PM

Post #9 of 13 (2595 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

All right, well I'm pretty much back to square one here. The car starts and runs again, but still don't know why it's running rough/getting poor acceleration, and it has the old computer in it right now.

Any thoughts on why it starts now but didn't yesterday? Also, any thoughts on what might be causing the rough running problem, and whether putting in the new ECM is necessary or maybe should I be testing different mechanical systems to see what's causing the rough running?

Thanks again.


Sidom
Veteran / Moderator
Sidom profile image

Jan 27, 2013, 7:53 PM

Post #10 of 13 (2590 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

With a PCM throwing that many codes, you really need to start checking power and grounds for the PCM.....Have your friend get his volt meter and start doing some voltage drop testing....Take a close look at all the grounds


IrJoWo
User

Sep 22, 2013, 8:01 PM

Post #11 of 13 (2319 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

Discretesignals-- sorry about confusing the issue with multiple threads. I was also confused about how to best organize my posting on this forum. I will keep this issue in this thread henceforth.

----------------------

Last Winter when I started this thread I was having constant rough running and poor gas mileage (Something like 8/gal) Last June I got this diagnosis: "dead misfire on #4 cylinder. Tested, found shorted ignition coil for #4 cylinder. Tested, Open circuit inside ignition module." Mechanic recommended "ignition module and ignition coil for #4 cylinder replaced then system rechecked." After this work things got much better (up to 16 or so mi/gal.)

Still, I am still experiencing some rough running in my engine; I notice that when I am stopped at a light and in drive, the engine runs rough and the car shakes noticeably. It seems to last a little bit as I accelerate but once I get a little bit of speed it seems fine, at least until I get on the highway and start shifting into higher gears. Basically, it seems that the car starts shaking as it's approaching a speed where it would shift. I have to give it a lot of gas, then it shifts and is fine. Stopped in neutral or park it seems smooth and normal. Problem seems worse on hills and even started mildly while going about 25 up a hill the other day.

Thanks for your thoughts!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 23, 2013, 2:52 AM

Post #12 of 13 (2312 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

You've been screwing with this for 9 months and making no progress. It's time to take it to a reputable shop for repair.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



IrJoWo
User

Sep 23, 2013, 10:01 AM

Post #13 of 13 (2303 views)
Re: 1993 Grand Prix won't start after new ECM installed Sign In

Fair point about me screwing around. I do feel I had some progress though-- the new coil seemed to make it run smoother much of the time as well as get much better gas mileage.






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