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1993 Pontiac Grand Prix -- feedback on rough running engine
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IrJoWo
User
Jun 4, 2013, 1:25 PM
Post #1 of 3
(1247 views)
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1993 Pontiac Grand Prix -- feedback on rough running engine
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3.1 Liter, Pontiac Grand Prix 1993
68,000 miles
OK, so this problem has been dragging on for me, but got some changes to report. I will summarize and post link to the thread from 4 months ago.
Basically, engine running rough occasionally, then about 1000 miles and sixth months ago it started running rough all the time, and had lowered acceleration/power.
I thought I needed a new ECM and bought it, but when I swapped it in the car wouldn't start, so I swapped it out again. Had little money and things went wrong, as I'll get into later, so it's been a long time, but I have the money now and got a diagnosis of the engine trouble.
(more details: http://autoforums.carjunky.com/Automotive_Repair_C1/General_Discussions_F5/Re%3A_1993_Grand_Prix_wont_start_after_new_ECM_installed_P136148/)
I talked to the mechanics who originally recommended buying the ECM. Apparently we miscommunicated and the reason they wanted the new ECM in there was to get a diagnosis of the engine trouble so they could avoid checking all the wiring/grounds.
I took the car in to a different dealership, and they "found dead misfire on #4 cylinder. Tested, found shorted ignition coil for #4 cylinder. Tested, Open circuit inside ignition module." They recommend "ignition module and ignition coil for #4 cylinder replaced then system rechecked."
He told me also that one piston isn't firing and the other is misfiring. He also said that all the extra gas that isn't burning could clog my exhaust system/catalytic converter.
A few questions:
1) What do you think of this diagnosis?
2) If it sounds accurate, do you think I could get cheaper parts/repairs elsewhere than the dealer?
Also...
I'm pretty sure I broke the new ECM I bought. It was in my trunk and found it wet (some pretty heavy storms recently.)
I unscrewed it to help dry/see the extent of damage. Had a few small parts that looked a little melted/corroded.
Worse is that while doing this I removed my fleece vest and noticed some static discharge when I touched circuit board.
Much information indicates it's almost certainly permanently damaged. Other sources indicate it might still function.
Still, I cleaned and dried the ECM as best I could, then took it into the dealer. I noticed when I was inside the case that it looked like a small part of the circuit board was missing-- just a hole with some sodder where some small part should've been it seemed. Also, they quoted the part at $200, but when I picked it up they charged $300, cuz they wanted the core back.
I'm trying to argue with the dealer that since they didn't tell me about the $100 up front, and also since they may have sold me a defective ECM (remember the car wouldn't start) that they should at least refund me the core price. Wondered if this has a snowball's chance?
Thanks much,
Ira
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Discretesignals
Ultimate Carjunky
/ Moderator
Jun 4, 2013, 3:47 PM
Post #2 of 3
(1209 views)
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Re: 1993 Pontiac Grand Prix -- feedback on rough running engine
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I talked to the mechanics who originally recommended buying the ECM. Apparently we miscommunicated and the reason they wanted the new ECM in there was to get a diagnosis of the engine trouble so they could avoid checking all the wiring/grounds.
Wow, that must be a very technical bunch of mechanics that work at that shop. It is supposed to be the other way around. Checking wiring, inputs, outputs, powers, and grounds before condemning an ECM is usually the normal diagnostic pattern for determining if an ECU has an issue. I wonder what they tell their customers when the ECM is over $1000?
If a misfire is caused by something other than fueling, it could cause the catalyst to overheat and melt, so that is correct.
You can get cheaper parts other than the dealer, but they probably won't install parts that a customer brings into the dealership. If they do, which would be rare, there is no warranty on labor.
The part on the circuit board you described is probably where a memory chip plugs into. Engine won't run without it. You have to take the old chip from the old ECM and put it into the replacement. The chip is called a PROM and basically tells the ECM what kind of car you have and how it should control the ignition and fuel injection systems.
You probably won't be getting a refund on returning the ECM. Most the time electrical parts bought from a dealer are non-refundable. They have no way of knowing if you fried something on the ECM plugging it in to the vehicle. Shorted devices can blow a new ECM, so it is important to check everything listed in in the first paragraph above before plugging another in.
I'm sure you didn't tell them it was sitting in water and was exposed to static...LOL.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 4, 2013, 3:57 PM)
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IrJoWo
User
Jun 4, 2013, 9:34 PM
Post #3 of 3
(1189 views)
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Re: 1993 Pontiac Grand Prix -- feedback on rough running engine
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Thanks much for the reply.
I think it was a miscommunication, partly. They thought the labor for checking all electrical components would be more expensive than putting in a new ECM and getting a new diagnosis. Also, from follow-up conversations, they may have meant using a "known good" ECM from the dealer's shelf.
They are actually generally nice, have done stuff for me for free, take time to explain things, and have one of the few businesses of any type with 5 stars on yelp (something like 20 or 30 reviews.) Sounds like they were wrong on this one, though, and I am a bit confused why they gave me that advice because pretty much everyone else I've talked to agrees with you.
Not the memory chip. When I switched in the new ECM, I definitely switched the PROM as well. It's a very small board component, there's dozens of 'em in there, but one was missing.
I did tell them about the damage to ECM; didn't want to try to pass it off as still good. In my opinion, I deserve most of the blame, yet it's still irritating to me that they charged me that extra $100, and that the ECM didn't work when I installed it (before it was damaged). The original ECM works, so why didn't the new one?
Again, thanks for the free advice.
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