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Were do I start when my computer gives out 7 different codes in my 1993 GTP?

J

JOHNNY GTP

New member
On 11/30/16 I was driving through heavy rain and my 1993 GTP stalls . I get it pulled over on the side of the road and try to start it. It idled but only when I fed it gas and then it would stall. I tried starting it several times but it would only stay running when I feathered the gas pedal and it would sputter and back fire when doing so. I had it towed to a small shop where a friend is the service writer. One of the mechanics checked for codes and found about 7 of them. He cleared them and they returned. Its unlikely that all of these things happened at one time? I've had this car for 17 years and it no longer has the 3.4 it has a 3.1 that I had installed with only 19,600 on it. It now has about 23,000 on the engine and about 195,000 on the car. The mechanic doesn't know where to start because it would cost so much money to chase all of the codes. I don't want to give up on it now. So my question is where should I go from here? What to check first etc.? Please help. Thanks
 


It's unlikely they happened all at once, but one problem could cause multiple codes. What were the codes?
 
if all 7 are something like o2, sure they can all be related. Without knowing what they are... we are more clueless than you.
 
those cars used to eat fuel injectors for lunch and dinner.
if you can unplug the injector harness and check to see if one batch of injectors ohms out differently from the other and you will probably find a shorted-out fuel injector
 
Turbocharged400sbc said:
those cars used to eat fuel injectors for lunch and dinner.
if you can unplug the injector harness and check to see if one batch of injectors ohms out differently from the other and you will probably find a shorted-out fuel injector
Click to expand...

Yup, spendy buggers too if I recall. I have one or two good ones that I could part with if that's what it ends up being. My 3.1 days are over.
 
I just had the car towed to my yard. The car will start for a minute or so but will then start to surge and die. The current Codes are 79,80,98,75,76,77,36,41,42,14,15,33,34,51,96.
About 2 weeks ago I noticed broken vacuum lines. I fixed what I could see and the car ran fine until this happened.
 


Good grief! I'm thinking bad power or ground or a faulty ecm. Code 51 is a prom/memcal error so something is definitely malfunctioning in the ecm.
 
Thanks for this information. My friend the service writer seems to think the same thing. I will in the next day or two take the overflow tank off and have a look around. I 've had some rodents under the hood last year and this year. They have pulled some of the installation down from under the hood and made a small nest I noticed this about 5 weeks ago when I put a new alternator on. About 4 weeks ago I had a new fuel pump installed by a shop that is a little bit closer to my home. I thought that I would give them a try but never again because after the install I started smelling gas and I could even see some on the side of the tank. Come to find out the seal at the top of the tank was leaking. I had a new seal/gasket installed last week where my friend works. I think that the shop that installed the pump should have recommended or included the gasket.
Could a bad vacuum line cause all of this? Also, If I bought a new ECM is it difficult to change the prom etc. inside that needs to be changed? Where could I have this done if I wanted some one else to do this? Thanks very much for your time
 
It's not difficult to swap the prom chip in the computer, although alternatively you could find a junkyard pcm from the same year and motor and it should work. I would check your harness first though. A lot of those codes are high & low voltage errors, which makes me think the ecm is getting erratic voltage and a critter chewing a wire would cause that.
 
Do the knuckle test on the ECM case.

With the engine started and running... rap on the case with a couple knuckles or gently twist and flex the case with just your hands.

There used to be a lot of micro fractures in the circuit traces.

The other possibility is that someone may have removed the wire harness protective sheath that goes across the top of the radiator and several of your wires are rubbed through and shorting to ground
 
If I found a 1993 grand Prix, Lumina etc. with a 3.1 and used it's ECM it too would need the prom changed because the 3.1 didn't come with the 4 speed auto trans that my car has.
I've looked at the ECM for sale and the info states that the prom etc. has to be changed/ taken from the original and then installed in to the new one.
I will take a look under the hood and tap on the ECM to see if there is any difference and if not I will then order a new ac Delco ECM.
Thanks for your help
 


Were the trannys different between the 3.1 and the 3.4? I didn't think they were, but its been a while. What ecm/prom are you using now?
 
From what I was told the 3.1 came with only the 3 speed automatic except the ones that came with manual shift and the 3.4 came with the 4 speed automatic and also a manual trans. I had my 3.4 removed and the 3.1 installed and I don't know how or what they changed with regards to the computer. I bought the first 3.1 from a yard in another state it came with ECM and some other parts as this one was broken (freeze plugs) and it was needed for the accessories , brackets, mounts etc. The second 3.1 was bought from another yard and it was pulled and shelved from a 1993 lumina that was hit in the rear some years prior with only 19,600.

Yesterday, I pulled the overflow tank so I could inspect the ECM, wires etc. I didn't see any intrusion to the wires so I raped on the ECM got in and started the engine and for a split second it ran rough but then it was perfect just like it was prior to Wednesday. I feed it throttle and it ran perfect. I copied the information off of my ECM so that when I order the AC Delco ECM they will have the info that's needed. I will then change the prom, as I watched a YOU TUBE clip where the guy changed the prom from a 1993 Buick's ECM. I will do the install and hope for the best. Also I cleared the codes and will start the engine today to see if they return. As of now there is no dash lights on. Thanks to all for your help
 
No problem. The 3.1 came with the 4 speed, I've never come across the 3 speed, although I know they are out there.
 
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