Computer?????

I bought a 1990 Grand Prix LE 3.1 a few weeks ago. The car had been sitting for 2 years. The man I bought it from said it was his wife's car and she passed away and he hasn't driven it since. Of course the battery was dead so I bought a new one. Drove the car, it ran fine. I noticed immediately that the gas light and temp light were lit for no reason. Every now and then the lights go off, but soon return. Gas gauge showed 1/2 tank of gas and temp gauge read fine. I went ahead and changed the fuel filter and t-stat and filled it up with gas. The speedometer reads 80 when you are going 40. The odometer read 80945. I have driven the car about 200 miles and it has only moved 8 miles. Trip doesn't move at all. The car drives perfectly one day, the next it stalls upon stopping or turning. It has even stalled driving 45 mph. Sometimes you crank it up and the idle is very high. You can get up to 55 w/o even pushing the accelerator. I check codes and the only one I get is a 51. One book says that it is the PROM and one book says it's the ECM. I have no idea which one to replace and can this cause all of the other problems?

UPDATE: Replaced the PROM to no avail......Still doing the same stuff. Any suggestions are desperately needed!!!!

The early 90s Grand Prixs seem to have a lot of problems with the instrument cluster. Mine had the same problems as yours. Before the odometer completely stopped working, it would sometimes go backwards! The link below has info on how to repair the idiot lights, which involves resoldering some of the connections, but it didn't work for me. I ended up removing the bulbs for those indicators since the fuel and temp gauges always worked fine. I tried resoldering additional components on the panel though I can't remember what. You might just look for anything that looks to have a bad connection. On the plus side, my speedometer hasn't acted up since I tried the repair. Have you done 90 in reverse? I used to do that. My odometer also started functioning again, albeit erratically. My Haynes repair manual says that the code 51 is the MEM-CAL or PROM. Both sound like they're basically the same thing. w-body.com says it could be the MEM-CAL or ECM, though it sounds like they lean towards the MEM-CAL. You could try checking that all connections to the computer are good, and make sure that the MEM-CAL or PROM are seated good. Disconnect the negative battery cable before doing this and touch a metal part on the car to discharge any built up static electricity.

http://www.w-body.com/service/checkgauges.html

The mem-cal and the prom are the same thing. Before replacing the prom I went ahead and checked the codes again. Only the 12 showed up this time. Went ahead and replaced the prom, still no other codes. Went to http://www.60degreev6.com/index.php?p=pages&pid=74
and did the relearning of the idle. This really didn't help. My main concern here is to get the car to run without using 2 feet. I can live with the lights flashing on and off. I guess I can go try the 90 in reverse now, lol.(banging head)

I took the car to autozone and let them run a check and they said it was the MAP sensor. Replaced it right there. Ran fine for about 15 miles then dies while accelerating. Hard to get it cranked back up. Keeps cutting off. As soon as I get it back home I checked the codes again. 51, back to the computer.....<sigh>

Do me a favor go to autozone and disconnect your throttle position sensor then go inside and ask them to plug there scanner into the car and tell you whats wrong I bet they tell you you need a new throttle position sensor and they will sell you a new one! Do you see where I am goin gwith this?

Do me a favor, go to autozone and disconnect your throttle position sensor then go inside and ask them to plug their scanner into the car and tell you what's wrong I bet they tell you you need a new throttle position sensor and they will sell you a new one! Do you see where I am goin gwith this?


I think I do see where you went with that............I haven't run across a single person in the car repair business that hasn't tried to rip me off at some point or another, hence the reason I am trying to fix the car myself. I am a female using a guys name under the assumption that I would then receive some help without all of the b/s. I was with the guy at Autozone the whole time and watched him like a hawk. The only thing he did was try to be helpful. I just wanted to see if their scanner pulled up something mine didn't. He never touched the car. I am assuming that with your credentials you could tell me what the problem might be. If you could focus on that I would really appreciate it!!

Girl to Girl here honey.. Can i ask you something?? when is the last time this car has had a tune up?? Especially from sitting there for 2 years I am sure it desperatley needs one.. I have a 97 GP and it did the whole stalling issue any time i was at a light i would have to put it in netutral and keep one foot on the gas and one foot on the break.. ended up i needed a tune up and a fuel filter.. Now when you got the car it had a half tank of gas in it?? Gas does go bad after awhile.. as well has condesation from the weather changes so there is a good chance you need to throw some dry gas in the car and changed the fuel filter.. and do a tune up.. everything with the speedo and lights just seems like is a seperate issue from the car dying all the time.. prolly just a mouse chewed on some wires since it was sitting.. And also you may wanna check your air filter to see if there are leave stuck in it or a mouse house in there or if it is still good.. that cause problems as well.. I would imagine that your speedo and dash problems are not related to why your car is stalling especially if you are having a hard time starting it back up.. So do yourself a favor get some plugs and wires and a fuel filter and possible an air filter and change it all and throw some dry gas and do an oil change and try to run all that old gas out of it and see it helps any i am sure it will..

oh and sorry just seen you replaced the fuel filter but give it a tune up i am sure it needs one and check the air filter

I also have a 90 GP and sometimes it stalls at stop signs, lights, etc.., it only does this when it is low on tranmission fluid. Since it has been sitting for 2 years you might have the filter and fluid changed in the transmission. Also, my speedometer reads 85 when I am going 60, but the odometer and tripometer are correct. Since it doesn't cause any problems I just speed up.

I have a 91 GTP, It is a pain in the but also! My car stalls becaue the fuel injectors get dirty. I ue fuel injector cleaner and it wont stall for the longest time.

I've got a 1989 Grand Prix SE 2.8L with well over a hundred thousand miles on it. (Not exactly sure how much, 'cause i'm working on getting the instrument cluster to display the odometer.) Anyway, I had great results with another older car (84 VW Rabbit) using Bosch multi-prong platinum tipped spark plugs and decided to install them in my '89 GP.

The engine had been running unevenly and it started and stalled frequently. The plugs I removed were fouled with soot and worn. The platinum plugs did the trick again--she starts up right away and runs smoothly. The real pain in the butt was tilting the engine away from the firewall to get to the other 3 plugs! I was afraid that the car wouldn't pass the stringent California smog check. After giving it a good run on the freeway to blow all the crap out of the pistons and valves, I had it inspected and it PASSED.

These plugs are well worth the extra cost (4-6 bucks each)--especially for older engines with lots of mileage.

Good luck.

http://www.boschusa.com/AutoParts/SparkPlugs/Platinum/

MrEguy, to get to the back first undo the bones on top/front of the engine. With the car in park have someone push it for you and after the car moves a little put on the emergency brake. There you would have enough access to change the plugs.
Hesitation is usually related to an intake (fuel/air) problem.
Coach, I have been on this forum for a while and from time to time there have been as**les but the moderators have really keep them at bay.
About your problem, it would be a lot better if you replace the MAP sensor, the O2 Sensor(These control the Air/fuel mixture ratio), the TPS, clean the TB plate and mouth, clean the IAC mouth, Change Air/Fuel filters, PCV, OIL Filter and reset the PCM. Because the computer have tried to adjust itself to the new readings of the fouled or dirty controls/sensors and if your replace them the PCM must learn that fact.
That would really help your car, that is a major tune up but if the car is in good shape it will worth it. Almost I forgot, make sure that there are no air leaks on the intake manifold. It would make the car idle herratically or even histation.