Firstly, it's a 94 c4 auto with a new (remanufactured) computer installed in my dad's c4 after a jumpstart gone awry fried the original one (installed about 2.5 years ago). For at least the last 1.5-2 years, the car has been horrible in city (stop and go, stoplights, 35-40 mph speed limit) driving on basically any day above 75 degrees F. If I goto a drive-through, the temp gauge will be pinned by the time I get my food and pull out (5-10 mins).....I'm guessing from all the sitting in one place. If I go on the highway and get some airflow into the car, everything is fine, but watch out for city driving. The car will surge when stopped (when the temp. spikes), and if you don't have your hard foot on the brake the car will actually jump forward. another problem that occurs, that I believe is conencted to the overheating: Trouble downshifting and upshifting gears (rpms will sit at 6k, and car won't know how to switch to the next gear, until you back off on the gas). Today the car was overheating again, the temperature gauge was pinned and the coolant temp ranged from 215-230 (is this extremely detrimental to my engine, as it's a couple time a week thing during warm months?). I stopped in the driveway with the car running, and the fans were on, although they didn't offer much help obviously. Any ideas what this could be? There have been no "service engine" lights or anything. My guesses are obviously some problem with the computer, or also maybe some sort of exuast leak in the engine bay (headers?).

p.s. I've also previously noticed some sort of greasy deposit on the top of the left valve cover (been there for a year or two)....a friend suggested it may be some sort of leak....what concerns me is that I now notice the greasy/oily deposit on the outside of the right valve cover, too. IS this something I need to worry about/get checked out (Obviously we're going to have the overheating checked out finally, probably by the dealer)? IF it makes any difference, we're in the bay area (if anyone can recommend a tuner to check/fix this stuff).

lots of opinions if possible, I'd really like to nail this down....thanks alot for all your help!


[Modified by YellowFvr, 4:37 AM 5/25/2002]


[Modified by YellowFvr, 4:39 AM 5/25/2002]


[Modified by YellowFvr, 4:40 AM 5/25/2002]


[Modified by YellowFvr, 4:42 AM 5/25/2002]

 

id say you have a dirty IAC valve along with the standard city cooling problems, both need fixing.

 

I have seen reman computers do all kinds of weird things. First I would check all the grounds to make sure they are clean & tight. If the problem persists, I would get it put on a scanner & see what the computer is doing. I would rather have a used AC Delco ECM than a reman unit. Good luck & let us know what the problem turns out to be- SCOTT

 

well, here's an UPDATE ...we took it in to a local, regular garage today and they're replacing the thermostat....I kinda doubt that'll help...they also suggested flushing the radiator, and acknowledged that the computer might get screwed up when it's hot outside. I was told not to worry about the greasy/oily deposits on the valve covers that seem to be increasing slowly. They also checked out a fan relay switch they believed wasn't working. then, they hooked up the computer to a scanner and told us that the computer was not communicating with the scanner. We had the scanner installed by Crown Chevy in Dublin, CA, frankly I'm fairly mad because the computer has never really worked correctly since they put it in. SHould the car be/have been tuned after the new computer was put in, and should crown chevy have done that? PLEASE LET ME KNOW WHAT THE NEXT STEP TO FIX THIS SHOULD BE....I'M CLUELESS. Maybe take it to some sort of tuner? Any good ones in the Bay Area? another interesting thing about my predicament: The engine oil temperature is totally normal, even when the coolant and engine/engine bay temperature is very hot......makes me lean towards and exuast leak....? Also, the bucking, surging, and gear selection problems don't always occur when the car is overheating (although I think the two are connected), sometimes just when the car has been driven hard for a bit, probably around 200-210 degrees engine temp.


[Modified by YellowFvr, 9:55 PM 5/25/2002]


[Modified by YellowFvr, 9:56 PM 5/25/2002]

 

TTT

 

Well, I'm still pretty clueless, and not too many people here seem to have an idea, either. I've got it down at Crown Chevrolet, and theys eems pretty clueless as to what's wrong with the computer, although they say they're gonna hook it up to a scanner or whatever and check it out. I looked at the computer and it says AcDelco on it, but it also says remanufactured....that new computer was installed by the same chevy dealer a couple years ago. My water pump seems to have given out, also....I'm hoping that might have something to do with it...possibly the water pump not beign able to move enough coolant, thus the engine compartment becoming extremely hot, then the computer itself becoming physically hot, and as a result the computer starts freakign out...I hope the water pump will be a fix, but I'm doubtful. I do think it may have somethign to do with the problems, however, as the computer will have problems even if the car isn't currently hot, as long as the car has been hot half an hour or so earlier. Also, when the car has sat for awhile (cooled), and is having no problems, the computer doesn't start to act up immediately when the car heats up, which makes me think my above opinion (that the computer itself becoming physically hot causes the problems). Also when the computer is acting up, I sometimes have trouble adjusting the air conditioning (I will try to up the fan speed or hit a lower/higher temperature, but the buttons don't work). Well, I guess all I can do is sit here and wait. I don't think this is solved yet, though....so please give me any opinions/suggestions/ideas you may have.

thanks!

 

RACE STREET AND RALLY (Santa Clara) (408) 980-0866 ask for Max, he is very honest and reasonably priced. I have taken my '89 to him several times and I've had only the best of service. :yesnod:

 

ok, well the water pump has been fixed, but the dealership still seems clueless about the computer stuff....they said they may think it's the optispark...is that the ignition system (?)....and does that make sense in my situation? I think i may take the vette to that place in Santa Clara, hopefully they service lots of vettes.....?

 

why would the opti have any affect on the cooling? that doesnt make sense unless its throwing too much power into the ECM, through a short circuit or loss of ground, and screwing it up :confused:


[Modified by vader86, 11:17 PM 5/28/2002]

 

Do a search on surging and you'll find alot of bad opti's. I had the same surging, would come and go. Finally pulled the water pump this year to look at the opti,(99k) and I found the water pump leaking out the rear bearing. Car hardly used any coolant. Pulled the opti and it was junk with water stains halfway up the cap! So new opti and waterpump went in and it runs cool with no more surging.

 

All they do are Vets. :yesnod:

 

ok, one last question: What's the optispark? (cap, ignition module, etc...??) We got an estimate of $1,000 to replace it!! We probably won't do that now, but soon in the future. Could I use an aftermarket iginition system (i.e. jacobs or MSD) instead to replace the optispark? Would it work as well or better? That would save my dad some real $$$$$.

thanks for all your help and advice guys!

 

ttt

 

the optispark is your distibutor. You will want to replace the cap and rotor while you are there. I had a 94 LT1 replaced at a dealer for the afformentioned $1000, and it was bad in another 60k miles. I decided to replace it myself. Ordered everything from autozone for about $300 and works fine to this day @157k. It is a little time consuming, so be prepared for a day at it if you do the repair yourself. While i did not notice any temp problems with mine, once it warmed up, the surging made it completely undrivable

good luck, david