jhaf11

a little history of the car.

I have an 89 corvette L98 AT that I have recently purchased from a friend who had it sitting in his garage the last 10 years. He purchased it new and drove it for its first 40,000 miles and parked it when the tires got bald and the Dash cluster started giving him problems. He would start it a couple times a year. Every year it started harder and run rougher until it no longer ran.

I trailered it home and found 8 psi fuel pressure and 2 injectors at 2 ohms. Replaced the injectors and fuel pump, cleaned egr and thottle body/MAF and it started right up a ran fairly decent for sitting all them years. I then replaced cap/rotor, plugs, replaced all fluids, new tires, repaired digital dash.

I drove it for about a week without any problems and loved it.

Then it started acting up were I need some help.

The SES light will come on and it doesn't want to idle and will kill if it is in gear. If you give it just a little pedal it will stay running but rough. If you step on it normally like when leaving a stop light it will pop multiple time thru the throttle body (like its lean) and will quit. If you give it more than 1/3 throttle it will launch and run right thru that off idle spot and run fine until you get the RPMs low enought to get back under that 1/3 throttle. During this the SES light will be on. Some times the light will be on solid, sometime it is flickering like a bad connection with no pattern to it at all and sometimes its not on at all.

It gets wierder, when I try to flash the codes by jumpering A to B the SES light will flicker like described above with absolutely no pattern, this is when its acting up, I have noticed when it is acting up the fan will come on right away when the key is turned on.

The above desribed problem is not always there. Sometimes I jump in it and drive the hell out of it and its perfect and I shut it off when I get where I'm going and hop back in it it acts up. When it's not acting up the fan doesnt come on when I turn the key. I can jump A and B and the fan will come on and it will flash code 12 at me forever like nothing wrong.

I have searched this all C4 forums a lot for and answers and have try alot of things. The collant temp sensor Ohms out to almost exact ohms for what my pyrometer is telling me. I have not replace O2 sensor yet but like to find problem instead of just replacing parts.

Could bad injectors stressed ECM so it flakes out sometimes. Any suggestions out there? Sorry this is so long but don't know how to explain the other wise. I have monitored the fuel pressure and thats fine, ohmed out new injectors again fine. unplugged Vacuum line to EGR , still runs fine one time not the next. Acts up cold or hot, no pattern I have been able to figure out yet.
HELP !!!!!!!

drive it

Yes, it sounds like ecm related. If you get a corrupted flash on a prom or the prom is not plugged in the fans will immed. run.
First drop the ecm and make sure the prom is plugged in tight. Usually if the ecm/prom is the problem it's a consistant problem, not intermittant which makes me say to check that the harness is plugged in tight and the prom is tight.
Also when it's running good start wriggling the harness and prom.
Let us know the results......

DOCTOR J

GM had a couple of general problems in the early days of FI:

1. There were issues with the conformal coating on the early ECMs - it didn't
age well, and when it broke down it left the main board subject to general
oxidation.

2. Wire insulation on the engine harness was subject to shrinkage/cracking with
age and heat.



Computers aren't immortal - you might want to pick up a spare anyway, while they
are still cheap and plentiful.

On a 20-year old engine, you need to clean all the electrical plugs/sockets anyway.
While there, look for solid insulation where the wires terminate at the connectors.
Any shorts will cause problems sooner or later - as will dirty connections.


By the time they got to the 90s, GM had improved the specs on electronics, and the
issues above became more rare.

Have fun.

Sam Lam

jhaf11: Do you have or know anyone with a scan tool? Use it when the engine is acting up. This will rule out sensors or other defective parts that may cause you to spend lots of $$$.

tjwong

The first thing to do is to check all the engine grounds and especially the ECM grounds. They are located at the drivers side rear of the engine block. If these grounds are compromised all sorts of weird things happen. As Dr J mentioned the car is 20 years old and crap happens, the ECM could be at fault, they are easy to find and available for a pretty reasonable price.

Sam Lam

jhaf11: What type of injectors did you install into the 89 L98 engine? What is the flow rate of the new injectors?

jhaf11

I put in Bosch EV6-22.5 from FiveOmotorsports, It ran great on them for a short period, I have ohmed them all out and they are exactly the same. Proir to putting them in I replaced the fuel pump and completely drained the tank and put fresh gas in. I took the fuel filter off and jumpered the relay and pumped fuel thru the line to clean it out. I then put new fuel filter on and again jumpered relay and pumped fuel thru line running up to rails. I cleaned the rails the best I could since they were off for new injectors. Again jumpered relay and checked fuel pressure as well as trying to flush any thing thru back to tank thru regulator. Spent alot of time trying to make sure new injectors were not subject to dirt inb fuel system, hope thats not the problem.

I will check the grounds tonight, thanks. I have a cable ordered from ALDLcable.com for my lap top for scanning and a manual from HELM on the way. In the mean time can anybody post were the ECM is located? New to Vettes, but not cars. Guessing passenger side under dash. Were is it and whats the easiest was to gewt to it?

Thanks for the help, I will continue to post as I find problems so maybe all this can help someone else.

jhaf11

Thanks everybody,

I cleaned up the grounds, pulled the ECM out, pulled the PROM out of ECM. I then cleaned the socket were the prom plugs in with contact cleaner and sprayed the whole board down with the cleaner and the connectors that plugged into ECM as cleaned up.

I have taken it on 2 rather lenghty trips with no problems, they arte really fun to drive when everything works right, I'm crossing my fingers that it was a bad connection

89 Bob L

For what its worth, a can of contact cleaner goes a long way. Due to the age of the car the contacts need cleaning. I had similiar problems in the past and found that the contact cleaner is the best and cheapest fix. There are several posts in the Tech Section for the dash cluster. The contacts can be bent back into proper position and cleaned with an eraser. While the cluster is out you might as well change the bulbs.

you had mentioned that the car sat for a long time. Fuel in the system for extended periods causes a shellac type build-up. It wouldn't be a bad idea to send out or replace the injectors and clean the fuel rails, also cleaning the injector contacts. (There are also alot of posts on injector advice).

Pete34

Congrats on getting it running again -- enjoy!

Just a small note on fuel injector drivers in the '89 ECM. The 'quad' drivers were designed to withstand a dead short in the wiring so, bad injectors shouldn't wipe out the ECM. .. pete

larryfs

89 had ECM problems.
I replaced mine with a rebuilt GM unit.