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 !!!!!!!

Mike_88Z51

The 89 ECM batch fires the injectors by bank. The 1,3,5,7 injectors all fire at the same time and the 2,4,6,8 injectors all fire at the same time. It is possible for shorted injectors to cause the ECM to have electrical problems. In your case, the ECM is working perfectly at times and faulty at others. My guess is that either you have wiring/connector issues at the ECM wiring harness, or you have a bad ECM.

You might want to double check the connections on all of the injectors and the wiring. Pull (gently but firmly) on all the wiring to the injectors. Also, physically pull on the battery cables and ensure that they are tight and uncorroded. My brother's 89 had a new battery cable that wasn't correct and the cable would vibrate at the retainoing bolt enough that it caused all kinds of intermittant problems when running at certain highway speeds. After 2 reputable shops checked it over and could not figure out what was wrong, he let me have a try. As I was physically testing all possible wiring connections, I pulled on the negative cable and it jiggled at the battery connection. The retaining bolt was partially broken inside and the cable would vibrate on the bolt into the battery post. A new cable solved the problem.

I once had intermittant issues similar as what you are experiencing. In my case, a scan of the car while driving showed 5 DTCs (Diagnostic Trouble Codes) in different sets of engine sensors being set ALL at the same time when things went bad. The central point of failure was the ECM, so I replaced it. That solved my problem.

Usually, if the ECM will not communicate through the ALDL properly, it is a real good sign of a faulty ECM that needs to be replaced. Since you have jumpered the ECM and had it act faulty at least once, I'd suggest getting a scan tool on the car and trying to repro the problem. If you don't have access to a laptop and scan tool, I'd take a chance and spring for a new ECM to see if that solves the problem. NAPA had them for around $120 last I checked.

One thing you might try before replacing the ECM is to pull it out and spray some quality electrical contact cleaner on the contacts in the wiring harness and the ECM connectors. It did sit for 10 years. I'd suggest the DeoxIT ProGold kit from Radio Shack. Excellent contact cleaner and protectant.

jhaf11

Thanks Mike_88Z51,

The more I read on this forum the more I believe I need a scan tool. I am going to order the cable thru ALDLcable.com for my lap top tonight unless I get advice fromn this post not to.

The other advise I have got is grounding issues. I am going to also order a manual from Helm tonight, my experience in the past with them is they usually have pretty good schematics and locations for wiring as well as other things.

In the mean time, is the ECM located under the dash on the Passanger side? wouldn't mind checking out connections on it will wait for above mentioned stuff. I know it seem likme a basic questioned, but I'm new to vettes and just hate pulling stuff apart under dashes to find out its noyt there.

msslp04

Look at your other post.

Mike_88Z51

The Factory Shop Manual (FSM) from Helm Inc. has excellent electrical schematics for the 89. Buying the FSM is money very well spent.

Yes, the ECM is located on the passenger side above the lower dash pad. Not hard to remove and replace. While you are in there, double check that no mice or other small varmits have done any damage to the wiring harness. A friend of mine sold an old Dodge that had been sitting for over 10 years in the garage attached to their home. Dislocated a small family of mice when the new owner showed up to tow it away.

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