Noobie here, actually the son of a first timer.

We are working on a 1987 C4, which has been an issue from the get go. 79K miles.

When we got it 8 months ago, seemed to run fine, since then it has progressively got worse. It would load up with fuel, then got to the point where driving it, when stepping on the accelerator it would die.

The local mechanic was reading the codes on the ECM. he mentioned he was getting bad signal and mentioned to replace the PROM. We replaced the PROM, still did the same thing, He then said to replace the ECM. We have since replaced the ECM, now we have a new bug.

When cold and you turn on the key, the coolant fan relay kicks on/off, thus turning on the fan. This will go on for maybe a short time, or a long time, no consistency. During this time if you try and start it, it will run for a second or two then die. If you wait long enough for the fan to quit running, the car will start and run, and run like a scalded dog. Also the dash lights will flicker when the relay kicks in.

After the fan quits I did watch the SES light and it would flash a 12 code three times then quit. (had to troubleshoot that circuit and found a burnt out bulb)

This is as far as I have gotten. I hope to get a scan tool to maybe help troubleshoot it more.

I am suspicious of the new ECM and think I may need to replace it.

We do have the Service Manual and have seemed to get quite familiar with it.

I have checked grounds, they seem fine.

Any help is appreciated.

Tink

 

So you went thru the harness grounds on the block under the oil filter?

and the power distribution post aka the jumper post?

I'd put the old ECM back...there was nothing wrong with it.
There is no telling what codes there were if the SES buld was burnt...old trick to PUT a bad bulb in there so the inspector does NOT see the SES lit when he does his visual inspection...

Go thru the MAF relays, set TPS to spec, and get fuel pressure and verify key on pump prime and pressure at start up.

Recon ECMs are always scary....especially when its usually not the ECM to start with.

If you have the FSM set then go thru the flow charts on "no run" or will not stay running and it will take you thru the rest of the process. Ohm the inj, set base t iming,and do the basics. And get some run time with the original ECM and then go back to check the codes it sets...that takes a few seconds of running...but you may get lucky with maf relays or harness conenctions...which are often the fault.
That car does not have the miles to have serious issues. relays and harness if anything.

 

 

Thanks for the replies, unfortunately I do not have the original ECM, it was sent back for core charge.

I will continue on and see where we go from here.

The bad bulb theory is a definite possiblity.

Thanks a bunch,

Talk to ya soon

 

Yep...I've seen the bad bulb inserted when the ECM was stuck in open loop but had been good enough to get past a smog...its the SES that gets the attention of the inspector and gets you an instant FAIL if its lit.

 

Forgot to mention that only after my Dad purchased this did he have me do a carfax. Bad News, it had been wrecked, at least 11 title messages, not to mention it was a lease vehicle when it was new, possible mileage discrepency. It had been rode hard and put away wet.

I knew something was up when the previous owner asked if we had brought the tube of alumaseal for the radiator, and the 'nice paint job' didn't match the gas cover. P.O. thought it was original condition. Boy he sold it well.

Can I hear someone yell LEMON.

Anyhow I get the joy of working on it and I don't mind. Love a good challenge.

But he's happy and that's what counts, unfortunately he hasn't put 500 miles on it since he got it because of the issues.

Also the a/b side of the ECM had been hot at one time as the plastic faceplate was brown due to heat, so someone redid the ends with a new connector. There were two solder joints one inch a part, thought that was the problem so we redid those, better know, but found out those had fed the instrument panel.

More investigative work to come.

With a great forum like this we will get it figured out.

Thanks again

 

i have the same problem,, let me know please!!!

 

lanecarpentry@aol.com I HAVE SAME THING, PLEASE!!! LET ME KNOW

 

i first replaced the fuel pump, then pulled the battery and changed the inline fuses to reg auto fuse, except the main fuse to the dash i ran an 80 amo, i changed nthe fuel relay and all woprked out. i suggest you change the relay for the fan as well. and get another ecm if you can afford it. this vette i have had sat out oopen in a field for 2 years, i put a lot of work doing everything myself. this forum helped more than the book. these guys are vette nuts like me. good luck my yellow 87 nconvertible is awesome. it just takes a lil pittling but once the car knows you loive her she comes around. good luck and may the vette force be with youLa. vette man

 

The ECM will turn on the fan if it sees high coolant temperatures. The fact that it "kicks on/off" says that you have intermittent power or ground connections (most likely a bad ground).

Check out the wiring:

The power for the ECM comes from the positive battery terminal and goes through a single pin connector (ECM reset connector) that is usually buried underneath the power brake booster. Follow the small wires and you'll find it. This is mine:



The grounds for the ECM and sensors go to a large bolt on the side of the block above the oil filter. This is a classic spot for problems. The negative battery cable goes here and there is also a copper braided ground connection that goes to the frame. There are about 5 or 6 black wires -- those are the ground connections to check out. The usual protocol is to remove the bolt, clean all the connections and reassemble. I used a small wire brush on mine. Here's what mine looked like right after I had a fire (that's why the loom is melted and the wires discolored -- and fire extinguisher powder on stuff in the previous picture):

 

i'm leaning towards the ECM as it did not do this until I replaced it. We replaced the fan relay before the new ECM as we determined it was bad. To me it acts like the ECM, its wierd as long as the fan it running it won't start, or will start and run for a couple seconds then quit, when the fan quits, it starts and runs fine. gonna keep going through the grounds and power. I'm not sure if I'm getting a bad signal to the ECM or what.

Thanks for the help and encouragement.

 

Cliff,

I have seen the bolt on the block and am in the process of trying to remove it. PITA.

Maybe if I rub her real nice she'll come around. From what I have gathered I am on the right forum for help. This place has been a great help so far.

Will keep you informed.

 

Update, grounds and power connections all gone through. Didn't look bad, but cleaned them anyway. Fan did not come on, however car would not start. cycled the key three times and it started. Also had to add the battery charger.

Car ran good, no codes, probably due to them being cleared with battery disconnected. Ran to operating temperature. everything seemed good.

Went to town to get parts, came back, had a difficult time starting, but did start. Now have a 36 code. I have diagnosed to the MAF relay possibly bad.

BUT, the fan kicked back on with the key on.It cleared itself rather quickly and was able to start the car. I have now noticed (SES with new bulb) that when this happens the SES tries to flash codes, just like when you short the ALDL for the SES to check codes. Almost sounds like I have a short somewhere.

Tink.

 

Think I'm getting closer. I noticed tonight that the car would quit and not start, but the fan was not running. Had a thought and put my test light on the input side of the fuel pump relay. Waited for the car to die again, sure enough fan did not kick in, but my test light went out.

Moved the test light to A1 on the ECM so I could watch it as I sat in the car. started the car again, waited for it to die, sure enough light went out right at the ECM.
suspecting the ECM at this point but time will tell

MAF update:
MAF relay for the burnoff circuit was the culprit, it was the contacts inside it, was able to tear it apart (it was still pulling in) cleaned the contacts and WALLA, this cleared the 36 code, now I have a 33 code. in the process of troubleshooting it now.

 

Guess you haven't got that FSM yet...
your still in the MAF and the source of ALL the problems...
Now go get a MAF power relay. Same relay as burn-off. $6 each and MUST haves.

BTW your fuel relay died because the pump gets its power from the ECM permission only when the dist sends a reference signal. No dist firing, no fuel pump power.

Your car starts and runs like a scaled ape sometimes because you;ve accidentally forced it to open loop. Closed loop with a bad MAF circuit will not run...much.

 

well said

 

I do have the Factory Service Manual. It's the only way I have been able to test this, along with the help from you guys.

I understand a new relay, but at midnight and 35 miles form the nearest parts store I was not able to got get one and that was the time I working it, pulled the relay apart to clean the contact to continue with the MAF circuit. That's when I was able to clear the 36 code and got the code 33. I let it run for 1 minute just as the FSM said and it cleared as well.

I am hoping to get to town today pickup a couple relays if they have them in stock.

I am going to continue with the troubleshooting and follow the FSM.
The ignition/fuel signals are next.

Thank you for the post.

 

My friend, this 87 convertible is my 6th corvette, i had bought 5 off ebay in 2007. I am a corvette freak /nut/junkie lol. I am in a wheelchair from a bike accident and the vette is the only car I can actually do all the work myself on. I feel deep down you have the vette lovers fever starting simply because your giving it so much attention, Just wanna give you a pat on the back and a hand shake and say welcome to the world of the finest american made street machine. a vette no matter the year is a statement of serious driving swagger,.lol anyway I am hoping soon to move to Florida and rent vettes out on the beaches there and let guys get to drive the dream for a reasonable price, i think it will work great. stay with it and as you say the guys here are better than the books.this I learned as well. they have hands on experience and actually a real vette enthusiest is drawn to other vette guys of the same nature. look me up on face book and meet some of my local vette buddies from Louisiana as well. Marty Dufrene in Gray Louisiana. good luck with ya machine buddy..be blessed

Thank you for the post.[/QUOTE]

 

Short update on where I stand and what I have done.

SES bulb burnt out/ replaced
MAF burnoff relay contacts bad, tem. fixed to continue troubleshooting, then replaced relay.
MAF power relay bad, tem fixed with other relay until new one arrived, then replaced with new relay.
Ignition system check, O.k.
fuel pressure good
intermittent fuel pump relay, replaced.
Found out I had a temp connection, now a definite open, from under the dash feeding power to injectors 1,3,5,7, thus the engine not wanting to run.
Working on tracing out the wiring harnes to find the 'open' in the power that feeds those injectors.

 

The power for the injectors goes through two fuses, INJ1 and INJ2, one for each bank. Check those guys.

The ECM side of all 8 injectors are connected together inside the ECM (light blue and light green wires), so you should be able to measure low resistance between those wires from one bank to the other.