Ok so I went out to fire the '89 vette up today...starter kicked over just fine except wouldn't fire the engine. Tried this 3 or 4 times - same result Car ran fine yesterday and the day before that and so on.
Voltmeter in the cluster says 12.8 volts. So I got out the volt meter to verify the 12v reading.....it was OK at the battery... but I found that most everything inside the car seems to be 8.4 volts instead of 12 Checked/probed the battery and fuseable links, behind the battery, with the same meter and everything seems to be 12v....but 8.4v in the fuse pannel. Pulled the ECM out from under the dash and measure/probed the ECM input power and it is 8.4....the injector drivers are firing but only @ 8.4 volts...which I guess is not enough to trigger them. Ohmed the all the Bosh II injectors and they were all ~16...so they seem good. Even the cig lighter is @ 8.4 and that thing is not feed by way of the ignition switch. I messed with this stuff for an hour or so but had stuff to do today so I took the other car (girlfriend's Pontismack) instead. Time to bust out the old FSM I guess.

So what do you think short or loose connection somewhere?



Oh...there are no trouble codes.

 

Ignition Switch?

 

 

Yes, I thought so too at first but the cig lighter socket is 8volts too...and it is hot (has voltage) all the time.
I'm thinking it it just a loose connection not a short but I'll check the battery voltage in the morning to see if it has dropped at all.
was just wondering if anyone else had anything like this before.

 

Very strange. A dead short should blow a fuse. A voltage drop of that magnitude seems to indicate a large unwanted resistance somewhere. It would also be indicative of a large current draw somewhere. Even though the engine won't start, does the starter motor turn over "strong" ?

 

Yep, starter is strong as are the rest of the systems out side the cabin.

After looking through my FSM and having a few beers I see the the problem is before the ignition switch. Either at the "jump start junction block" or at the firewall junction 42 cavity plug "C100" bulk head connector. I'll have to probe the primary wires at the fusible link one more time to figure out which is the problem. I know I pulled, scraped, cleaned the brown goop crap off this connector and seal it back up with RTV around the edges 4 or 5 years ago. I'll take a look at this closer tomorrow and post the findings.

 

Ok so I checked the battery this morning to see if I had any voltage drop over night from a possible short. Nope - no drop in voltage at the battery and the electrical inside the car was still reading ~8.5
So I pulled the side panel off the car and probed the wires w/ the fusible links on the "jump start junction block" and found that they all had 12 volts....so those were fine.
Disconnected the battery and removed it to gain access to the firewall junction 42 cavity plug "C100" bulk head connector. It took a great deal of time to remove all the RTV I had packed around the connector from the last time I messed with it. By the way, the bolt in the center connector of the bulk head connector is a 1/4". Removed the connector and found that a bunch of the "black tar goop" that the factory used to seal the connector had seeped back onto the pins from the wire side. I didn't seem damp or wet inside just black from all the OEM tar stuff. I did find 2 pins that seemed like they were pushed back into the connector housing a bit so I pulled them out to match the others and they seemed to lock into place. I'll have to look the pins up in the FSM to see what they go to exactly. Cleaned both sides of the connectors with a very small stiff wire brush and about 200 Q tips using alcohol. Applied RTV to fire wall side of the connector and buttoned everything back up. I also cleaned 1 other connector just behind the battery...not sure what this goes to...but it is now clean!
Measured the voltage at the cig lighter and it was back at 12v. Hit the key and the engine sputtered a little then hit the key again and the old girl fired right up. Let the car run for 15 min or so and then shut it down, came back to it an hour later and it started right up. Seems like all is well again.

Thanks!

 

Glad to hear you nailed this one. Weird how some of the pins "slipped" back into the connector...... time and vibration I guess. Ho many pins on that "C100" bulhead connector ?? Does it have a lock tab ?

back on the again......

 

There are 42 I believe....didn't really count them. The connector looks like one big plug but they are really 2 interlocking pieces that make up the one side in the engine compartment. 2 seperate wire bundles goes to each 1/2 of the connector plugs. I might have been guilty of pushing the pins back last time I cleaned & reseated the connector they were only back about 1/4 inch or so...not sure this was a problem since the connectors seem to insert 3/8-1/2 inch. This time I took extra care to wiggle the connector while tightening the connector hold down bolt. There are plastic covers which go around each of the 2 wire bundles and they have locking tabs but they don't perform any function regarding holding the 2 halves of connector together or securing it to the cockpit side of the connector. The only thing that holds the two sides together is the bolt in the center of the connector. Time will tell if this was infact the problem area. Maybe the car just wanted some TLC.

 

Congrats on the repair. This could be helpful in the future.

 

I have never even looked at the connector. Maybe I should, for preventive maintenance. I was shocked() when I looked at the FP relay and saw how melted back the wires were.

 

It is not hard to get to if you remove the battery. Make sure you have a full can of a CRC (electronics cleaner), some alcohol, a full box of Q tips, RTV, about 2 hours of time, and some patients. You can substitute beer for the patients...I did.

 

Glad you got her running again.
A buddy with a C3 emailed me to let me know how many vettes and classics were on the road today
It was about 60 degrees up here today and sure wished mine was running again.

 

C4's have all kinds of crazy electrical gremlins

glad to see you fixed it.