Ok, brief service history to line things up: '82 CE, 65K miles, ran perfectly all last year and even over the winter. I had the valve seals replaced (in car service) about a month and a half ago, and while driving home I noticed the tach was jumping.. a little odd, I thought, so I called the tech that worked on it and he said he hadn't touched anything electrical that would cause that. My thought was if you had to basically take everything off the top of the engine, then you had to have touched something electrical, but I digress. Car made it home (10 mi) with no issues, so I parked it in the garage. In the meantime I replaced the fuel pump with the 1984 "upgrade". Having bought the car used and previous owners with deferred maintenance, I thought it prudent just because. Pulled the pump and hey! Looks like someone was in here before with a relatively new pump and filter setup - and even had the same plug ends as the one I bought. I swapped it anyway and kept the "used" one as a spare. Forward 3 weeks.. with rain every weekend, I never had a chance to get it out on the road. Went in to turn it over just to let it run and found the battery dead. Ok, hmm.. new(er) battery. Jump, start, and good to go. Repeat that for the next 2 weekends - dead battery, jump, start, ok. Finally the battery wouldn't take a jump at all - I could smell the "acid" smell when they get hot from trying to take the jump charge, so I pulled it and got a new battery. Put the thing in and got nothing when I turned the key. Not even the lights came on. Popped the hood and the hood light was on. Huh? Checked and double checked the connections - everything was tight. Went in to look through this forum sticky to see if there were any ideas (didn't find much), went back outside, opened the door... and I had interior lights. And it started. HUH?? Almost like there is an auto-reset breaker somewhere (there isn't, at least on the fuse block). Ok.. seems to be fine. Ran it around the block - tach still jumpy - but seemed fine. Forward to today - a perfect weekend to cruise. Start out everything is fine. Tach still jumped from time to time. Got about 15 minutes into my ride, powering up a hill, tach really started jumping and the car lost power - not all at once, but like I had taken a lead off the battery and put it back on in rapid succession. I dropped my speed a little (50 mph) and it seemed to quiet down, but I was already looking for an off-ramp just in case. And sure enough, the tach started jumping wildly again, car bucked three or four times and died completely - no power anywhere, not even hazards. But.. the hood light was still on! So.. called for a tow truck, he got there about 20 minutes later (and we were focused on getting the car back to the mechanic shop), he had the cables on ready to winch up and dammit - the car got the power back and it started. I'm at a complete loss as to where even to begin. I can't find a single loose wire. I'm starting to think that maybe the fuel pump was wired backwards and it's pushing a code to shut the car down, but then it wouldn't operate, would it? Reading through the sticky portions, it seems that there is some sort of wire bundle that tends to fail around the distributor with loose grounds. Another possibility? Did I fry the ECM trying to jump start it so much? Just trying to get a list of possible options to work with the shop when they open back up on Monday.
Thanks,
Rick

 

With switching out of a couple of batteries, I would think those connections are good. But have you cleaned the starter connection and the engine ground? What is the condition of the cable ends, especially where the wire enters the connector?

 

One would think, yes. I have not looked at the starter and engine grounds. Could be some of the jumping may have toasted one or two wires. I have to get it on a lift to check - hence making a list for the shop so we can both go over it.

 

Have the battery cables been replaced? The original cables often corrode internally so they appear fine but have a high resistance.
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This is a long shot, but anywhere you can reach behind the dash with your hands, slightly move the wiring bundles while the engine is running to see if you can cause the tach to act-up......do the same to the engine bay wiring bundles.

Be SURE to remove any rings on your fingers and your watch FIRST to prevent electrical shorts.

 

Battery cables front to back? I don't think so, but good place to start. We can run a resistance check on them. As for the wiring bundles.. yeah, I'll give that a shot, but the jumping tach and the power loss seem to go hand in hand.

 

You can't properly check the resistance of any of the main wires unless you have a special low resistance meter.

I'd tend to be looking at fusible links coming off the solenoid and then the firewall connectors. There are a number of main power wires passing through the firewall connectors a few times on an 82. Look for red, red/black and red/white wires.

 

You have a ground problem. You need to find someone who understands automotive electrical systems. It's always difficult to tell if things are related but with cars problems lay dormant in till the correct algorithm of events come together. Ground problems typically behave exactly as you describe. Resistance tests will not likely help you. You will most likely need to do some voltage drop testing.

 

I agree with the grounding issue, the dilemma seems to be that it happens when the engine is hot, if I read the post correctly, when it cooled down the power came back. I don't know if the voltage drop test would show anything because I didn't read about any issues that the engine is turning over slowly.
I think a low cost dyi could be to cut off any suspected bad connector or battery terminal, go back an inch or so into the cable and install a new connector.

 

It sound to me like the alternator is throwing out AC or too much ac ripple- the diodes have broken down/ or bad connection internally/ or issue when the alternator gets hot.

The acid smell- the battery is trying to filter the AC from the alternator-

The tach jumpimg-there's actually a filter from the factory to filter the AC.

And the ECU does not like AC.

Start the car up- put your meter on AC and see how much you have at the battery terminals -should be no more then .5V.

Richard

 

Ok... great points. Yes, it seems that it only happens once the engine is up to temp; I had considered grounds and will most certainly check them. I kind of thought that the mechanic must have knocked something loose doing the valve guides or missed something on the 'putting everything back in place' part. I would suspect not hard to do with an engine with this many hoses and connections (relatively speaking for it's age). The alternator: didn't think about that but it was quite warm when the engine first died - warmer than I thought a working alternator should be for the amount of time the car had been running. Another to put on the list to check. How badly would a wonky alternator damage the ECM? Should I start looking for rebuilds/replacements just in case?

 

Did you even notice the Batt light coming on or flickering?

 

Nope, not once. All the gauges showed good, no flickering from the warning lights until the tach started jumping and the car started losing power.

 

Oh- another symptom that points to bad alternator- is when the battery smells like rotten eggs- it's also is getting really hot- chemical reaction going on. When the battery cools down- it will "work" again. That's your auto-reset.

Yes- the ECM can get fried...every try plugging in a battery powered radio into a wall outlet?!!! IIRC GM wired the ECM directly to the battery - to help protect it. The battery not only starts you car but filters and stabilizes the voltage.

Richard

 

Thanks Richard. Well, I hope that it's as easy as the alternator. I tried tracing the wiring diagrams in the assembly manual but that's like trying to read Sanskrit, especially since some of the pages have been copied and recopied and the text gets lost!

 

Did you get the acid/rotten egg smell with all the batteries you tried?

When you first start up the vette, have you checked the voltage at the battery. How about when the alternator started getting really hot?

 

Actually, only with the last two. Bought the car 3 years ago. The PO said he had put a new battery in it months before I bought it, so I took him at his word (my mistake due to lots of deferred maintenance). But the car started, ran and drove fine. Over the past couple winters it usually sits, so that battery had slowly died - took a jump for only so long, so that's when I did the first replacement battery. And that one almost right from the get go never held a charge (I only really smelled the acid when I was trying to jump it). So we wrote that battery off as just being bad right from the get-go. Installed the current one and everything seemed fine. I only smelled the acid when I popped the cover to check the actual battery terminal connections this time. I haven't checked the voltage at startup... the gauge registered around 14v which was what it normally reads, but I never put a meter to the alt or the battery... yet!

 

Two for two with new batteries...and maybe the first one makes number three ?

The smell of acid ...either the Alt is overcharging DC- but more than likely you'd be burning some bulbs out (dash ones usually go first!) or what I think-putting out way too much AC voltage.


No doubt it's the alternator.

Richard

 

I find it very hard to believe the alternator is at fault if you always seeing 14V on the voltmeter. But then I find also find it very hard to believe the alternator could cook the battery enough that it goes dead and causes the car to shut down yet completely recovers after sitting a bit so the car will re-start while not showing any signs of this happening.

 

We'll find out tomorrow. So far it's a possible loose ground(s), internally cracked wires, fusible links or the alternator. If the alternator is failing once it hits a certain temperature, then that would make sense for the rest of the symptoms. But a loose/corroded/broken wire somewhere could also cause the issues...

My mechanic will have fun with this one...