C4ProjectCar

Intermittently, I've found that my car won't start. Jumping it or putting a charger on it seems to do the trick, so I thought my alternator might just be weak. However, it happened this morning when I was at home, so I was able to check things out with a digital multimeter. The battery voltage reads 12.4v, which by all accounts should be able to start the car, but it won't crank, and it doesn't even make the clicking I've always experienced when trying to start a car with a dead battery. I turn the key to "on", and the fuel pump primes, then I turn to the cranking position and it's just dead silence.

This has happened probably 5 times in the past 6mo, and it always starts right up with no indication of low voltage as soon as I jump it.

I read up on possible causes, and bad wiring or a bad connection seemed to be a common problem. However, I measured just about 1Ω from the negative post to the block and from the positive post to the hot wire on the alternator (I know, I should measure to the hot wire on the starter, but I can't jack it up right now). Besides, I would think not much (if any) current is flowing if it isn't even clicking, which shouldn't cause a significant voltage drop over bad wiring. I'd also expect to experience the starter clicking sometimes if the battery happened to be at an intermediate voltage between what it is now and what it is when the car will start.

Any suggestions? The starter is 5 years old, and the battery and alternator were both replaced less than a year ago.

Paul Workman

The symptoms would suggest perhaps the clutch safety switch (or the like) OR the neutral/park position switch not powering the starter solenoid may have become intermittent; a common problem with C4s up until 93 (ZR-1s) when that circuit was redesigned to eliminate the high current through that switch.

Corroded battery terminals, for example, would be indicated by that chattering sound in the starter when switched in the START position. But, because you have no sound (of the solenoid "clicking") at all when switching to the START mode says (to me) the solenoid isn't getting juice; indicating something isolated to that circuit not working.

.Note: I bypassed that clutch safety switch on my Z, which freaks out some ppl. But, I learned to drive farm machinery and a '54 Ford pickup LONG before they put "nanny switches" in cars. SOP is putting it in neutral FIRST before touching the ignition switch. Never an issue in 50+ years of driving.

C4ProjectCar

Clutch switch crossed my mind, but I ruled that out because jumping made a difference every time.

Figured it out though. I had initially ruled out VATS because I had just replaced the ignition lock cylinder, and jumping it fixed the problem. However, it really seemed like the symptoms were just like when my VATS had gone out. I cleaned the contacts on my key, gave it another shot, and it started. I realized past times I've had this issue I didn't clean the key, so I'm guessing VATS just sometimes glitches and it's more a function of the 5 minutes it takes to reset.

The key is new and the lock cylinder is new, so I don't know why this would be giving me issues. Anyone aware of a reason VATS would mess up every now and then?

Paul Workman

Well, you wouldn't get a passing grade in my class by conclusions made w/o direct corroborating evidence. In other words, IF you found the cause and fixed it (and apparently you arn't sure?), it is IN SPITE of conclusive evidence and not because of it.

Never assume...is my point.

C4ProjectCar

By "ruled it out", I meant that I was sufficiently confident it was not the cause to move on to other more plausible explanations, not that I was 100% confident it could not possibly be related to my problem. Switches can stick, and they can break, but I am not aware of a common problem with a switch that would be resolved by putting jumper cables on a car (either resulting from the voltage change or the time it took to hook up the cables). Each time this has happened, I have tried to start it 4-5 times, fully releasing and depressing the clutch pedal each time. It seemed pretty unlikely to me that the switch would suddenly work on the one attempt I hooked up jumper cables each of the 4ish times this has happened.

I'd love to publish a detailed analysis of the issue, but given that it is not reproducible except by chance I wouldn't hold your breath. I'm fairly confident the issue is VATS-related, but it'll probably be a good month or so before I can put that to the test. I don't know that at this point there's really anything you could call "conclusive evidence" supporting any potential cause.

I don't really get the reason for reproach here, but I appreciate your help.

FAUEE

Vats was sketchy when new, now 25 years later it's very problematic. I'd bypass it and never look back. I spent over a year troubleshooting an intermittent no start issue, and it was vats the whole time.

C4ProjectCar

I'm not quite ready to bypass it. Even though it has its quirks, for me the peace of mind is worth a 5-minute delay every month or two. If it gets worse, though... we'll see.

FAUEE

Theres a few situations where you need to make a quick exit, and that 5 minute delay is a real issue. I didnt want that, haha.

C4ProjectCar

Yeah, I get that. If this problem sticks around after a bit more troubleshooting, I'll definitely reconsider the bypass.

C4ProjectCar

It seems to come and go. It happened a few times in a row two weeks ago, and it only happened maybe once since. Then it happened last night and twice this morning. My car leaks water pretty bad, and last night was the first rain we've had in a while, so I'm wondering if water is getting in somewhere. If I have time next time it happens, I'll take apart the dash and measure the resistance across the VATS wires to see if it's in the range prescribed by the GM.

Since I'm running a chip emulator, I realized I could just disable it in the tune if it gets bad.

johnnymo63

Undo the negative cable on the battery and jack the car up.
1st check to make sure the positive cable is tight on the starter solenoid.
If it is, then I would drop the starter and open up the solenoid. There could be dirty/burned contacts in it.
You can take it apart and clean off the burned carbon inside. (wire brush) It's all copper under the plastic end cap, so if it's black and crusty, that could very well be your problem.
(And it's free to check and fix)

hcbph

If you want something to try, here's an idea. It is plug-and-play and is reversible. You can get a dongle from several of the parts suppliers that will match the resistor on your key (you provide that info). Pull the hush panel on the drivers side and look for the wires. They come out of the column near the floorboard and there's a connector around 12" from the column and there's an orange wire in it IIRC. Undo the connector, plug the dongle into the wiring going up into the dash towards the DIC and you've effectively eliminated the need for the resistor on the key. If you no longer have your no starter condition (given time to test thoroughly) then you've likely found your issue. You can then either find and fix the core issue or continue using the dongle. To undo it, disconnect the dongle and plug the original wiring connectors back together.
Here's an example of the dongle I was referring to: https://www.corvettecentral.com/c4-8...ts%26count%3d9

fake

Load check the battery and you might have a flat spot on your starter. Most likely if battery is old it is time for a new one.

confab

If you think it is VATS, can't you just jump the solenoid?

Tom400CFI

Just look at the "security light" on the dash when you go to start it. What's it doing? That will confirm or deny VATS as the culprit, instantly.

C4ProjectCar

Thanks for the suggestions. I'm almost certain it's VATS though, see below. Correct me if I'm wrong.

I don't think so - I believe VATS cuts the starter and the injectors. I've tried to push start it in the past, and no luck.

Yep, that's what led me to my diagnosis. When it won't start, the security light illuminates solid with the key on. After one or two 5-minute waits, the light stays off with the key on, and the car starts.

I've had some issues with my O'Reilly alternator in the past, and I suspect it's not putting out quite enough juice. At times my turn signal slows down quite a bit, and the voltage needle swings pretty significantly with the signal going on and off. Could low voltage be impeding the CCM's ability to read the resistance?