Engine won't turn over when warm

[Crusin]

I presently own a 1990 ZR-1. After driving for a while and trying to start, the engine doesn't turn over . As soon as jumper cables are put on the battery, the engine starts right up. Had battery and alternator checked out okay. Problem persisted. Had battery changed and starter rebuilt. After driving 60 miles or so turned off and tried to start later and still got the same problem with no start. Had key checked and is okay. I would appreciate some suggestions. Thank You

[GOLDCYLON]

Bad clutch switch or your starter is suspect. My money is on the clutch switch as the culprit. A lot of members have bypassed the switch as to not get stranded. Look in the solution area and that should walk you through the process.

Heres a link below on how to run the bypass

Welcome to the forum. GC

http://www.zr1.net/forum/showthread.php?p=98493

[Crusin]

Thank You for your suggestion, I will have that looked into.

[rhipsher]

Need to make this one a super sticky. Its like Deja vu all over again.

[Brad Sewell]

I would also check the starter ground and the negative battery terminal for corrosion and clean the connection points on the frame

[Kevin]

if you haven't done it bypass the clutch switch. did many years ago and never had another problem with that

[scottfab]

Battery......
If you put cables on and it starts right up then it's battery.
I assume by "cables" you mean a jump.
The car is very sensitive to a marginal battery.

Also, I'd leave the clutch switch in place. It's a safety feature.
They only burn up if you don't have the clutch fully pushed
when you turn the key.
Many get in the habit of turning the key as they press the clutch
and this put a hurt on the switch (arcs inside)
I've never had an issue with my clutch switch in 15yrs of driving.

[Paul Workman]

Originally Posted by scottfab

Battery......
If you put cables on and it starts right up then it's battery.
I assume by "cables" you mean a jump.
The car is very sensitive to a marginal battery.

Also, I'd leave the clutch switch in place. It's a safety feature.
They only burn up if you don't have the clutch fully pushed
when you turn the key.
Many get in the habit of turning the key as they press the clutch
and this put a hurt on the switch (arcs inside)
I've never had an issue with my clutch switch in 15yrs of driving.

ABSOLUTELY!!! I was just about to say this very thing!

A while back I posted a schematic for a relay to do the heavy lifting, leaving the clutch switch to simply activating the relay - vastly reducing current draw through the switch. However, in retrospect, the problem with the arching is simply moved from the switch to the (mechanical) relay. So! I think I'll re-design the circuit and put a MIL spec solid state (FET) in place of the relay (read: no arching ever).

That said, Marc Haibeck made the comment once that he bypassed the clutch switch because pressing on the clutch puts a good deal of force on the thrust bearing in the LT5, a bearing that can be very dry, depending on how long it has been between startups. So... There's that to consider.

This discussion is warming to a tech article for the Registry, methinks!! But, in the mean time, I agree - we should be a smashin' da clutch afore turnin da key, doanchaknow!!

P.

[Crusin]

I would like to thank you all for your suggestions in regard to my current problem with engine not turning over when hot. Keep on Motoring Guys. CHEERS:

[scottfab]

Originally Posted by Paul Workman

However, in retrospect, the problem with the arching is simply moved from the switch to the (mechanical) relay. So! I think I'll re-design the circuit and put a MIL spec solid state (FET) in place of the relay (read: no arching ever).

Not a bad idea as long as the FET is clamped with a zener to protect it from the inductive kick of the starter solenoid. (similar to class D amps).
Then, like any mods, it's a matter of documenting it well and in a place you'll find it if something goes wrong down the road. (or for the next owner) One of the biggest lessons I learned on custom mods was to document well. There's no amount of "oh I'll remember what I did here" that works

Originally Posted by Paul Workman

That said, Marc Haibeck made the comment once that he bypassed the clutch switch because pressing on the clutch puts a good deal of force on the thrust bearing in the LT5, a bearing that can be very dry, depending on how long it has been between startups. So... There's that to consider.

There will always be this pressure on the thrust bearing either before start or after. Failure will not be due to pressure on the bearing but the spin of the bearing dry which would happen regardless. (IMHO)

Originally Posted by Paul Workman

This discussion is warming to a tech article for the Registry, methinks!! But, in the mean time, I agree - we should be a smashin' da clutch afore turnin da key, doanchaknow!!

P.

Best overall solution would have been in the initial design. That is the NO (normally open) clutch switch in line with the high current starter solenoid is bad. Better would have been a NC switch in the gear lever at neutral. No one would be moving it while turning the key.

A noted and well know author and owner of a ZR-1 once said of the GM designers, "these are highly skilled, highly paid engineers that focused on these designs for years. They know more than shade tree mechanics." (paraphrased) That statement comes to me every time is see someone on this forum struggle with some of the more notorious failures. Fact is we've had decades now of experience that those engineers did not have. Improvements are not only needed but necessary for the good of the car. However, I've always made my mods "backoutable" just incase it's important to the next owner. (very likely after I'm gone)