I've had this problem for the past few years. Intermittently, the car will not start. It's not the DME. The battery has voltage reading of 12.6v at rest. When running it's ~13.8v. The car may start normally, drive normally and I turn it off and then it won't restart. This may be after a 5 minute drive or a 30 minute drive. It can also happen when the car has been sitting at rest. There is no click and the engine doesn't turn. I can hear the pumps priming and the windows/lights all work normally. I will cycle the immobilizer to no avail. Then after 1-10 minutes of trying, it will suddenly fire up.

I had the car checked at my shop. Of course, they could not reproduce it. They checked the ground strap, ran their diagnostics and found nothing wrong. I was running the Immo-block at one point and it still did it. I was wondering if the immobilizer could be acting up, but it's not clear to me.

Any thoughts? Really need a solution and I'm out of ideas.

Video of my attempt

 

Original starter motor?

 

No experience with this, but perhaps intermittent/corroded/pitted ignition switch "start" contact? Or clutch switch?

Ron

 

The video shows the immo is disarmed so it's not that. Could be the clutch switch as Ron noted above, or starter relay R61. To rule out both those, remove R61 and jumper terminal 3 and 5 and try restarting.

 

Which model year is this car?
It could be a worn-out ignition switch.
Cheers,
Tore

 

Yes original. The thought crossed my mind that the motor could be at fault. Not sure how to check for that - I specifically asked my shop if it could be the motor when they looked at it and they said it was fine, though I don't know what (if any) diagnostics they ran on it.

Good tips. Thanks!

Good thoughts. Might be worth preemptively swapping these out. My light switch was corroded and had to be changed, so I could see the ignition being an issue.

It's a '98 C4S.

Edit: Just realized the ignition switch may be tougher than I thought.

 

^An easy test to rule out the start contacts in the ignition switch is to remove R61 and apply 12v directly to terminal 5 (make sure car's in neutral). If this test and the R61 jumper test don't get the car cranking, then you can get into the more difficult starter motor tests.

 

Mine would ALWAYS start first time when cold. It began to not start at any point after that (within a few hours until completely cold).

It couldn't be the starter as it ALWAYS started from cold...... could it?

I swopped out the starter (for a 996 turbo version) and it's been perfect ever since. I did replace the starter ground strap/wire at the same time, so it could just have been that.
But the 996 Turbo starter spins it up sooooo much faster, it was worth the cost whatever the reason was.

 

As has been suggested, it could be the clutch safety switch. By-pass it with a jumper at the pedal cluster. It's just another government-mandated "nanny" we can do without.

 

Had the same problem years ago. Chased it for two seasons and finally replaced the clutch switch and the starter relay. Problem solved and never reoccurred.
Follow Jay’s advice replace both

 

I'm sure this is a dumb question...but is there any downside to just installing a bridge adaptor relay and calling it a day if I don't care about having an immobilizer or clutch switch?

 

I installed the same jumper in relay slot R61 to improve reliability. With it, you won't have to worry about issues with relay R61 OR the clutch switch. The only "downside", if you can call it that, is that the car will crank even if the immobilizer is ARMED. This can be confusing as normally no-crank is the first indication the immo is armed.

 

Following up this thread - I installed the bridge adaptor relay bypass in R61 and the issue has not returned to date.

I could try and replace the clutch switch to nail this down further (I suspect that's the issue) but I'm leaving it alone. Works fine as it is.

Thanks all for the helpful advice.