Strange Loss of Power

[jeffnhiscars]

I was on the interstate yesterday in the 87 Zinno Cab going about 65 or so when the engine just stopped...tach went to zero and NO warning lights which means a total loss of juice. About 10 seconds later it came back and that was that.

Battery and terminals are secure. Could be the ignition switch or.... ?

[jlevie]

If Hot in Run and Start circuit from the ignition switch lost power the DME would shut down and there'd be no warning lights on in the cluster. The same would occur if the DME lost timing data from the CPS. As a diagnostic, a test light connected to the Hot in Run and Start circuit will tell if the problem is the the next time it happens.

[Andy348]

Could it be a loose main relay?

[jlevie]

Could it be a loose main relay?

That should turn on the Check Engine light.

[jeffnhiscars]

I've thought about the CPS since about 1 out of every dozen cold starts take 2-3 attempts, but would a bad CPS shut down all power and kill the dash or just to the fuel system ?

Alternatively, where besides the ignition switch could cause main power cut out ?

Keep in mind that every ground in the engine compartment, the main underdash (to the left of the steering column), under the back seats & in the trunk has been taken apart, cleaned and reassembled with dielectric grease.

[Chriskbmx]

sounds like a cps issue to me. i had a saab c900 that had a cps issue and it took me forever to diagnose it. the car would randomply loose all power then come back. and would start right up. eventually it got to the point where it wouldn't start at all once the car got hot. sounds like the same issue. if the dme isn't getting a cps signal wouldn't that cause the dme to shut down?

[jlevie]

I've thought about the CPS since about 1 out of every dozen cold starts take 2-3 attempts, but would a bad CPS shut down all power and kill the dash or just to the fuel system ?

Alternatively, where besides the ignition switch could cause main power cut out ?

A bad CPS or bad engine harness would just cause the engine to loose spark and fuel and also cause the tachometer to go to zero. In some cases it will cause a CEL pointing to an injector or fuel relay problem.

A problem in the circuit from the ignition switch will shut down the DME and may cause the CEL to light. The radio and other things may still work. The circuit from the ignition switch is pretty simple. The only thing between the switch and C101 would be the code relay on cars with a 13 button OBC. A problem with the fusible link will also shutdown the DME.

[jeffnhiscars]

A bad CPS or bad engine harness would just cause the engine to loose spark and fuel and also cause the tachometer to go to zero. In some cases it will cause a CEL pointing to an injector or fuel relay problem.

A problem in the circuit from the ignition switch will shut down the DME and may cause the CEL to light. The radio and other things may still work. The circuit from the ignition switch is pretty simple. The only thing between the switch and C101 would be the code relay on cars with a 13 button OBC. A problem with the fusible link will also shutdown the DME.

It came and went so fast but Im 99% certain there were zero lights. Is a bench test on a CPS reliable ? Is the code relay the same thing as a coding plug (in the cluster), can they be tested effectively and how interchangeable are they ?

[jeffnhiscars]

Update on my slow start issue. Last night it simply would not start at all (which is another good reason I keep the 318i insured). This morning a light came on (in my head) and I went to swap the main relay between the Zinno and Alpine Cabrios. Wouldnt you know, now that a new CPS is on its way, that the no start problem followed the relay.

Its 12631711266 replaced by 61361729004. I think its $12 from the dealer.