Distributor cap and rotor replacement problems

Hamiltonhiii · Post by **Hamiltonhiii** » 28 Feb 2009, 16:09

I have now replaced the cap and rotor three times on my 1992 940. After replacement, the car ran fine for a day or so, then suddenly died. Swapped in a new set and was up and running again- breifly. There must be a short somewhere? Any ideas?

Steven242 · Post by **Steven242** » 28 Feb 2009, 18:29

Have you tried plug wires, plugs, and coil?

Or chase down the two wires that run from the distributor to the control box under the hood, maybe they got rubbed bare and are shorting eachother out? they run behind the crank pulley and timing belt...

Hamiltonhiii · Post by **Hamiltonhiii** » 01 Mar 2009, 07:42

I have replaced the plug and plug wires, and this didn't seem to matter. I haven't replaced the coil and have considered this.
The two wires you're talking about...are they the two ground wires that are on the gasket cover and run to a little box at the firewall? They are not insulated but thick, wide and woven. Or do you have something else in mind?
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Kmaniac in California USA · Post by **Kmaniac in California USA** » 01 Mar 2009, 08:37

Have you made any evaluation of your fuel delivery system?? A failing fuel pump (intermittent operation) or a flakey fuel pump relay will cause the same symptoms. Rule out a fuel issue before throwing anymore money at the ignition system. I learned this lesson the hard way.

Hamiltonhiii · Post by **Hamiltonhiii** » 01 Mar 2009, 08:53

I don't think it's fuel because I can spend $30 on a cap and rotor again (not that I'd do this again before finding the problem!!!) and once I put a new set on there it runs on the first crank!

Kmaniac in California USA · Post by **Kmaniac in California USA** » 01 Mar 2009, 09:02

Here is my suggestion to you if your car is not starting right now. If you have an inductive pick-up timing light available, I suggest you connect it to a spark plug wire, then crank the engine with the timing light button pushed. If the timing light blinks AND the car does not start, you have a fuel problem. If it does not blink and the car does not start, you have an ignition problem. Figure out for sure where the problem is before you start throwing money around, or else you will go poor in a hurry. Or, you can ignore my advice. The choice is yours. Please don't make me say "I told you so".

drsugg · Post by **drsugg** » 01 Mar 2009, 10:17

92 940? You may have a problem with the rpm sensor on the flywheel. When you are r&r'n the distributor cap, you may be disturbing the lead going to it. Remove the cap, get flashlight, look straight down behind head to bellhousing. You will see a large wire coming out of bellhousing and ending up by your right hand in a 3 wire connector. If the insulation is cracked, worn away, you MAY have found your problem. Should set code, if you check them.

Hamiltonhiii · Post by **Hamiltonhiii** » 28 Mar 2009, 13:47

Dr. Sugg: I think you've hit on the problem. They were bare (how the heck are they related to my problem anyway?) All I did was wrap some electrical tape around them and it cranked to life. I guess I should replace this wire!!! Do I have to.
You win the prize and I'd name my next child after you if I didn't have so many of the little !@!@$@% already. I guess I should send you a slightly used cap and rotor, slightly used coil, and slightly used distributor. I think they're all good- who'd a'thunk it!

Kmaniac in California USA · Post by **Kmaniac in California USA** » 28 Mar 2009, 14:03

I'm glad to see you found the problem. My 1986 doesn't have a crank sensor, so I would never have thought of it. Bad insulation on wires can mess you up big time.

Hamiltonhiii · Post by **Hamiltonhiii** » 28 Mar 2009, 14:19

But why would replacing the cap and rotor work to fix it? That's the thing- everytime I put a new cap and rotor on it, it started up immediately. That would last a few hours and then the car died again. Put a new cap on- run again. That makes not sense!
In fact, I knew I had found my problem when after taping these silly wires (bare right down at the bell housing), I got an old cap and rotor to make the car start. (you damn skippy I'm taking that new $80 dollar NAPA cap and rotor back today!) I'm amazed.