Engine cuts out while driving!

[UserError]

Having a strange issue with my 5/86 325, where the engine quite literally cuts out randomly while driving. The solution so far seems to be to key the engine off, and then back on, and the car suddenly starts working again. Driving it, it quite literally feels like I turned the ignition off while driving.

It tends to happen more often when turning, though how hard i'm taking the turn doesn't seem to affect it. It doesn't happen on bumpy roads, though occasionally it does seem to be caused by hitting a bump. I swapped to my spare ECU, and will try a spare ignition coil tomorrow. Anyone else have any suggestions on tests to perform, or parts that might cause this sort of problem?

[Cabriolet]

check your main relay.

[jlevie]

That sounds like it could be a bad main relay, flaky DME power or ground connection, bad CPS, bad ignition switch, bad engine harness, or a wiring fault. Probably not difficult to fix, but finding the cause could be interesting. I'd start by replacing the main and fuel relays and CPS with new parts. If missing or broken, also replace the wire chase that keeps the CPS, etc away from the water pump pulley.

[UserError]

Huh. Never would've suspected the main relay. I'll bench test it this evening, see if it's in fact alright.

[riceh8r]

+1 on the cps

[HippyEarly]

i like everyone elses idears, but to add, i had a similar issue with two bumps id drive over daily and the car would cut out. I got all 69'd with my steering wheel with my head at the pedals and started pushing connectors together. found one that was loose but not disconnected, problems been gone for about 8 years now.

[UserError]

Bench tested the main relay. It clicks, but when I tested the resistance on the coil side, I could get the resistance as high as 2.5Mohms, which is obviously not right at all. New relay it is, then.

[UserError]

Hokay, swapped relay, still cutting out. Checked the under dash connectors, they're all nice and tight, there doesn't seem to be a cam position sensor on the car or in the diagrams, which might be because it's an early eta car. If this thing was actually capable of posting codes, maybe I'd have somewhere to start looking. AFM tests good, moving the harness around doesn't do anything, I'm at my wit's end here.

[Andy348]

I had the same problem. It wasn't the relay itself, it was how it sat the piece below it. I didn't even need a new relay, just pushed it a certain way.

Test the CPS @ the flywheel as per the bentley manual and see if that's fried.

[UserError]

Swapped crank position and engine speed sensors, seems to have reduced the instances of the problem occuring some amount. In a bit of testing, I noticed that the car won't cut out while idling, though if it would normally stall, adding throttle immediately cuts the engine out. The headlights remain on, so I'd guess that the main relay keeps working, though the tach cuts out completely. Would the PCM ground cause this? This keeps getting more complicated, though the more I test and adjust things, the less it seems to happen.

[MTechnikII]

also check or replace the fuelpump relay, it hapened to me too , engine would die at random, just because a relay clicks doesn't mean that it's good, the contact points in the relay might be burnt or corroded, just swap the relay with a working one or a new one,
good luck
Henry

[UserError]

Car broke down and wouldn't restart last night. Had it towed to Dan Martin, where he figured out that it was the wire leading from the battery to the main relay. $200 or so later, the car's back in business.

[LowR3V'in]

I was going to post that this happened to me and turned out
to be the main relay, but you figured it out :P