'88 325 Randomly cuts out

[G-man55]

Hey guys, I picked up my first E30 a few months ago, and I noticed the car would randomly cut out at times, both while driving and idling. Sometimes I'd be able to pull the car over, turn it off and back on again, and it would fire right up, other times it just wouldn't start at all. I replaced the fuel pump a few weeks ago, and for a bit it was getting better, but then cut out twice last week (started right up after stopping/restarting engine), and again today (still not starting). Any ideas what it could be? Stomp test isn't giving me anything either (not even the 1444).

[Gregs///M]

Start by removing and thoroughly cleaning the idle control valve. Its not too difficult to remove and clean. Spray it with brake cleaner and shake vigorously. This valve is responsible for idle speed and will cause a hard to start condition if clogged up.

Also rule out any vacuum leaks. Any vintage car usually develops vacuum leaks which will cause all kinds of running problems. Inspect all rubber, especially the throttle intake bellows boot and the valve cover oil re-circulation hose. Try carb cleaner trick to find vacuum leaks but a smoke test is the most conclusive test for finding leaks.

A smoke test should be considered one of the most important maintenance items for your car.

[SpecM]

I don't know if it is causing you whole problem or not, but if you are unable to retrieve fault code via stomp test, you likey have an issue the TPS, its adjustment, or its wiring

elaborate on the symptoms of the "cut out"

and check for vacuum leaks regardless!

[G-man55]

Thanks for the replies. ICV is fine, there are no vacuum leaks either. I pulled two spark plugs, and it would sometimes give me a single really weak spark when I first started cranking the motor, but then wouldn't spark. Ignition coil is getting voltage, spark plugs aren't worn.

As for the cutting out, it would happen randomly (while starting, under power, cruising along, etc). There were no warnings before cutting out, the engine would stop, tach goes to zero. Sometimes it would restart by itself, sometimes I'd pull over and crank it once, sometimes I'd be there for 15 minutes trying, this time it's not starting at all.

[SpecM]

I would start with a new crank sensor and main relay. get both new from your local dealer

[G-man55]

Real quick, does the CPS tell the ECU the engine RPM? Every time the car dies, the tach immediately reads 0, even if the car is still in gear, and the engine should still be spinning.

[SpecM]

Real quick, does the CPS tell the ECU the engine RPM? Every time the car dies, the tach immediately reads 0, even if the car is still in gear, and the engine should still be spinning.

yes it does

start with a CPS, but the wiring harness may be starting to flake out and not carry the signal to the DME

Just ask Jim ;)

[mzollo]

check the C191 injector harness plug. had a similar issue for about a year chased it down to the bad plug. good luck

[G-man55]

Pulled out the CPS today, it's reading normally (540 ohms), so I cleaned it off, plugged it back in, and it still wont start. What do I check next?

Mzollo, where is the harness plug, and how do you check it?

[G-man55]

Found it, it was underneath the intake manifold. There's some blue colored grease on the female end of the connectors, but it doesn't look like there's any corrosion here.

[accident]

The tachometer dropping to 0 indicates that the ECU has lost power. Under the small black cover near your fuse box are 3 relays. One of them (the one all the way on the left, if I remember correctly) is the main relay. Start the car and tap on the relay with a screwdriver. If the car stumbles you have found your culprit.

[G-man55]

So the CPS sends signal to the main relay, and from there it goes to the ECU?

Only the tach went to zero when the car stopped. Speedo still worked, check light starts flashing, CEL stays off, and all other electrics are fine.

Is the Main Relay and the DME the same thing? Also, I can't get the car started, so I don't know if I'll be able to run it long enough to tap on the relay. Maybe I'll go pull a bunch of relays from Pick n Pull tomorrow and try them out.

[SpecM]

the CPS sends the signal to the DME, which then signals the tach. the main relay just sends power to the DME.

get NEW parts. used electronic parts are a no-no

[G-man55]

What is the difference between the main relay and the DME? Is the main relay the one to the left (toward the front of the car) to the fuel pump relay, in front of the driver side strut?

[SpecM]

What is the difference between the main relay and the DME? Is the main relay the one to the left (toward the front of the car) to the fuel pump relay, in front of the driver side strut?

DME = the computer (aka PCM, ECU...)

the main relay just sends power to the DME and fuel pump relay. It is usually the center relay in the group of three at the drivers side strut tower. its a 5-pin relay and usually a differnet color, the other two (fuel pump and o2 heater) are 4-pin