320i Won't Start

[Mike316]

Hoping someone can help me here. My normally healthy 1989 320i (M20) suddenly won't start. Engine turns over, battery fully charged. Have spark at plugs. Plenty of fuel in tank. Have fuel at FPR. Tested fuel pump relay as in the troubleshooting guide on E30 Wiki - no problem. Swapped fuel pump relays with my E24 and E24 still starts, E30 doesn't. Same with DME relays - tested OK using troubleshooting guide and swapped with E24: DME relay is good. Checked that air flow meter is not stuck open - it isn't. The engine will not fire at all.

So I'm stumped. What have I missed? Any help would be really appreciated!

Mike

[Grrrmachine]

Just to confirm, this is the Troubleshoot guide:

http://www.e30zone.net/e30zonewiki/inde ... oubleshoot

So you've removed a spark plug and confirmed you've got one sparking from the distributor, not straight from the coil? And what condition are the sparks in? cafe latte, or sooty black?

If you've got both spark and fuel, it's either a dead ECU, overfuelling from the blue temp sensor, or an air leak somewhere.

[Mike316]

Thanks for this, Grrrmachine.

Yes - spark at each of the plugs from the distributor. The plugs had some carbon deposits and were wet with unburned fuel. I cleaned them all up but still not a hint of starting.

The car is in almost daily use and the engine had been running normally without any obvious problems until parked up a few days ago.

It still doesn't fire when I connect DME pins 30 to both 87s. I do have power to both pins 30 and 86 when tested with a multimeter. Does this mean the ECU is working and can be eliminated?

Thanks again.

Mike

[Grrrmachine]

ECU might be buggered and need resetting; disconnect the two battery cables and join them together for a minute or two to reset it. They can go fatally wrong, but not very often.

I'd be tempted to unplug the blue temp sensor and put a basic resistor across it (1k ohms) to trick the ECU into thinking the engine is warm - that might identify an over-fuelling issue.

Have you done a thorough check for air leaks - especially the rubber bung under the throttle body? Is the main rubber boot perished or cracked?

[Mike316]

No luck resetting the ECU and I cannot see any split or perished hoses at all. I am not able to do the blue temperature sensor test today, as I haven't anything to act as a resistor but I might be able to get something from work tomorrow.

Thanks for your suggestions so far. Looks like it'll have to be the E24 for work tomorrow, despite the snow and the road salt and the lack of winter tyres...

May have to be a tow truck for the E30. I'll post the outcome.

Thanks again

Mike

[Andyboy]

It could be the ECU but it's rare for these to fail. If you want a spare I've got one you can have for 20 quid. If the plugs are wet with fuel it suggests the spark is too weak or it's flooding.

[Mike316]

Thanks - it might be a weak spark. I've had the distributor cap off and it is clean and dry in there with good contacts. I'm stuck with my work schedule this week but I'll try a coil swap when I get the chance to see if it could be that. It's the suddenness of failure which is odd. No performance issues or poor starting until this happened.

Thanks for the ECU offer - it doesn't seem too likely, I agree.

Mike

[Mike316]

Grrrmachine - thank you. The resistor test on the blue temp sensor circuit showed there was a problem. Replaced the sensor today and the engine starts and runs very well.

Thank you to everyone for suggestions. Brilliant forum.

Mike