E30 325 wont start - Buzzing DME Relay

Post Fri Mar 13, 2015 3:31 pm

Hi,

I have a 1988 318i which has been converted to 325 for quite some time now.

The other day I got a bit excited with the pressure washer and ever since the car won't start.

The obvious symptom was the white relay (DME?) was buzzing really loud. I read on here about shorting pins 30/87/87 and this successfully starts the car.

I picked up a new relay today but it still buzzes.

Upon further inspection of the wiring I found a cut in the loom just below the PAS and brake fluid reservoir. I can see that the red/yellow cable has melted and is completely exposed.

I unwound a load more harness and found that the red/yellow wire is pretty much burnt through its entire run from relay to C101 plug.

My guess is that the pressure washer got this lead wet (through the open cut in the harness mentioned above) and has caused my starting problems.

My question is can I cut this wire at both ends and forget it ? I understand that it is an ABS wire and my car does not have ABS so no loss?

If this cable is causing a problem somewhere how come the car still starts with pins 30/87/87 shorted?

I'll try and get some pics up shortly...it looks a mess! I have the car booked in for an MOT tomorrow so I'm looking for a quick fix to get through that. Then once its passed I will get a replacement harness sorted as a lot of the wiring has now melted outer casing.

Post Fri Mar 13, 2015 3:53 pm

This is the red/yellow wire (or whats left of it)

As it is exposed will it be the likely cause of my buzzing relay? Especially as I got it wet the other day....

Post Fri Mar 13, 2015 6:32 pm

Update:

I've checked the other side of the C101 plug and I can see the brown wire has already been cut by the previous owner (Eko) so I can only assume the melted red/yellow wire is a little bit of a red herring, albeit something that still needs to be sorted. Unless perhaps the recent water ingress has amplified an issue?

Another symptom....when the relay is plugged in and buzzing, the rev counter is also going mad.

I have removed the ECU and it doesnt have any obvious signs of water ingress, I've got it in the house regardless to dry it out.

Please help!

Post Fri Mar 13, 2015 8:22 pm

Done some more reading on the wiki and I think I need to be looking for breaks in wires that connect to pins 85 and 86 on the DME relay. Based on the fact that the car starts if pins 30/87/87 are bridged.

Does that sound reasonable?

Post Sat Mar 14, 2015 12:48 pm

Found the problem. Poor ground connection between pin 85 on DME Relay connector and pin 36 on ECU. Cut it at both ends and wired in another run of cable and it starts fine on the relay with no buzzing or jumpy rev needle. Shame I couldn't fix in time for the MOT this morning but never mind.

Post Sat Mar 14, 2015 2:20 pm

This loom has been clearly been badly damaged at some time by falling foul of the red/yellow and brown wire problem, and should ideally be replaced. Failing that, you should strip it down along the whole length that the red/yellow runs, chop out the red/yellow completely, carefully examine all wires that have been in contact with it, individually insulate them as required, then re bind the whole lot with loom tape.
Does the cut brown wire in the body side of the C101 look like it's been cooked as well?
Also, remove the plug from the bracket under the alternator, where the oil level sensor plugs in, turn back the rubber boot on the plug on the engine loom and examine the state of the brown/orange wire. This is another wire that can overheat under certain circumstances and cause serious loom damage.

Post Sat Mar 14, 2015 10:41 pm

Thanks Brian, I've sourced a replacement loom as this one is way past its best now. I will check what's left of the brown wire again, I can't remember if it looked toasty or not body side.

Post Wed Mar 18, 2015 9:21 am

Loom in the post and MOT rebooked for tomorrow.

Is the engine harness hard to swap out?

Post Wed Mar 18, 2015 9:38 am

Ideally the loom should be attached to the engine while it is out of the car, but changing it on a M20 isn't too bad with the engine in place. Hardest bit is fitting it under the inlet loom, with various hoses in the way and limited access.
Your car is a 318i, which doesn't have any provision for the oil level sensor, so don't connect the plug to the sensor under the alternator. If this plug is connected, you will get another loom fire if the main engine to body earth strap ever fails.
Make sure you check out the condition of the plug and socket for the injector loom to the main engine loom, especially under the rubber boots, before you fit it.

Post Thu Mar 19, 2015 8:19 pm

Thanks Brian, I'll have a go at tackling this at the weekend. The first job will just be to label up the plugs before anything is removed, so I know where all the new loom plugs go!