newb. dme issues.

[swedmonds]

Hi all, I am new to the "I care and know about my car" community. My knowledge is limited and my abilities are even more so. Thanks for your expertise and your patience. Hopefully one day I can be of help as well. March 2014 I purchased my Hellrot 1995 BMW 318ti A US KOMP from a friend. It had a clean, un-abused history. Over the summer, the water pump started leaking, I had it repaired as soon as I could, but it managed to overheat. After the repair, all seemed well. About a month later she started running a little rough and over a day or so it got considerably worse. I parked her and got her towed to a shop. They told me the radiator had a leak, the fan worked itself so much that the motor burned out, needed a head gasket. There ended up being a few other things that needed to be replaced...temperature sensor, not sure what else. She was running fine for them for a few days, and then...she wouldn't. On a cold start, the temp gauge would be pegged hot, the tach wasn't reading right. Jiggle the wiring harness, and issues would change. Sometimes it'd start perfect, other times nothing. - So, before they began trying to trace wires, they told me all of this. And seemed very pessimistic about being able to find a new harness. Their conclusion is that the wiring (harness) is probably damaged due to the overheating and it'd be easier to replace. If that's what needs to happen, I agree. - I've been looking online for the right part (wiring harness/DME), and I can't be certain if I've found it (different part numbers and other acronyms that I don't know what they stand for). So I started looking for a service manual for part numbers and more clarity, and that was just as much if not more of a mess. Help! And thanks!

[hotmilk400]

I can give you some useful information but I cant tell you for sure what the issue is without being there.

The wire harness that connects the DME to the fuse box is directly above your engine. The DME is behind the battery in a sealed compartment. The harness goes from the battery directly over to the fusebox, minus a few connections that are made to the engine(like your alternator, starter, O2 sensor, ect). At the fuse box, it uses two twist connectors that connect the harness to the fuse box. there will be a 3rd that connects below the fuse box to your brake pump.

Basically, the harness are easy to remove because of the twist connectors. The intake will likely have to be removed to get to some of the other connectors, especially the starter. (Some people can get in there, but not me)

As a side note, if the shop replaced your head gasket, they would have had to take your entire engine apart to do it, meaning they would have had to disconnect all of those wires and reconnected them.

If they did not spot any burned wires or burned connectors, i would have to say that I doubt the harness is bad. I am no professional on the issue, but if I was a shop and I saw a burnt connector or harness, I would fix it or replace it.

Maybe someone could shed some light on the issue, but maybe the DME is just bad.



For me, i would check every fuse first, especially fuse 46.

Your brake light fuse controls about 1 million other things, so have a second person confirm that the brake lights work properly. make sure they light up when you have the lights on and they get twice as bright when you hit the brake pedal.

If the wrong tail light bulb was used, the fuse blew out, or sometimes if the light burned out, the temp and odometer will go crazy. the car should start fine tho.

I would also check the ground connection from the battery to the chassis. I would also check other ground connections. They would have had to remove some of them when dealing with the head gasket, so their is a chance that the connection is bad.

[xxxJohnBoyxxx]

Originally Posted by swedmonds

Hi all, I am new to the "I care and know about my car" community. My knowledge is limited and my abilities are even more so. Thanks for your expertise and your patience. Hopefully one day I can be of help as well. March 2014 I purchased my Hellrot 1995 BMW 318ti A US KOMP from a friend. It had a clean, un-abused history. Over the summer, the water pump started leaking, I had it repaired as soon as I could, but it managed to overheat. After the repair, all seemed well. About a month later she started running a little rough and over a day or so it got considerably worse. I parked her and got her towed to a shop. They told me the radiator had a leak, the fan worked itself so much that the motor burned out, needed a head gasket. There ended up being a few other things that needed to be replaced...temperature sensor, not sure what else. She was running fine for them for a few days, and then...she wouldn't. On a cold start, the temp gauge would be pegged hot, the tach wasn't reading right. Jiggle the wiring harness, and issues would change. Sometimes it'd start perfect, other times nothing. - So, before they began trying to trace wires, they told me all of this. And seemed very pessimistic about being able to find a new harness. Their conclusion is that the wiring (harness) is probably damaged due to the overheating and it'd be easier to replace. If that's what needs to happen, I agree. - I've been looking online for the right part (wiring harness/DME), and I can't be certain if I've found it (different part numbers and other acronyms that I don't know what they stand for). So I started looking for a service manual for part numbers and more clarity, and that was just as much if not more of a mess. Help! And thanks!

Ok I dont think you need a harness unless when they changed the head gasket they pinched a harness wire. What I see from your post is the temp gauge pegged hot. The temp sensor could be bad but I think it is the wiring to the temp sendor. The only way to get a pegged hot when the car is cold is a temp wiring direct short to ground. This also tells the DME that the car is super hot so fuel injection will not supply enough fuel to start a cold car. I forgot to plug in my temp wiring on the head and my car would not start at all and when I got running with extra fuel the car was not drivable with the temp sendor disconnected. Hope this helps, it could be other sensors wired wrong or pinched to ground. If you had a ELM or bluetooth OBD-II and scantool you could find the issue immediately

[swedmonds]

Hi all,
Thanks for your suggestions. I'll get back to them and see how those things can help. Follow-up to come.

[alika808]

Download the wiring diagram here:
http://wedophones.com/BMWManualsLead.htm

Here the BMW parts catalog, you may cross reference here:
http://bmwfans.info/parts-catalog/

[swedmonds]

18/1/2015: Update: According to the mechanic, all of the grounds are good and the sensors and wires have been replaced. He showed me while we spoke and to my untrained eye, I'd have to agree. After a long search a used wiring harness was found and is on the way. - Here's some information that I've heard/learned along the way: *My 1995 318ti Auto USA m42 needs a #12511739948 wiring harness. *Part #12511739948 is discontinued. My research suggests this happened in 2011. *Part #12511739948 was also used in earlier e30 models *Engine wiring harnesses should be able to be repaired if you have the right mechanic. *The crossover from m42 to m44 happened as early as 9/1995. - Thanks again for the help and I'll let you know how it turns out.

[alika808]

The wires are repairable and it's easier just to repair it instead of replacing the harness. That harness goes beyond the firewall and you have to remove the dashboard in able to remove and replace from the other side. If I were you, just repair it if you can pinpoint which wire need to be repaired. By the way, do you trust your mechanic who troubleshooting right now? I am wondering why he recommended to replaced the harness instead to pinpoint which wire is broken. If the wire was fried, then you can just cut the wire harness bundle insulation and you can visually inspect and I hope you can see where the fried wire.

[sde36]

And the DME box was dry right? no signs of moisture? it might be a long shot but still a possibility. http://forums.pelicanparts.com/101-p...ng-eratic.html