Author Topic: Dead cylinder (Read 10643 times)

dvmotorsports · « **Reply #15 on:** December 19, 2009, 03:45:14 PM »

Quote from: dj91318is;83256

Joe - It dose sound like you have a problem on the pin with 8 volts. This is strange on a 12 volt system. It could be Carbon Feed Back/Shorting in the Connector you did state that the #1 connector is cracked.
Can the Spark Plug it's self be bad? Did you check the other coils with spark plugs to be sure you were grounding them properly? How about a stuck/burnt Valve have you done a compression test? Is the spark plug cavity full of oil this will short out the wire? GL

Spark plug is good. A don't think a stuck or burned valve would cause an electrical problem though. The plug cavity was a little damp with the sparkplug grease, but that has since been remedied.

Quote from: DesktopDave;83258

Did you do a resistance or continuity check on the harness to DME wire? Seems like you've eliminated every other possibility.

That is the next step. Do you have a DME pinout and the check values? I can't seem to locate one.

dvmotorsports · « **Reply #16 on:** December 19, 2009, 03:49:02 PM »

Wait, I think I found that it's pin 25

Can someone verify that?

nicknikolovski · « **Reply #17 on:** December 19, 2009, 09:23:39 PM »

Pin 25 - output - Cyl 1 ignition coil control - that's correct. The original coils in the BMW M42 engines had a known fault where the coils would crack and therefore damage the engine ECU. I think these where on Bosch coils, which were replaced with Bremi coils. Test pin 25 for output voltage with ignition on. Should be 12V.

When looking at the coils in mounting position, pins are 1, 4a, 15. There should be 12V between pin 15 and a ground point on the vehicle, not between pin 15 and the other pins. For coil resistance, ignition must be off to check resistance. Check each coil between pin 1 & pin 15 for 0.4-0.8 ohms. You have done this correctly - so coil 1 is out of spec. Secondary resistance cannot be tested.

In the bentley manual, it also states that if there is no spark at a cylinder, check the wiring between pin 15 on the coil and the ignition switch.

Also just a heads up, be very careful when testing ignition circuits as very high voltage is present.

dvmotorsports · « **Reply #18 on:** December 19, 2009, 09:39:01 PM »

In a resistance test between the DME harness and the coil harness, here is what I have. These are all connector side readings, i'm getting ready to do loom readings.

pin #25 1.3ohms
pin #24 0.4ohms
pin #52 0.5-0.6ohms
pin #51 0.4ohms

dvmotorsports · « **Reply #19 on:** December 19, 2009, 10:00:55 PM »

the reading from pin #1 at coil harness #1 on the loom side still has 1.3ohms. i am opening the loom and working my way in. as of now, i am 16 inches down the harness with high resistance still present.

i'd start on the DME side, but i am trying to avoid opening up the loom on that end. so that means i can get a loom side reading at the DME yet.

dvmotorsports · « **Reply #20 on:** December 19, 2009, 10:25:44 PM »

okay, so i pulled the sheathing back on the DME harness and opened the access cap. when probed pin #25 on the loom side, i got a reading of 0.4 which is normal. so i checked the pin side of the DME and got a good reading as well.

kinked wire perhaps?

dvmotorsports · « **Reply #21 on:** December 19, 2009, 11:20:09 PM »

Update. After checking resistance at the DME harness on the pin and wire side, the resistance was variable from 0.3 to 1.4 with some higher spikes. I'm pretty sure it's the connector. Going to try and change it tomorrow or Monday and I'll report back. If Anyone else has input, feel free to share.

DesktopDave · « **Reply #22 on:** December 20, 2009, 12:02:32 PM »

Nice job...keep us updated.

Gret example of why your multimeter is absolutely the most important tool for a mechanic. Especially when they sell for $4 at Harbor Freight...

dvmotorsports · « **Reply #23 on:** December 20, 2009, 06:47:05 PM »

Okay, so now I am totally lost. After a little trying, I pulled the pin from #25. I ohm checked again in various places at DME and back on the wire roughly 6-8 inches. I am still getting variable resistance. However, most of the readings are 0.8ohms which is in spec. But then I got to something strange on the harness. Here are some pics of my harness and my wifes harness.

Mine is nice and clean, no issues

Hers has some yellow caps in the harness which are not in mine. Our cars are them same build date 06/90 and all original in the wiring department. The only electrical difference that I am aware of between the two cars are the tweeter speaker by the side view mirrors. So what the hell is going on in this pic? I figured the loom should be identical...

dvmotorsports · « **Reply #24 on:** December 20, 2009, 07:54:19 PM »

So prior to my previous statement I assumed I didn't have those yellow connectors in my harness. I assumed this because her harness had the connectors clearly visible before removing the tape. My was not that way. So I opened it up and I have them too. This leads me to believe one of the harnesses has been opened in the past. Either way I'm at a loss for the readings I'm getting. Going to BMW to buy the connector in the morning.

dj91318is · « **Reply #25 on:** December 21, 2009, 11:11:23 AM »

Joe - You have stated that the Coil Plug Connector is Cracked. Well with some moisture in the crack at some point in time and the repeated voltage surges it will create a carbon trail which will conduct continuity and will short out the voltage. With the harness disconnected from the ECU and the Coil Connector at #1 Coil. Is there any resistance from any of the pins to each other? and from each pin to ground? We know your getting voltage but only 8 volts could be the result of a carbon trail short which is why their is no fuses blowing or smoking of rubber around the wires. Is there any Wire Discoloration on the wires leading into the Connector? GL

dvmotorsports · « **Reply #26 on:** December 21, 2009, 04:58:51 PM »

Nailed it!!!!!

I went to the dealer and picked up a new connector for the DME. Came home and swapped it and got the ohm's down to 0.3 Then I fired the car......still not firing. Swapped DME's between her car and mine, fix't!

So I conclude that the cracked coil back fed into the system, and ruined the connector at pin 25, and it also busted the DME.

So now I need to track down a DME.

Thanks to everyone for your help. I feel so much better as I have always sucked at electrical and I nailed this problem.

dj91318is · « **Reply #27 on:** December 21, 2009, 07:39:56 PM »

Merry Christmas! Good to hear that you found the problem.

DesktopDave · « **Reply #28 on:** December 21, 2009, 08:07:00 PM »

Quote from: dvmotorsports;83361

Nailed it!!!!!

I went to the dealer and picked up a new connector for the DME. Came home and swapped it and got the ohm's down to 0.3 Then I fired the car......still not firing. Swapped DME's between her car and mine, fix't!

So I conclude that the cracked coil back fed into the system, and ruined the connector at pin 25, and it also busted the DME.

So now I need to track down a DME.

Thanks to everyone for your help. I feel so much better as I have always sucked at electrical and I nailed this problem.

I have a spare...PM me an offer. I'll even test it for you. If you want, send me the old one back for a post mortem.

GermanPath · « **Reply #29 on:** January 01, 2010, 12:23:35 PM »

Hi.

First I apologize for my bad english

When there is no signal from DME to ignition coil mostly the ignition transistor is busted. (Bosch 30011 or 30014). You can replace them easily with an BU323Z transistor for a few Dollars. In Germany this transistor cost around 2,50€ from the cheapest dealer.

Greetings from Berlin,

GermanPath