M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: dvmotorsports on December 18, 2009, 08:02:16 PM
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So my wifes M42 has a dead hole. #1. Being as I also have an M42, i swapped the plug wires and the coil packs but that did not remedy the problem. What triggers spark on this motor? Is there anything in the system between the wires running to the coil and the pickup itself?
Thanks
Joe
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hey joe, Crank position sensors trigger spark, as well as the camshaft sensor.
Im getting a new(er) crank position sensor, and can send you the the old one, if you want to troubleshoot.
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Ignition timing/spark is controlled by the DME which is the Engine ECU. It does this by using sensors on the engine. The crank position sensor - engine will not run without it.
The cam position sensor - It monitors the position of the exhaust cam to determine where the camshaft is in relation to the crank position. Once the engine ECU knows the position of the crank and cams, it provides power to the ignition coils and fuel injectors and controls them depending on the inputs it is recieving.
Just so I know where you're at, are you saying that there is no spark at cyl 1 or are you saying that there is no compression at cyl 1? A dead cylinder usually means no compression. Then you've got an internal engine problem. If no spark - you've got an electrical problem.
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Is the connector on the #1 coil pack good? Any corrosion? I'd be tempted to dig out the elec troubleshooting manual and find where those wires go. IIRC, the DME grounds the coil to collapse the field & fire the plug.
Did you test the plug(s) out of the engine, plugged to the coil & wire? Remember that the plug must still be grounded to fire properly. Coil packs are hard to diagnose without professional diag tools. That would isolate a possible engine compression problem from a spark problem like nick said above.
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Nick - yeah, no spark at #1 and i suck at elec diag
Dave - The connector at #1 is good. It is cracked though. However, I took the coil pack assembly from my stroker which i drive everyday, and the problem still exists. I also chased the wiring underneather the plastic cover at the windshield base in the engine bay. Came to three relays, 2 orange, 1 white. Replaced those with known good units, problem still present.
What I am curious to know is if the firing system in the DME is individual per cyl or grouped. Basically, can the firing of one cyl fail in the DME, or do they all go out together.
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Also the DME in my 318 is on the floor for the moment as the dash is out, but still connected. I could swap DME units, but I am trying to avoid that
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Swapped DME, didn't fix it. If there is nothing between the DME and the coil, must be a broken wire somewhere. So....yeah....this is gay. Anyone else have input?
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Okay so since I suck at electrical, follow me on this.
I volt tested each connector from the DME to the coil at the coil. I also took Ohm readings on the coils. The ignition was obviously on. Here we go.
There are three pins on the connectors at the coil, one is + the other two are ground i'm guessing. Thus I received two reading on each connecor.
#1 8v and 12v
#2 12v and 12v
#3 12v and 12v
#4 12v and 12v
Coil ohms
#1 0.3
#2 0.8
#3 0.8
#4 0.7
So it appears there is a problem not only with the coil, but in the wiring as well. Like I said before though, I swapped with a known good coil and still had the same problem.
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everything has been referenced to my operable motor and the results are the same as listed above with the exception of the voltage test on coil #1 harness which read a normal 12v and 12v
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Move the Coil / Wires see it problem moves.
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I'm glad you tested both resistance and voltage on the coil pack. But I can't recall which of the terminals is positive & which is primary/secondary. Let me look that up...
I'm suspecting that you have a bad coil...and it might have damaged the IGBT that fires #1 coil in the DME. That might explain the readings. From what I've seen the coils usually don't cause DME troubles. What caught my attention was the 8v reading on the harness. I'm suspecting that your #1 transistor is damaged, not sending a solid signal to the coil. Or you have a bad wire/connection from DME to coil pack.
I'd tear that DME out & take a look for broken solder joints or burned out transistors, then test the wire from the DME connector to the coil wire for resistance. I wouldn't switch DME's in case a damaged wire will overload the good one the same way.
I found this (http://www.bimmerfest.com/forums/showthread.php?t=303424) over at Bimmerfest:
From the u shaped Ignition Coil Harness in the manual there are 3 connectors- 1, 4a, 15. It says that 15 is positive (+) and will be the one tested against ground. Coil primary 1(-) and 15 (+) resistance = approx. 0.8 ohms, Coil secondary= N.A., Spark Plug connector= Bosch- 1k ohm +/- 20%, Beru- 1k ohm +/- 20%. This is based on M52TU+ engines.
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this thread has lots of good info keep us posted
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Move the Coil / Wires see it problem moves.
I completely changed the coil and wire assembly with the one from my car. As well as the DME. Problem still present. So I am thinking that the neg is grounding out in the harness.
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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
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Did you do a resistance or continuity check on the harness to DME wire? Seems like you've eliminated every other possibility.
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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.
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.
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Wait, I think I found that it's pin 25
Can someone verify that?
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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.
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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
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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.
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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?
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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.
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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...
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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
(http://img.photobucket.com/albums/v260/dvmotorsports/IMG_2292.jpg)
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...
(http://img.photobucket.com/albums/v260/dvmotorsports/IMG_2293.jpg)
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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.
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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
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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.
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Merry Christmas! Good to hear that you found the problem.
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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.
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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
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Maybe someone spliced a WBO2 or some other piggy bank system? Pull off those caps & definitely solder the wires. Maybe you won't need any parts at all.
BTW, I have a spare engine harness too. It's from an '87 325is, but that's also a Motronic car so it should pretty much match right up. I'd think a few wires might be different colors, but it'd probably be worth doing this in the long run.
You could isolate the problematic wires, swap pins & solder the cut wires to be sure you have solid connections. FYI I get good results with a 100w gun, liquid electrical tape & fabric "friction" tape for my electrical work. The 25w irons aren't powerful enough for 14-16 gauge wire.