Dead cylinder

[dvmotorsports]

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

[fiftytakedowns]

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.

[nicknikolovski]

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.

[DesktopDave]

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.

[dvmotorsports]

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.

[dvmotorsports]

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

[dvmotorsports]

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?

[dvmotorsports]

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.

[dvmotorsports]

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

[dj91318is]

Move the Coil / Wires see it problem moves.

[DesktopDave]

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 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.

[fiftytakedowns]

this thread has lots of good info keep us posted

[dvmotorsports]

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.

[dj91318is]

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

[DesktopDave]

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