M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Electrical => Topic started by: dvmotorsports on June 29, 2010, 01:23:17 AM
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This time it's on a friends sons car. He picked up a 1991 318is for $250 because of a cylinder misfire. Pretty good score, but it has some rust which is typical of an original Hawaii car.
Some of you may remember this "Misfire" thread about my wifes car.
http://m42club.com/forums/showthread.php?t=10406 (http://m42club.com/forums/showthread.php?t=10406)
This is similar to hers. But her car was a complete no fire in the cylinder. This one is intermittent.
Anyhow, here is where I am at with this. Cylinder 3 has an intermittent misfire. I pulled the plug wire and you can here the spark for 3 to 10 consecutive duty cycles and then it will drop out for a few seconds, repeat.
I diaged it for about 5 hours today.
I have tested and or replaced the following parts
DME
Coil Pack
Cam Pos. Sensor
Plug Wire
Spark Plug
I have voltage and ohm tested all parts but the misfire is still present. All the values I got back from the meter are within the acceptable range. I also swapped the coil and plug wire between cylinders, but #3 is still intermittently missing. So the problem has to be before that. But even when I swapped the DME and tested the front and back side of the connector at the DME harness, still present.
I am ruling out the Crank Pos Sensor as the motor won't run without it.
What else is left in the system?
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Could there be a short in the wiring to the coil?
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Could there be a short in the wiring to the coil?
That is what the consensus seems to be. I am thinking the voltage is grounding somewhere due to a break in the wire insulation. And I am guessing this is in the loom somewhere. I am going to rewire everything for cylinder three. That should do the trick.
Where is Desktop Dave.......
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Desktop Dave is my hero too. Lol. Good luck to you.
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Okay, so after snipping some wires, I found out the Black wire from the DME to the coil is shielded. After stripping the shielding, it appears there was some internal arcing. Am I seeing things, or could that be the source? I'm thinking so.
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It could be. If it shorted somehow, it could have heated the wire and damaged it, even inside the shielding. maybe a trip to the jy or some rewiring is the answer. Can you test with a multimeter? See if you can test the resistance on the wire.
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That is what the consensus seems to be. I am thinking the voltage is grounding somewhere due to a break in the wire insulation. And I am guessing this is in the loom somewhere. I am going to rewire everything for cylinder three. That should do the trick.
Where is Desktop Dave.......
Undeserved, but thank you anyway.
Desktop Dave is my hero too. Lol. Good luck to you.
I am honored. I figured I should add some pithy Zen saying but I can't think one up.
I'm thinking the wires too. I was unaware that the common was shielded. I'd assume it's a bit of very high-quality work by the Bavarians if it's lasted this long. I'll do some snooping to see where a substitute might be found.
I'd assume an e36 could provide a nice bit of loom for splicing, but those little coax cables are troublesome. I've spliced some VGA looms in my day and it's not an easy job.
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I was unaware myself. And this is not shielded in a sense similar to a household coax. They way this is configured is as such
There is small gauge 18ish with the insulation. Around that insulation is another woven wire set followed by the outer insulation. Then end result appears to be a stranded 14 gauge. So there is no metal shielding. It's wire, insulation, wire, insulation.
On another note, 400 posts! Kinda sad it took me over two years to get there.
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I'm sure your M3 build will help with the post count... :cool:
Found this odd little tidbit...http://www.picoauto.com/tutorials/trigger-signals3.html
I'm off to dig a bit more.
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I really wish I had an oscilloscope.
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I was thinking about one of the sound card 'scopes. This one is only about $30 (I'm not sure of quality as I've lost my bids):
http://cgi.ebay.com/Sound-Card-Oscilloscope-Spectrum-Analyzer-Probe-audio-/120580967632?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item1c132f8cd0
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It sounds to me to be similar to many computer peripherals use for wiring. They use a braided shield to protect low voltage signals from radio interference. It would stand to reason that the wire you're tackling has a similar function.
It should be repairable if the damage is a short section, strip back the outer cover, separate the inner wire from the outer "shield" wire, and make any repair solder joints staggered. Be sure to use heat shrink generously on the inner wire, and over the outer.
Otherwise, donor wiring would be nice to have laying around. I thought I might have some wire similar to what you described in my project box, but it was super light gauge. Unless this is 20+gauge, I don't think it'll fly.
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Analog PC video cables have three nice coax cables internally. I'm not figuring it'll do well at high temperatures though. I'd suspect some RG6 wouldn't do the trick either...
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Agreed. Wasn't there a harness is the fs? I wouldn't even know where to source that kind of wire, and I run about 2-300 feet of wire every month. mcm electronics has oodles of wires, coax and shielded, but nothing I know of for higher temps.
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You guys are confusing the hell out of me.
I will say this, the wiring has a name on the insulation. "KabelMetal"
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rg6 is cable television coax. I'll see what I can find on "kabelmetal".
anything here (http://www.alibaba.com/showroom/flat-wire-power-cable.html) look like it?
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I can't dig anything up. That's really odd. There is a KabelMetal of Hanover that specializes in wiring of this type but I found nothing else relevant.
I'll bet that this wire is shielded to prevent overloading the coil transistors in the DME. These coil packs have been troublesome for BMW. I'd bet you could splice a bit of normal auto wire in there and it'll run like it should. The amount of RF interference on coil wires is really high, I'd figure BMW put this wire there to eliminate DME resets. It fits in with my theory that BMW over-did many things on the M42 (forged crank, sodium-filled exhaust valves, coil packs, etc) that can safely be eliminated.
If you wanted to restore the factory wire I'd just cut a length from a less fortunate M42 in a scrap yard.
I did find this great site again...
http://www.bba-reman.com/content.aspx?content=bmw_wiring_harness_faults_and_problems
They have some really in-depth technical explanations of BMW service recalls. Scroll down until to the lower section of the page and browse the links in the BMW section. I find that I worry a lot if I read too much of it...
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DesktopDave sounds spot on, as usual. It is highly likely this type of wire is overkill.
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rg6 is cable television coax. I'll see what I can find on "kabelmetal".
anything here (http://www.alibaba.com/showroom/flat-wire-power-cable.html) look like it?
This is the closest, but there is no outer strand.
http://www.alibaba.com/product-gs/235928320/Flat_Flexible_Power_Cable.html (http://www.alibaba.com/product-gs/235928320/Flat_Flexible_Power_Cable.html)
I'll try and get pictures of the dissected specimen up for you guys to have a gander at.
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If you wanted to restore the factory wire I'd just cut a length from a less fortunate M42 in a scrap yard.
You have a better chance of finding a Ferrari in the junkyard here. However, I did just junk my blue 318is. If I can find what yard that is in, then I have a chance. Otherwise i'm up shit creek.
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Luck. Lots of luck.
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If I stop by at my favorite yard I'll take a look. Might be able to pull a bit for you.
Never mind, I think I found a solution...I'm trying to delete an alarm from my '89 325i...and guess what?
There are three or four of those wires running through the main harness into the DME plug! I think they're the same, I'll take some pics when I'm a little further along.
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Cue the superhero arrival music. Desktop Dave to the rescue!
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More like "Dave just happened to be taking apart a BMW and saw what you needed." That happens more often than not...
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injector or intake mani leak...
also check the plugs see how they look
and check the Crank position sensor
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injector or intake mani leak...
also check the plugs see how they look
and check the Crank position sensor
This is a weak and intermittent spark which is neither of the first two. But I did check the Crank PS, with no luck.
Here is the picture of the wires dissected.
The wire on the left goes over the smaller black wire that is second from the left.
(http://img.photobucket.com/albums/v260/dvmotorsports/Photo-0088.jpg)
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And is there any way to Ohm out the crank sensor? What would the target value window be?
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Look for about 560 ohms on the meter. Take this with a grain of salt, as it is lifted from r3v. I need to get a bentley manual.
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check the spark plug wire boot
my M52 was missing when the coil boot went bad and i went through 7 spark plugs B4 i figured it out
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Look for about 560 ohms on the meter. Take this with a grain of salt, as it is lifted from r3v. I need to get a bentley manual.
That is damn high. Make sure you get the right book. The common E30 bently doesn't cover the 91 318.
check the spark plug wire boot
my M52 was missing when the coil boot went bad and i went through 7 spark plugs B4 i figured it out
Already changed the wires. No luck.
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Already changed the wires. No luck.
hmmm... when it happens is it when its warm or cold? or just completely random
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All the time. It may spark for 8 duty cycles and then drop out for 3 then back for 2 and out for 7. It does this hot or cold.
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hmmm almost sounds like an ECU problem if u have already replaced everything else
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I changed out the DME with two other known good units I have. Still no luck.
So I need to buy a wiring harness. If somebody has one, let me know. I will make a post it the classified section as well.
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i have a harness off my M42 :D
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i have a harness off my M42 :D
Want to sell it?
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Want to sell it?
yes i do! PM me and we can work sumthing out!
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I'm working another deal at the moment from my WTB thread. If that falls through, i'll let you know.
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I'm working another deal at the moment from my WTB thread. If that falls through, i'll let you know.
allright sounds good! i have my completel M42 with everything except my ECU