Brantley

I've been troubleshooting a no-start condition the last few days and believe I've narrowed it down to the ignition coil.

I don't believe it is a fuel delivery issue as I have done the following -

- Replace the DME Relay
- Jumper the relay and heard the fuel pump running

I don't have a gauge to measure the fuel pressure at the fuel rail so I can't think of doing anything more related to fuel at the moment so moved on to checking spark.

I bought an inline spark tester and stuck it between the ignition coil and distributor and didn't get any spark. So, tried the following -

- Measured 12V at the positive "+" and negative "-" lines to the coil with the key turned on so the power to the coil appears fine
- Measured resistance from the output and - lines at 5700 Ohms which is in the correct range of 5000 to 7200 Ohms
- Measured resistance between the + and - at 3.2 Ohms which is well above the range .4 to .6 Ohms.

So, my conclusion is that my no-start condition is caused by a failed Ignition Coil. My question is whether or not this is a normal way for the ignition coil to fail with a higher resistance than what it should have?

I am going to buy one tomorrow but would like to avoid that if perhaps the problem is somewhere else? Does anyone local to Orange County, CA have one that I could borrow to validate the failure?

Any other suggestions would be appreciated.

Thanks!
Mike

Brantley

Well... I was able to try another ignition coil today and that did not fix the no-start. So back to the drawing boards.

I still don't get a spark in my inline spark tester between the coil and distributor. I did measure 12V at the lines to the ignition coil. Could it be my DME?

I did also do new spark plugs and wires last night. I looked at the Distributor and Rotor and they looked okay.

If anyone has another other suggestion that would be appreciated! I am going to double check all of my numbers this evening.

jmj951

I assume you have tach bounce? Just asking, to make sure you ruled out the speed/reference sensor connections to the DME.

An easy test I have previously done to confirm if the DME is sending a signal to the ignition coil is to take a 12V light with terminals (for example, I pulled the one out of the glovebox, easy to remove and attach terminals - you could alternatively pull the one out of the hatch area). Wire up the terminals on the light, test the setup by connecting the wires to battery. After a good test, connect those wires to the DME wires on the coil. With long enough wires, you can run the bulb back into the car, or just place it on the windshield where you can see it when you're cranking. When you crank over the engine, you should see the light flash with each signal the DME sends to the coil. Please try this and post back.

miragezero

Make sure you didn't put the a chip in backwards (I just did that >_<); make sure your idle stab isn't reversed if you've screwed with it.

Brantley

Thanks jmj... re: Reference sensors, there was a crack in one of the plugs connecting into the harness. I went to wiggle it and it started crumbling - see picture. I actually had an extra one so I installed it but still no start. I get a very slight jump in the tachometer on the first crank but then nothing on subsequent ones. Should I see the tach bounce every crank? The other sensor doesn't look all that great either. I'll see if I can measure the resistances, etc, on it before replacing.

Thanks also for the recommendation to test the DME. I'll start wiring something up to test that as well.

miragezero - thanks for the recommendations but thankfully I didn't mess with either of those items prior to it failing to start so they should be good.

azbanks

When my coil went out, I could get the car to start and run very rough by disconnecting one plug wire. The engine would die if I plugged in all four.

Brantley

okay... strange, but I'll try it!

Tom M'Guinn

Tach should bounce/twitch for as long as you crank the motor, not just once... That connector is a goner. Others probably aren't any better. Have someone wiggle the wires as you crank to see if you can get it to start. Several places sell replacement jumper harnesses since the connectors on both the harness side and sensor side tend to go bad. Focus all efforts on getting the tach to bounce with good sensor wiring...and then go from there. You can cut off the bad connectors and hard wire together if needed to test...

homerj

i would check ref sensors. if tach bounce only once id say sensors. when my coil and rotor went the car wouldnt idle or would stumble on itself. when the dme went i wouldnt get tach bounce. ill look for the part number but u can get bmw sensor from pelican and its much cheaper for the same part. hope it helps

Brantley

My better half gave me 10 minutes to work on the car this evening... so quick results...

I built up the "12V light" test as jmj suggested to test the DME. Went to Radio Shack, bought some wire and a 12V light to connect to (just a few bucks). Tested the light / wiring on the battery which illuminated no problem. Stuck the lighting on the Coil with the power lines (DME wires?) connected and nothing... did not light up. With key set to accessory - nothing, cranking - nothing. If I put another simpler tester on it for electricity this does light up. Perhaps I am not getting an entire 12 volts to that line hence no spark through the coil? Perhaps I have a grounding issue? I'll test further with my multi-meter tomorrow.

Tom, thanks. My bounce is no where near what you say. It bounces about 1/16th of an inch the very first crank than nothing on all subsequent / consecutive cranks. I'll do more testing around the reference sensors tomorrow. I did replace that one that crumbled, though, I only had one spare. We'll see how the 2nd one is.

Definitely feeling the issue is caused by no spark... hopefully I am getting close to the culprit. Thanks for everyone's help!

Brantley

Hi Homerj - well, I'm not getting much tach bounce so maybe this issue is caused by a failing DME.

I'll be focusing on the reference sensors tomorrow as well as cleaning all the grounds I can find. If you find the BMW part, post it up. Thanks!

Tom M'Guinn

Here's a good video from Rogue showing what the tach should do when cranking. If it doesn't bounce like this, start by figuring out why...

Brantley

Found the problem!! Car starts and runs great now!

Went through and cleaned all the grounds. Found some exposed ground wiring and boost tubing that is dried out and starting to crack / crumble. Did what I could to address that. Tried to start it and still no tach bounce.

Went to check the resistance and voltage on the reference sensors via the connector to the DME by following this video -


Once I got the panel off I noticed that the factory alarm wires were not fully seated in to the alarm module. Reseated them and the car fired right up with the proper amount of Tach Bounce preceding that.

This is a new to me car over the last few weeks so I hadn't had the DME / KLR out yet. The alarm connector must have just been hanging by a thread and come loose causing the no-start.

Thanks for the help all!!

fbgh2o

If you have not changed the other sensor I would strongly recommend replacing it. It's likely to be in bad shape too.

Martin1986

Wow what an adventure!
I too have a non starting situation and found that one of the crank sensors is defective by following a similar path above.
Can you tell me how you dealt with the rubber grommet the cables run through?


Got in through the wheel see pic Used a small ratchet with 5mm hex and got the sensors out. However the rubber grommet with the 3 wires running through it is a real pita. I believe a that as long as I do not mess with the sensor bracket itself I should be able to swap with a new sensor without worrying about the distances. I’ll probably take that rubber out



Tried to get the rubber grommet out