car wont start still

[Eric]

I thought I had a bad ignition coil on the car since I would not get spark from the coil. So tonight I replace the coil and still the car will not fire.

what should I look for now?


Also I had a Snap-on battery charger that was showing 17.xx volts. I don't remember if the car started before the charger was on, but it has not started since. do you think i could have friend the computer?
thanks
Eric
88M3
95M3

[HANDBLT]

Reference sensor(s).

[whakiewes]

I am fairly sure that you know this, but have you tried replacing the plugs. I have fouled 3 sets of plugs due to the previous habit I had of starting the car...backing it up 3ft, then quickly turning off. Since the first time I keep the socket, wrench, and 4 cheaper(NGK) plugs in the car for the next time it happens.

Wes

[Eric]

I don't have a spark plug removal tool that will work on the car. I havent pulled the plugs, but I have a feeling that they wont be getting a spark anyways, this is my theory.

I pull the lead from the ign coil to the distributor cap. I have person #2 hold the lead up against one of the metal nuts on the valve cover (the pretty 10mm ones) I start cranking on the engine, and at 1am in the morning with no other light, I figure we should see some kind of spark jumping to ground, correct? well there was nothing.

this makes me think that
1. I have fried the ECU or something that is in between the battery and the ign coil.
2. I have fried something else
3. my car does not like me anymore
4. a main relay is bad?
5. something else is wrong that is way to obvious for me to notice.

thanks for you help
Eric

[Eric]

Originally posted by HANDBLT
Reference sensor(s).

what are those, what do they do, and how will they effect the car?


Edit: are those the metal sensors on the drivers side of the bell housing? I havent touched those in over a year, but it still is possible one could go bad, correct?
what do I do to check to see if they work?

[whakiewes]

I would bet a lot of money that it is the plugs, as I don't have a clue about much of what you said in your previous post. Either way, good luck.

Weds

[Eric]

Originally posted by whakiewes
I would bet a lot of money that it is the plugs, as I don't have a clue about much of what you said in your previous post. Either way, good luck.

Weds

what didn't you understand? I have added new text in bold that I think make myself sound a little more clear. correct me if I'm wrong.



I don't have a spark plug removal tool that will work on the car. every tool that I have tried to use is either too large to fit down into the hole, or is too small to fit around the spark plug. So since I cannot remove the plugs, I havent pulled the plugs, but I have a feeling that they wont be getting a spark anyways, The reason I think that I will not be getting a spark is described below. It was a test that i did late last night to see if my new ignition coil was working. this is my theory.

I pull the lead from the ign coil to the distributor cap. I then have person #2 (my friend) hold the lead up against one of the metal nuts on the valve cover (the pretty 10mm ones) I then start cranking on the engine, we were doing this at 1am in the morning, so it was very dark outside. I figured you would be able to see a spark especially when it is dark out. (since the actual jumping of electrodes commonly know as "arcing" creates light. very similar to a very very small bolt of lightning accross a night sky. I'm sure you know what a spark, or "arc" looks like) correct? well there was nothing. there was no spark between the ignition lead to the engine ground.

Since there was no spark, and the ignition coild was brand new, it made me think that something else could be wrong with the car. I have listed 5 things that I think could possible be wrong with the car (some of these are me joking, especially #3) this makes me think that;
1. I have fried the ECU or something that is in between the battery and the ign coil.
2. I have fried something else
3. my car does not like me anymore
4. a main relay is bad?
5. something else is wrong that is way to obvious for me to notice.
I hope this helps, let me know if you still don't understand
thanks for you help
Eric

[H a n]

Eric,

If you are not seeing spark from the ignition coil, it's either the computer or the main relay.
I had the same problem when I installed my new motor (we used the same method to check for spark).

Han

[Eric]

which relay is the main relay? the metal, purple or orange relay behind the coolant tank?

thanks for the help

[H a n]

it's the silver one.

[Beau]

I'm betting reference sensor. That was my problem. I went through the EXACT same ordeal. Thought it was the coil, but it wasn't... I have power there, but pulling a plug and testing it just as you did against the valve cover proved no spark.

The reference sensors are what you're thinking of. If you pull the plastic cover on the top of the fire wall you will see 3 plugs, 2 that run down, and one that goes somewhere else. The Bentley shows them. Anyway, it's really REALLY easy to test them, just unplug both ends and test for continuity with a meter. Another thing, supposedly if you swap the sensors, it should start ONCE I was told by BavAuto because then you reset them and it uses the base config or something - I forget exactly, but I didn't try this anyway. I knew I had one bad sensor, ordered it for $78 from Maximillian (only place I found with them in stock) and it started up immediately.

If it's not one or both of them, then yes, it will be the main relay or the DME. And the main relay isn't necessarily silver. As far as I can tell, if it's been replaced before it may be orange, silver, or black (I no longer have silver relays anywhere) Someone hopefully has a chart that shows specifically which it is... I can't remember right now. I think someone posted this in a different thread.

[Eric]

I thought the refrence sensors were on the bell housing right? so what do I check at the firewall? is that where they terminate?

I'll check the koala CD tonight, that has usually been OK for engine related stuff.

when testing for continuity, can you explain this a bit further. all i need is to have my VOM beep and they are working? how are these sensors designed to work?

(i'm not trying to sound dumb, I just like to figure out how things work, so if a sensor shows continuity when the car is off, or on, it is a bit confusing.)

thanks for the tip, I'll check it out in 1 hour and 15 minutes (i've been waiting all day to nurse my car back to health:p )

[Beau]

You've got the idea, they run from the bellhousing along the fire wall and plug into a harness that's behind a 4"x18" plastic cover on the up-most part of the firewall, just below the hood seal. When you take it off, you'll see three plugs (similar to the AFM plug) lined up next to each other. 2 lead down, one goes somewhere else (can't remember). Anyway, if you unplug them they have 3 pins I think, maybe 4... I'm not near the car or else I'd go double check all this for you. I will be working on it tomorrow though so I could go get better directions then.

Anyway, unplug the top side (under the cover) - I misspoke earlier when I said to unplug both ends. Then set the needles of your meter to the pins each side (like pin 1 and 3, then 1 and 2, then 2 and 3). I forget which combination it's supposed to give a reading, but at least one of them should show a connection. A bad sensor won't give any signal under any combination. The car doesn't need to be on, or even have the battery in it since you're not testing for power, just whether it's connecting the circuit. It would be rare for both your sensors to be blown, so at least one of them should show to be good... otherwise I've told you how to do it incorrectly, or you're not doing it right!

Since this is a back-woods way of testing it, even if this test doesn't show you a problem, it still might be the sensor anyway (and it's a helluva lot better than a new DME). I just figured this out by trial and error with my father's assistance (he's an electrican - go figure). When I called BavAuto (who doesn't have one), the guy told me that if I swapped my sensors, it would start once. When he told me it made sense, but I've since forgotten the reasoning behind it all. Sorry to be so vague, I'm trying to remember all of this from last weekend, and I'm not doing so hot

Let us know what you find... I may or may not be around later, but I'll definitely be back here tomorrow with a M3 in front of me so maybe I can make more sense.

[ColinM]

You also want to test the resistance in the sensors. They should be 960 Ohms +/- 10%.

Sometimes they'll check OK cold, but give a funny reading when warmed up.

[Eric]

great, thanks for the ohm reading. where did you get that information?