My car suddenly died while in traffic. I turned over the motor and the tach didn't move so I thought I had a broken timing belt. I got the car tore down to the belt and its not broken. So am I lookin at a ECU or is there a crank sensor? maybe a bad coil wire or coil? I have already bought a 8v head and parts which sucks. but I'm really aprehensive about buying any more part until I know more.

 

Check the reference sensors. DME relay is another possibility? How are the cap and rotor?

 

I would start by looking for.....SPARK.

(sorry...could not resist !)

Seriously...go to clark's garage and follow their testing procedures....

 

new cap and rotor are installed and have checked for spark already

 

Start with the DME relay (Second relay in from the fender on the main relay board) It controls power to the DME (Bosch Motronic control unit) and the fuel pump. There's a procedure to make a jumper on clarks.
If that checks out, the next culprit would be the engine speed and reference sensors. You can do a cursory check with a volt meter by checking the resistance, but you really need an oscilloscope to be sure they're working correctly. If in doubt, you might want to replace them anyway...

 

When you turn the key in the ignition, the following sequence should happen:

1. Power to DME relay
2. Power from relay to DME
3. Ground from DME to fuel pump (you can listen for this)
4. Key turns to start
5. Starter turns engine
6. Speed and reference sensors send info to DME
7. Coil is grounded for spark
8. Signal to tach (you should see it bounce)
9. Engine fires ( you will hear it catch)

I'm going from memory here, so I may have forgotten something. If you don't hear the fuel pump running or tach bouncing you can narrow things down. It's also worth putting a timing light on the coil wire to check that if everything else seems ok.

 

if you crank and the tach doesnt bounce its either the ref sensor or the dme relay- basically. Try swapping out - or jumpering - the dme relay. You can pull the top off the relay and make sure both contacts are pulling in- if one is not there is your issue. If its working and still no tach, one of the sensors is not reading. Try checking the plugs or replacing.

 

thanks for all the info, ordering a dme relay and then moving to replacing reference sensors if that doesn't do the trick.

 

You have to look close at the TACH. It will only move about 1/16" if the reference sensor is good. No bounce, bad reference sensor. Wiggly the wires gently as the connector gets brittle and loses contact.

Cheers,
Larry

 

I just went thru this same problem. I had thought (incorrectly) that it was the coil, as I got power going into the coil, but not out of it. Instead, the issue was with a wire which came disconnected when I lowered the engine in the car (while dropping the crossmember). I know you didn't just do that, but still, you might give your wires a once over, make sure nothing has giggled free.

 

well got the dme relay on the way. if the tach does'ntmove at all am I looking at which refrence sensor first?

 

Here is a link to show you the speed and reference sensors. I'll add another for you.

http://www.944online.com/944_referen...tallation.html

http://www.944online.com/944_referen...djustment.html

Cheers,
Larry

 

There are two sensors on the top of the bellhousing. They're identical. One reads every tooth on the flywheel to tell the DME how fast the engine is turning, the other reads a single steel screw in the flywheel to tell the DME where TDC is.
There's a resistance check you can to to tell if there's a short or open coil in the sensor or a break in the wire, but it won't be 100% conclusive that the sensor is good.
If you do a search on the forum for "BMW reference sensor" you should find a BMW part number you can source for about half the cost of the Porsche parts.