Dmitry S.

I bought a non-op 951S a couple weeks ago that had a no start problem. It had an aftermarket alarm wired into the DME Relay - So i fixed all that wiring and returned it back to the factory setup. The DME Relay is good, and power is going to the DME Unit. For some reason, the car didn't come with a DME or KLR Unit - I put some in from an 87 951. From what I asked before - the car should still run on this setup, just not boost smoothly. I check the coil, the resistance is within spec, and it is getting power. I believe something is causing the DME not to send a signal to fire the coil. Where should I start? I read the FSM on how to check the refrence sensors, but don't quite understand. Is there a checklist I should go through? What other sensors would cause the DME to not send a signal to fire the coil?

Dmitry S.

Nobody knows?

jerome951

The speed and reference sensors on the top of the clutch bellhousing send a signal to the DME indicating TDC and engine RPM. I don't have a testing procedure and specs for those, but I'm sure someone does.

AlexE

PUll the dme........and check the following.

reference sensor - pins 25 & 26 should have ~900 ohms resistance *** If you feel adventurous try and read a voltage of the sensor whilte you crank the car ...a voltage spike can be picked up by a multimeter (~0.5 volt).... . Ideally i would use an oscilloscope and look for >2.5 volt spike. (or you can look at your tach and it should jump to ~200 rpm while you crank.)

Mike S

Dmitry,

A couple things to look at.

1) When you're turning the car over does the tach jump? If not, then the reference or speed sensor has gone bad.

2) If it does jump, then use the procedure from Clarks-Garage to test them. He has the resistance values laid out for you. www.clarks-garage.com .

I'm assuming that the 87 DME and KLR was from a known running car?

Dmitry S.

Yes, the DME and KLR came from a running car. The tach does not move at all while cranking. I'll check the resistances when I get home tonight. How much are the refrence sensors? $100/ea?

Mike S

Yeah...somewhere in that range. They're not cheap.

Bret 944

There's supposedly also a BMW part number for them that is a tad cheaper, I think it's in the $80-$90 range, but I dont' know the part number off hand. Have you visually inspected the speed/reference sensors ? They should be on a bracket at the back of the engine bay, those plastic connections start to break off after many years. Mine have apparently been siliconed back together by the PO, and sometimes I have to jiggle them around a little to get the car to start.

Matthew951

One thing you might want to check is, check for continuity from the pin on the DME, to the pin on the connector for the speed/reference sensors. Dan87951 had a similar problem with his car, and we spent many long days trying to figure out the cause. The problem was that the ground wire sheilding had cut into the signal wires, and was shorting out the sensors.

Thats where I would start, before spending $200 on new sensors...

Matt

Bill

I assume you checked the condition of the cap, rotor, plugs, plug wires.

Did you remove a spark plug, lay it onto the block, crank the engine and look for spark. Also did you crank the engine with the cap off and see that the rotor is moving? (broken belts, loose set screw on rotor). If the rotor does not turn you will not get spark.

Do a visual of your engine compartment and wiring harness. Check the speed and ref sensor connectors, to make sure they are firmly connected. Look for damaged wires or electrical tape on the harness for old hidden issues. Do the easy stuff before you start dismanteling your ECM or purchasing expensive sensors.

Dmitry S.

Engine has compression (So the belts aren't broken). I'm checking spark out of the coil - not from the plug wires. I also took a test light, and the negative side of the coil was not flashing (Indicating no signal from DME). The DME does have power from the DME relay. I'll check wiring and connection tonight.

Matt - I'll definately check that first before i spring for some new sensors.

Tom M'Guinn

Dmitry, I should have two spare sensors in my garage if you want to give them a try, and promise to give them back. They both came out of my running car when I discovered one had a cracked connector. PM me if interested. I within walking distance of Cupertino.

BTW, I assume you have tried swapping the connectors, in case you have them mixed up?

Serge944

A loose rotor will cause the engine to make a popping noise. from the misfires, and it might even run with a lot of throttle application. So that can't be it.

azmi951

no spark, no fuel and no tach.......my money is on the sensors. One came loose on me at a track day, scared the **** out of me. gave them a jiggle and they were good.

Lorenfb

Check out this web site ( www.systemsc.com) on the Diagnostics page under
Typical Sensor Values & No Start.

Also, check out the Troubleshoot & Waveform pages for additional
insights into your problem.