HELP: Porsche 944 no spark

Is there a pulse at the injectors?

There is plenty of fuel in the rail. We haven't' checked the injectors yet because we were unable to get spark. So we wanted to solve that problem first. They are unrelated, right?

-Jon

Could be any of these, but I would try the DME relay first, this is the classic failure of these vehicles. I had a similar failure on my '88 and it ended up being a combination of bad coil and poor solder joints in the DME (likely caused by the bad coil overheating the coil driver) but if you are confident in your diagnosis of the coil as being good try the DME relay. You can bypass it temporarily, look for a procedure on Clark's Garage.

nate

Yes, but if there is 12V at the coil, should it be sparking? there is

12V at the terminals on the coil, the impedances are correct, but we aren't getting any spark.

Simple presence of 12 V at the coil does not guarantee a spark, if that helps any.

There are a number of different types of ignition circuits around, and I dont know what that Porsche uses...

So, if there is 12V there, can we rule out a bad DME or bad speed and reference sensors? asked another way: would a fault in the DME, or these 2 sensors cause no voltage at the coil?

When you try and start the engine, does it pulse? If not, it's not getting proper signal.

Makes sense. Coils fail occasionally, but not very often. And usually when coils fail, it's because they're not being driven correctly.

Okay, sounds good.

The coil is fine. One of these sensors is bad, or the ECU is bad. Pull the codes off the ECU and see what the ECU has to say.

There will almost always be 12V at the coil.

--scott

The spark is actually produced by taking away the 12v. The DMA will ground the coil for every time it needs to spark. You can try testing the coil by using Clark's website suggestion. I tried this and I thought I would see more of a spark. I actually had a hard time seeing the spark so I had to move the coil and battery into a dark room like a walk in closet to see it.

My guess is if your coil measures good it probably is good. Do you know about Clark's web site. Here is a link to the troubleshooting section on "No Spark":

go to "Garage Shop Manual" click on "T" for Troubleshooting and then on "TS-01" BTW my problem was a bad ignition switch.

No. Both the spark and the injectors are commanded by the ECU. If the ECU doesn't know that the crankshaft is turning, it won't fire either one.

If your coil were gone, you would not have spark, but you would still have plenty of fuel coming out of the injectors. But you'd have noticed this if it were the case because the exhaust would have smelled strongly of unburned fuel.

--scott

Voltage does not cause the coil to spark. The CHANGE in voltage causes the coil to spark.

If there is 12V on BOTH sides of the coil, there is no voltage across the coil anyway.

--scott

The ignition coil works by rapid collapse of the voltage in the primary coil. If the primary and secondary show propter resistance then the coil is probably OK. The sensors can only be tested with an oscilloscope. They may have slipped in position. You need to check this. Go to

for more specific data.Have two 944's and have been through this drill a few times. If youhave an older model that has been stored outside your problem isprobably a bad connection on the blade connectors on the relaypanel. Try wiggling the wire mass when starting to see if it fires.

others have explained about coil and sensors. I would just about guarantee the coil is good. I would check that the two sensors at the back of the engine that provide reference and mark information by sensing flywheel position are both properly connected and measure them for continuity - that is the most likely cause outside of a DME relay.

You can lift the cover off the DME relay easily and check for bad solder connections where the upper relay in the package is soldered to the little circuit board - this is a VERY common failure and takes all of 5 minutes to fix for no $$ at all

** Posted from **

It was a bad crank position reference sensor. Thanks everyone for the help. My friend has several E30 BMW's and the sensors are the same. So we tested the resistances on my sensors, found that the crank reference one was bad, swapped in his... and it started right up! Thanks everyone.

And you should not.

If the engine is not cranking, there will be no spark.

If there is no spark when the engine cranks, suspect the ignition module, distributor pickup, or associated wiring.

DME relay

Try using a three-way jumper plug to replace it. This has 3 spade connectors, like the wide ones on the bottome of the relay, connected by two wires. Picture the old McDonalds "M".

D> Hi Group,

good work - do not discard the old sensor - believe it or not, I've repaired them - just find the break in the coil and fix it

** Posted from **

HOLD THE FONE HERE. ARE U SURE THAT YOUR COIL IS WORKNG?. ALSO CHECK FUEL PUMP RELAY, I THINK ITS JUMPED 30 - 87 OR 87A CAN SOME WON CONFERM THIS PROBLEM THIS PERSON HAS...

The DME relay just switches on the fuel pump, idle stabilizer circuit and O2 sensor WHEN the engine is cranking. Check for power on fuel pump fuse WHEN the engine is cranking. Bad relay can be temporarily bypassed, take it out, connect pins 87 and 87b to 30 which is always ON, you should hear the pump running, engine would start and run normally.

Nothing to do with spark. Regards, Martin

TRUE OR FALSE?.....THE DUTCH VERSION 997 OR BETTER POLICE CAR, IS A MYTH?