944 Ignition Problem

[BobFitz]

New 944 owner, old amateur mechanic. I have no spark with plugs in, spark with plugs out.
Any ideas?

[mytrplseven]

Hard to say if you have bad ignition wires because I don't know how they were handled. How do you know you don't have spark with them in?

[BobFitz]

I put timing light on coil wire unplugged from dist. cap.

[jhowell371]

Make sure the coil is good and hooked up with proper polarity. If weak or hooked up backwards coil will still spark but with diminished strength.. It will fire under atmospheric pressure but not well under engine compression.

[BobFitz]

Originally Posted by jhowell371

Make sure the coil is good and hooked up with proper polarity. If weak or hooked up backwards coil will still spark but with diminished strength.. It will fire under atmospheric pressure but not well under engine compression.

Coil wire is not connected to cap in either plug in or out.

[BobFitz]

Originally Posted by BobFitz

Coil wire is not connected to cap in either plug in or out.

Coil not connected to cap in both plug in or out. Monitoring with timing light on coil wire.

[onrails]

is this an "S" model? the computer can change what voltage goes where. the "S" and turbo have more to their ignitions. (help me out folks if you differ) my "S" stumped me on that once before. it could have an ignition control module in the drivers fender behind the headlight. very fragile if hit. again im the novice of some what but I have never taken mine to the dealer other than belts.

[mytrplseven]

Originally Posted by onrails

is this an "S" model? the computer can change what voltage goes where. the "S" and turbo have more to their ignitions. (help me out folks if you differ) my "S" stumped me on that once before. it could have an ignition control module in the drivers fender behind the headlight. very fragile if hit. again im the novice of some what but I have never taken mine to the dealer other than belts.

You can see by the pic that this is an "early" car. It has the cookie cutter wheels and external antenna. Good looking car.

[BobFitz]

Not an "S" model.
Fuel pump functions OK. I think that means relay is OK.
Checked coil (disconnected) with 12v on + and intermittent ground with spark plug on high voltage terminal. Had very weak spark or no spark sometimes. Ordered a coil- should be here today. I'll post results.

[Dave Colangelo]

My 924S (same engine as your 944 NA) had a no spark issue and it turned out to be a bad DME/ECU (engine computer). When you have a no spark issue it is most likely one of the following thing, keep in mind it really can only be a limited number of things so lets start and work though the spark system.

It could be your crank sensor. These are common issues and easy to replace. There are 2 of them and you can find lots of DIY articles on replacing them. If memory serves there is an audi part that also works if you cant get one of the Porsche ones. They can be bad or intermittent and can be tested with a multimeter. These sensors tell the ECU when to pulse the coil. If they are bad the ECU will never be told to pulse the coil.

Bad ECU. This can come in a few forms and it could be a host of issue in the computer that care causing the issue but in the end of the day this is tough to test unless you pull the computer and put it in a known good car or make a bench test rig. There are a few places out there that will test and or rebuild ECU's for you. If you narrow it down to this I advise sending the unit off to one of them.

Bad coil. Sometimes the old coils are just bad. A new coil is not that expensive and worth replacing just for piece of mind.

Dirty/Bad/Broken distributor cap and rotor. Just replace it, this should be part of your maintenance ever year or so. The constant sparking causes carbon to build up on the copper bits inside them, dont bother cleaning them just replace them (unless they look very new)

Bad plug wires. You can see this in a dark garage. When you crank you will see small white arks from the cable shielding to ground. If you wires look old and dry I would replace them anyway.

Spark plugs. Unlikely they are all bad but should be replaced as part of yearly (or more often) maintenance.

Wiring harness issue. The wires to be concerned about here are from sensors to ECU and ECU to coil. You can pull the big connector that goes to the ECU and test the pins to the end of the wires. I dont remember the pin numbers off hand but they are in the haynes manual (worth getting if you dont have it).

Bad DME Relay. This is the relay that powers the computer and fuel pump. They go out ALL THE TIME SO CARRY A SPARE. With out it the computer wont turn on and thus you will get no spark.

This about covers the bases of the spark system however I may have forgot something...

Regards
Dave

[BobFitz]

OK- coil took care of no spark problem. Now it backfires like it is out of time.
Cap and rotor look good- no carbon tracking and clean. Wires are correct with firing order.
What is best way to check timing?

[DannoXYZ]

Originally Posted by BobFitz

OK- coil took care of no spark problem. Now it backfires like it is out of time.
Cap and rotor look good- no carbon tracking and clean. Wires are correct with firing order.
What is best way to check timing?

Timing light that lets you dial back to zero. Then read off the timing on the dial.

[BobFitz]

Originally Posted by DannoXYZ

Timing light that lets you dial back to zero. Then read off the timing on the dial.

And where do I read it on the engine?