How do I test a 964 coil?

Jcon · 02-06-2005, 04:05 PM

I'm trying to trace a slight stalling in my 92 964 motor. I disconnected my secondary dist from the coil and the car starts fine.

If I disconnect the primary dist from the coil it sputters and coughs, but won't start.

It's either the coil or the dist belt has skipped a tooth.

How do I test the coil??

Rotors and caps have about 1,000 miles

Jeff

Jcon · 02-07-2005, 08:38 AM

Bump

Thomas Owen · 02-07-2005, 08:58 AM

From my tech manual:
Measure values with an ohm meter:

Between Primary terminals 1 and 15 : .4 - .6 ohms
Between Secondary windings 4 and 15 : 5.0 - 7.2 kohms

Where 15 is '+' terminal, 1 is '-' and 4 is the large connection for main coil wire to distributor.

Good luck

Early_S_Man · 02-07-2005, 10:26 AM

I think you skipped a few possibilities ...

1. Bad connection in wiring harness/DME connector/at coil ...

2. Bad driver transistor or solder joint in DME ... that drives the coil[s] ...

3. Spark plug wire[s] ...

4. Intermittent short/open inside coil ...

Of course ... if you put the ignition system on a Sun Analyzer ... you might get a bit closer in narrowing down the problem, rather than 'shotgunning' it to depletion of wallet!!!

tholyoak · 02-07-2005, 01:54 PM

There is only one signal wire from the DME that is split at the two ignitors so I think if 1 coil fires and the other doesn't it is either the coil, the ignitors, or a wiring problem. Since it is your secondary distributor that is working this would rule out a broken distributor belt.

A less dangerous way (to you and the DME) of testing the 2 ignition circuts is to disconnect the ignitor connections not to remove the coil wires to the caps from the coils. You can do this with the car running and see if the idle speed changes when you disconnect one circut or the other at the ignitor connection.

I would test the coils the way Thomas says, if they pass my money is on a bad ignitor.

There is a test to check the output from the DME at the ignitor coils but you need an oscilliscope according to the factory manuals.

You can also check that term 15 on both coils has battery voltage when the key is in the run position.

If you want to swap known good parts, I have a pair of coils/ignitors that work fine.

Todd

Lorenfb · 05:39 PM

"1. Bad connection in wiring harness/DME connector/at coil ...

2. Bad driver transistor or solder joint in DME ... that drives the coil[s] ..."

Neither of the above is connect, as the 964 DME does not directly drive
the ignition coils as Todd has pointed out. The 964 ignition system is very
simple to diagnose; 1 - DME signal, 2 - ignition modules, 2 - coils, 2 - distributors.

1. If the car runs on one or the other module/coil/distributor, DME is O.K.
2. Then use the good running parts (module/coil/distributor) to isolate
the problem.

The system is easier to trobleshoot than a 3.2 DME system.

Note: Ignition coils may test statically, but fail when producing a spark
the result of high voltage breakdown in the coil secondary.

Jcon · 02-08-2005, 09:35 AM

Thanks

I'm actually taking tommorrow off to dig into this issue. This info is great.
I recently resolved to end my days as a checkbook mechanic and dig in and do more things myself so lot's more questions coming.

Todd - Thanks for the offer, I'd take you up on it if you were closer.

Jeff

kang · 02-08-2005, 12:28 PM

Can you swap ‘em? Connect the primary coil to the secondary distributor and vice versa? I think you said if the primary coil is disconnected from the primary dist, it sputters. How about connecting the other oil to that dist?

What makes one coil primary and the other secondary? I thought both plugs fired at the same time?

Jcon · 02-09-2005, 04:35 AM

When you say "Ignitors" are you refering to the ignition control unit listed in pelican???

Jeff

Lorenfb · 02-09-2005, 09:00 AM

Ignition Control Module
Ignitors
Switching Unit
Ignition Unit

All the above terms are interchangeable (synonymous).

Each ignition system (of the two) should INDEPENDENTLY run the 964/993 engine.
All of the ignition components are interchangeable and can be use for troubleshooting
each of the two systems.

Jcon · 02-09-2005, 11:41 AM

Well it looks like it was the DME relay. The coils, ignitors, dist belt all checked out. This time I unhooked the ignitors to test each side of the dist.

The relay was partly out of it's case and had some evidence of moisture. I put in a new one and drove with out any stalling. The problem I was having was a kind of instantaneous shut down, like 1/2 a second and then the engine would catch. no sputter no nothing. Just like an on off switch.

The problem was very intermitent so i'll have drive a while to see if I've actually solved it.

Interresting note the DME Relay used in the conversion was the carrera relay. The pin style vs the 993/964 spade style. It came out of a 91 c2 with this configuration.

I'll post a pic later of what looked like some evidence of moisture.

Here's another question. What should the resistance be on a good plug wire?

Thanks

Jeff