SC with 3.6 Trouble

Jim Smolka · 03-16-2008, 03:13 PM

Been working on an running problem with the SC with a 3.6 conversion. The motor is from an 90 C4

Usually, it will not run, but ocassionally it hits perfect then it is back to spitting and
sputtering etc.

For simplicity lets say the ignition coil module closet to the firewall is CM1, and the one closest to the distributor is CM2. The connector to CM1 is now C1 and C2 goes to CM2.

This is what I discovered today:

1. With both ignition modules connected, the car spits and sputters.

2. If the C1 is disconnected from CM1, the car rus OK.

3. If C2 is disconnected to CM2, the car spits and sputters

4. If C1 is connected to CM2, the car spits and sputters

5. If C2 is connected to CM1, the car runs OK.

Maybe the belt, but I an not convinced.

Thoughts???

EarlySport · 03-16-2008, 08:05 PM

Can you pull the distributor caps off and have someone crank the motor while you watch the rotors, and make sure they're both turning?

Jim Smolka · 03-17-2008, 12:30 AM

Yes, they both turn.

Jim Smolka · 03-17-2008, 04:46 PM

Took a look at the dizzy belt, it looks OK.

DW SD · 03-17-2008, 05:08 PM

Could you define C1 and C2? Are they the distributors?

If I'm understanding, I would guess one of the coils is bad. Can you try a spare? Can you measure against the good one with a meter?

Does the 964 have independent ignition modules (signal amplifers of some kind which trigger ignition pulse to coil)? The 993 has one ignition module, two coils, two distributors.
Doug

jevvy · 03-18-2008, 10:59 AM

IIRC the 964 has 1 igniter per coil and they are mounted next to the coils as opposed to near the ECU like on a 993.

The first part of your test seems to indicate that CM1 (coil and igniter) may be faulty - not sure the second part of your test is actually of use as you may get those results swapping things on an otherwise good car.

You would have to swap the CM (coil and igniter) out at the next level up(swap the cables that feed the CM) to tell if the problem moves with the CM.

Good luck keep us posted.

MURF · 03-18-2008, 11:43 AM

recheck your firing order top and bottom..could be crossed wire.or bad dist cap

ischmitz · ischmitz's Garage

So anything off coil #1 makes the car spit and sputter. Since it runs fine with just coil #2 being driven it is not likely a miss-wired plug from distributor #1. It would still idle at least as good as with coil #2 only.

To further diagnose you can move a coil, cap, and spark plug wires. It will be tedious but cheaper than throwing parts at it. You fault is downstream from coil #1. By the way both ignitors are driven off the same signal line from the DME. So there is nothing wrong with the DME.

I think you have either a faulty coil #1, cap #1 or coil wire from cap #1 (most likely) that generates enough electronic interference to reset the DME. The 964's are known for being extremely sensitive to any sort of electric noise. Check you spark cables when it is pitch dark. Sometimes if the insulation is cracked you can see one or more wires arcing to the grounded metal of the engine.

Ingo

Jim Smolka · 03-18-2008, 06:05 PM

Sorry for the confusion. C1 is the plug connector from the DME (~5 pin connector) to ignitor for coil 1 which is closest to the fire wall. C2 is the plug connector going into ignitor 2 coil.

I could be some time of noise issue with a bad cap.

When connecting c1 to ignitor 2 that goes to coil 2 (C2 disconnected), the car spits and sputters. C2 to ignitor 1, the car runs (c1 disconnected). This leads me to believe that the coil, cap, wires are OK. It also leads me to believe that there is something wrong with the signals from C1 since the spitting and sputtering seems to follow C1.

ischmitz · ischmitz's Garage

Jim,

In a 964 there is only one DME signal for the ignitors at pin 5 of each ignitor. It's a shielded wire. Maybe a dirty connector or missing GND at connector 1?

Jim Smolka · 03-19-2008, 01:56 PM

Thanks... I will take a look at the ground on Pin 5

DW SD · 03-27-2008, 06:41 AM

Jim,
What's the wrap up? Is this resolved?

Doug

Jim Smolka · 03-28-2008, 03:15 PM

Doug,

This project had to take a back seat... working on a friend Turbo, clutch blew up...

The SC runs OK with just one distributor, so I can move it the driveway for now. Hope to get back on the problem in a couple of weeks.

johnsjmc · 09-16-2008, 05:45 PM

Did you ever resolve this? I may have a similar problem. Mine cuts out intrmitently. Replaced the DME relay and reflowed 2 suspicious solder spots in the DME. Runs OK with 1 dist connected runs rough( one backfire) with other dist only connected. Belt is turning sec dist.but appears loose.

Jim Smolka · 09-17-2008, 04:20 AM

Not yet
Been working on other projects
Thinking of replacing cap and rotors