Start with one ignition coil lead disconnected
 

Gents, have been having some issues recently as follows:

1. Alternator belt broke. Drove car until battery drained and could no longer provide voltage for ignition system.

2. Belts (alt., fan, A/C) replaced and car seemed to run fine for approximately 500km

3. Went to start one morning and ran very rough, misfiring, would hesitate when accelerator pressed, sometimes stall. Spare DME nowhere in sight so I left it for the weekend to troubleshoot.

Poked around the engine a bit, removing and re-seating ISV connector, AFM connector, distributor connector, and basically any electrical connector in sight. Also removed and re-seated relays in boot. Checked dizzy belt and it was intact. Started engine and it ran perfectly. Normal accelerator response and good idle. Had no time to test drive so left that for another day.

Another day came along and same problem, rough idle, etc., etc. Spare DME still missing so installed DME jumper at pins 30, 87, & 87b. Car started fine. Removed jumper and installed suspect DME. Car started fine with normal accelerator response and good idle. :confused:

Took for 60 km test drive and ran normal. Voltage at battery with engine running 13.5V. Stopped and started engine 2-3 more times with normal idle noted.

Started her this morning and same thing, rough idle, etc., etc.

Haven't had a chance to check ignition coil resistance.

One other check I did when all this started was remove the primary distributor coil lead and start engine. Engine started fine on the secondary distributor only but would not start when secondary distributor coil lead was removed i.e. only primary distributor firing.

I would think the engine should start no problem with only primary distributor firing but not sure. Anyone seen this before? Does the above check provide any clues or is it a bad idea and cause more problems?

Also wondering if running the car with no alternator belt until battery drained could damage DME relay, coils, ignition leads, ???.

Had the car for 5 years and put about 60k km on her (~125k km total). Dizzy caps, rotors replaced about 3 years ago and fuel pressure regulator replaced ~4 years ago. Ignition leads have not been replaced since I've owned the car so no idea how old they are.

Any info you can provide is greatly appreciated.

Rgds,

Martin

Hi
Our dual spark 964s are super sensitive to ignition. I believe it was engineered in due to the distributor belt connecting the 2 distributors.

You are running on the secondary, which confirms the belt is intact.

How about when you run only on the primary? Starts but rough? No start?

Given your trouble started after a required alternator repair, and the car ran well before, it's got to be related to the work done recently.

I'd check the seating of all the lower plugs (primary). It's easy to fit the wire boot into valve cover thinking its seated on the plug and have the wire jammed off to the side.

If the wires are confirmed seated, then work backwards by inspecting wires and coil.

You can switch out the connections so you run only the secondary dizzy with the other coil to be sure that is good.

Also make sure the dizzy rotors are in sync, there are marks on the housing you can see with caps off.

You are very close to confirming the exact cause.

My guess is either wire at plug or bad coil.

Good luck

FS

Hi FS, thanks for the reply. When I disconnected secondary coil wire I get no start. That's what I thought odd as I would have thought it should start and run on either distributor.

Did another start today when I got home from work and same problem, rough idle, and long hesitation almost stall when pressing accelerator. Removed DME relay and installed jumper, same result.

Seems DME relay not the problem. Will have to dig deeper suspecting coils, ign wires, fuel press regulator. Maybe battery / grounds?

If only I had a proper garage and spare time to work on her.

Isolate distributors by disconnecting the ignition modules not by disconnecting the coil leads.

Perhaps it is a coincidence that this problem started after your broken belt? Or perhaps it is a result of it?
If you have never changed your coils, you might want to consider changing them.

Finally got around to re-checking the distributors per Vandit's instructions of isolating with ignition modules. Same result, no start on primary coil but did start on secondary. Also, swapped the primary side ignition module to the secondary coil and same result.

Gained access to the coils and primary coil was not looking very good. Greasy sticky substance around the top and terminal looked corroded (see photos). Took resistance readings of suspect coil primary and secondary windings and surprisingly they were all good.

Also had a look at the primary distributor cap and rotor. Appeared to be some carbon buildup on the internal contacts and rotor tip. Cleaned these up and tested again with same result.

Installed new coils, caps, and rotors. Amazing how correctly functioning coils will improve throttle response and general smooth running of engine! Feels like an extra 50HP in the car now. Number obtained from highly accurate butt-on-seat dynamometer.

Thanks for the help and advice guys.

Rgds,

Martin



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