So.......following on from my recent thread:
...'88 V12 engine dying when hot and stuck in traffic. Restarts 10 mins later. I have replaced the ignition amp module as a first step, plus new complete AB14 unit on order. Rather than try and replicate the slightly problematic fault on the road, I thought I would test the old module.

Awesome methodology below:


photo of old module:



My understanding of general electrical principles is so weak that I am unsure where lead No.1 in the above diagram should attach to the module.
Thoughts?
Thanks in advance,
Quentin

 

Attached #1 to the bolt hole. It’s a ground.

 

I have found that you need to use only the genuine GM/AC Delco module. I have used several aftermarket modules that were worse out of the box than a failing GM module. Replaced with a GM module and all the problems went away.

 

Quote:

Rather than try and replicate the slightly problematic fault on the road, I thought I would test the old module.

Great idea....but unless you heat up the module first I'm not sure the tests will be conclusive. Maybe test it at room temperature and then throw it in the oven for awhile and test again? Not sure what temperature to set the oven, though. 150ºF?

Cheers
DD

 

If you are stuck on the road. the bottom left condenser is for radio noise and can short out. It is ok to to disconnect. Top right hand corner is protection diode and will short to ground if it has failed or there is too much current, it too can be removed to see if it is problem. If disconnecting diode and disconnecting the condenser do not fix your problem, then it is the module. If the module is good, then the pickup or wiring to pickup in the distributor could be problem. Also the ignition coils fail with heat and come back to life when cooled down.
Rgds
David

 

d

 

Thanks!
I actually tried that and then realised my test light was not working. Will re-try with new light, or I guess just use my voltmeter

 

AC Delco D1906 is the one I bought. Believe correct.

 

DD,
Ahhh....... good point!
Will try at room temp and then after oven heating.

 

David,
Thanks. Really good info!
It has the single coil mod which was done fairly recently as I recall, but does not mean its not the problem. Is there a way to check the coil, but again. It would have to be hot. Will investigate ignition amp components further before looking at the coil. I guess just replace it in a process of elimination.

Will check pickup. The ignition amp was moved to the top of the radiator 2yrs ago, so wiring okay, but will check connections. Also have new coolant temp and air temp sensors on order.

 

Yes, that's the one to get.

 

I had a intermittent heat failure for some weeks, but by time I was ready to Trouble Shoot, it was working again. I left car overnight at a shop for lube, oil change and rear brake pads. He could not start the car in the morning, and found a bad ignition coil. (ignition coil was only a year old, and I had resisted changing it because it was new!!!!!). I could have changed it for $56.00. He charged 1.5 hours for T/S plus parts. (wife and I have agreement, I can keep the Jaguar as long as I don't crawl under It. There hasn't been an earth quake in Central California since I stop working under a jaguar on Jack stands!!!)
Rgds
David

 

Point well taken
Yikes, working under a car is taxing enough without wondering if the 'big one' will hit and car topples.

Quentin

 

OMFG the oven heating diagnosis procedure actually worked!

Did the test intially with the part at room temp and it passed i.e. working.

I then flambayed the module at 170degF for 15 mins in the oven until al dente. Connected it to a 12V battery and it failed the test I.e. defective. Repeated the test after it had cooled down post-heating and it passed. That mimics my problems on the road!

I am 99.7419% certain I nailed the problem (margin of error + - 100%).

 

The failure with heat is actually the reason the AB14 is mounted on the intake manifold. It's a huge heatsink, and the module generates heat when in operation - the thermal paste that is supplied with the new module is very important to use. The module also needs a good electrical ground and bolted to the engine provides that.

All the idle air goes through the left intake and of course that banks air when off idle, so the intake is an actively cooled heatsink; and is the coolest spot in the engine bay. As the revs rise, the module generates more heat, but also more air goes through the manifold increasing the cooling ability. There is a reason Jaguar engineers put it where it is, it wasn't random.

 

But they then moved it to above the radiator presumably because the air intake too hot a location? My thoughts are the metallic intake sits atop the engine block so inspite of theoretically being cooled by air flow within it, must suffer dreadful heatsink from the block e.g. when engine at idle?

 

The factory never moved that module above the radiator. Even at idle, it still has air going through the manifold to provide some cooling. All of the idle air goes through the left bank, it's only off idle that air starts flowing through the right intake. That's why the left air filter gets dirtier faster than the right. I have measured my engine's temperatures, and that is the coolest spot. Above the radiator bakes when stopped in traffic, as it's sitting above a heat source and there is no air flowing over it to provide any cooling. It will bake after shutdown, but that's true above the rad as well.

The later cars with marelli ignition have some sort of modules above the radiator, but it's a different function ( I think). I'm not exactly sure what that component is in the Marelli system.