I posted this under the "1994 V12 ABS" thread and got no response (I understand the problem is unrelated to the ABS) so, here it is again:

I went for a drive on Sunday and immediately noticed that I had a huge decrease in power and the exhaust smelled wierd. There appears to be agreement that I have lost a Marelli coil or burned thru the distributor rotor.

A few questions: how difficult is it to repair the suspected problems (I am a novice but I love working on the car and feel like I can learn to do about anything with a little patience)? How much money am I looking at in regards to parts (and possibly service)? Can anyone reference me to the applicable page numbers in the service manual (I have tried looking but have only had the manual for two days now)? Are any special tools required? As always, many thanks.

 

I removed the distrib. cap and rotor and everyhing looks fine. The metal "ends" of the rotor did look as if they had been exposed to slight heat (think shiny copper), but I assume that's normal. The distrib cap gasket was broken and I intend to use the "window sealant" treatment described by Kirby Palm on the rotar, so it was worth the trouble checking these issues anyway (and a fun experience I might add).

So, based on everything I have read, I assume the problem is a bad coil. The question is: which one and how do I check? I still cannot find anything on this in the manual.

Additionally, there was what I would call an inordinate amount of "oil buildup" on the left side of the engine where the manifold connects. It seemed kind of fresh and there was none on the right side. This could have been there when I bought the car (it has that plastic cover over the distrib. so I could not have seen it too easily). Could this be related to my problem?

I did not reinstall the distrib cap and rotor (waiting until I get the gasket). Is that ok?

 

Hi Cassidy. I'm not as familiar with the Marelli ignition as others are here, but all ignition systems work similarly. If I remember correctly, the Marelli set up has one coil for each cylinder bank. If one of the coils has quit, the engine will still run, but solely on the opposite bank. The easiest way to check which coil is working is to put the cap and rotor back in place, disconnect the coil wire where it plugs into the distributor and put it close to the block where you can watch for spark when you crank the motor. No spark means either your coil has quit or the ignition module has.

Oil buildup on one side such as you describe sounds more like valve cover seepage. It's fairly common and although annoying, isn't usually a problem unless excessive.

You can leave the cap and rotor off for awhile as long as it isn't exposed to moisture for any length of time. I would suggest you consider buying graphite spray to lubricate the lower distributor assembly. You'll have to remove the 4 small screws and the plastic cover, then use the thin plastic tube on the spray can to squirt around the shaft down below the magnetic pickup.

 

Thanks Jamey. I'll reinstall the distrib. and rotor when I receive the distrib. cap gasket and perform the check. Hopefully, all I'm looking at is replacing one of the coils. Any advice on where to get one for a good price? I finally found them in the parts manual but I can't read the part number.

Describe excessive. Upon further inspection, there did appear to be some standing oil in the nut holes, though I never noticed any of the oil until I removed the cover, i.e., it's not like it is all over the engine or anything, just along one side and not what I would call especially thick.

I was really scared when the car lost power. I'm very fortunate that I had just left the drive when the problem occurred and that I didn't try driving the car any further. Another question that comes to mind is: what about the fuel that was dumped into the catalyst for the short time (maybe five minutes) that the car was running after losing one of the banks?

P.S. What is the purpose of the graphite spray lubricant?

 

Those coils aren't anything you can't get from a local parts store, they should be able to look up the correct application for you without problems.

Excessive to me is when it causes smoke constantly, or leaves a large puddle under the car, or if you find you need to add oil constantly to the crankcase. Otherwise, I just think of it as continuous rustproofing.

I doubt that short running time will cause an issue. Most of the gas dumped into the cat will have evaporated by now.

The graphite spray is to lubricate the springs and centrifugal weights that control the timing advance. It is a common problem for these to seize up on these V12's.

 

Thanks again Jamey. The oil situation is definitely not to that extent (I'm a little overly cautious with this thing) and I'll be picking up a can of graphite spray on the way home today. Hopefully, I'll be back on the road this weekend!

One more question: When testing the coils, do I have to turn the engine all the way on (which I'm scared to do), or just turn the key so that it activates the electronics? (please forgive my ignorance)

 

Jamey: You mentioned in post #3 that it could be the ignition module that has went bad. How do I know if it is the coil or the module? I don't want to have to buy any unneeded parts (especially a $200+ module).

 

First, check to see which coil has spark and which doesn't. Yes, you'll have to make the engine spin, but it won't start with the coil wires detached from the distributor cap. You won't have to make it spin much, you should see spark quickly.

You can use a tester to determine if it's the coil or the module, but if you don't have one the easiest way would be to switch the coils after you've tested them. If you've determined one coil is good, and then you don't get spark after the switch then you know it's your module. You also may not have to spend that much on a module if it uses the same type as mine. Inside the aluminium module case is a GM module that costs around $20

 

Awesome. But "aluminum module case"? Mine appears to be composed of a piece of plastic on an aluminum plate which is mounted to the top of the radiator. Are we talking about the same part? The part number I have for the module is DAC 11520. Do you have a cross reference number for the GM module? Thanks.

 

Ahh, that's why I said "if Marelli used the same module as Lucas"...which after some research I found out they don't.
Still, the troubleshooting method is the same so before you give up hope on the module, check the coils, wires and connectors for corrosion. Those are more likely to be a problem.
There may be other applications that will fit the module, you'll just have to do some detective work!

 

I saw a spark from both coils. What now?

 

Best way to diagnose the problem is to remove only one coil from the dissy (the Marelli dissy has 2 coil inputs on the top) and start the car, if it starts then this coil is OK, put it back on and remove the other one, the car most likely will not start. For the moment we will assume this is the situation.

Next you will need to determine if it is the coil or the igniter (unfortunately my ROM does not have the Marelli wiring). The Marelli system uses 2 igniter modules located on the radiator top support, swap the connectors between the igniters if the problem moves then you have a bad igniter if it stays with the same bank then your coil is bad.

As you fault find write everything down and only make ONE change at a time, if this does not resolve your problem then post back as there are other things we can do to diagnose if the problem is in the dissy.

cheers Warren

 

Wouldn't the v12 start with only one functioning coil? Also, when I peformed the "spark check," should the distrib cap been on (I left it off, waiting to perform the silicone squirt)?

 

Yes the engine will start with 1 good coil and run on 1 bank - if you only have 1 coil connected and it is faulty the engine will not start.

the spark check will not determine if the coil is bad as there is no load on the coil - this will only work if the coil is totally dead which is unlikely - mostly what happens as the coil fails is it can not deliver enough spark to fire the plugs.

the only way to do a spark check like that is to use a spark plug and check the spark across the gap.

 

If *both* coils are providing output spark but only *one* bank of cylinders is firing I have to think that you have a problem with the the cap or rotor...even though they look OK on initial inspection.

We're accustomed to "Marelli failure" being an obviously burned rotor...but perhaps there are other failure modes? I dunno. Just thinking out loud.

Or...perhaps something as simple as one of the coil wires being bad? By this I mean the king leads from the coils to the cap. Or perhaps corroded terminals on the king leads or the sockets they fit into? Worth a look.

Maybe I've missed something (between here and Jag-lovers) but I think we've all been assuming a Marelli failure and loss of an entire bank of cylinders when in fact the low power problem might be something else entirely. I'd reinstall the cap and rotor and check for presence and quality of spark *at the spark plugs*. Check a couple on each bank.

Cheers
DD

 

I agree. A coil can degrade but not be totally dead.

Cheers
DD

 

Thanks again guys. Here's my plan: I'm going to forego the silicone squirt (still waiting on a tool that will cut off the stub) and go ahead and reinstall the rotor and disrtib cap (it's hard for me to conclude that either is faulty considering their condition) with the new gasket. Then I'm going to disconnect one coil and see if the engine will start (then check the other of course and rule out ignition modules). Hopefully, this will prove my problem despite me getting a spark from both coils. I will also check spark plugs and wires for corrosion and fire.

Question: please describe, with as much detail as possible, the best method for checking the spark plugs.

Also, do I risk damaging the car by attempting to start it knowing that one bank is not firing? I don't want to take any chances with experiencing a "Marelli Meltdown."

Assuming all ignition components check out, what other mallady(ies) might be causing my problems?

 

Remove a sparkplug and reattach the wire. Hold the base of the plug against a ground and have a friend crank the engine. You should see a blue spark. You might wanna use insulated pliers so you don't get zapped....or buy a spark tester





If you disable the fuel pump (pull the relay) you'll be OK






A fault in the fuel injector circuit rendering the injectors inoperative, perhaps.

Between here and Jag-Lovers we have an awful lot of cooks stirring this kettle of soup. You're getting good advice so I'm bowing out of this thread.

(I'm not angry or anything. Just trying to keep things simple!)

Cheers
DD

 

Whoa Doug, don't run off so quick. If anyone is making this thing complicated, it's me.

I still confused as to checking the sparkplugs. How do I access them?

What about trying warrjon's coil test -- which the folks at jag-lovers don't appear to like? I'm concerned that it might actually be one of the coils despite me getting a spark and would like to definitively rule that out, if possible. Thanks again for all your help. If you ever find yourself on the Gulf Coast, suppers on me!

 

First do you absolutely know that 1 full bank is not firing?

As long as the car is cold you will be ok. What causes the Marelli meltdown is unburnt fuel getting in the HOT Cat. To test this you dont need to leave the car running. Just start it and if it fires into life and runs turn it off again immediately.

I would rule out the ignition first other wise you will end up chasing your tail. First rule in diagnostics is start with the most obvious likely cause and rule it out.

Come back and let me know if you have 1 totally dead bank - easily checked by starting and putting your hand near each exhaust. It will be obvious if 1 bank is not firing. Run the car for as short a time as possible.

Report back and then we will formulate a plan to diagnose. I will write up a detailed howto for you.

cheers Warren