1993 Engine is Missing -- EDIS

Hello,

My Grand Marquis has an engine miss. I put a timing light on it that has inductive pickup that clamps on to the spark plug wire. I then would watch the timing light flash to see it was irregular or not - indicating a miss.

The coil on the drivers side was flashing the light a little irregularily so I pulled it and found it to have visual cracks in a few spots. I thought cool this must be the problem. Just to be safe I also pulled the EDIS module and had it tested at Autozone.

So I went to Autozone, they tested the EDIS module and said that it looked good so I bought a new coil figuring I had this problem on the run for sure.

Well, I put the car back together and it still misses!

I pulled the timing light trick again and sure enough, the flashing had some unsteadiness to it. I put my timing light on the wifes car that is running great to verify my method and the light flashes nice and steady.

So now I don't know what to do. I'm $60 in the hole for the coil. That EDIS module is $150, and my old one tests good (at least at Autozone).

Tonight I also made sure to check both the drivers side bank and the pass side, the irregularity on the timing light flashing is on both sides.

Any Advice???

Thanks.

I hope you get this problem resolved quickly and inexpensively.

Obviously, your GM has a standalone PCM that drives the EDIS coils. Later models (95-97, I believe) merged the PCM into the ECU. Regardless of year group, the EDIS coil packs use two coils outputting high-voltage to four wire terminals. In your case, if the PCM is outputting a pulse for that cylinder at all, then the PCM "should" be okay.

I'm sure you already know that this is a wasted spark ignition system that fires both on the power stroke of the active cylinder and the exhaust stroke on another cylinder. It's possible you have leakage in the wire on the shared coil or a path to ground either on the missing cylinder or the other cylinder that shares that individual coil. In other words, you may have bad wires, bad plugs, both of these, or none of these.

I just finished an engine swap on our 1997 GM after the head gasket blew on Bank 1. The gasket leak started out very minor, but progressively worsened until there was so much coolant leaking into cylinder 1 that it grounded every spark. This caused some sort of galvanic reaction between the wire and the brass connector in the wire terminal on the coil pack, which corroded the terminal severely (which stresses the importance of boot grease on ignition wires). I wasn't able to fully clean the corrosion off of this terminal, and ended up swapping the coil pack after attempting to use it on the replacement engine (we were getting a spark, but a very weak one).

I've also pulled plugs on misfiring cylinders and found the electrode has been bent, grounding the plug. That made me look like an idiot on one occasion after putting in a fresh set of pregapped plugs on the 1997 GM and not checking the gap before installing them.

Hmmm. I wasn't going at this with the "wasted spark" system in mind.

I went to the bone yard yesterday and plucked a couple EDIS modules and a nice looking coil pack, but I think I better back up the bus a bit and go clean my boots where the connect to the plugs.

I was thinking that once a spark left the coil it was all done, I forgot to consider that back and forth - one thing affecting another situation on the wasted spark system.



I have had a couple instances where I had a misfire because of liquid in the boots, both happened a few years ago. Once was when I chgd the thermostat and some antifreeze got in there, the other was when I was fooling around running the car through about 6" of standing water in a rain storm.

Yup, had water in the spark plug holes again. That wasted spark thing threw a wrench into my troubleshooting plan.

After a whole afternoon of messing around to get everything dried up its finally running good again.

The pouring down rainstorm we got must have sent water down the windsheild and on top of the motor some how. What a great design that is to have the spark plugs sitting at the bottom of a vertical facing hole that can fill up with any liquid that gets near them.

On the last round of cleaning the spark plug wire boots I thought to hose them down with silicone spray and then wipe them off with paper towel, that seemed to help. Not only does the silicone offer some dielectric properties, it also seemed to remove a bunch of dirt and grime.

I've put about 35 miles of commutting on it now with no missing so I think its good to go.

THANKS!