1988 7MGE Misfire - Stumped!

[cre]

It's mounted right under the ignition coil. Aluminum box.

[excaliburdj]

Ah...got it. I suppose that's a dealer only part? I found a used ECU on eBay, but igniters are probably pretty rare.

Have you heard anything about aftermarket coil/igniter packs? Accel makes one that's supposedly designed to replace both boxes, I think.

Or for a daily driver would you recommend just replacing the factory box itself?

[cre]

I don't know of anything by Accel which would replace both. MSD makes an electronic ignition which would though.... but it's costly and not a direct replacement.

Don't just start buying parts because you think it *might* be one thing or another... you'll be broke long before you fix anything.

Have you checked the galleys for oil or water?

How old is the cap (not the rotor) on the distributor? If the contact for 3 and 5 have a lot of carbon buildup they can loose spark as well.

As for the igniter, typically when that goes it's not consistent like you've found... personally, I'd keep looking for something else which would be causing problems. The igniter and ECU are possibilities, but they're remote possibilities.

[excaliburdj]

When I re-checked the plugs and wires I checked for fluids in the galleys. Cyl 2 had some, but I think it was from pulling the coolant hose off the intake and not having the rag in the right place to catch it all.

I even went so far as to switch the spark plugs that were in 3 and 5 to 1 and 2 to make sure it wasn't the plugs.

Nope...no change. Still 3 and 5 misfiring (or NOT firing, more accurately.)

The distributor cap is new. Just replaced it on Saturday to make sure that wasn't a problem.

Maybe I'll see if I can post a Youtube video of the engine idling or something. It's weird, because about 1/4 of the time it runs just fine, but I can't seem to tell what makes it kick in and out of that. It's not when it's warm, because sometimes it'll run fine from a cold start, and then kick in later with the misfiring.

I've been reading all day trying to figure out specifically what could be plugged/clogged/bad that would control the firing of the cylinders as opposed to an engine function like idling, and I'm coming up empty.

[cre]

Have you tried different plug wires or tested the ones you're using? Are you sure the contact inside the boots is actually connecting to the cap's contacts and spark plug contacts?


Not dumbing it up... sometimes it's easy to get carried away and forget the little things.




Okay, what are all the possibilities? These: Coil, Igniter, IGt wire from the ECU to the igniter, CPS (cam position sensor in the distributor providing inaccurate info), bad wires, bad dist. cap, bad rotor, poor connections in the spark plug wires.

A bad ECU, or CPS should give error codes pretty much every time. A bad igniter may not, but it shouldn't be so perfectly off.... but I could be wrong. A bad rotor usually causes weak spark and intermittent misfires on ALL cylinders. A bad cap CAN cause what you're seeing depending on what's wrong with it. Bad wires or poor connections can definitely cause what you're seeing. Spark plugs not properly grounded (not terribly common) can cause similar problems too.

I would start with this: unplug the wires and on both sides push the wire into the boot so the contacts are much further forward and are sure to make good contact. When you reinstall them push the boot hard enough that once the clip connects the boot will slide forward over the spark plug and over the cap's outlet. NEVER remove spark plug wires by pulling on the wire!

Then, failing that, pull the cap and rotor. Clean all contact surfaces thoroughly with a brass wire brush.

If still no good, try installing a better ground in the igniter: IGNITER GROUND... crispics - SupraMania (That's for the GTE igniter, but I've been told the GE igniter is similar and just as poorly grounded.)

[excaliburdj]

Heh...you're right, of course. The simplest solution is often the correct one.

I'll take all the wires out of the harness and see if maybe I can switch 2 and 3 or something - get one to stretch to the other plug hole, just to see if I get a spark there.

The cables LOOK OK, but that doesn't really mean much. Other than that, I don't really have a way to test them.

[cre]

Of course I'm right....

I edited my last post.

Yeah, looks don't say a thing for plug wires. Try swapping 2 and 3... I think they're about the same length, same for 4 and 5... or was it 5 and 6?



EDIT: Oh, and BUY A MULTIMETER!!! Even a cheap one.... you're going to need it. Actually I can't believe you've been trying this without one.

[excaliburdj]

Oh, I have a multimeter around here somewhere. Problem is, I just moved not too long ago and most of the non-essentials are still in a box somewhere.

I unpacked all my tools, though.

I'll see if I can find it.

I'll report back. Thanks for the help!

[excaliburdj]

Cleaned all the contacts in the distributor and re-grounded the igniter per the instructions in your post.

No change.

Changed spark plug wire 2 to the 3rd cylinder and vise versa.

No change.

I can pull the plug wire off at the distributor cap and see the spark jump from the port on the cap to the end of the wire if it isn't far enough away, so it looks like both cylinders are getting spark.

But still...cylinders 3 and 5 produce no discernible change in the idle when I pull the wires off.

I re-re-re-verified the timing. Still right on at 10 degrees BTDC.

What's next? Am I looking at an injector problem or something?

[cre]

Injectors. Look at the TEWD and see if those two are paired to one specific line... the injectors are wired in pairs, but I didn't think 3 and 5 were paired to each other.



EDIT:
3 and 5 are paired together, MK3 TEWD On-Line