Explosion, now no start.

[vikenabm]

7MGTE ignition system wiring specs


WARNING: post edited - had error in my wiring which I hope I corrected. this is my best understanding of how it is supposed to look.

adapted from another forum, TEWD, and also my TCCS manual from the Allen Instutute training manual from 1990


Coil pack order is: (left to right from front of motor)

Coil pack____________To cyls__wire colors

Coil A Passenger coil____1&6____Black, Tan

Coil B Middle coil_______3&4____Green, Tan

Coil C Driver side coil____5&2____White, Tan

To Engine harness per TEWD:
(Here's where it gets messy! The TSRM appears to have the WRONG pin numbers in their diagram on page IG-15 for the ignitor test procedure, where pin 3 and 4 appear to be labeled in reverse. The test procedure should not work as diagramed because the IGDA and IGDB signals do not appear to be correct. More on this below. Also, the functions from the CPU don't wire to the same function at the ignitor. The functions labeled at the ignitor in the diagram don't make sense and my TCCS manual from the Allen Institute says they are WRONG. The functions from the CPU make perfect sense so I included these in my table below. They mean "IGT = ignition trigger, IGDA = ignition determinant A, IGDB = ignition determinant B, and IGF - Ignition Fail)

CP wiring___CP connector _Engine harness wire color __Ignitor 6 way con._____Function __|_ CPU Activating Function__Ignitor 4 way con. pins to activate
Black__________Pin 1 __light blue/red stripe__________Pin 2______________"IG1" __|___IGT and IGDB__________ 2&3 in TEWD (and TCCS manual)
Green_________Pin 3 ___yellow___________________Pin 4 _____________ "IG2" _|___IGT and IGDA __________2&4 in TEWD
White_________Pin 2 ___light blue/yellow stripe_______Pin 1______________"IG3" ___|___IGT alone _________ 2 Alone in TEWD
Tan___________Pin 4 ___Black/orange stripe_________Pin 3______________"B+" -goes to ignition switch and EFI resistor pin 2


coil firing order: Note coil packs fire vehicle right to vehicle left, ie passenger side to driver's side. . that is how most sources number the coils 1-3 or A-C:

Coil A, plug 1 (and 6 wasted) ie "IG1" , IGDA=0, IGDB=1
Coil B, Plug 3 (and 4 wasted) ie "IG2" , IGDA=1, IGDB=0
Coil C, Plug 5(and 2 wasted) ie "IG3, IGDA=0, IGDB=0

Coi. A, Plug 6 (and 1 wasted) IG1 again
Coil B, Plug 4 (and 3 wasted) IG2 again
Coil C, Plug 2 (and 5 wasted) IG3 again

SO to test the ignitor, it should be the following procedure:

Apply a constant +3v where indicated in first column then touch pin 2 with a +3v pins on the ignitor 4 pin connector:

constant 3V transient 3v read resistance
none ignitor Pin 2 coil C connector (center coil) white wire pin 2
ignitor Pin 3 ignitor Pin 2 coil A connector (passenger side coil) black wire pin 2
ignitor Pin 4 ignitorPin 2 coil B connector (driver side coil) green wire pin 2

Note: my digital voltmeter, which is a high end model, does not respond quickly enough to reliably see the drop in resistance in the coil connector wires. I made a bracket for my plugs to watch them fire and confirmed that they work as expected when wired and tested this way.

[vikenabm]

Well it took a while, because I fried a few links and fuses jumpering the car too late at night and not paying attention. Now I can say the car is back to where it was before the explosion, when it just wasn't quite starting and was misfiring. It catches slightly and sputters just barely for a second. It seems to barely combust, and disconnecting the fuel injector resistor to cut fuel leads to a stronger sputter on the first try. It's like it is flooding before starting. then checking timing while cranking, I get almost no gun flashes, like it's not picking up a spark current. Pulling plug one and trying with plug exposed shows it sparking erratically and weakly and fouled but not wet plug.

So I think I have a problem with spark. I have tested coil and wire resistance, all fine, but I put in new irridium plugs after I tested compression, and i went with a colder plug due to my increased compression ration and plan to boost to 20 or 25psi eventually. I will try again with plain old copper plugs, retest coils and wires, check ignitor transistor, and report back here for posterity.

Questions: when people run colder plugs for high boost do they generally also have aftermarket ignition? WOuld there be any benefit to keeping my plugs and increasing spark power via different ignitor or coils? What are the best upgrades to the ignition, if any?

[cre]

No, you don't need to make any changes to the ignition system because you're running a colder or hotter plug. The thermal transfer characteristics of a plug have little effect on the spark. Why are you running a colder plug? Preignition problems, damaged spark plugs or high EGT?

[vikenabm]

Yeah, I thought about that after I posted: plug gap should be the overriding determinant of spark. I'm running colder based on various postings on plug choices. I haven't run the engine enough to know where my EGT's will be in various conditions, but that's an obvious and interesting way to select plugs. I'm surprised I haven't noticed that approach posted.

So it's down to the ignitor or coils. And ignitor makes more sense to me. Clearly my spark is inconsistent, and it sure seems like the ignitor fires inconsistently in the TSRM transistor test, no matter how carefully I clean the probe and terminals> I have a replacement from a running motor to test when the weather allows. Thanks.

[cre]

I don't see that you've mentioned running an extreme amount of boost. It doesn't matter much. It won't hurt anything, they'll just foul frequently if they're too cool.

There's a thread in the FAQ, I believe, about a known grounding problem with the igniters (it's an internal issue). See if you can find it and see if the fix listed works for you.

[vikenabm]

Originally Posted by cre

I don't see that you've mentioned running an extreme amount of boost. It doesn't matter much. It won't hurt anything, they'll just foul frequently if they're too cool.

There's a thread in the FAQ, I believe, about a known grounding problem with the igniters (it's an internal issue). See if you can find it and see if the fix listed works for you.

Thanks. I already had the ground mod in place. I replaced the ignitor and it is not much different. WIth all the injectors unplugged it behaves EXACTLY THE SAME as with them plugged in. I believe it is sputtering a bit and firing into the intake runner due to fuel from the cold start injector. It sputters a bit more consistently maybe with the new ignitor, but no real change. Also no different with plug to injector resistor connected or not.

So without the injectors making a difference, and good fuel pressure, is it fair to conclude that I'm down to injectors not opening as my problem? If so, i've already tested the injector resistor with an ohmmeter, simple device. So now am I to check wiring continuity to the ECU, repeat the voltmeter tests at the ECU from the TSRM, and then swap ecu if those check out normal?
I am out of other ideas at this point.

[cre]

Are the injector's grounded at the correct location and is the ground clean and sound?

I've had issues like this on a couple MKIIIs and it's always something different. Wiring harness, CPS drive gear installed 180? out after a rebuild or on a new (reman) unit, igniter and coil pack grounds were the issue in all of those cases.

You can measure the timing of the injectors against the crank pulley with a timing light. If you don't have an adjustable it's just a light show and you have to guess what the timing is but nonetheless if the injectors aren't getting power or don't have a good ground you shouldn't see anything. You just connect the pickup to the injector's wiring clip, shine the light on the markings on the balancer and while someone cranks you watch for a consistent pattern. I think you'll be looking around the 50? range but I'm not positive, I haven't done this on a 7M. The timing isn't important though, this SHOULD show if the injectors have a solid signal.