Explosion, now no start.

[vikenabm]

Originally Posted by cre

... Ok, I re-read your post and am a little confused I suppose. Go over the thread linked to below and make sure everything is 100% correctly aligned. If you've removed the cam gears at any point make sure the dowels were installed in the center hole on each cam and likewise on the gears. If you're running adjustable cams dial them to 0? initially.

Got this but apparently my response was swallowed by the Verizon network.

Rechecked timing this week. it was set according to the exact procedure you linked to, and cam matchmarks and crank mark are still aligned correctly. The pictures are very nice and clear, and I've set the timing many times before. Unfortunately, the timing advance can't be set without the engine running, but I can approximate it with the engine cranking using a timing gun. I think that type of electrical test for timing would be a good reality check anyway and I hope that will be sufficient proof without pulling the CPS again. The CPS was the last thing I had pulled and reset - and done carefully - before posting the problem on here. The timing gears were removed when rebuilding, They are the stock gears, so position is set by the fit of the gear on the cams.

I will
1) verify that the cam lobes are aligned as expected with the match marks, just to be extra certain, on Saturday.
2)Will check each cylinder for spark with inductive timing gun to verify correct sequence as wiring from igniter to coils was extended and soldered due to fraying and breakage.
3) remove CPS cover and verify armature alignment with crank and cam timing marks at TDC.

I'll let you know when this is completed.

Thanks.

[vikenabm]

Good instincts on looking at timing. the timing was all set correctly: cams, crank, CPS installation, but I found two wires reversed on the connector to the CPS.

My understanding from the TEWD is that the engine harness connector is supposed to look like:

Blue Red
pin1 pin 2

Black Yellow
pin 3 pin 4

I had black and yellow reversed when I fixed the worn connector. How i had any spark at all I still don't understand.

Now the coil packs are still confusing. In the tewd it doesn't clearly say which wire from the igniter goes to which coil, but labels the wires
IG1 to coil pack connector pin 1,
IG2 to coil pack connector pin 2
and then the third wire to pin 3 isn't labeled with a moniker
coil pack pin 4 is B+ common.



Fixing and putting engine back together. will report back.

[cre]

The coil pack wiring is a common upset but, oddly enough, it's not something which has made its way into my repository of Supra tech info. It has been posted here in the MKIII forum a couple times though. If you find a good thread with solid info on it let me know and I'll copy it into the FAQ section... I'd look for something but I've got company and had to sneak away to get on here for this long.... The wife's just real funny about me not paying her family enough attention.

[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.