A Really random supra ignition problem...

[Blackmk3]

Hey guys im having a very intermittent issue with my supras ignition..

The car is a 1988 JDM facelift Auto 7MGTE, and is totally and utterly bone stock, ive just done a head gasket job and a trasmission swap and now im having some issues with the starting

The car starts fine and runs fine all six cylinders Etc for a week or so and then it will (this happens when the engine is hot or cold) when you turn the key it will crank the engine coughs and then will continue to crank until the battery goes flat with no attempt to start, the spark is being disabled
if i stop cranking and crank again it will do the same thing again "crank cough crank with no start"
resetting the ECU does not change things it just continues to do this issue,

The car has no alarm system..

But if i pull out the spark plug lead on cyl 1 and short it to the engine, the car will crank for about a second then all of a sudden start throwing a spark the engine will start running on 5cyl and number one is shorting strong to the engine. If i then turn it off and plug number one back into its spark plug the engine cranks and starts immediatly with no problems...its only a intermittent fault and only does this every week or so

I have no CEL comming up and i have checked the codes with nothing stored

After a bit of a search around i found a thread on the ignition system of the 7mgte http://www.supramania.com/forums/showthread.php?t=39298

Reading through i found this line "The coil packs are all powered from one 12 volt wire through the ignition switch while the igniter supplies a ground through the big transistors"

I am thinking maybe i have faulty igniter thats not providing a ground when this starting issue happens?

Or this line "One last detail: Wire # 4. The fourth wire between the igniter and ECU is called IGf (IGnition fail). Unlike the other signals, which are sent from the ECU to the igniter, IGf is sent from the igniter back to the ECU. When a coil pack is fired the igniter senses the firing and generates an IGf. It's a confirmation spark occurred. The ECU needs to know a coil pack fired when it was told to because it if didn't bad things could happen. No spark means unburned fuel would be sent to the catalytic converter for example. So the ECU expects to see an IGf for every IGt it sends. If IGt and IGf don't "add up" for more than a few seconds fuel injection is halted and code 14 is stored in diagnostic memory. You read that right...the engine will stop"

Could there in some way be a dodgy connector or faulty igniter that is not sending this IGf signal back to the ECU? therefore halting the spark?
Expept im just not getting the code 14

Maybe when im shorting the number 1 plug lead to the engine the igniter is waking up and starts sending a IGf signal back to the ECU?

Has this happened to anyone else out there?
Sorry for the really long post

What do you guys think that this problem could be caused by?

Thanks heaps
Nick

 

[Nick M]

resetting the ECU does not change things it just continues to do this issue,

That is for after you do repairs.

If the computer shuts down injection from no IGf, a code will be stored. It isn't like it doesn't know if it shuts it down.

A cough indicates to me you are getting some fuel. Checking all of your ECU grounds to make sure they are secure(and the wiring) is a good check.

Are you sure nobody removed the CPS, and forgot to tighten the locking bolt?

 

[jdub]

There's a couple of things that have to happen before the IGf signal is generated. The ECU must see at least one G1 or G2 signal and the NE signal generated by the CPS. Failure of these signals will normally cause a code 12 or 13, depending on if it occurs during crank or above 1000 rpm.

Read this:
http://www.mkiiitech.com/forums/viewtopic.php?t=868


I had a similar problem on my old motor...the wiring was hard/cracked going into the CPS. So were the CPS wires going across the top of the cam gears (USDM). I was throwing no codes either...I replaced the wires and it solved the problem.

You could also have an ignitor ground problem...if not grounded properly, the ignition system will not function and no code will be set.

Read this:
http://www.mkiiitech.com/forums/viewtopic.php?t=857

 

[billspreston01]

i hd that same problem for the longest time. once in a while the car would decide not to start. i'd get out, jiggle the cps wires and she'd start right up. check the cps via the tsrm. mine also gave that little cough as you called it. crank crank cough crank crank cough.

 

[Blackmk3]

Thanks heaps for the information guys, ive been thinking the CPS wiring is at fault so i will replace it and the loom plug

Also pull apart the igniter and clean up the earths and noted in that link, and ECU grounds on the intake manifold

Thanks heaps ill have a look and keep you posted on the results

Thanks
Nick

 

[87CandyBlueT]

I had the same issue several months ago. It was my cps wiring. I hardwired mine with 40/60 rosin core solder. I would only suggest doing this if a wiring kit is unavailable to you or if you do not plan to frequently disconnect the cps.