Kce

I have a 1993 sc400 with 106k miles.
It has been sitting for 8 months (I was waiting to get my rebuilt ecu back, but there were shiping issues).

Once I got the rebuilt ecu, it started strong but shuts off after 2 seconds of idle. That caused a cel code 15. I've chased the whole ignition circuit to find no loose ignition wires or by the ecu, both coils working well (clearly on all 8 cylinders). Swapping igniter plugs triggered the same code 15. I also tested the ecu in my friend's sc400, works no problem (1994).

When I hold the throttle while starting, it doesn't even idle, just seems to instantly die from too much air.

I've read & been informed that this is not be a fuel related issue, and I'm stumped. I've tried the fuel pump ecu bypass (can hear the fuel pump humming), maf is good, I've turned acc on and off 10 times as instructed for syncing the ecu with the (I think) IACV.

I understand that there are a lot of code 14/15 forums, but all of them that have a similar issue end in no solution. I would really appreciate a point in the right direction. I've considered a new fuel pump / fuel filter but I am hesitant as code 15 is supposedly not fuel related.

Thanks in advance! (please help)

Arsenii

Hello,

How old are the spark plugs?

When the Igniter is triggered ON on Pin IGT, it charges the coil, when to start charging it and for how long is determined by the ECU from running parameters. After the coil is charged, ECU triggers the Igniter OFF, which cuts the Ground to the Coil, causing it to release the stored charge through the Secondary winding, connected to a spark plug. Counter-EMF created during that discharge is converted to a signal by the Igniter and sent back to the ECU as a Confirmation Signal on Pin IGF that the Coil have indeed fired.

Without such signal, there could be chance that the car is pouring raw fuel into the exhaust, which can cause a bit of havoc.. Code 14/15 mean just that - the ECU is not getting IGF Confirmation Signal from the Igniter, and as a fail-safe method, it can shut off all the injectors, which could be the reason why the car won't stay running..

To diagnose this, you can first check if you are even digging in the right direction by seeing if it is Injectors that keep shutting off, causing the car to stall. To do so, take any 12V LED light and connect it straight to the Injector wiring, if the light would stop flashing right before the engine dies, you will know it is the issue and you will need to proceed this way.

If the first step yielded results, check that you are getting a Confirmation Signal on Pin 1 of the Igniter and on Pins 58 (IGF1) and 59 (IGF2) of the ECU, both pinouts are linked below, then compare signals from both Igniters. If there is signal at the igniter, but no signal at the ECU, the wiring between Igniter and the ECU is damaged somewhere, if the signal is present both at Igniter and the ECU, since the ECU unit is known good, it could be a bent or damaged terminal in the wiring.



If there is no signal at the Igniter, or the signal on the affected Igniter is weaker, it may indicate that the Igniter itself is at fault, but since swapping them does nothing, it probably means that the Coil is not producing the spark strong enough to be picked up by the ECU, triggering the Code 15. Try swapping the Coils around, if that won't help, get a spark tester like this one and compare the spark strength on both sides.

Hope this helps and best of luck!

Kce

Hi! Thank you for the reply. I assume the spark plugs are quite old (no maintenance papers along with the other papers).
Pin 1 connector for the culprit igniter looks good on a multimeter.
I did buy a new coil, and that didn't fix the issue (returned it). By unplugging the coils/igniters and checking which code is triggered, I'm certain it's related to the top coil pack's circuit, so I haven't tried swapping them. The wiring for the top coil pack is much harder to see than the bottom. From what I can see, it looks good.

How can I test my ecu's plug (IGF1/2, I understand this is the confirmation signal back to the ecu). My multimeter tips don't quite fit. Also, do I just leave the car on ACC when testing that?

This seems like a strange issue for having the vehicle just sit, although it has been a while. I thought that maybe a rodent wrecked the wire, but it seems weird there are no other issues if that were the case.

Arsenii

Old spark plugs are one of the most common reasons for fried Ignition Coils, since gunk on the tip makes it increasingly harder for the coil to strike through. If the spark plugs haven't been replaced in a while or you don't know the service records, you should take them out, then inspect and/or replace them. Check the resistance of each wire while you are at it, as well as making sure they are not confused, which is a common error, here is a link for more information.

What do you mean by that? Pin 1 of the Igniter should only have something on it right after each time the coil has fired, it is a return signal from each trigger of the coil. When the car is off, you won't see much other than some noise on it.

What is a Coil Pack? The Ignition Coil in that car only contains the coil itself, nothing else.
Which coil did you replace, the one on the top towards the Passenger side or the one under the head on Driver side?

I would still suggest swapping the coils around, just in case..

IGF is the Confirmation Signal, but it is only sent right after each time the coil has fired, checking it without at least cranking the engine would barely yield any results. As for the leads, you can leave them alone for now, until you have reasons to reach for the ECU, but after that, you can get a wiring kit for a multimeter like this one, or get a thin needle with an alligator clip to reach the pin in question.

It is a possibility. My ES300 had a common issue with the wiring in the trunk snapping over time. In my case, the wiring has snapped in such a way that both reverse lights went out, while all the rest of lights still functioned, which set me up for nice few hours trying to diagnose it..

Hope this helps and best of luck!

Kce

Hi, thank you for the replies! It took me a bit to finish taking a look into this.

All the sparkplugs have ~ 0.04 inch gap (on the high end, but still to spec). Some of them look a little grimy, or very slight residue on them (oil?) near the tip of the threads, no gunk on the tips.
Here are the ohm readings from the distributor caps:
8 - 10.44 7 - 10.70
6 - 16.36 5 - 15.78
4 - 15.24 3 - 14.62
2 - 4.78 1 - 4.88

Everything here seems to spec.
I also did a visual inspection of the wiring for the passenger coil. Not much to see, but from what I can see, everything looks properly connected.
Any advice relating to code 15 (passenger side IGF Confirmation Signal). It very much seems like the fail safe kicking in. Thanks again!

Kce

How would I go about testing this, with a multimeter?

Arsenii

Did you check the distributor rotor? Check in its edge is eroded or has any gunk on it.

Did you check if the Injectors shut off in the first place, as described above?
Multimeter would probably do in a pinch, but to really get an accurate result, you will need something like this.

Hope this helps and best of luck!

Kce

Turns out that the plastic clip for the coil pack plug snapped off. If it is not secure enough, in my case, the coil was igniting, but wasn't properly sending the confirmation signal back (probably more secure on one side than the other).

Kce

Actually, the issue turned out to be that there was an aftermarket car alarm system installed. It was routed into the ignition system. Since the car was off for so long, the alarm system reset, causing the fail safe to pick in. The fuse was also burnt. Remove the fuse or reset the alarm system (small button probably by the driver's seat feet area