Ice 996 no start, pops fuse C2

[gerglmuff]

Backstory, I had my 996 out on the frozen lakes racing. pretty common done it a half dozen times with this car, but it was particularly wet this last weekend. 

Drove it home, 1.2 hours away, turned it off, and now wont start. turns over plenty fast no issues there. 

read the codes, even though there was no CEL, and it was all 6 coils dead. found a post somewhere saying that the C2 fuse controls that, and lo and behold the C2 fuse was popped. installed a smart fuse, it pops when you turn the key to run. 

that post also said, with the smart fuse in, start checking connections. so i pulled the fuel pump relay, still pops, pulled the MAF, still pops, pulled each 02 sensor, still pops. and pulled coils 1 and 4, still pops. didnt pull the other coils cause id have to take off the exhuast to get in there, and i dont think the short is there anyway. doesnt match the symtoms. 

i figured id kicked up some snow/ice into the foot well and there is some water in the fuse box/relay box. but its been two days in a heated garage, with a box fan blowing and all the doors windows etc open, and still popping C2. 

oh, i also got it fire up once, when i was rustling with fuses, and i had a jumper in the fuel pump relay, and it started and ran. but i have not been able to repeat that. now it pops whenever the key is turned. so something is/was moving though the system. 

so like the engine is fine, everything works, there just is a short somewhere, and i have no idea where. still thinking its water intrustion. i had some weird problems with another ice racing car due to water getting into the iginiton switch, and they just went away when it dried out. so i think thats the problem here, but no idea how/where to look next. 2 days with a fan blowing on it seems like it should be enough. no visible water found anywhere on the car now after sitting in a heated garage for 2 days. 

video for clicks: 

 

[gerglmuff]

checked the vario cam solidnoids, both ohmed to 12 ohms, so close enough on my cheap meter. 

oh, its a 99 FYI. 

 

pulled the fuse box off the back wall of the footwell, it seems dry, i dont see anything. 

 

 

 

 

i litterally have no idea what to try next. it should work. it did work.

[Loren]

C2 (30A) is:

- IGNITION

- INJECTION

- OXYGEN SENSOR HEATER

 

Had any problems with your ignition switch?

Any custom wiring (i.e. aftermarket radio?

 

[gerglmuff]

yup, i found the wiring diagrams. C2 is linked to a lot of stuff but the first place it goes is to the fuel injection rely. but pulling that relay, still pops the fuse. so its between the relay and the fuse, but there is nothing there. the other place C2 goes to is the oxygen sensor relay. i did pull all the oxygen sensors, and it still pops, but i have not pulled up the rear seat to look at the oxygen sensor relay. 

power to C2 comes from the 80 amp main (F5), but if the 80 amp main had popped because of the ignition switch, there would be no power at C2, to pop C2. so its between C2, and the rest downstream, but not on the fuel injection relay side. and not the oxygen sensors themselves. so its in the wiring to the relays likely right? 

no aftermarket wiring that i know of. no issues with ignition switch that i know of. 
 

Edited February 26 by gerglmuff

[Loren]

I mentioned ignition switch because they are a common failure and your car is over 25 years old.

[gerglmuff]

yeah and its a common failure for sure. its also a place water can get into the system and you not notice, and weird things happen when water get into an ignition switch. i had a miata on the lake once, water in the ignition switch and it wouldnt turn off. key in the off position, key pulled out, it would happily run. had to kill it with the foot on the brake, pop the clutch, and then go in the back and disconnect the battery because otherwise it would drain, cause the ignition was still on. 2-3 days, the water in the switch dried out, never had a problem since. 

i'll see if i can check that out tonight. its as least as likely a source of a weird electrical issue as some wire no one has touched in 25 years suddenly having a short it in. i dont see it in the prints, like how a short in the switch would lead to a popped fuse, but you never know. 

[gerglmuff]

ok, new data

i checked the ignition switch, blew it out with compressed air, didnt seem to have any effect, looked clean/dry etc. 

then, following the wiring diagram, i found and pulled the oxygen sensor ignition relay (#2 in the rear seat relay box). and that shut it up. i tried to start it like this, but it didnt take. 

i tried switching out the relay for one of the spoiler relays (they look identical), and C2 popped again. 

so, i think that means the short is somewhere behind the relay, right? that means its a coil, or injector thats shorted? or the ECU? 

[gerglmuff]

more data ... 

pulled out the ECU, cause i was in there. again looking for water etc. has a sticker on it from "specialized ECU repair" that says it was in for "testing only (set)" in 2021. 

feels kinda like the ECU popped. 

[Loren]

Hmm... sounds plasabile.

 

[gerglmuff]

it was not the ECU. 

gotta be a short somewhere. ill start digging as soon as i get the ecu back.