As the title says, I have a very intermittent and random electrical issue in which the #46 fuse in the under hood fuse box will blow causing the engine to stall. Once the fuse is replaced, it starts and runs fine until it happens again. The first time it happened, it was within two minutes of start up (engine was warmed up though) and was at a low speed on a smooth street coming up to a stop sign. All the other times, it has happened at around 35-50mph under normal load after driving for 20-30 minutes. As far as I can find, there doesn't seem to be any specific condition (speed/load, temperature, road surface quality) that will duplicate it.

Engine was fully overhauled about 5-6k miles ago almost two years ago and this just started happening a month or so ago. The car was being modified to accommodate a turbo build, so with the engine out, the battery got relocated to the trunk and fuse box to the inside of the passenger fender. All electrical components in the circuit for that fuse are stock. I have put the vehicle on a lift, pulled back all the fender liners, and with the car running, inspected and wiggled every inch of harness I could in the fenders, on the engine, and under the dash and inspected where the harness was rerouted between panels-no issues seen and the car never stalled. Took it for a test drive and the fuse popped after about 20 miles.

Also, not sure if it is related, but a week before the fuse started blowing, I was merging into traffic with pretty heavy throttle when out of nowhere, there was a surge in power and the green immobilizer light was flashing. It only lasted a few seconds and went away and the car felt normal again. Scanned the car, and no codes were set.

So it would seem like one of the components is pulling too many amps or there might still be a wiring issue I couldn't see. I don't feel like any of the components themselves are shorting because of how long it takes to duplicate.

Any ideas or suggestions? It's an my03 by the way

 

What circuit is fuse #46 associated with, in your car?

Thanks!

 

Fuse 46 pertains to the DLC and the PGM-FI main relay.

Pin 1 on the relay is fuel pump control from the ecm
Pin 2 is voltage supply for ignition cranking from fuse 21
Pin 3 is ground
Pin 4 is output to fuel pump
Pin 5 is voltage supply in ignition ON from fuse 2
Pin 6 is power input to ecm (goes through immobilizer receiver unit)
Pin 7 is voltage from fuse 46 which is hot at all times.

 

Have you tried swapping out the main relay?

 

Sorry for the late response, haven't had a chance to mess with the car lately until this morning. Changed out the relay with a new oem relay. According to the ETM, terminal 6 of the relay is what specifically receives current from the fuse which is constant voltage supply to the injectors, IACV, Immobilizer Reciever Unit, and ECM. To start trying to isolate the issue, I've installed inline 5A fuses in the yellow/black wire at all four injector connectors and the IACV. The fluke instance of the Immobilizer light flashing randomly while driving has become a fairly regular occurrence since my initial post.

Today after replacing the relay and installing the fuses, the light flashed once on our way into town for lunch and 5 minutes later the engine stalled with no warning (about 40 miles after repair) Luckily I had enough speed to get pulled off the main road. Just for shits and giggles, I cycled the key and the car restarted immediately and was idling fine....(this is the first case it has randomly stalled that wasn't the result of the fuse blowing). The car drove fine the rest of the way to lunch. The light flashed again once going back home but it made it back without stalling.

The light has flashed about 7 or 8 times before today. The last time it did was back to back and I drove it straight to my shop and scanned it for codes and found nothing.

 

Double checked the G101 ground on the back of the head for a clean and tight connection, no issues found. I drove the car last night and the immobilizer light came on once, but did not flash this time, it remained constant for 3-4 seconds before going off-did not notice any change in drivability. Drove it the rest of the way home (about 5 miles) and it stalled pulling up to the driveway and once again, no fuses blown and it restarted just fine. It has stalled five times now since replacing the relay and installing the fuses, but has not blown a single fuse.

 

Is your immobilizer bad? I'm actually having this same issue, except the light only flashes for a millisecond and has only almost stalled once.

 

Would you happen to have a pic of the fuse 46? I assume this is the block under the hood, but couldn't distinguish which one was it was.

I'm troubleshooting no volts to fuel pump issue myself. Pump fuse is fine under dash. Sounds like there is a bigger fuse under hood that runs a few systems, maybe pump included.

 

Yes it's located in the under hood fuse box. Between fuses 43 and 49. It's a 15a. There are two fuses in the under dash fuse box that are part of the fuel pump circuit- fuse 2(15a) and fuse 21 (7.5a). All three fuses opporate through the main relay before reaching any other components



This is the diagram for the leg of the relay fuse 46 provides power to.

 

UPDATE:

So I'm pretty confident I found my issue. After I spent some time yesterday reexamining the ETM diagrams and trying to make sense of what was going on, I decided to poke my head back under the dash to check the ECU connections. All were fine but while lying there looking at everything and just brainstorming, I had the urge to mess with the clutch pedal. I pushed it in and noticed the pedal was contacting the large bundled portion of harness at the firewall. Upon looking closer, I could see where at least one wire had been exposed. I unplugged the harness, pulled it through the firewall into the engine bay and removed all the tape and wire loom. Two wires were found to be exposed, one of which was a YELLOW/BLACK wire going from the engine side of the harness into a blue plastic splice block. All of the components on the leg of the relay I was chasing receive a power signal from a yellow/black wire. Looking back, I can't distinguish whether any of the times it died on me if I was just driving I can definitely say for several of the instances, I was either shifting around the time it happened, or I was coming to a stop and had the clutch pedal pushed down and if the pedal were to contact the yellow/black wire just right, it would create a short to ground on the circuit.

I repaired the harness and secured it out of the way. I've put about 15-20 miles on it since without either symptoms returning but I plan on taking it for a good drive after work today.