2003 Murano Stumbling (dead cylinder?) and Blowing ECM Fuse 82 after Changing Injectors

[walczyk]

This might be a convoluted story, but I believe I may have fried my ECM.

I was replacing my rocker covers and injectors (remanned ones off ebay) when it snowed with the intake manifold off (it was covered in towels but they got soaked from snow that slid down the windshield). I removed the spark plugs and turned the engine over to blow out any water (there was none), but the ground on top of the engine was disconnected (it bolts in at the front of the engine near cylinder 2). I put the car together and find the car doesn't start and I track down the fuse and replace it. The car now runs like a cylinder isn't running, it is loud and shaking.

I turn it off and think about next steps, and think perhaps one of the injectors is dead, and should try unplugging coils cylinder by cylinder to look for no change. I turn on the car and 30 seconds in the fuse blows again.

Could a shorted injector do this? Could the ECM be fried now?

Thanks in advance, this really sucks

[VStar650CL]

The injectors would be blowing fuse #1, so it can't be a direct issue there. Pins 33 and 35 in the IPDM are fed by fuse #82 through the ECM Relay. Pin 35 goes only to the ECM and spark coils, 33 goes to a bunch of other stuff, IVT's, MAF, CKP, CMP's, evap vent valve, swirl valve. First I'd suggest unpinning 33 from the connector and see if the fuse still blows. If so, you know the problem is in the coils or ECM. If not, you know it's in one of those other systems and you can disconnect them one at a time till you find the culprit.

[walczyk]

The injectors would be blowing fuse #1, so it can't be a direct issue there. Pins 33 and 35 in the IPDM are fed by fuse #82 through the ECM Relay. Pin 35 goes only to the ECM and spark coils, 33 goes to a bunch of other stuff, IVT's, MAF, CKP, CMP's, evap vent valve, swirl valve. First I'd suggest unpinning 33 from the connector and see if the fuse still blows. If so, you know the problem is in the coils or ECM. If not, you know it's in one of those other systems and you can disconnect them one at a time till you find the culprit.

Would the engine start with pin 33 removed? The car ran and blew a fuse while limping along, but if I can't start the engine with pin 33 removed then I don't think this will tell anything diagnostic wise. Thank you for the help! I need to buy some fuses. The MAF might have got rainwater on it. This could be the culprit perhaps? I don't think the engine will run with the MAF disconnected..

[walczyk]

The injectors would be blowing fuse #1, so it can't be a direct issue there. Pins 33 and 35 in the IPDM are fed by fuse #82 through the ECM Relay. Pin 35 goes only to the ECM and spark coils, 33 goes to a bunch of other stuff, IVT's, MAF, CKP, CMP's, evap vent valve, swirl valve. First I'd suggest unpinning 33 from the connector and see if the fuse still blows. If so, you know the problem is in the coils or ECM. If not, you know it's in one of those other systems and you can disconnect them one at a time till you find the culprit.

Also where is the CKP and swirl valve?

[VStar650CL]

Yah, if it won't blow the fuse unless it's running then pulling 33 isn't practical. Since you have a miss, my guess would be you have an overheating coil that's loading the circuit, but not enough to blow the fuse until it heats up. That's a fairly common behavior for dying 3-wire COP coils on any brand, not just Nissans. It will help if you can identify which cylinder has the miss (although I know that's a PITA on a tran-sverse VQ if the culprit is in the back bank).

[walczyk]

Yah, if it won't blow the fuse unless it's running then pulling 33 isn't practical. Since you have a miss, my guess would be you have an overheating coil that's loading the circuit, but not enough to blow the fuse until it heats up. That's a fairly common behavior for dying 3-wire COP coils on any brand, not just Nissans. It will help if you can identify which cylinder has the miss (although I know that's a PITA on a tran-sverse VQ if the culprit is in the back bank).

It's crazy bc I replaced two out of the box... so it would be most likely that one of the new ones failed. This sucks, I need a whole bunch of fuses and I need to swap multiple times, taking the intake manifold on and off.

[walczyk]

Yah, if it won't blow the fuse unless it's running then pulling 33 isn't practical. Since you have a miss, my guess would be you have an overheating coil that's loading the circuit, but not enough to blow the fuse until it heats up. That's a fairly common behavior for dying 3-wire COP coils on any brand, not just Nissans. It will help if you can identify which cylinder has the miss (although I know that's a PITA on a tran-sverse VQ if the culprit is in the back bank).

Would you be able to explain with Pin 44 does? Is it like a signal to engage the relay?

[VStar650CL]

Sure. The ECM needs to be able to turn itself on and off without the key, so it can test the evap and fuel tank integrity while the car is parked (EONV test). To allow for that, it controls the relay by grounding the coil using pin 44. Normally the ECM only wakes itself up whenever it sees an ignition signal from the key, but when the temperature and fuel level conditions are right, it will wake itself up for as long as 40 minutes to evaluate pressure/vacuum signals from the tank.

[walczyk]

Sure. The ECM needs to be able to turn itself on and off without the key, so it can test the evap and fuel tank integrity while the car is parked (EONV test). To allow for that, it controls the relay by grounding the coil using pin 44. Normally the ECM only wakes itself up whenever it sees an ignition signal from the key, but when the temperature and fuel level conditions are right, it will wake itself up for as long as 40 minutes to evaluate pressure/vacuum signals from the tank.

Thank you! That was a really good explanation. I was able to figure out the issue thanks to your help! Cylinder 3 ignition coil was causing the fuse to blow (cylinder 1 was the only coil I couldn't unplug with the tools I had with me), but also Cylinder 4's ignition coil was missing a spring so it was also a dead cylinder (must have fallen out when I cleaned the oil out of the coils). She sounds good now, thank you again!

[VStar650CL]

You're most welcome, glad to help. Happy motoring!