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I've recently been suffering from misfires under load and traced the problem back to water inside the power loom. Some of the 12v and grounds were corroding quite badly so I pulled the whole power loom out and replaced around 50% of the wiring. Whilst I was replacing things I decided to upgrade the the two main ground's coming from pins 13 and 14 on the ecu connector as they were only 0.5mm wire, I upgraded to 0.75mm wire.

I installed the loom back in the car and the engine fired up no problem, but I have constant rpm drop outs, every 1-2 seconds rpm will drop to 150 and back up to 1000 again.

The sensor loom hasn't been touched and I find it hard to to believe that a crank sensor has failed but I won't rule it out.

My gut feeling is electrical interference from the coils, maybe the wiring was holding them back and now they're producing a stronger spark with more interference. I'm not ruling out water in the sensor loom either but that crank sensor is one continuous shielded cable all the way to the ecu so I think it's unlikely.

The ignition system has coils mounted on the bulkhead with long ht leads to the engine, the leads are copper! (been copper for years). The plug boots have about 5kohm resistance and i run ngk Resistor plugs. My first thoughts are to change the leads for resistance type.

Anyway it's very strange and It's got me baffled, for now

Any crank errors in the diagnostics?
Log the crank errors, and see if they rise as the engine stumbles.

It's the cam sensor!

It was throwing thousands of cam errors so I turned sequential off and rearranged the coil outputs and it runs.

Doesn't idle all that smoothly compared to sequential though.

Crank scope next, see if the ECU is seeing anything from it at all

Changed the cam sensor and it was no better!

Did a scope trace and everything checked out fine.

Plugged the sensor connector fully into the ecu and everything is fine.

I'll get my coat!

gnutz2 wrote:Plugged the sensor connector fully into the ecu and everything is fine.

That does tend to help!

Cam errors and cutting out came back

Straight away I looked at the sensor connector, checked the cable, checked it was fully inserted, it's all fine! Even tried different cam sensor positions in the software but no avail. I noticed when moving the wiring loom the engine started to run fine, figured out that if i disconnect the ground wire to the ecu case the errors and cutting out disappear. Electrical interference it is then!

The upgraded wiring on the coils must be causing some serious interference with the sensor loom. For now I'm going to leave the ecu ground off the case because the car drove fine without it the other day but it must need grounding for a reason.

My ecu case ground goes to the same point as the power loom ground, should that be a problem?

I think that's what it shows anyway ?

Most cars will work perfectly fine with no case ground, I think mine was the first ( or certainly one of the first ) to exhibit problems with the S-Series first came out !

stevieturbo wrote:I think that's what it shows anyway ?

Most cars will work perfectly fine with no case ground, I think mine was the first ( or certainly one of the first ) to exhibit problems with the S-Series first came out !

So you had problems when grounding the case? What kind of problems?