Intermittant loss of power

[Rob_the_Sparky]

I have been suffering on and off for a while now with a total loss of power that occurs for approx. 0.5s to 2s, it is like someone turns off the fuel. At the moment it occurs during warm-up but previously it has occurred when hot (it is a long story and trying not to write was and peace!)

The two relays have been swapped (fuel pump and ?) and then the throttle pot and each time the symptoms have changed or stopped only to return.

I have plugged it into RoverGauge and the log shows that the throttle pot value becomes zero (when closed throttle is ~1.1 so this is definitely a problem) but at the same time the "idlebypass" opens very rapidly.

I'm assuming that the "idlebypass" in RoverGauge is a command to the stepper motor as AFAIK there is no feedback from the stepper motor. I'd also assume that there is no reason for this to react to the throttle pot so there is something larger going on than a dodgy throttle pot. I.e. some sort of EMC or power related issue.

The car has had an engine replacement recently, could this be caused by a bad earth connection? I.e. earth voltage rises and causes all the sensors to mis-read? I had no such problem before the engine work...

Rob

[Tom The Cat]

Hi Rob

for me it looks like a bad earth or wire is broken somewhere in the harness.

hope you find it soon .. TTC

[blitzracing]

The TP showing a sudden zero will cut the fuel at that point, so the error fits the results. A TP should be about £60 not hundereds as supplied by TVR people.

[Rob_the_Sparky]

Already replaced the TP and the problem only occurs during warm up. Also, could the TP going to zero explain the sudden rise in the idlebypass? I'm assuming that the idlebypass is independent of the throttle pot but if I'm wrong then it could well be a second duff TP, just seems unliklely.

Rob

P.S. during the event the RoverGauge shows no change in the injector duration. This seems to contradict the other results. I'm guessing that this is duration is from the map but the error condition caused by the throttle pot means that this is overridden, I.e. despite the map the injectors are actually off, causing the lack of power. Bit of a guess though.

[Loubaruch]

Do not discount the replacement TP failing. This is precisely what happened to my S3 a while back.

With the S3 you can disconnect the TP and the engine will run albeit not very efficiently, not sure if the same applies to the Griffith. No doubt Blitzracing will know.

[blitzracing]

The stepper is used to raise the idle as you shift down between gears, so you dont get lock up, so what you are seeing is the idle being lifted when the RPM is still above idle and the throttle is seen to be closed, ie when the car is between gears. To be 100% on the throttle pot- run the logs for the AFM output alongside the TP- you will never get a low throttle pot reading with a high airflow (anything over 35% on direct reading) if the TP is working OK. Dont forget the TP needs 5 volts from the ECU- so if you are loosing that 5 volt rail for any reason the TP output will drop, same as if the resistance track is breaking. It would be worth putting a test meter on both the 5 volt rail (can be as low as 4.5 volts) and the TP output to check the actual DC values, as RoverGauge is telling you what the ECU sees- that may not be the same as the DC voltages if you have a loom issue.

[Rob_the_Sparky]

Thanks, I'll have to have a play on the drive and see if I can re-produce the problem.

[Rob_the_Sparky]

Thanks all, I can re-produce the below idle throttle pot reading when the engine is off if I move the throttle very carefully, looks like a second duff throttle pot. Lets hope number three is a bit better!