SX running problem

[adam quantrill]

I've jut had a recurrence of a strange running problem on the 400SX.

Initially I thought this was a dodgy batch of 99 octane and when I got to my destination stuck in a bit of octane boost, and the problem went away.

However it has happened again, this time half way through a tank.

Symptoms are:

- rough running on the motorway, doesn't want to rev much above 3000.
- if you make it rev above 3500 it loses most of its power and backfires (could be unburnt fuel)
- if you let the engine cool down and then run it again an hour or 2 later, the problem has gone, smooth pulling all the way.

Water temp and oil pressure appear normal. It hasn't lost any water. I'm tempted to follow my maxim of checking the water temperature sensor, but any other ideas most appreciated. Perhaps the rev limiter could be faulty? It's a MicroDynamics one.

[tvr 3x]

Try unplugging and replugging the resistor pack.
On my car this is mounted above the nearside front wheel, marked Lucas with a fairly heavy loom running into it.
If the car is idling lumpily try wiggling the loom and see if it makes a difference.

The resistor pack controls the volts getting to the injectors.

Russ

[350zwelgje]

Coil on it's way out perhaps. Did cure my lookalike problem for 2 months. Nice Bosch coil on now. Problem came back, and it was the ECU (flapper type) that was at fault in the end.

Rob

[adam quantrill]

Coil - yeah it's a possibility, it does feel similar to when you get a load of water all over the ingition harness, like the spark is dying.

I'll try swapping it out.

[wedg1e]

Could this be another instance of the distributor pickup failing; seems to be the year for it. IIRC someone else reported the same defect above 3000 rpm. Mine stuttered above 5300 for months before finally packing up one day.
You could always unplug the rev limiter; I have a Micro Dynamics unit on mine and I suspected the same, but it wasn't faulty...

[GreenV8S]

Sounds like a wesk spark as others have said.