Intermittent Electrical Fault

[schueymcfee]

Okay, I know when it comes to electrics it could be one of many things but.....

I have what I think is an electrical fault somewhere.

When the car is running good it runs good and sounds great, pulls all the way through the rev range, rev counter works, and it doesn't cut out while idling.

Then all of a sudden for no reason the rev counter will stop working or indicate half the revs it should do, the car will struggle and stutter running up through the gears and revs, it will hunt and cut out at idle.

Do these symptoms ring any bells to a known problem? It's like the car loses half of its power.

I have changed the coil (which made it slightly better), I have run a new cable from negative battery terminal to the engine because I did have a bad earth which caused the car not to start, this is now cured so I think the earth is okay.

Thanks for any suggestions.

>>> Edited by schueymcfee on Tuesday 16th March 13:31

[trefor]

I would suggest ignition amplifier, but I'm not sure if/how the revcounter could be affected by this.

Small black box - either bolted to the plenum next to the coil or right next to the dizzy. Simple swap, but costs around 40 pounds.

T/.

[greenv8s]

There are probably a million things that can cause this problem, but one that is easy to check and fix is interference between the HT leads and the signal from the distributor to the ECU. There should be a single wire that goes from the ignition amplifier, over the near side rocker cover, under the throttle assembly and into the front of the passenger's footwell. Make sure this is routed well away from the HT leads. They often end up running close together which can lead to interference.

[v8 racing]

if you trace the white with a black tracer wire from the neg side of the coil they have a small resistor which the terminals can often corode on give them a good clean, and also pop the dizzy cap off get a knife and clean all the points on the cap and make sure you have a genuine LUCUS rotor arm if not put one in

[taylormj4]

This sounds like the engine rev sensor is at fault. This feeds the rev gauge and also the ECU. If the ECU does not know what speed the engine is going round at, it cannot determine the correct fueling for the injectors. The idle speed control will also be affected. If the ECU does not know when the engine is running down towards idle speed, it won't kick in the stepper motor and prevent a stall.
Check the wiring, condition of the sensor and its earth.
Matt

[schueymcfee]

taylormj4 said:

This sounds like the engine rev sensor is at fault. This feeds the rev gauge and also the ECU. If the ECU does not know what speed the engine is going round at, it cannot determine the correct fueling for the injectors. The idle speed control will also be affected. If the ECU does not know when the engine is running down towards idle speed, it won't kick in the stepper motor and prevent a stall. Check the wiring, condition of the sensor and its earth. Matt

Thanks for the suggestions, I'll have a look at these points.

By the way, what does this rev sensor look like and where is it on the car?

Thanks.