Code 4 after running for 30 mins

I got approached by a Local Beat owner who lives about an hours drive from me who's Beat goes into crawl mode 30 minutes after starting from cold. The ECU is showing a code 4 (Crank Angle Sensor).

I've already met up with him and have tried another ECU which we know is OK so this is not the culprit. I have been informed that the crank angle sensor has been changed by a local mechanic as the old one had melted!

Any tips on where to go from here?

The owner is in his 80's who is full of life and has a awsum car collection. Hoping to get his Beat back on the road and go for a spin with him soon.

As always any help will be appreciated.

Julian

P.S. My Beat is still going strong :)

The Crank angle sensor is in the distributor, so 4 way connector going to the distributor should be checked.

Has it already had a new distributor if the sensor has been replaced, or has it actually had a new CYL sensor (behind the cam sprocket, as that has a habit of melting)

If the distributor has not been replaced, then check that as failing bearing inside can cause its freeplay to damage the sensors.

Both the TDC and Crank Angle sensors resistance can be checked (should be between 800 - 1300 ohms), it is presumably breaking down when hot.

Otherwise as you have eliminated the ECU, then wiring from engine back to ECU would be next to check.

Thanks Steve,

I believe that the distributor has be changed recently, but will get confirmation of this. Hopefully I find the time at the weekend to have another look.
I think it's heat related too so will check the resistances and wiring and go from there.

I think I may still have my old distributor, which is about 9 years old and was replaced 1 year ago after not many miles, possibly unnecessarily, as unbeknownst to me at the time, I was being led astray by a senile ECU which thought a sensor in it was faulty. Could possibly dig it out and sell on if you're interested.

Update. Had a good look at the car at the weekend. The Distributor has not been replaced which makes me think Steve's guess that the CYL sensor was replaced was spot on!

I've checked the wiring to the distributor and all seems fine there. I also checked the resistance of the both the Crank and TDC sensors, both seem fine whilst the car is not running, but the car stalls if I connect my multimeter when it is running so I'm not able to get a reading. Strange as it does not happen when I do the same test on my own beat!

Thanks Bruce, If you still have it then that would be fantastic.

I think I bought this Beat (80 year old in a little village in Essex with lots of old small German cars...).

It doesn't cut out, but the engine management light remains on from start, but fades after a few miles. It fades less in cold or humidity, it goes out quickly on hot dry days. Could this be the MAP sensor? I have replaced the capacitors in the ECU and this has not made a difference.

Otherwise the car is running very well, and the engine management light coming on doesn't seem to have any impact on the performance of the car.

Anything you can tell me about what you did or checked on this would be much appreciated, especially re the crank and TDC sensors.