Fuel in sump, but car starts

[Maltloaf]

I have just rebuilt my 2e bottom end on a Digi mk2 8v, I also replaced the head with a TSR pack A while I was there.

I now seem to have some kind of over fuelling issue. The sump seems to have petrol in it but after a few tries the engine starts and runs really well. It only seems to be when the engine is cold, when it is cold I sometimes loose all compression on random cylinders, sometimes it is number 3 then number 1, etc.

I do not think it is the ECU or ignition amp as I have changed these with spare ones and I would not expect the engine to run at all if this was the problem.

Is there a chance it is simply the blue temp sensor or fuel pressure regulator?

Finally should the fuel pump run continually on my car (1991), or should it switch off when it is up to pressure? It always used to run constantly but I would like to know if this is correct or not.

Thanks in advance.

Matt B.

[rubjonny]

could be the blue sender, or a poor earthing issue.  Remove and clean up all the battery/starter/alternator wires with sandpaper till shiny and refit.

The fuel pump should prime for a few seconds then stop when you turn the key 1 click, if it runs continuously thats a classic symptom of a blown ECU.

[Maltloaf]

Thanks for that.

I found the fuel pump problem, someone in the past had bridged the fuel pump relay. I think this might have been to mask another problem but I am not sure what yet.

I was going to get the injectors checked out, I know a place that can clean and test them for £20 an injector, and also replace the o-rings as well.

I will be getting a new blue temp sensor as well. I don't suppose that anyone has the resistance graph for this sensor (temp verses resistance)? The information I have got suggested that it should be the same as the air temperature sensor in the AFM, but mine is about 1k ohms out (AFM was 3.5kOhms and blue temp was 4.5KOhms) both were 12 degC.

[rubjonny]

just buy a new one, £13ish from VW. Its possible for em to return resistance values that are close to what you expect, but for the curve to be wrong or for them to fail intermittantly