P38 Diesel Hot-Start Issue Cause

I've just fixed this on my P38, and not by adding a work-around like the timed relay with a resistor.

It turns out - this issue is caused by a cheap dodgy lift pump. I only figured it out because I started having the problem only since I changed the lift pump. The good ones have a non-return fuel valve in them (you can't blow into the outlet pipe). The bad ones that cause the hot start issue don't.

Unfortunately, both the good ones and bad ones go on eBay for about £45, so it's hit and miss.

So if you have a hot start issue where it'll always start right up when cold but won't start from hot even after a minute of turning it over, this is probably a good place to start looking.

Anyway, I hope this is helpful to someone who is going nuts with this problem.

So if there's no fuel there how come it start with the glow plug immediately? (using the hot start)

Because the cold start relay operates both the glow plugs and the lift pump.
Otherwise the lift pump is only trying to work while the engine is cranking, at which point it's a bit late to be priming the injection pump while the volts have already dropped to about 10V instead of the normal 12-14V. This is another part of the problem - good pumps will still prime even at 10V, whereas some (but not all) cheap chinese knock-offs, like the one I just pulled out, won't.

Both of the pums I have definitely work (when I attach 12V to them, the fuel squirts out the top). But one of them causes the hot start issue and the other does not.

How about fitting a non return valve at the filter end while the iffy pump is fitted just to test the theory??

stupid question ,,,, when is the lift pump local at a P38 diesel , I can find it ?

cheongthong said:

stupid question ,,,, when is the lift pump local at a P38 diesel , I can find it ?

Click to expand...

The lift pump is in the Fuel tank...often refered to as In Tank Pump