Power Issues Under Load - Diesel

[scorpio]

Just wonder how you had got on with this as I have the exact same symptoms and I am struggling to find the problem.

I can hear both pumps running, but under load around 2000-3000 revs the engine management light comes on and I lose power for a split second and then it runs fine. As soon as I am running at between 50 & 70 mph nothing seems to happen.

[olliewarwick]

HI Peter,

Nothing yet however, it is going onto a T4 shortly. Interestingly the management light hasn't been coming on when it happens to me although the symptoms sound exactly the same.

I'll let you know how I get on.

Cheers,
Ollie

[olliewarwick]

Hi All,

A little update on the issue. I took it down to Chris in Fareham (great chap, helped me out with a few bits) and although we didn't come up with anything conclusive, we suspect it might be the return valve on the diesel fuel line described here:

https://www.the75andztclub.co.uk/for...d.php?t=107978

So the obvious question is does anyone have one available from a scrap car? Or know a good scrap yard within reasonable distance of Guildford?

We also noticed a couple of pipes are going so I'll replace these too. I'll start another thread for that.

I'll keep you all up to date, and a special thanks to Chris and Brian who have helped out with it.

Thanks,
Ollie

[HarryM1BYT]

Originally Posted by olliewarwick

Hi All,

A little update on the issue. I took it down to Chris in Fareham (great chap, helped me out with a few bits) and although we didn't come up with anything conclusive, we suspect it might be the return valve on the diesel fuel line described here.

That part appears to be a pressure limiting valve, the low pressure fuel system pressure limiting valve. Apply too much pressure and it should open to release that excess pressure.

My own take on that, is that it would either leak at too low a pressure, or work properly. If it leaked at too low a pressure it might make it difficult to start, rather than failing as you suggest at higher fuel demands.

[olliewarwick]

So with that theory, if it became weak and opened too early, that is to say at a lower pressure than it should, the system wouldn't be providing as much pressure to the HP pump?

As it happens, I did have a fuel leak from that area a while back and although I didn't track it down I tightened up everything and it went away.

I don't suppose you have the part, or know where I can order it from?

Research makes be believe it is a pierburg part.

Thanks,
Ollie

[HarryM1BYT]

Originally Posted by olliewarwick

So with that theory, if it became weak and opened too early, that is to say at a lower pressure than it should, the system wouldn't be providing as much pressure to the HP pump?

If you were replying to my post....

I was suggesting if it opened too early and the pressure too low, then your engine would be disabled to protect the HP pump. So I am suggesting that valve therefore must be OK.

I would suggest your way forward would be to put a meter on the LP sensor and see what happens there.

[cb750chris]

Hi Harry,
We tried driving the car with the fuel pressure sensor unplugged (not recommended as it removes the protection built in by using that sensor) and the issue persisted, suggesting it is not something being sensed by LP sensor, so probing the sensor static will not help. (The issue apparently only shows when the car is being driven, so not able to reproduce with a meter on leads)

(If the low pressure side fuel pressure drops below 134(?) KPa then the car will drop in to limp mode).

The Valve on Ollie's car has been rubbed quite severely at some point in time, and has worn a fair sized hole in the metal band holding the valve together.

The in tank fuel pump was weeping diesel out of the top pipe (back in to the tank), which wouldn't help the low fuel pressure.

Ollie did suggest after a bit of work around on the car that things had been improved slightly, and the car was running ok after a short while, but initial driving was still problematic, which I am currently suspecting may be due to air being let in by this valve when the fuel pumps are stopped. This is the route Ollie is following at the moment, as there is nothing obvious apart from this.

Chris

[Arctic]

HI Ollie & Chris.
I presume you are talking about pressure limiting valve in the photo's below, if I am correct and Ollie is struggling to get one he can drop me a PM and could sort him out with one of my spare ones I have I have noted in the past also that the hose coming from the valve and the T joint to the UBFP start to rub if not clipped back in situ for one reason or another if they have been disturbed. Arctic

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[olliewarwick]

Thanks Artic, PM sent.

Cheers,
Ollie

[olliewarwick]

I have ordered all of the other pipes to fit at the weekend.
Three were a number of them that had clearly been rubbing against other parts.
Cheers,
Ollie