Thread: V8 fuel pressure and associated things

The fuel pressure regulator is a non serviceable unit so not much use looking inside. It's function is determined by the fuel pressure gauge you should have for diagnosis, and the presence of any fuel coming out of the vacuum connection. They don't fail all that often so a second hand one may suffice. You can get cheap aftermarket adjustable regulator kits complete with a gauge for around $50 off ebay, giving you a point of adjustment.

Universal Fuel Pressure Regulator Blue Gauge Rising Rate Ford XR6 Turbo | eBay

Thanks, I was more thinking from the point of view of satisfying myself that it was definitely stuffed but I like your suggestion of the adjustable regulator anyway. I'm sure I'll get round to the injectors at some point too.

Paul

OK, update on the above.

Changed fuel pressure regulator made no difference, so I have stripped everything down. Removed plenum and ram housing and cleaned both. Removed fuel rail, cleaned injectors, replaced O rings and refitted everything.

Diaphragm on vacuum advance had gone too so I replaced that (and confirmed it now advances).

Base idle and timing now set correctly.

It starts first time and idles a lot better BUT there is a definite lack of power when pulling away (especially on a hill) and there is a popping/backfire noise under acceleration.

I should also add that it still has a slightly "breathy" noise (only way I can describe it) that I had originally put down to a vacuum leak in the plenum/ram seal but I have redone that and confident it is good now.

My only remaining diagnosis is worn camshaft and hence leaking exhaust valves. I wish I had taken the rocker covers of while I had the plenum off (but I didn't)

Anyone any other thoughts?

Paul

Not exactly LR but I once heard a 4.2 Holden V8 with a worn out camshaft lobe sound like that. The valves were fine but one exhaust valve didn't open far enough to purge the spent gases under full load, meaning some came back up the inlet tract.

Thanks bee_utey

I am actually favouring an exhaust valve not closing rather than inlet valve because the backfire sounds more like it is coming from the exhaust.

I have bitten the bullet and been out today and sourced another Disco so the pressure is off to get the repair sorted immediately. I plane to strip both banks back and probably end up replacing both camshafts plus tappets, chains etc (I guess it is all original as it has only done around 135k).

Anyone have any suggestions for what else I should be doing while it's in pieces? I'm off to the UK next month so obscure parts may find their way into my luggage :-)

The new drive is a 2003 D2 S V8 which looks to have been pretty well cared for mechanically so my plan will probably be to fix up the D1 and sell it but I may as well make sure it is in good order for the new owner.

Paul

If your getting a cough in the exhaust that is unburnt fuel in the exhaust yea?
Are you running rich? like going through more than "normal" fuel consumption?

Have you put a vacuum meter on it to test?
There is not that many places it can leak from i would have thought??
Does your cruise control work?
Not sure that matters but just curious as it use vacuum.
You said you could basically close the intake with a rag and it still runs. I find that odd and thats why i keep thinking vacuum problem.

If you had an exhaust valve not closing a compression test should identify that quickly.
Plus you would have to loose idle or atleast a stable idle. It would be lumpy because of the lost cylinder.
I imagine it would get hot and burn the valve worse very quickly and make it a useless cylinder?

No, I don't have a vacuum tester but believe me there were good seals everywhere and the rag in the air intake was an original symptom before I had ironed out most of the issues. A rag now would just about stall it.

I finally got round to doing a compression test today and wasn't that a real eye-opener! I got 135-140 PSI down the whole of the left bank (1-3-5-7) and ZERO down the whole of the right(?)

So, plenum, ram housing and fuel rail off (again). Both rocker covers off and that was the eye-opener. I'm a bit more used to messing with bikes than cars and this is my first V8 - I was expecting a camshaft under each rocker, which I why I said I thought I might end up changing both camshafts. And when I got no compression on one bank I thought it was going to be a broken timing chain on that bank. Thanks for not pointing out my silly mistake :-)

I am having to take the whole top end apart to get to the root of it. So far one rocker shaft off (the bank with ZERO compression) and no obvious issues - the pads on the rockers aren't particularly worn and the push rods are all straight and don't appear worn.

It is not really leaking any coolant and there was no sign of water in the oil. It is leaking oil a little but nothing to suggest that the cylinder head gasket on that bank is gone but otherwise what could it be???

I'll have a look at the other side tomorrow and take the inlet manifold off etc.

In the meantime, any ideas?

I guess I know what people mean when they say these things are too forgiving - the poor engine had effectively been running on four cylinders. No wonder it didn't like steep hills :-)

Paul

On the bank with zero compression, set every cylinder to TDC in turn, apply your breath to a length of heater hose pushed up to each plug hole and see where the air leaks out. You can also make a fitting up out of a dead spark plug to blow compressed air into the cylinder, or adapt the end of your compression gauge. A reminder that if you refit the rocker shaft, the hydraulic lifters will take a while to leak down and therefore show zero compression until they do. The best way to tell that the lifters have leaked down is to spin the pushrods when the valves are closed, they should spin freely then. They should be held in place without any noticeable valve clearance.