i think i have fuel supply problems

[maxgreenwood]

i've had a problem that until recently i have been able to live with, but seems to have gotton worse.

er.. yes .. on the car

accelerating or decelerating gently from any given steady speed with the engine running between 1-2000 rpm, the car lurches forwards and backwards, most noticeably and annoyingly in third gear. It has been confined to between 1-2000 rpm until recently but now seems to remain thro to 2.5-3000 rpm. Only keeping the accelerator dead still on a level road can i stop it, or it goes on accelerating hard too. So i'm doing a fair amount full throttle accelerating up to 40mph or whatever the limit is what else is the turbo for?!
initially i thought it was due to the worn lower engine mount, but i think its just making it more noticable.

The factoids:
The engine always idles perfectly, no fluctuation and revving is smooth.
New fuel filter recently and i have swapped the fuel filter housings (same on each) on my cars as the primer in one was bubbling fuel from under the plunger. The replacement seemed ok, but i guess it might not be.
The metal fuel lines under the car i replaced 6 months ago.
Pretty sure its not the clutch.
I could replace fuel lines with clear from filter to pump to check for air, that could be my 1st step, but I'm wondering what else i could check. The last rubber bits near the tank must be pretty hard to get at/replace?

The diagnosis:
Any thoughts on a likely candidate? :

a/ a knackered pump (lucas/roto) - seals etc?
b/ a blockage in the tank - is there a filter in there before the fuel supply line?
c/ leak off pipes between injectors - these are looking pretty perished and frail, although the longer ones on the pump look good.
d/ rubber supply pipes before or after fuel filter admitting air

PS. Cooling system overhaul stage 1 commences this weekend!

[ken newbold]

My guess would be air in the fuel system somewhere.

Not much help I know but it's the first thing I'd look for.

When you fitted new fuel filter, did you coat the seals lightly with grease?

[maxgreenwood]

hi ken,
no i didn't actually, is that standard practice?

[ken newbold]

Yes, most times you will be OK, but every now and then, one will let you down and allow air in.

[DLM]

I'd act on Ken's advice and start with the filter assembly.

I've only once encountered surging myself in several years of driving BX diesels, and that was due to a leaking filter diaphragm. Air in diesel, even in very small quantities, can make life very unpredictable, so I'd get going on this sooner rather than later.

[maxgreenwood]

still not had time to check filter housing and fuel pipes. this weekend hopefully!

incidently, the problem is not there when the engine is cold, don't know if that might give further clues. Probably just whatever's leaking being sealed through being contracted when cold.

[BX Bandit]

For some strange reason, my Dad could never bleed the 1.9 n/a. On the motorway, the car would surge forward almost turbo like and it was really unnerving. As Ken & DLM mentioned, have a good bleed and make sure all your fuel line connections are jubileed up nice and tight!

[maxgreenwood]

bandito, a good bleed?, as in the bleeding fuel like, what the bledding hell is that all about?

[BX Bandit]

yeah, as in priming (on the filter housing, there'll be a bleed nipple at the top. Undo it (make sure the spanner is nice and tight 8mm I think) with some tubing on the end leading to a glass jar. push the primer plunger thingy many times until fuel with no bubbles comes out of the tube. Give the filter housing a little tao now and again to help the air out and keep priming until you're happy there ain't more air inside.)

You may find symptoms persist for a bit if there's any air in the pump or lines but you should be ok.

If your fuel lines were replaced, make sure the rubber hoses are secured tightly at both ends and on the fuel filter inlet/outlets.
If it was pump seals then fuel would leak out as opposed to air getting in as the internals are under pressure. (It may draw air in when cooling down but I suspect for that to happen you'd see big leakage when running)
Broken fuel leak off pipes will just make a mess as the fuel returns to the tank and not the pump
There's no filter in the tank.
Are you sure the replacement filter housing was good?
Did you replace all the seals
Is the bolt holding the filter and housing together secure and tight (not too tight cos the housing is aluminium/cheese mix!)

[maxgreenwood]

Thanks Bandit this is all very helpful stuff.

yeah, as in priming (on the filter housing, there'll be a bleed nipple at the top. Undo it (make sure the spanner is nice and tight 8mm I think) with some tubing on the end leading to a glass jar. push the primer plunger thingy many times until fuel with no bubbles comes out of the tube. Give the filter housing a little tao now and again to help the air out and keep priming until you're happy there ain't more air inside.)

I didn't know about this.

If your fuel lines were replaced, make sure the rubber hoses are secured tightly at both ends and on the fuel filter inlet/outlets.

There was no jubilee clip on the feed pipe at end near the tank, maybe i should put one here, there were a couple of push fits.

If it was pump seals then fuel would leak out as opposed to air getting in as the internals are under pressure. (It may draw air in when cooling down but I suspect for that to happen you'd see big leakage when running)

Thats reassuring

Are you sure the replacement filter housing was good?
Did you replace all the seals
Is the bolt holding the filter and housing together secure and tight (not too tight cos the housing is aluminium/cheese mix!)

The housing seemed good, all seals were replaced, tight as i could without bending the aluminium-mooncheese alloy as you say.
But i only primed by plunging the button on top and kept trying ingnition till brought fuel through.
the diaphragm the plunger operates i think is split in my other filter, it bubbles when pumping. But thats a sealed unit - or is it? I'm sure i've seen pictures on here of it being opened?

[BX Bandit]

Never seen one opened mate

[jonathan_dyane]

As regards bleeding of air, I think that the pumps have a self-bleed capacity which can deal with a small amount of air, and that the 'bleeding' process is in actual fact 'priming' rather than evacuation of all the air; the only solution to dealing with excess air bubbles in the system is to locate and repair the leak where the air is entering.

[DavidRutherford]

I think that the pumps have a self-bleed capacity which can deal with a small amount of air, and that the 'bleeding' process is in actual fact 'priming' rather than evacuation of all the air; the only solution to dealing with excess air bubbles in the system is to locate and repair the leak where the air is entering.

This is truth. Once the engine is running it will quickly clear any air in the lines and spit it out back to the tank. Only if there is air constantly leaking in will you have a continuous problem.

Question: If you hold the engine at 2000rpm off load (IE in neutral) does the engine speed "hunt" (IE drift up and down) or does it hold a rock-steady engine speed?

[Brian]

This is the link "primer pump dismantling".

http://bxclub.co.uk/forum/viewtopic.php ... highlight=

Good luck

[maxgreenwood]

Question: If you hold the engine at 2000rpm off load (IE in neutral) does the engine speed "hunt" (IE drift up and down) or does it hold a rock-steady engine speed?

No, in neutral, engine has been running pretty much perfectly, although recently it has developed a very slight slight up and down of revs, noticable on dashboard lights getting brighter and dimmer.
I primed the filter today before driving and its moved the problem at its worst from 3rd gear to 2nd gear
I'll check the filter housing and seals, and then maybe replace the rubber feed hose, then put clear ones on to see if i can see bubbles.