Hello folks

Having a very annoying problem with my 1999 300tdi manual disco here

She's started running very lumpy and missing when at full throttle. It feels like she's drawing air when it happens but the lines seem OK. I cleaned the sedimenter out which seemed to cure it for a couple of weeks but then it happened again so I did bowl again and she was ok again. Anyway, it started happening again last week so I thought there must be unwanted 'stuff' in the tank that's getting into the sedimenter so I drained the tank but it was very clean inside, I took pipes off the lift pump and took the bowl off again and blew all the lines out. However, after putting it back together and putting fresh fuel in the problem is still there and not even given me a few days of good running.

She's done 97k, is well serviced with the usual stuff like decat, egr blank, slight diaphragm tweek. The boost hoses seem OK (by the way how do they collapse when on full boost???) fuel lines seem OK, and all filters are new.

A while ago there was a fuel leak from the bolt in between the injector pipes that leave the back of the pump (i think it is where a dti gauge is ment to go for timing) is this area ment to be full of fuel, and is there any problems with these pumps or little gauze filters anywhere I should be aware of, or any other less common problems that might be causing this problem???

Please help people this is starting to put me off my otherwise loved disco

Thank you

Towsey

I've put a new lift pump on as well

Towsey

towsey956 said:

She's started running very lumpy and missing when at full throttle.

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towsey956 said:

A while ago there was a fuel leak from the bolt in between the injector pipes that leave the back of the pump

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Your engine principally needs 3 things to function correctly, 1/ a clear flow/charge of filtered air, 2/ a properly metered injection of fuel delivered at the correct time. 3/ Cylinder compression enough to build the heat necessary to combust the fuel/air mixture. It is generally when one of those 3 is interrupted the engine has problems.

So starting with the air, remove the flexible hoses on the turbo piping and check for obvious internal damage, sometimes they look ok from outside but have de-laminated internally, also ensure the air filter element is in good clean condition.

Next, fuel, you have already looked at the sedimenter but go over all the fittings and little hoses from the tank pickup through to the lift pump, what I have done is slightly pressurise the system with a light application of regulated compressed air pressure in the fuel tank filler, do not put any more than a couple of PSI in otherwise you could blow the tank apart, this will show up any leaks from the tank to the lift pump because that section is normally under suction pressure and you'd be surprised how much air can be drawn in a small crack in a rubber hose or a leaking bowl seal, also have you checked that the main fuel filter on the firewall is full of fuel after one of these "missing/rough running episodes, maybe replace this filter and re-prime the system, because from what you are describing it sounds like a fuel starvation problem due to air in fuel line ingress.

Compression, you maybe need to remove the valve gear cover and have a quick check that all the valves have at least their .2mm clearance, check the rocker shaft is still firmly bolted to the head and pushrods are straight and properly engaged, you could check the compression but if the engine is starting cold ok and coming up straight away on all 4 cylinders that is a good indication rings/valves are ok. You say that you have changed the lift pump, if you pump the manual lever with the fuel inlet to the IP cracked at the banjo does fuel flow out constantly whilst pumping?

You are correct, that hex headed plug in the centre of the IP distributor head is for the installation of a DTI to set point of injection, it should not leak it seals on a copper washer, but the body of the IP is constantly under lift pump delivery pressure, any leakage on the body of the IP anywhere can cause problems with starting after prolonged periods of standing.

If your Disco has been running ok previously then it will be only something simple, check the easy stuff first.

Thanks for the reply gazbo

The air filter is new and pipes have been checked. I have also had the sender out and everything checked and cleaned out but I have not put any pressure in there. Although the lift pump is sucking from the front, would a fuel leak still not show itself in the line when the engine is off, you know wot oils like for weeping? The fuel filter is also new and remains full at all times. I have not yet had the rocker cover off tho but I will be doing soon anyway so il go over all that then. I will crack the banjo at the pump as well and check flow there...is there one of those little gauze filters in there, or anywhere else come to think of it?

Now to the starting bit...she does start ok and on all 4 pots but the revs have always been a little low for the first few minutes and this has been the case since I've had the disco and I've not come across another 300 that does this quite as much as mine, but this isn't a worry really and all comes good soon enough. But, the first couple of times it started missing, it also took more starting on a morning but then was ok for the rest of the day, and was generally a bit sluggish no matter the revs or amount of throttle used. But then cleaning out the sedimenter also cured this and it fired on second compression every morning, which was what made me think there was s*^t in the tank, but nothing. Also, when she's in one of her moods there is more of a black haze left behind me, especially when trying to send her on to see how she's running.

I know these vehicles are not racing cars but I know there is a problem and just want it sorting... Oh and it does about 10 mpg less when playing up.

Thanks again

Towsey

And I'm lost as to why cleaning the sedimenter out worked twice but now it seems to make no difference, is this a clue to the problem???

Towsey

towsey956 said:

would a fuel leak still not show itself in the line when the engine is off,

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I can only say what I have experienced regards that question, fuel is a lot denser than air, my Disco had an air leak where a plastic fuel line had worn against the chassis, no leakage out was obvious and it was only when I had filled the tank to the top prior to a trip and parked the Disco on a steep slope, (our front yard), with the front of the car facing downhill, just happened the next morning to notice a fuel stain on the RH side chassis rail, I had to cut the line and use a piece of rubber to rejoin the severed line.
I had been having cold starting problems after the Disco was parked nose uphill over night, I found initially there was an air leak around the IP throttle shaft that was allowing fuel to drain back to the tank via the excess fuel return lines, after that was repaired I was still getting a small amount of entrained air accumulating in the main fuel filter that was giving problems, all cured after repair of the fuel line.
The black smoke problem really is endemic to the species,(old tech mechanically injected diesels), but part of it can be due to air intake issues, also has the fuel pump been played with, (sometimes a small movement of the so called "smoke screw" can upset the engine), it will make it pull hard but will give the EPA a reason to put you off the road.

Was the new lift pump a good make, inferior lift pumps just don' t

Well the brand of lift pump did cross my mind, but it was a mates spare given to me cos he now has v8s instead, when I changed it there was no difference at all, not a bit worse or a bit better just exactly the same so I crossed that off my list but I know where your coming from.

Think I might need to pay another visit to the main fuel pipe and maybe apply some pressure and see what happens. The disco came from a woman who had it since 2001 and I'm confident that I was the first person in the pump and all I've done so far is a mild turn of the diaphragm/boost pin and I don't intend doing any more until it's on bigger wheels and tyres and that's not happening until I'm happy with it in standard form.

Have we any info on how boost pipes manage to collapse when their full of compressed air, I imagined they would expand instead???

Thanks again tho and keep the ideas coming, especially anything on the rare side and anything the pumps are prone for

Towsey

By the way which pipes is it that delaminates and collapse

Cheers

Towsey

usually between air intake and turbo, as they are under vacuum when the turbo spools up
if de-laminated, inside can collapse under the vacuum with no real visible sign from the outside

Cheers disco me

I was told it was the two bottom boost pipes that collapse but I wondered how if all pipes after the compressor housing are running boost, thanks

also could be boost pipes collapsing as vacuume generated by suction of engine can outweigh boost preassure of turbo, apologies if this is confusing

Not confusing at all, but would engine suck exceeding turbo blow mean that an engine wouldn't be very powerful, sort of like running with no boost type of thing. And would turning up the boost like most people do overcome this...although it obviously won't fix the pipes

I almost bought a 3 silicone hose kit as well but I just got the one for blanking the egr instead, I knew I should of got the 3 pipes then just made a plate, oh well

Cheers

Towsey

So is the engine sucking harder than the turbo is blowing a common found thing then or does it mean you have a dodgy actuator or something else?

Towsey

could be something as simple as a blocked air filter, not allowing air flow and putting intake system under vaccum or just worn out rubber de-laminating

All filters are new and before I serviced it i tried it with airbox lid open and it was the same, cheers for idea tho

Personally I think the problems between the tank and the pump, or even in the pump. But a dodgy actuator did cross my mind, (boost coming and going and puffs of black smoke as she over fuels) I'm in the process of borrowing a boost gauge to check this. I find it odd that cleaning out the sedimenter cured it twice and she drove and went perfectly for a while tho.

I think wot it does and how it drives feels like it's drawing air but I can't find any anywhere, nor can I find a leaking pipe but I'm going to try pressurising the tank while the engine is off and see if that helps a leak show its self. It doesn't just get to a certain amount of revs then just lose power, I can feel it trying to pull through the problem, like its trying to go well but there's just a little something making it miss and chuff in an irregular pattern

Cheers tho and all ideas appreciated

Towsey

have you checked fuel pipes at the sender unit

I haven't had tank out yet but when I took the sender out to clean out the tank the unions, pipes and tank were all as dry as a bone, and are again now

Towsey

It does sound like either air being drawn in or a restriction in the line.

I know you've had the sender out but have you checked the pick up pipe is clear?

A clear section of pipe up front can help spot bubbles if that's the problem and blow the line through front to back.

Blocked leak off pipes can case some funny issues as well so worth checking.

Yes, all pipes from the pump back have been off and blown through with the bowl off and sender out. The sender was also blown through at the same time and sender and sedimenter seals are ok. The three braided leak off pipes are brand new, BUT, the plastic one that goes from no.1 injector back to the banjo on the rear of the pump has not been off or blown through, mmm I like this idea. Clear pipe is on the to do list but I've not found any suitable stuff yet.

So wot and how do blocked leak off pipes cause, I'm curious

Cheers

Towsey