Disco 1 300TDi Idles but won't rev!

Hi All,

My 300TDI Discovery has been parked up for about a year awaiting my attention. Now having had opportunity to look at it again it has developed an engine problem.

It will start and idle but will not take revs. I have changed the fuel lift pump as I thought that would be the problem. It isn't. From there I have checked and blown through the flow and return fuel lines. Cleaned the water separator at the rear. Removed the fuel filter and checked the lines there. Blown out the injector lines after removing them from the injectors and injection pump. I noted some leaks on the injector return lines between injectors so I have replaced them.

Ive started with the air intake taken off and checked the exhaust for blockages. Nothing is blocked and I have good air intake and constant exhaust.

I have lessened each injector pipe and have fuel flow at them all. If slackening the injector one at a time the engine runs even more lumpy before returning to low idle when retightened.

When I unplug the injection pump the engine stops. So I am hoping the problem isn't the injection pump.

From here Im out of ideas so any advice is greatly received.

I should have kept it on the road but some other projects and the extent of the welding I've done on it forced my hand.

Hope the video helps show the problem.

Hi, it seems very reluctant to start and when it eventually does fire up it isn't running well at all. I am by no means an expert but I had a similar problem a few years back and it turned out to be drawing air into the fuel system at the sedimentor, fixed that and away she went, could be something similar, check all joints in the fuel system, like I say I'm definitely no expert but it's behaving exactly the same as mine did.

If you run a gravity feed fuel supply direct to the injection pump ans see how it runs,
This way you eliminate everything back to the tank, if it’s runs ok fingers crossed then work backwards to the fuel tank, could well be the outlet from the fuel sender unit in the tank corroded and letting in air,
If your direct feed makes no difference then it’s probably corrosion in the pump,
Diaphragm or lift pin could be stuck, worth a check,

If it’s is the injection pump I would highly recommend Diesel Bob for the repair,
Plenty of post singing his praises,me included,

Europa486 said:

If you run a gravity feed fuel supply direct to the injection pump ans see how it runs,
This way you eliminate everything back to the tank, if it’s runs ok fingers crossed then work backwards to the fuel tank, could well be the outlet from the fuel sender unit in the tank corroded and letting in air,
If your direct feed makes no difference then it’s probably corrosion in the pump,
Diaphragm or lift pin could be stuck, worth a check,

Click to expand...

That’s a good call trying a gravity feed temporarily. The more I look at it the more I’m seeing air ingress somewhere.

Europa486 said:

If it’s is the injection pump I would highly recommend Diesel Bob for the repair,
Plenty of post singing his praises,me included,

Click to expand...

Fingers crossed it isn’t the pump but I will keep this in mind if all else fails.

DiscoRay said:

Hi, it seems very reluctant to start and when it eventually does fire up it isn't running well at all. I am by no means an expert but I had a similar problem a few years back and it turned out to be drawing air into the fuel system at the sedimentor, fixed that and away she went, could be something similar, check all joints in the fuel system, like I say I'm definitely no expert but it's behaving exactly the same as mine did.

Click to expand...

Yes I’m seeing more and more likely it being air ingress. I’ll give it another look this Sunday and see what else I can find. Thanks.

Have you had the Banjo bolts out on the pump? You don't mention it but they have different size fuel ports and give your symptoms if you mix them up.
Smaller port is return.

Lift the boot carpet and check the top of the tank. Any holes before the pump will suck in air, after pump they leak diesel.

did this ever get sorted ... as i had it before where i put the fuel lines on the lift pump the wrong way round and it was just the suction that was caused by teh engine drawing the fuel through .

An update would be of interest to many of us and it might be helpful to others with similar problems either now or in the future.

Hi All,

Sorry all I've only just managed some time on this today. I'm self employed and with the current situation I haven't had any free time until today .

First. I've checked the sender unit under the boot floor. Although signs of corrosion all joints are sound. No signs of fuel leak and no air intake. I get clean, bubble free fuel at the filter bleed screw.

Second. I removed the lift pump fuel supply hose and fitted a hose directly into a can of fresh diesel so bypassing the fuel system from the tank to the lift pump. Again the same symptoms presented. So from there I removed the outlet hose from the fuel filter, so bypassing the new lift pump and filter. Again no joy on anything but a rough idle.

I have noted today when operating the throttle at the injection pump it didn't die out and stall but did nothing. Its become harder to start and idle however.

So to confirm.

- No air ingress is showing on the flow or return from the tank to the lift pump - injection pump back to tank.
- Separator is sound and water free.
- New lift pump has been fitted and is operating as it should and pipes are the correct way round.
- Using a secondary fuel store and new fuel and pulling fuel directly into the lift pump same symptoms exist.
- Fuel is reaching the injectors.
- Inlet is clear and pulling air in freely.

At this stage I am really struggling to come up with anything else other than the injection pump. I don't have pump support tool but considering one and getting the pump off and having it checked. Also the spend on it is starting not to be worth it if the IP is at fault?

So in short still looking for a solution.

Help again please.

Flossie said:

Have you had the Banjo bolts out on the pump? You don't mention it but they have different size fuel ports and give your symptoms if you mix them up.
Smaller port is return.

Click to expand...

No not until today and they are the right way round.

ronsealdeath said:

Lift the boot carpet and check the top of the tank. Any holes before the pump will suck in air, after pump they leak diesel.

Click to expand...

Had this open today. All clean, dry dust and no fuel. Corroded but sound.

DiscoRay said:

An update would be of interest to many of us and it might be helpful to others with similar problems either now or in the future.

Click to expand...

HI yes, Sorry, Free time is limited at the moment but any input is very gratefully received. I will post back what ever the outcome is.

Any chance you were able to get to the root of the problem?

Having the same issue on my defender and hoping it ain't the injector.