Thread: Disco 1 TDI losing power

Originally Posted by Riverinarover

Hi, i recently brought a TDI discovery 1 and after towing a horse float 600ks i now have a intermittent power problem, symptoms are: drive normally can happen at any speed/time of day and loses power like you're taking your foot off the accelerator, then changes down gear (auto). Wait a minute or two and its fine again.
Any suggestions?
I have ordered a auto transmission service kit

Guessing:

- does it seem too slow accelerating some times? Could be vacuum line issues at turbo - the line runs from turbo to injector pump.

- split in large rubber pipe connecting turbo to intercooler - could be loosing compressed air through intermittent opening of the split - or loose pipe connections.

- any fuel leaking around injector pump or lift pump? Leaks along the pick up line from the tank?

Fuel supply issue.

Originally Posted by Red90

Fuel supply issue.

As Red90 suggests.

Air getting in somewhere, maybe through a chaffed line running along the chassis. I had a chaffed line, but only to the point it would let small amounts of air in, but did not seem to leak fuel much if at all - only found it by feeling the line rather than looking for fuel staining.

I once had to remove water from the tank right up to the injectors. Got my lines crossed when putting the sender unit back in the tank. In this situation the shorter return line to the tank was picking up fuel while the longer line that reaches the bottom of the tank was returning fuel. Once the tank got about 2/3rds empty the shorter line started sucking air with the fuel - usually resulting in loss of power - of course on hillier roads the shorter line could only get air and the engine would stop altogether - roll to a flat and it would start again.

In theory the injector pump can pull fuel from the tank if the lift pump has failed, provided there is no air in the line. If you have air and want to prime then you'll need a functioning lift pump.

Thanks for the help, I'm going through the process of elimination at the moment. When you say air getting in somewhere and fuel issue, i have noticed a fuel leak at the top of the injector pump, looks like a deteriorated gasket would that let in air?

Originally Posted by Riverinarover

Thanks for the help, I'm going through the process of elimination at the moment. When you say air getting in somewhere and fuel issue, i have noticed a fuel leak at the top of the injector pump, looks like a deteriorated gasket would that let in air?

An injector pump is well fed by a working lift pump - if the injector pump leaks fuel (usually a weep) then the lift pump will quickly replace the fuel, the injector pump will not need to suck air in to replace the fuel deficit. That's the theory...

Is the fuel coming from a top gasket as a weep, or really coming as droplets from the rubber nozzle or boot on the top of the injector pump? The rubber nozzle lets air in and out of a diaphragm system - when an o-ring fails around a fuel needle the diaphragm gets flooded and fuel exits the rubber nozzle. This could be a potential for irregular fuel feed to the injectors, although when it happened to me the vehicle was parked and just being revved by hand at the injector pump - the pump was removed, the fuel needle given a new o-ring - never road tested in the leaking condition to know if we would suffer power loss.

Do the 'easy' stuff first - check the supply line from the tank running along the chassis. Then any other lines, filters, bleed screws, lift pump. Vacuum line from turbo to injector pump. Intercooler line and pipe clamps.

Note that the lift pump is really only efficient on a particular angle on the cam drive - hand rotate the engine (socket and ratchet) until you feel resistance in the lift pump increasing ie pumping more fuel. Best crack the bleed screw on top of the filter mount to visually prove you are shifting fuel. If you can't detect resistance on full rotation of the engine and no fuel is being pushed out the bleed screw (or very little) then the lift pump is probably faulty. Finally, to be sure, remove the lift pump, put your tongue on the suction pipe and pump the lever - if vacuum fails to form or vacuum forms but quickly falls away to no suction then dud.

Then injector leaks.

Not a likely issue, but...the sender unit in the tank is combined with the in and out fuel lines and is made of brittle plastic (as usual). There is an inspection hatch in the steel floor of the boot that gives access. You will need to lift the boot carpet (not too difficult), then cut a square in the insulating material (if not already there). Before cutting the hole try to judge that you are cutting it over the hatch in the steel floor. You can inspect the outer elements of the sender unit for cracks. Removing the big hold down ring will allow you to remove and inspect the sender unit and its plastic filter and other bits, and cleanliness of the tank - some say they have had trouble with algae bloom in diesel clogging filters, but I never have. And if you do go down this route use two spanners to undo the fuel lines or you WILL break the plastic moulding...and remember which is the fuel lift and fuel return line when reconnecting.

First thing I would check is the fuel filter, then the fuel lines and lift pump as others have suggested.