AIr in Fuel Line

This is a follow up to a previous thread i've listed on here. I have been trying to bleed the fuel line of my 96 disco with no success in fact it's getting worse and now stalls out at junctions and islands etc. Can anyone out the help with simple step by step instructions as to how to bleed the system properly. I've tried as suggested having the engine running and cracking the bleed screw but this is making things worse.

Hi,

You may have tried this already,

1. Locate the screader valve on the fuel rail it looks like the kind of valve you find on the tires.

2. Remove the valve cover, get a rag and press down on the valve with a flat headed screw driver. BE AWARE of fuel spraying out of the valve under pressure, the rag is to stop fuel leeking over the engine.

3. This should remove any air from the fuel lines, once finished, put the cover back on the schreader valve and re pressurise the fuel system by turning the key to ignition 1 / 2 (or until your lights come up on the dash), you will here the fuel pump run then stop. You should be ok to start the engine.

Hope this helps, but whatch your eyes when you press the valve.

Thanks

John

A 300tdi is self purging of air in the fuel lines. You don't need to bleed anything to get rid of air, just run the engine. It also has a mechanical fuel pump not an electric one.
If you constantly have air in the fuel lines, you have a leak in the pipework somewhere which is allowing air to be drawn in by the fuel pump.
The common suspects are the pipe connections to the fuel sender in the top of the tank corroding, the fuel pipes themselves corroding, the fuel sedementor body perforating or the seals leaking,the fuel filter bleed screw leaking, the bleed pipes between the injectors perished.
If you work thro that lot you should see an improvement.

if the 300 tdi is a self purging system is there a process that does a system flush??? some say ignition to position 2 and pump the throttle 5 times in the first 10 seconds and then wait!!!! is this the case or is it myth????

Cheers Dean

In all the years I've had mine after replacing fuel filter and /or cleaning out sedimentor all I do is switch engine on and let it idle for a few minutes.
Then drive it as normal.
Never had any bother.
Switching the ignition on and off etc does nothing as far as purging air is concerned.

Autos have the drive by wire EDC system, which may be different, but as far as I know, the 300 Tdi is a totally mechanical system. As another poster has said, the system is largely self bleeding.

If you do need to bleed, first loosen bleed screw on top of fuel filter, and then either manually operate fuel lift pump (recommended), or crank engine until no more air comes out. Engine should now start. If you want, you can slacken the injector pipes at the injector join as well, and bleed up to there. Be careful if you do this as the fuel is under high pressure.

The advice from another poster about key in position II sounds like the Td5 bleeding sequence, but I don't think it's exactly what he says.

For your problem, the Tdi uses a low pressure system, but the fuel lift pump on the side of the engine effectively sucks fuel out of the tank. Therfore, if you have a leak on any of the pipes from the tank to the pump, you are going to get fuel shortages, so I would suggest following these back all the way to the tank, and looking for small leaks.

The Disco 300Tdi has a fuel sedimentor under the rear wheel arch - the seal in that should be replaced when the sedimentor is cleaned - it could be something like that. I had a problem when I had a Tdi in Zimbabwe - got to quarter tank and vehicle lost power. Turned out that the poor quality fuel had blocked the fuel pickup in the tank - as the level dropped, theer was a smaller and smaller hole for the fuel to come through.

Hope that helps!
Cheers!

If you can get the engine running then just crack open the bleed screw on fuel filter to remove any trapped air, works for me that way anyways

Are you sure that the lift pump is working,otherwise if it is running just of the injection pump,they will pull air rather than fuel,from any leak-the same applies if the filter is blocked

I had exactly same problem untill yesterday,air getting into fuel system. I had to cut a fuel line to remove sedimenter, when reconnecting i warmed pipe with heat gun & pushed it on to connector, same as all other connections. Started engine, checked for leaks, all ok or so i thought!
I found out that fuel pipes come with these joints factory fitted, in my case although no fuel leak, the joint was sucking in air , fitted a hose clip problem solved.
I have also fitted a section of clear fuel pipe between lift pump & fuel filter to detect any air in system in future.
Hope this helps.

docdean said:

if the 300 tdi is a self purging system is there a process that does a system flush??? some say ignition to position 2 and pump the throttle 5 times in the first 10 seconds and then wait!!!! is this the case or is it myth????

Cheers Dean

Click to expand...

Hi Dean, that advice refers to TD5 not TDI 300.

also the pipes rot where they enter the tank and the sediment filter inside the rear wheel arch if this is your probelm you will never get the air out
as said above they are normaly very easy to get the air out when i change the filter on my old 200 and the works 300 i just swop the filters and start it up works every time

Right an update guys, Yesterday i replaced the fuel filter turned her over and let her sit a little while before taking her for a run. Came to start her this morning and still the same problem. I managed to speak to a local mechanic who said to crack the injectors and if any of those where a problem then when cracked no difference would be noticed. Cracked all four and each one in turn had a noticable change to the engine tone. I seem to be getting air in the system from somewhere and it's doing my head in. I've followed the line right back to the tank and can't see any leaks. Not even a slight drop of fuel leaving the system anywhere from tank to injectors. If my lift pump was not funtioning how would i test it???? short of buying yet another part to try ????

You 100% sure air is getting in?
If so, have you tried running from a jar of diesel? If you do this at various points in the fuel line (before sedimenter, before filter, before injector pump) through process of elimination you can work out where it's coming from.

Does the problem affect only the first start in the morning? If so, do you park with the engine higher than the rear? If so, it's likely that the internal diaphragm of the fuel lift pump has gone, and that is letting air in which allows the fuel to drain back into the tank.

I had that problem in Zimbabwe with my 300Tdi - had to park pointing downhill until I was able to replace the pump - they're cheap and easy to replace.
Cheers!

If the lift pump isn't working, and if running just off the injection pump, would it pull air into the fuel system????? is there a way of testing the lift pump???? the fuel filter is brand new and the injectors all function properly. I'm gonna drop the sedimentor tomorrow morning as another elimination step. Failing that i think i'll be pulling all the boot floor up to get to the fuel pump in the tank. It's certainly been a steep learning curve. Failing all this i've got her booked in at a garage for next tuesday cos i'll have ran out of ideas. Any other suggestions will be appreciated in the mean time.

Graham Carter, Bessie (as my kids have named her) is usually parked with nose down hill as my house is on a sloped road.

gR@HaM, I'm not 100% sure but it seems that way. I've bled the fuel filter a few times and when i changed it yesterday the old filter was almost empty. Something somewhere is either letting air in or there is something pushing the fuel away.

As martinhollings says check the condition of the two steel elbows on the top of fuel sender in the tank. The elbows corrode and perforate letting air in. Common problem, yours should be just about due.
Lift access panel in rear of boot floor to access.

had you cleaned the sedimenter prior to this problem? the first time I did mine I put it back on and the seal had twisted and it let air in the system :doh: nice easy fix though.

thanks nicedayforit. I think ill swap my elimination order around and check the elbows before i have a crack at the sedimentor. If i have time i will do both but working late shift this week so one thing at a time. If i do find the elbows leak i think a temp fix of good old fashioned gaffer tape will have to do until i get replacements sourced

I've not had the sedimentor off yet, that is second on my list of things to check, first being the elbows coming off the tank pump.