Fuel Problems

[wizard101]

A few weeks ago the Mav started to run a bit rough, coughing blue smoke, low power etc. Ah, I thought, fuel. So I changed the main fuel filter - ran sweet as a nut for about 10 miles and then back to rough. I had read about the gauze filter in the Injector pump banjo, so read the procedure in the Download section (thanks to the Author) and got stuck in, Two surprises - no spring or filter under the banjo and also no fuel present when I slackened the banjo off. Surely there should be fuel present in the banjo at all times - not air. This might also explain why the engine is slow to start - I have to turn it over for 15-20 seconds before first cough. But where does the fuel go? I had thought that there was a non-return valve somewhere to stop it draining back into the tank, and in any case the fuel can only run out if there is some way for air to get in.
As I obviously don't really understand the workings of the fuel system properly, can someone please shed some light!
Thanks
Peter

 

[iandouglas]

hi wizard 101
went to clean mine out no spring or filter. cannot recall much fuel spillage on release of banjo bolt.
have you tried priming the hand pump on top of the filter housing. both before starting from cold .to see if it starts quicker.
are you confident the heater plugs are working?
when the engine is running rough have you tried using the hand primer
to see if it improves rpm., if it does it sounds as though its pulling air in somewere.
these trucks have a reputation for fuel pipes rusting into pin holes nr tank.plastic replacement usual option.
rgds.iandouglas

 

[rustic]

Hi Wizzard, quite a few posts on this,
1. I changed my fuel filter and caused more problems than it solved because air was getting in past the seal. I replaced the filter with a better quality one and was soon ok.
2. If the tank vent on the filler is blocked it can cause a partial vacuum that can suck the fuel back. Sometimes I take my cap off it lets air into the tank...
3. Return pipes on the injectors can let in air.
4. rusty fuel lines
5. Fuel tank fault even.

If you do a search on few of these topics you might get some ideas.
If you originally had smoke and rough running at the start it could be the heaters, then if it got worse after the filter, then check that.
hope this helps
best regards, Rustic

 

[wizard101]

Thanks to iandouglas and Rustic. Quite a few ppoints to check there. I started at the back end as I had suspected a lingering smell of fuel but had put it down to spills when filling up. Lifted the cover in the floor of the load area and there is definately fuel on top of the tank. The whole thing is a bit of a nasty mucky mess so difficult to see exactly what is going on but for sure there is fuel where there should not be fuel - thanks for the tips about rusting fuel lines.
All I need now is some decent weather so that I can spend a day under the truck - don't fancy dropping the tank in the present arctic conditions!

Comments about using the hand pump to prime - yes it does make a difference. Fuel filter seems tight - I put a Fram filter in so don't really expect a problem with the filter itself. All pipework on the engine looks OK including the injector return pipes. I have never noticed the fuel tank sucking air in when I open the filler cap so assume the tank breather is OK - though it is certainly covered in a thick layer of crud.

Are there any tricks/points to watch in dropping the tank?

Thanks again to all
Peter

 

[JonathanM]

Re fuel injector return pipes, mine perish quite regularly, yet I've never had a symptom of air in fuel, I thought that the fuel return pipes simply put the un-injected idesel back into the fuel system, ie didn't effect running becuase the injector has already had its dose of fuel?

They are really easy to spot if problematic, becuase they tend to pee diesel all over the engine!

 

[iandouglas]

fuel problems

hi wizard 101.
sounds as though you are on the right track with fuel lines .just cut out the rusted erea and fit rubber replacement. a couple of tye raps will be enough to seal it.
sorry never dropped fuel tank. can you get at any nuts and bolts with WD40 or simular product .
only thing i can think of is to empty as much as you can out.
hope the weather improves soon.
dont you know some one with agarage.?
good look.
rgds.iandouglas

 

[Reton]

Having spoken to the Lucas diesel mechanic, have found out that the mini filter and spring under the banjo bolt can simply be removed. I have done this and the difference in proformance is substantial. For the first time i can feel the turbo working when i hit 3000rpm.