Hi folks
My tdi mk2 auto has developed a starting problem when left for a while like it's got air in the system and runs on three when it finally does run then after a while runs perfect I drove 170 miles non stop perfect, I've changed the filter checked the fuel lines for leaks put new clips on hoses etc.
Yesterday I removed the tank pump and cleaned the gauze on the bottom which was solid with black crap and flushed the pump through etc and put it back
there's a little improvement but still like it's got air in the system when starting.
could this blockage have weakened the pump and slowed the priming process?
Could be a number of faults causing that.
1 camshaft sensor failing,have you had a code read done?
2 injector seal leaking causing fuel run back.
3 tandem pump leak causing fuel run back.
4 thermostat valve seals on fuel filter causing fuel run back.
Do you park facing uphill?
Could try fitting some clear fuel lines between filter and engine see if gets air bubbles when left parked. Or clamp fuel lines from tank to filter just by where they enter the filter see if that helps. Just make sure you only do it to try a start then remove them.
Could clamp the fuel lines
I've fitted another non return valve between the tank and filter to see I this helps
I park it on flat ground the new valve has eased the issue slightly eg it's not running on three when started just sluggish starting but not lazy it's a new battery and alternator
Certainly sounds like a leak somewhere causing run back if non return has helped.
Have you got vcds? Sounds like could also have a lazy starter,the PD needs approx 250rpm when cranking before injectors fire if you have vcds can check measure blocks see what cranking speed is.
I'm taking it down the local garage to plug it in he said he would do it for a tenner, where is the crank sensor located ?
Front of the engine at the gearbox end near the flywheel/ drive plate. If you put 'crankshaft sensor' into the site search you should get a few posts come up relating to it.
EDIT: What I posted relates to the diesel, but your profile says you've got a V6 as well!
Cheers, does the diagnostics pick up intermittent faults with the relays eg 109 etc?
I would say not because relay 109 faults would kill the power to the whole engine management system, therefore no faults would be recorded!
Fingers crossed it's a sensor fault!
Right no fault codes recorded (sorry its been a while mega busy at work)when starting from cold it starts ok but runs a bit rough on tickover for a few seconds then picks up fine and then you drive for half a mile then cuts out and is a pain to start but fine after that!!
Air in fuel system I would think,try fitting some clear fuel line between filter and engine so you can see if any air is getting in.
when we had tdi had a similar thing, turned out to be the o ring seal on the fuel filter, got a new assembly from ebay of the plastic section that the fuel pipes push onto and needed a real good push to seat it on the filter, but it cured a very similar problem that had bugged me for years !
got the info from local bus depo mechanic who i knew as it was a common thing on the buses.
I'll try that out cheers :)
Yes the thermostat T piece can be a common problem with drawing in air,especially if non genuine filter is fitted. But injector seals and tandem pump are also other common problems.
Personally I found fitting clear fuel pipe as temp measure enabled me to see air bubbles in system,I then clamped some pipes overnight to narrow down source of air ingress.