has it been staring me in the face all along?

[turbopete]

sorry to keep banging on about this folks, but i really need to sort this starting problem out. i spent most of the night laid awake thinking about this and it occurred to me that ive had suggestions that the fuel pressure may be low, hence the suggestion to change the overflow/pressure relief valve on the injector pump.

what would happen if the LIFT pump on the side of the injector pump failed or lost most of its efficiency? last time i saw this (on a petrol car) it didnt start too well but seemed to run ok, but what about on a diesel? could the injector pump suck enough through to run with a lift pump thats not pumping as much as it should?

also the 'injector rattle' my car has, gets worse when hot than cold and slightly more noticeable (to me) after being driven hard. if i leave the car idling long enough i sometimes see a little cloud of smoke then the injectors go quiet (or at least much quieter!)

on top of this, if i hold the car (out of gear) at around 1500 rpm, i can feel what seems to be a very slight misfire. could all this be related to a faulty lift pump?

im considering trying to borrow an electric fuel pump (from a car with an exterior pump, maybe a volvo 740 or an early xr3i) to (hoefully) tel me if a replacement lift pump will cure the problem, thinking it could be fitted in-line as a temporary measure at the rear of the car, where the rubber pipe from the tank strainer joins the metal pipe, and wired via inline fuse straight to the battery, with a joint where i could kill the pump and start it as required.

all advice/opinions are gratefully recieved. i dont want my beast to die just yet!

 

[Number_Cruncher]

If;

you see a reasonable amount of fuel going back down the return line to the tank

AND

you know the relief valve is OK

THEN

you know the fuel lift pump is OK.

 

[turbopete]

relief valve is brand new. looks like i need to borrow some clear fuel hose and see whats what on the return side then. the pipe t the relief valve has got stained inside. no idea what previous owners ran it on, but i cant see through the pipe!

 

[turbopete]

ok just been out and disconnected the return pipe with the engine running and theres plenty of fuel there.

i cant see how this "overflow valve" as mercedes call it, does anything really! i can blow through them, both the old and the new 1. it seems more like a restriction than a relief valve as i was thinking of!

looks like im going to need the help of a specialist here then :cry::cry::cry:

i cant think of anything else it can be! if its getting air in, it has to be coming in at the pump. theres nowhere else for it to get in. it does seem to start better after very short periods of standing if that tells anyone anything, but still not right. i took some videos but they wont load up on here.

also at certain rpm there are tiny bubbles seen in the fuel. is this anything to worry anout? just 1 every couple of seconds. dont know if this sheds any light on things?