Now desperate for ideas! 300Tdi Overrun cutting out problem!

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crabots

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Nr Carcassonne, France (midway between Toulouse an
Hi, this is my second post for this problem and I desperately need some ideas/things to look for/check.
Briefly, the Disco runs normally in traffic (low engine speed/low throttle openings). On the open road, after driving at 50/60mph, if you take your foot off, the engine “dies” on deceleration. Jigging the throttle produces thick dirty grey smoke but it won’t pick up. When it eventually does (sometimes have to pull over first), then runs normally till next deceleration point…..Help!!!
( ps. Engine oil level has remained static for last 3000 miles+)
 
Hi again, I just tried something which I think may narrow the problem to the injector pump…Was driving at about 3500rpm (on straight road, no traffic etc.) and I switched off the ignition (and so pump stop valve). I didn’t touch the clutch but allowed vehicle to slow under engine braking until about 1500rpm. Then Switched on ignition and pushed throttle pedal and the vehicle pulled away with NO HESITATION and NO SMOKE! Could this point to a problem within the pump? Advance mechanism? Boost compensator? Loose drive pulley, or something else??? Please, if anyone has suggestions it would be appreciated. PS; This is a non EGR/ECD pump, Not "fly by wire".
 
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Thick grey smoke after overrun is oil burning, likely drawn in from the turbo bearing perhaps. It's hard to say exactly where the oil is from - bores / valves / Turbo since I don't know the condition of filters etc etc.

Grey smoke is ALWAYS oil ....

Bet the smoke looks like this >> Smoke
 
std non edc pump with just singal pump solenoid wire ?could be a pump issue but id want to check it has good air free feed to it by fitting clear plastic pipe between filter and front banjo on injection pump ,they are know for sucking air in at fuel sender under plate in boot floor pipes rot ,sedimenter (blocks and corrodes ) and poor lift pumps ,but because injection pump self bleeds not allways noticeable to start with
 
For it to be only diesel related I'd expect black or sometimes white, never grey smoke.

Black = too much fuel too little air
Blue / Grey = too much fuel sufficient air
Black / Grey = Lot of Oil
Blue = Traces of Oil
White = Unburnt fuel
 
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BenKenobi said:
Thick grey smoke after overrun is oil burning, likely drawn in from the turbo bearing perhaps. It's hard to say exactly where the oil is from - bores / valves / Turbo since I don't know the condition of filters etc etc.

Grey smoke is ALWAYS oil ....

Bet the smoke looks like this >> Smoke
Click to expand...
Hi Thanks for the reply. I hear (and see!) what your'e saying but surely any oil would be drawn past rings, tubo bearings, valve stems etc. whether or not the ign was on or off and both situations would result in smoke?? I don't get smoke if I turn off ign whilst decelerating from 70mph to 30mph then turning on and accelerating???
 
jamesmartin said:
std non edc pump with just singal pump solenoid wire ?could be a pump issue but id want to check it has good air free feed to it by fitting clear plastic pipe between filter and front banjo on injection pump ,they are know for sucking air in at fuel sender under plate in boot floor pipes rot ,sedimenter (blocks and corrodes ) and poor lift pumps ,but because injection pump self bleeds not allways noticeable to start with
Click to expand...
Hi, The disco always starts "on the button" and cruises for hours at 70-80mph up hill and down with no loss of power (just "cuts out" when decelerating to leave the Mway and smokes like hell if you try to "catch it" by jigging the throttle)
 
Then I am doubting here that it is thick / dirty grey smoke more like the blue grey which is a sign of overfuelling - the rack on the injector pump not closing down and flooding the engine so you would be more blue/grey potentially white. I don't know the specifics of the 300TDi injector pump I'm afraid.

Do you still have the EGR fitted ?
 
its a rare fault and could be issue with the pump ,but since you can only know that by swapping it or having it bench tested ,worth trying simple firstis egr blanked ,stuck egr can give similar sympotoms ie poor running lots of smoke
 
BenKenobi said:
Then I am doubting here that it is thick / dirty grey smoke more like the blue grey which is a sign of overfuelling - the rack on the injector pump not closing down and flooding the engine so you would be more blue/grey potentially white. I don't know the specifics of the 300TDi injector pump I'm afraid.

Do you still have the EGR fitted ?
Click to expand...
Hi, I was leaning to the overfuelling idea myself as the mpg is not brilliant on long, fast runs and the dipsick hasn't moved for 3000+ kms. There is no EGR or sedimenter fitted. I don't know too much about diesel pumps but wondered what might make it overfuel? "The rack not closing down"?? Is this something I could check or eliminate?
 
I'd need to understand more than I do about the injector pump the 300TDi is using. There is no really consistent way to handle certain things like overrun on diesels in cars or trucks - the trick with a diesel is detecting overrun in the first place.

Some use mechanical means, some a vacuum diaghragm, some electrical solenoids, some don't use anything. If your injector pump is closing down to idle levels of fuel delivery then I am wondering

a) What your fuel pressures are like
b) What your compression is like
c) What state your injectors are in

Running without a sedimenter is a singularly bad idea, I know people do but it can prove an expensive test. Water will destroy both pump and injectors because of the pressures involved - scoring and pitting, any rust or sediment from the tank and it is even worse.
 
if pump was sticking it wouldnt idle but rev at that position ,you can test an injector by fitting it to pipe upside down ensuring you go no where near spray
 
That's one way but not exactly an accurate way to test the delivery volumes.

It could be that the pump isn't closing down to idle properly or quickly enough at higher rpm even though the throttle has been released - do mechanical 300tdi pumps monitor boost pressure?

I'd check the throttle cable and associated adjustments as a starter, disconnect cable and see how cable and pump 'feels' then connect and properly adjust. Could be dirt in the pump or damage, how bad is mpg when you say it isn't good.

I take it that your intake system is clean - intercooler cleaned out recently, airfilter OK no leaks in any fuel pipes ? ...
 
obviously not testing delivery volumes but lets you know if its just pouring out at idle , true condition of pump and infectors would only be found off the vehicle at a specialist ,the pump is shutting down otherwise revs would stay high as with sticky badly adjusted cable ,egr pot is connected to throttle shaft
 
Just thinking out loud, don't know a whole lot about 300Tdi's, learning fast about TD5's, trained on much bigger Diesels a very long time ago before all the electricery - actually at the dawn of electricery control ..
 
OK, Never any smoke emitted at all during overrun so I would normally discount valve guides, turbo bearings...However, if vehicle is allowed to decelerate until stopped with the engine "cut out", it will not turn over on the starter. I have to wait 5-10 minutes, then it will turn over (but sluggish) and start, with the now familiar cloud of smoke. After this it will run as before. Battery is new and cold starting is never an issue.
Whilst "thinking aloud", I'm tempted to imagine fuel swilling around in the bores, causing high compression and so preventing the starter doing its job (bit like water ingress when wading!?)....then seeping past the rings until level reduced enough to turn over....I'm probably in cloud cuckoo land????
 
that would give clunk and stop as you turned engine over does it ,or not turn over at all ?, what pump is it single wire solenoid ,3 wire ,edc ?
 
The valve guide type rules only really apply on engines that require manifold depression for operation - petrol - there shouldn't be any of any significance in a diesel, so whatever oil is getting in is being pumped in or via the bores but that would imply overfilling which has already been disregarded.

If it is suffering hydraulic lock but restarts after a time that means that whatever causes the lock must be draining away - yet the sump level isn't rising - or is it is oil being consumed and replaced with diesel? if there is a lock the 'liquid' must be going somewhere or there isn't a lock and it is something else /(though what that may be is a bit of a mystery).

When it is in this 'locked' state can you turn the engine over by hand? if yes it isn't locked ...
 
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