Overrun/running on

OK - hopefully someone can help on this one. Been trawling these boards and the web all afternoon and can't find anything which looks similar.

I've got a 51 plate TD4, which is running for a couple of seconds after turning the engine off...worse, it's not all the time (although it tends to be when the engine's warmer rather than colder).

It doesn't seem to be burning oil, there's no other faults I can see/hear and there's no smoke coming from the tail pipe (so pretty sure it's not the turbo seals....I hope ).

I've done the EGR and the crank case breather (the old breather was oily but not too bad). There's no running/starting problems either (turns over even on freezing cold days without waiting for the glow plugs)

I did have the management light reset a couple of weeks ago (fuel rail pressure sensor - will post the actual codes later when at home)...the garage at the time advised to see if it comes back (which it hasn't). It "feels" like after you've turned the ignition off, it's just burning off the last of the diesel in the pipes (i.e. it's not rough and it's always no more than 2-3 seconds).

The only other think I can think of that's been done at the moment is the seal on the fuel tank lift pump (the pump wasn't even bolted down when I got the car - that was 1/3 of a tank of diesel wasted)....could it be that this pump is still running and causing the problem, and that by removing and refitting it, I've uncovered an underlying problem? It's around about the same time as the problem started, but can't see that I've done anything there.

Any ideas on any tests I can do to find the cause of this one?

Can't speak for the TD4 but there's usually a solenoid activated fuel valve either in the fuel line or on the high pressure pump on common rail injection systems, I would suspect this valve is slow to close, this valve used to be a common fault on some early Cummins engines.

it sounds as though someone has had those problem with it before and yes it would be getting fuel from some where to carry on running

Thanks teddywood1 and nickcc - I'd had the thought that it might be a solenoid closing slowly...my next task is - where the heck is it?

To add to the problems - the tailgate regulator cable's just bust tonight as well .

there's a fuel pressure regulator .. wired to the ecu .. on the h.p. fuel pump
a.f.a.i.c.s that could be the gizmo that cuts fuel off when the ignition is turned off

page 19/20 :
http://www.rover-club.net/graphics/manuals/16/m47r_diesel.pdf

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shouldn't the injectors close when engine is turned 'off' ?

Thanks hd3 - that's a useful manual to have (now got a copy this end ). Still finding my way around the engine at the moment, been on petrol engines for the past several years and finally decided to grow up and slow down

I too would have thought the injectors should close once the ignition is turned off though, which is the bit which is worrying me...unless the injectors themselves aren't closing/seating properly?

I had the thermostat done last week - I don't know how long it had been running cold (I've only had the Landy for four weeks) - could it be that it's been running "cold" for a while and carbon's built up around the nozzles, stopping them sealing properly...in which case maybe a little snake oil might be the solution?

EDIT: Forgot to put the OBD codes on I promised earlier.

P1195 - Pressure control valve
P1190 - Rail pressure control
P1612 - Diagnostic light malfunction (really?)

Looking at the second one - the rail had a problem with pressure. My understanding is that it's supposed to maintain a constant pressure while the engine's running. Could slightly open injectors be causing a loss of pressure on the rail (although the light hasn't come back on yet two weeks after reset)?

Yes, looks like the solenoids in the injector close and stop the flow of fuel when the ignition is switched off. Looks like one of the injector solenoids is slow to close allowing whatever fuel is still under pressure to pass and cause the slight run on.

have seen it before, normally caused by solenoid valve on high pressure pump.

booboodag said:

have seen it before, normally caused by solenoid valve on high pressure pump.

Click to expand...

OK - something else to look at, thank's for the pointer and thanks everyone tonight for your help so far.

Something I don't understand though - it only "appears" to happen when the engine is warm...any ideas?

it only "appears" to happen when the engine is warm...any ideas?

Click to expand...

only that heat expands metal ..
and the h.p. pump pressure regulator .. and the injectors .. are needle valves

maybe over the years .. a contaminant / by-product .. has built up on a needle or its seat ..
needle gets hot .. expands .. and won't close as fast as it used to ..
maybe the stickiness is in the solenoid electric gubbins ( hp pump pressure regulator )

with lubricant low in regular modern diesel fuel .. gotta cause some wear and tear
i.e. with needle valves ..

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edit : 15th dec.
**correction ** .. h.p. fuel pressure regulator is a ball and spring type valve
see page 62 of that .pdf document
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dunno .. that's the only theory i can come up with at this hour of day
don't know if it ( theory) holds any water .. or leaks like a buckshot riddled pop can ..

'n i don't know what happens regarding the ecu when the ignition is turned 'off'
i.e. will the injectors still get the 'open-close' signals if the crank is turning ?
hp pump is mechanical .. so that might still try and pump a remnant of fuel
when the crank turns ..

and there's probably still some fuel under low pressure after the lp pump is turned 'off'
.. for a second or two ..
i.e. between the lp pump and hp pump intake ..

sort of leaves the hp pump fuel pressure valve as the likely culprit ..

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trying to remember what would cause a carburated petrol engine to do the same
even though the spark ignition was off ..
cylinder heat ? .. glowing carbon deposits ?

but that setup still gives the opportunity for fuel/air into the cylinders ..

unlike electronic operated injectors .. in theory ..
unless the injectors would still operate despite ignition being 'off'
( or dribbling injectors with worn needles )

wish i knew just what commands the ecu gave out .. and when ..
and under what conditions ..

~~~~~~~~
off-topic .. but i've just noted the in-cab diagnostic connector ..
is '12v-live' even though the ignition switch is 'off' ..
( if i've read the vehicle elec. schematic right .. and the 'scangaugeII manual as well )
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it's past midnight .. out of ideas for now

hd3 said:

only that heat expands metal ..
and the h.p. pump pressure regulator .. and the injectors .. are needle valves

maybe over the years .. a contaminant / by-product .. has built up on a needle or its seat ..
needle gets hot .. expands .. and won't close as fast as it used to ..
maybe the stickiness is in the solenoid electric gubbins ( hp pump pressure regulator )

with lubricant low in regular modern diesel fuel .. gotta cause some wear and tear
i.e. with needle valves ..

dunno .. that's the only theory i can come up with at this hour of day
don't know if it ( theory) holds any water .. or leaks like a buckshot riddled pop can ..

'n i don't know what happens regarding the ecu when the ignition is turned 'off'
i.e. will the injectors still get the 'open-close' signals if the crank is turning ?
hp pump is mechanical .. so that might still try and pump a remnant of fuel
when the crank turns ..

and there's probably still some fuel under low pressure after the lp pump is turned 'off'
.. for a second or two ..
i.e. between the lp pump and hp pump intake ..

sort of leaves the hp pump fuel pressure valve as the likely culprit ..

~~~~~~~

trying to remember what would cause a carburated petrol engine to do the same
even though the spark ignition was off ..
cylinder heat ? .. glowing carbon deposits ?

but that setup still gives the opportunity for fuel/air into the cylinders ..

unlike electronic operated injectors .. in theory ..
unless the injectors would still operate despite ignition being 'off'
( or dribbling injectors with worn needles )

wish i knew just what commands the ecu gave out .. and when ..
and under what conditions ..

~~~~~~~~
off-topic .. but i've just noted the in-cab diagnostic connector ..
is '12v-live' even though the ignition switch is 'off' ..
( if i've read the vehicle elec. schematic right .. and the 'scangaugeII manual as well )
~~~~~~~

it's past midnight .. out of ideas for now

Click to expand...

hd3 - know the feeling about past midnight - thanks for the ideas though.

My "training" was on early 20th century farm pumping engines, where the diesel would run happily without computers until the fuel was cut off (it was so simple in those days )...Hell so long as there was compression and fuel, they'd run, and run, and run......

I think for now the best bet is a solenoid somewhere, whether on the HP pump or one of the injectors (best at the moment is the HP pump....surely a duff injector would make the overrun rough unless it's all of them?)

My first port of call is going to be to stick some snake oil (aka two stroke oil) in the tank at the next fill-up at the weekend and see what happens. After that - I'll look at the HP pump solenoid. Whatever, it definitely appears to be fuel related rather than turbo seals or anything along those lines...and that's a big sigh of relief. It means (to my mind) that there's no hurry to sort it out (the engine runs fine apart from this)

Thanks to everyone for your help tonight. As I said in my welcome post - I'm a noob with Freebies (I'm more used to Toyota's - especially MR2's!, so reaquainting myself with a diesel engine, especially the way the TD4 is designed is a challenge), and apart from the tailgate window regulator snapping a cable tonight (already on order), there's not a lot wrong with the car thankfully (OK - I need to order a recon VCU ready for the snow, but I know where to get the from and can re-fit without any problems)

Thanks again

Wayne

Has the harness from fuel pressure sensor to ecu been replaced, could be the cause of the faults.

BigRog - you might have hit the nail on the head

Early days yet, but spent the day doing various jobs (replaced crank case breather with the BMW mod, cleaned the MAF sensor, replaced air inlet hose)...as if by magic the over-run has stopped. I'm just wondering if moving it while I changed the breather has done the trick.

Following last year’s adventures of ridding the FL1 TD4 back from its smoking habit, and after much frustration along the way, it was successfully MOT’d last October. But shortly after getting the MOT a new niggle emerged, being that the engine would occasionally run on after switching off, illuminating the MIL light. Initially I was concerned that in fitting the new turbo core I’d not primed it enough before running, so was back to a leaky turbo seal problem. But when I checked with the Hawkeye, it was reporting 'P1195 Fuel Pressure Valve Power Stage Failure’.

Seeing that there was no significant oil in the induction hoses was a slight relief, as I was in no hurry to strip off the turbo again, so it got me hunting around on here for thoughts on if this could really be a fuel pressure regulator issue. So I tried swapping back in the old regulator I’d fitted as part of my other journey of eliminating the smoke. And hey presto, it seems to have worked. For a couple of months now, and plenty of journeys I’ve had no overrun or P1195 messages appear.

So maybe there is something in HD3’s notion that the injectors still receive signals while the crank is moving. So if the regulator is not going to the position where it sends fuel back to the tank, to relieve pressure, it means the common rail remains under pressure because the mechanical HP pump is still turning, allowing fuel to still go via the injectors, until the LP pump's output pressure is spent, and the HP pump can no longer do its thing.

Anyway it works. And touch wood will carry on that way for a while. ( I still have a Stanley blade just in case of an emergency )

My L Series diesel is not common rail and uses 'simple' injectors - so if the pump outputs fuel, it will be injected.

However, the TD4 is common rail and the injectors need to be told to inject fuel by the ECU - not because there is pressure from the pump. So the pump could produce as much fuel as it wants, if the ECU does not tell the injectors to open, no fuel will be injected.

But, the injectors are known to leak!

I thought the same about the injectors, and instinct made me think the worst, that it was oil causing the run on. But a couple of posts buried on this site suggested the injectors are controlled by the ECU to run for a moment after switch off to help release the common rail pressure, and stop fuel leaking Into the cylinders. https://www.landyzone.co.uk/land-ro...fter-ignition-turned-off.262543/#post-3156157 post #14.

If this is what really happens, I’m not expert enough to know. It seems plausible though. But with the fault code relating to the fuel pressure regulator, and me changing the regulators seems to have put a stop to the running on I was having.