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2.4 Diesel 'Misfire'.

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saljo View Drop Down
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    Posted: 04 Jan 19 at 10:15
Hi,

Hope someone on here can help. We've been trying to solve this problem but no luck so far.

The vehicle, a camper, has the VW (Volvo) D24 2.4 6 cyl non turbo
diesel. 184,000 miles and used with care over the past 24 years of our
ownership. Annual oil/filter changes and fuel filter changes. No veg
oil ever used. Slow warm ups before using higher revs.

Symptoms: Engine runs smoothly at low revs, up to around 45mph in top &
from 50 + also smooth. Runs rough between 45mph & 50mph, just
like a misfire on a petrol engine. Same symptoms for similar revs
in the lower gears, so its rev rather than speed related pointing to
an fuel issue. Particularly noticeable when you hit the 'bad' spot going up hill.

No smoke when warm. Symptoms came on over a two day period but
haven't got any worse.

Performance, such as it is, is about the same as ever and MPG again
pretty much the same at 27mpg. Engine sounds ok when running smooth.
ie, no nasty mechanical noises. Same when 'misfiring'.

What have we done so far?

   - Injector pump changed for recon unit with 12 month guarantee.
   - Injector nozzles professionally cleaned.
   - Injection pump timing checked as ok.
   - Fuel filter changed.
   - Fuel system bled several times, no sign of bubbles in the
     supply pipe to the injection pump.
   - Vehicle run from separate fuel supply to eliminate any fuel
     pipe issues.

Local diesel expert (well thought of) is mystified and we are getting
poorer by the day!

If anyone has come across this before, or has any ideas, I'd be grateful to hear.

Regards,

Saljo.
saljo
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tellytubby View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tellytubby Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 19 at 12:04
Interesting problem as there is little else to look at that has not been changed / checked already.

Despite all this work have the symptoms remained exactly the same?

Given that most of the fuel system should be good thene the only remaining thing that could be affecting the fuel delivery would be the actual timing gears in the engine but this would be a long shot.

Are you convinced this is a fuel delivery issue - does the engine continue to pull strongly despite the "misfire"?  You say the problem disappears at 50+? If it does keep pulling then the issue could be engine / gearbox mounts , propshaft bearings or similar.

Vince


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AndyT View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyT Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 19 at 15:58
I'm thinking the same as Vince, does the misfire occur if you rev the engine out of gear?.

LT28 1979 2.0 Pampas Nevada Camper LPG 93K, 1980 T3 A/C Camper 98K,1994 RRC 3.9 LPG 120k , 1998 Audi A6 Est 2.5 V6 diesel 127k

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saljo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote saljo Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 19 at 19:41
Vince/Andy,

Many thanks for your speedy response. I hadn’t considered engine/gearbox mounts and will check these when I get the LT back on Monday.

The ‘misfire’ gets progressively worse as I go up through the gears. As it’s in a relatively narrow rev band you drive through it quickly in 1st & 2nd where it’s pretty much unnoticeable, more obvious in 3rd and definitely an issue in 4th & 5th. The engine seems to pull through it ok then gradually smoothes out at about 47mph and by 50mph it’s gone. So I can drive it all day on the motorway with no problem provided I can keep the speed up. Mixed single carriage driving in a hilly area is a real challenge!

There has been some improvement in power but I’ve put that down to new injector nozzels & pump – the rough running is pretty much the same.

No sign of the problem increasing the revs in neutral - it only occurs when it’s under load. We’ve ruled out prop shaft in-balance as it’s rev related. So, yes maybe something to do with the mounts/chassis.

Thanks again for your thoughts. If we find it, I’ll post the cause.
saljo
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AndyT View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyT Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 19 at 21:43
Have a good look around the drivetrain underneath, it's possible that something is touching the bodywork and causing the vibration you feel. Had this on an Omega and it was the exhaust but only under load.
LT28 1979 2.0 Pampas Nevada Camper LPG 93K, 1980 T3 A/C Camper 98K,1994 RRC 3.9 LPG 120k , 1998 Audi A6 Est 2.5 V6 diesel 127k

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