M51 engine idle issue HELP !!

Sasizza · Nov 2, 2014

HELP NEEDED PLEASE
I have a 1998 p38 dse man M51 engine done 68k miles.... It has developed a fault that no one seems to know how to cure.... As you come to a halt and the revs drop as they should, it misfires until it comes to a complete stop then settles back to running on all 6 cyl....
It is not injectors and its had a new inj pump.... No fault codes are apparent when diagnosed at standstill and if diagnosed when driving have had fuel actuator ( in the inj pump which is now replaced ) and lift needle in inj 4 which governs the idle and is also new....
Has anyone had the same fault ??? Joe

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Datatek · Nov 2, 2014

Sasizza said:
HELP NEEDED PLEASE
I have a 1998 p38 dse man M51 engine done 68k miles.... It has developed a fault that no one seems to know how to cure.... As you come to a halt and the revs drop as they should, it misfires until it comes to a complete stop then settles back to running on all 6 cyl....
It is not injectors and its had a new inj pump.... No fault codes are apparent when diagnosed at standstill and if diagnosed when driving have had fuel actuator ( in the inj pump which is now replaced ) and lift needle in inj 4 which governs the idle and is also new....
Has anyone had the same fault ??? Joe (

Worth looking at the in tank lift pump to see it's working, at 68K miles it should not have needed a new injection pump.
Has the fuel filter been changed recently?
Was the replacement injection pump a re-con unit or just secondhand?

Sasizza · Nov 2, 2014

Thx for that will check the lift pump.... Inj pump is brand new direct from bosche

Datatek · Nov 2, 2014

Sasizza said:
Thx for that will check the lift pump.... Inj pump is brand new direct from bosche

I hope whoever fitted it got the timing right.

Grrrrrr · Nov 2, 2014

Only 68k miles? That's nothing. Did he miss a digit off?

Surprised anything needed changing at that mileage. Has it had any biodiesel or similar put through it?

wammers · Nov 2, 2014

Diesels don't misfire unless there is a duff injector or a sticking valve.

Sasizza · Nov 3, 2014

Have been told its the low speed idle valve or sensor, will post the results to help anyone who may have the same problem ....

Datatek · Nov 3, 2014

Sasizza said:
Have been told its the low speed idle valve or sensor, will post the results to help anyone who may have the same problem ....

There is no low speed idle valve or sensor

Take it somewhere that know what they are talking about.

JohnnyCrash · Nov 3, 2014

Datatek said:
There is no low speed idle valve or sensor
Take it somewhere that know what they are talking about.

Ah beat me to it! lol

JohnnyCrash · Nov 3, 2014

Sasizza said:
HELP NEEDED PLEASE
I have a 1998 p38 dse man M51 engine done 68k miles.... It has developed a fault that no one seems to know how to cure.... As you come to a halt and the revs drop as they should, it misfires until it comes to a complete stop then settles back to running on all 6 cyl....
It is not injectors and its had a new inj pump.... No fault codes are apparent when diagnosed at standstill and if diagnosed when driving have had fuel actuator ( in the inj pump which is now replaced ) and lift needle in inj 4 which governs the idle and is also new....
Has anyone had the same fault ??? Joe (

Have the same issue, if you hold the RPM at 1000 while using the left foot on the brake pedal it's fine

soon as you let off the gas pedal idle bounces (like a petrol misfire) then cuts out :-/

I'm not using my RR at the min but I'm guessing it's the in tank pump causing my issue as no fault is logged on the Nanocom, and I replaced my pump with a cheap and cheerful eBay special

wammers · Nov 3, 2014

Sasizza said:
Have been told its the low speed idle valve or sensor, will post the results to help anyone who may have the same problem ....

There is no idle valve. But there is an idle switch on the throttle pot that engages at a low throttle position. That engages idle control were the idle fuel is controlled by the ECU via the quantity servo, according to engine load speed, extrapolated from CPS sensor readings.

JohnnyCrash · Nov 17, 2014

JohnnyCrash said:
Have the same issue, if you hold the RPM at 1000 while using the left foot on the brake pedal it's fine

soon as you let off the gas pedal idle bounces (like a petrol misfire) then cuts out :-/

I'm not using my RR at the min but I'm guessing it's the in tank pump causing my issue as no fault is logged on the Nanocom, and I replaced my pump with a cheap and cheerful eBay special

following up from this, today I removed the in tank pump and set up a bench test, and seemed to run fine. This is not really what I wanted as I suspected the pump was causing the idle issue.

Datatek · Nov 17, 2014

JohnnyCrash said:
following up from this, today I removed the in tank pump and set up a bench test, and seemed to run fine. This is not really what I wanted as I suspected the pump was causing the idle issue.

Generally, they will idle fine with a dead in tank pump especially if the tank is more than a quarter full.

JohnnyCrash · Nov 17, 2014

Datatek said:
Generally, they will idle fine with a dead in tank pump especially if the tank is more than a quarter full.

will replace and move onto the next thing, the FIP :-(

Datatek · Nov 17, 2014

JohnnyCrash said:
will replace and move onto the next thing, the FIP :-(

Maybe the fuel quantity servo end stop is worn. Been reported a few times including a repair.

JohnnyCrash · Nov 17, 2014

Datatek said:
Maybe the fuel quantity servo end stop is worn. Been reported a few times including a repair.

can you buy just this part of the FIP??

Datatek · Nov 17, 2014

JohnnyCrash said:
can you buy just this part of the FIP??

No idea, Wammers is the injection guru. I think the guy that repaired it either turned the brass stop post round to present an unworn surface, or sleeved it, can't remember which.

JohnnyCrash · Nov 17, 2014

Datatek said:
No idea, Wammers is the injection guru. I think the guy that repaired it either turned the brass stop post round to present an unworn surface, or sleeved it, can't remember which.

I've a spare FIP I can pick up tomorrow to strip for parts, and I'll have a dig around on here for the thread

Datatek · Nov 17, 2014

JohnnyCrash said:
I've a spare FIP I can pick up tomorrow to strip for parts, and I'll have a dig around on here for the thread

There were photo's of the notch worn in the stop post.

M51 engine idle issue HELP !!

Sasizza

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Datatek

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Sasizza

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Grrrrrr

Technician, Bodgit & Scarper Ltd

wammers

No longer with us, RIP

Sasizza

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Datatek

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wammers

No longer with us, RIP

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