Technical Management light on code P0638 2009 2.3

[tidewatcher]

The waste gate is not seized, you can get a 16 m open end spanner onto the little lever that moves the waste gate and it is free to move though the spring pressure is quite high. It operates only on pressure there does not appear to be an electrical connection. I have now driven the van for four hundred miles using top grade diesel and the hunting and lumpy tick over is still there. A real pain in stop start traffic. No management light has come on. I started the van again today and the sequence goes like this.
Engine starts and ticks over fine for three to four minutes then the hunting begins.
If I increase revs then slowly close the throttle it ticks over smoothly but another blip will bring back the hunting.
I removed the vacuum pipe from the the solenoid to the egr valve, no change.
I felt for vacuum pressure on the egr valve inlet and it seemed reasonable.
All pipes on the egr valve and lumpy tickover, block off the vent to atmosphere little pipe/filter and the engine goes to smooth tickover over.

Reckon it’s either an air leak on the vacuum pipes though I cannot see anything untoward or more likely a partially sticking egr valve. I assume as it is vacuum driven not electrically operated the management system may not know what’s going on.

Had to use the van and also have been busy in other areas so back on the case now. Removing the egr valve look a little testing but needs must.

 

[tidewatcher]

And the latest is… isolated the egr valve by removing and blanking the feed vacuum pipe but leaving it connected electrically. Van was much more responsive to drive and felt “ right” if you know what I mean. However the dreaded hunting and chugging was still there. Reinspected the vacuum pipe between the vacuum pump and the brake servo and found a small area that had chaffed. Just managed to wrap some bodge tape around it and hallelujah the hunting stopped! Wiggled the pipe and it started again, pressed the tape back in place and it stopped.

Sooo replace the hard plastic Fiat pipe from the pump to the servo, keep the egr blanked off and for any reason it needs to be reconnected then it is one minute job. The only very slight downside is when turning off the engine it may just fire once before stopping, apparently the egr closes down to stop that.

It’s been along road but I think it’s on the verge of being finally sorted. Let’s hope so and that maybe this saga will be of help to others

Please note this is a 2009 2.3 engine probably in the last few that were fitted with the mechanical vacuum operated egr, this would not be appropriate for the later electrically operated one.

 

[jackwhoo]

Deleted

 

[tidewatcher]

Here we are again! Have only just been able to replace the vacuum pipe that feeds the servo and the egr valve controller above and in the centre of the engine. The van now runs well and the tickover is clean which is a win. My temptation now is to remove the vacuum pipe that connects the control valve to the main vacuum pipe and blank it off thus effectively stopping the egr valve from operating. I did notice that when the engine was on tickover although the engine revs remained constant the egr vacuum valve was making a regulate noise like a baby frog with constipation. Anyone know why that is?

 

[Anthony489]

Hi

The vacuum control valve (centre mounted, under the scuttle) will always buzz due to the nature of its operation, the rubber mounts are supposed to stop this noise from being transmitted into the cab though in my experience you can still hear it faintly when warm idling at traffic lights for example. I can't remember if new valves come with new mounts, if they don't it's possible the old ones have hardened and aren't doing their job.

It's probably worth trying removing and plugging the inlet and outlet hoses from this unit if you want to try running with a closed EGR valve, assuming the EGR valve itself is not stuck. If this is successful you could also disconnect the electrical connection to the vacuum control valve to keep it quiet.

However, it's my understanding that the ECU uses both the EGR valve and the Throttle body as a "double act" to control manifold pressure. I don't know if disabling one of these will cause an upset.

Tha anti run-on function is performed by the throttle body, which closes completely upon switch off to starve the engine of oxygen.

It sounds as though you had a vacuum leak. With this fixed, you may find the brake servo is more effective !

 

[tidewatcher]

Hi

The vacuum control valve (centre mounted, under the scuttle) will always buzz due to the nature of its operation, the rubber mounts are supposed to stop this noise from being transmitted into the cab though in my experience you can still hear it faintly when warm idling at traffic lights for example. I can't remember if new valves come with new mounts, if they don't it's possible the old ones have hardened and aren't doing their job.

It's probably worth trying removing and plugging the inlet and outlet hoses from this unit if you want to try running with a closed EGR valve, assuming the EGR valve itself is not stuck. If this is successful you could also disconnect the electrical connection to the vacuum control valve to keep it quiet.

However, it's my understanding that the ECU uses both the EGR valve and the Throttle body as a "double act" to control manifold pressure. I don't know if disabling one of these will cause an upset.

Tha anti run-on function is performed by the throttle body, which closes completely upon switch off to starve the engine of oxygen.

It sounds as though you had a vacuum leak. With this fixed, you may find the brake servo is more effective !

Many thanks for your reply. It took some time finding and in retrospect there were some occasions where the brake pedal pressure was greater than normal but not significantly so. It was a long journey finding the fault and as they say every day is a school day!