[GG_Gramps]

Evening all, I'm trying to solve a hesitation issue at light throttle and initial pull away only during dpf regeneration conditions. I've replaced various parts, some were faulty and some as preventative maintenance such as the lambda sensor, egr valve, throttle valve, egr vacuum solenoid switch, fuel quantity control valve, MAF sensor, MAP sensor and I installed a clean egr cooler just yesterday. The dpf pressure sensor reads negative with ignition on/engine off and at idle so that might be next on the list.

It did have a hunting idle during regen which appears to have been solved but the hesitation remains. One thing I have noticed is boost pressure drops to below barometric pressure on idle only during a regen, I understand the throttle partially closes on idle during the regen process which would create a vacuum condition but should boost be maintained through increased egr flow?

If someone could help me try to chase down this issue it would be much appreciated, I'm also interested in warm idle air mass and calculated load at warm idle too, I'm at around 25kg/h and 40% load which seems high but might be perfectly normal.

[phils2]

Curious that the expected throttle position is 0%.
I'm guessing it refers to the anti shudder flap(if my M47 is similar).

[phils2]

What I meant was the discrepancy between actual and expected.

[GG_Gramps]

I'll check shortly but I suspect that expected value is a default value or app error, I've got the same with regards to expected air mass being stuck on an inflated value regardless of running conditions.

You're right though it is the same as the anti-shudder valve just named differently. I believe it's working correctly, closing during regen and it fully opens under normal running conditions.

I've been doing some reading regarding the influence of the exhaust pressure sensor (EPS) on turbo spool, mine reads a negative value (ignition on/engine off) and continues to report negative on idle until I give it some throttle but even at a steady 2k rpm it stays low. Could a faulty EPS that indicates a low value be the cause of lower than optimal turbo spool hence the low boost pressure during regen? The effect being exaggerated during regen when the car closes the throttle valve.

It might not even work this way, I'm just throwing mud at the wall and hoping more knowledgeable people can make it stick.

[phils2]

My pressure(on carly) reads 0 not running, between 10 and 20 hpa on idle and up to 250 hpa, under full throttle and load.

[phils2]

I'll check my warm idle air mass tonight also.

[GG_Gramps]

Thanks Phil, I've replaced the dpf pressure sensor and I have normal readings now which is good. Swapped out the glow plugs yesterday, and I'm still getting hesitation. When going through a regen and in light stable throttle you can feel it push and pull the car, fuel pressure is up and down and egr valve is opening and closing. I'm not sure which one is reacting to the other, the egr valve is brand new.

Dodgy fuel rail pressure sensor maybe? No codes and why only during warm up and regen though.

I'm stumped.

[phils2]

My warm air mass is 36kg/h @idle, 43 @1000 and 74@2000.
It's a tough one.
Might be worth swapping fuel pressure sensor, but as you say, theres no codes.
I had hesitation, but only under full throttle. Fuel filter fixed that.
The fact that it's only on warm up and regen should narrow it down, because warm up uses more fuel as does my regen, especially when it starts the process.
I'd recommend removing battery leads and touching them together.
It might not help whatsoever, but I do it on every car I work on and it's free and easy, also I like to remove, check and replace every fuse and relay.(not with new unless found to be blown)
The battery trick did fix her A6 with dodgy fuel gauge and a code saying the float was faulty.
Does air mass or throttle position fluctuate when it surges?

[GG_Gramps]

Phil I may have found something...

[phils2]

Ah. The golden ticket hopefully.

[phils2]

Never had mine out. Is that drivers side next to brake fluid reservoir?

[GG_Gramps]

Passenger side, just had a new one installed and the remap cloned across. I'll update once it's had a run around with a regen taking place.

[phils2]

Just had mine out.
Looked ok.
Had yours been getting water in?

[GG_Gramps]

Yeah, I took the box out completely and there was an inch of water on the metal tray underneath. I removed the rubber bung to drain it and I'll leave that off going forward now as the water wasn't escaping any other way.

The DDE wasn't contributing to the warm up hesitation and dpf regen issues though. I decided to unplug the egr valve and egr cooler bypass flap solenoid switch and the car runs perfectly so the issue is the egr valve. It's a brand new Wahler valve so maybe I just need to get the adaptations reset properly, or just have it mapped out. I'm running it unplugged with an EML showing for now.