906 Sprinter brief power loss

[firesnail]

I have a long term temporary power loss issue which only seems to occur on climbing a hill.

The power drops for about 8 to 12 seconds before coming back. It's always after the start of the hill climb and it doesn't need to be a very steep hill.

Sometimes the auto transmission will shift down and the revs will go up (no limp mode), but there is still not much more power and I can't speed up or even slow down despite pushing further down on the accelerator. When the power kicks back in, it's at the level you would expect it to be.

(311 CDI)
Checked:
Fuel filter (replaced)
Air filter (replaced)
EGR
MAF
Brake switch /sensor (replaced)
Lamda sensor (replaced)
DPF pressure switch (replaced)
Has been to independent who couldn't find cause and there are no OBD/Star fault codes.
Injection cleaner and dewatering additives didn't help.

My thoughts are on fuel supply, engine sensors, air or turbo, but I don't get why there is such a power loss with no fault codes. It looks like a condition which the system considers normal or for which there is no sensor or code. But when it happens it's like a switch has been thrown -there is no power fade in or out.

Any ideas?

 

[Tuercas viejas]

The two stage turbo is vacuum operated, so vacuum issues, & leakage come to mind since the water pump is vacuum operated and/or a sticking EGR valve created a sensor reading excessive back pressure in the exhaust system. System must have 18 to 20 "HG minimum to work as it should.
Knowing what are the EPB and differential pressure readings are would be useful .
Also a reading at idle off of the MAF sensor in live data (MG/Hub) might start giving you some indication.
No fault MIL lamp codes are best found by running the vehicle in live data connected to a scanner starting with in KOEO , then in KOER and then road testing to observe the fault when it occurs.
Sometime installing a flight recorder to the MIL (diagnostic) connector might help you to pinpoint the fault if its intermittent) .
Tuercas viejas

 

[firesnail]

Thanks. I've had the EGR valve out. It's in good condition and not sticking. There is no MIL illumination or other warning at any time. The MAF has been measured by the garage. I've also had it out and it's spotless. No current or stored codes which are relevant. When the power loss occurs, it actually drops a bit like backing a foot of the pedal. It's not just that it doesn't increase. Speed might drop from 50 to maybe 40 mph over 10 to 15 seconds, more accelerator might give it 45 with possible shift down, then suddenly it will decide to kick back in and accelerate strongly uphill.

Probably time to invest in an OBD reader and take it for a test drive. Hope an iCarsoft MB V2.0 is up to the job.

 

[Tuercas viejas]

Thanks. I've had the EGR valve out. It's in good condition and not sticking. There is no MIL illumination or other warning at any time. The MAF has been measured by the garage. I've also had it out and it's spotless. No current or stored codes which are relevant. When the power loss occurs, it actually drops a bit like backing a foot of the pedal. It's not just that it doesn't increase. Speed might drop from 50 to maybe 40 mph over 10 to 15 seconds, more accelerator might give it 45 with possible shift down, then suddenly it will decide to kick back in and accelerate strongly uphill.

Probably time to invest in an OBD reader and take it for a test drive. Hope an iCarsoft MB V2.0 is up to the job.

Yes you need something like a Carsoft to read live data when there are no codes .
Cheers
Tuercas viejas
(We fix 4 Sprinters per day on average )

 

[firesnail]

Well, now have my OBD readout device. Attached is a recent trace. Region marked X is where the trouble hits part way up an incline.

That the speed reduces with constant accelerator on an incline is not surprising. The problem is that depressing the accelerator further in that range does not affect revs or power.

After the unresponsive period the engine kicks back in by itself and power /revs return while still on the same incline, as can be seen at frame 29 (numbered at bottom).

 

[firesnail]

Today I had code P1955 which I see some sources say is a throttle body issue (and very consistent with the symptoms). Does that make sense for a 311CDI and if so where should I look for it on the engine?