Sudden dip in power when cruising, drives fine other than that

[Natman151]

Hi all, I've been getting a strange problem with my MK4 DFSD Caddy maxi, the only way I can describe it is a momentary loss of power, talking less than a second, it feels like someone tapped the brake. The van runs fine, no lights on the dash, power feels normal too, I did a scan with VCDS and the only fault that has come up is one for the O2 sensor. Has anyone experienced this problem before and could it be related to the o2 sensor? The fault code is
Oxygen (Lambda) Sensor B1 S1
P2195 00 [01100000] - Signal too Low (Lean)

There were other faults, which I cleared and the P2195 is the one which has come back after a few days of driving.

I've had the dips in power twice on the motorway and another time whilst going round a roundabout.

Any ideas would be great!

[Kris88]

hey man, did you ever get an answer for this?? I'm having the EXACT same issue!!! lol
no errors showing on computer and iv just had a full service, changing filters etc... and its still happening.
Very hard to describe "ow it feels" to my mechanic, but I'm pretty sure you've described mine to a T and I can't find any answers online lol
Regards
Kris

[Natman151]

Sadly not, I’ve still got the issue, it got worse a few times and repeatedly “misfired” but still no codes for it. I’ve been leaving it in the hope something will happen and I get a fault code, recently had a glow plug fault, when I pull my finger out and fix that I’ll let you know if it fixes the issue.

Glad it’s not just me suffering!!

[Kris88]

Iv recently had the EGR valve mapped out of it hoping that would fix the issue… but unfortunaly not… so im back to the drawing board too.
Iv been reading a few threads started on here about the same issues but no1 seems to have found the exact problem yet

[Natman151]

EGR was going to be my next thing so thats annoying, saved me some money though. It felt like a fuelling issue, I thought it might have been the fuel pump or injectors but all the research I’ve done they seem to just die. How often does it happen to you?

[STP]

How about doing a live data recording session, log airflow, rail pressure and maf airflow, see if anything jumps out when it has happened.

Another thing, VAG cars have a thing where if you touch the brake pedal at all, even on full throttle, the ECU will cut the engine immediately to idle. Could be you have a maladjusted brake switch, which is occasionally triggering when driving and cutting the engine back to idle.

Try pressing the brake very lightly when on the throttle, not enough to actually brake, you'll see it cuts out the electronic throttle immediately.

[Kris88]

EGR was going to be my next thing so thats annoying, saved me some money though. It felt like a fuelling issue, I thought it might have been the fuel pump or injectors but all the research I’ve done they seem to just die. How often does it happen to you?

It never seems to happen when in and around the town.. if it does happen? i just dont feel it going up n down through the gears… but my journey home requires a 15min trip on the carriageway and it almost always time does it at least once that trip… somtimes twice (like this morning)
Always seems to be when im cruising at 60mph and without any apparent reason happens

Still no answers

[Natman151]

Is yours automatic? Seems different to mine, I sometimes get it when I’m accelerating on the motorway but I get it more often when I try to pull away or asking for power. I tested it today trying to accelerate and taping the brake pedal, it’s a different sensation so I think the brake sensor is fine. When I get the problem it jolts the van. Feels like the engine doesn’t fire correctly and does so out of time. But it’s not constant which is super weird. And it’s a diesel so it’s not like a spark is firing out of order

What’s the best way to do a live recording session? It doesn’t happen every trip so I don’t really want to lug my laptop around every day running an instance of VCDS

[Natman151]

What should rail pressure normally look like? I had a cheap OBD2 scanner too connected to Torque and the rail pressure fluctuates as I open the throttle

[STP]

At idle a common rail should be in the rough range of 280 to 300 bar, rising to maybe 1900 at full throttle. Hard to say what it would be at a given rpm between those extremes. Those are general values and various vehicles may differ slightly but gives you a baseline.

[Kris88]

Iv still no answers… but iv a strong feeling its somthing to do with the DPF… its the only small issue i know my van has and recently the DPF warning light has come on… and iv noticed a very strong diesle smell from her when shes running…
I dont know when im driving on the motor way at this 60mph and maybe the van tried to regen here??? And cant? Or maybe that is it regening… i duno but i think i may try getting the DPF filters all cleaned…

[STP]

The regen should complete in about 15-20 minutes of normal driving when required, at a steady speed on a motorway or main road. It will even do it in town but will stop and start as you do in traffic.

If the dpf is not cleaning itself then it may be full of ash, what mileage have you done?

The light coming on means there is a problem. It doesn't do that normally for a regen. The light means an error has occured with the dpf.

The dpf pressure sensor is upper left engine bay near the expansion bottle. Small black cube with tubes coming from it. Could also be faulty and cause this.

[Kris88]

And do you think any of this could be related with my issue of the van “lagging” monentarily when driving at a steady speed in the motor way?

Ps iv done 80k miles

[STP]

Hard to say for sure. Do you have any way to scan it for fault codes with a proper tool, not just some generic thing? VCDS or similar.

[Kris88]

Crank shaft censor apparently