[Tambohamilton]

2007 M57 330d 6mt (uk), 160k miles, completely stock.

So the car runs and drives absolutely fine...sort of. It normally gets 40-47mpg, but recently been around 33mpg. That along with generally poor running - feels laggy and a bit rough under 2000rpm, but basically fine beyond that. When cruise control fades in after coasting down a hill, it sometimes lurches a couple of times.

No codes in the DDE (scanned with INPA and Protool) Smooth running monitor is all good, fuel pressure is on target... boost is harder to tell visually, but seems ok.

Any suggestions on what to do next? What should I check, probe, log?

Thanks

[lnxguy]

Thermostat?

[Tambohamilton]

They were both replaced about 35k miles ago with genuine parts. Holds 90degC no problem.

Glow plugs and controller were also replaced at a similar time.

Thanks for the input

One thing I do wonder about is the condition of the DPF. It's never given me any issues, and still no warnings/codes now. But a while ago it came up with the mileage based end of life thing - I just reset it without replacing. I don't think that coincided with the current issues though. Could that have been a bad move? How can I check it's condition/what are normal values for ash mass, soot mass, etc?

[Tambohamilton]

If I had a leaky injector, the OBC would still think everything was fine, right? So it would still display ~40mpg even though the real mpg is ~33 because of the leak? Just want to rule that out, if possible...

[lnxguy]

Use ISTA to check the DPF. That might absolutely be your issue. Great excuse to remove it.

[Tambohamilton]

Will have a go later

[Tambohamilton]

Originally Posted by lnxguy

Use ISTA to check the DPF. That might absolutely be your issue. Great excuse to remove it.

OK, that took a while to get around to...pesky house renovations and kids and life...!

Just ran the exhaust backpressure test in ISTA. Well, I ran the first 2/3, because I didn't fancy holding the engine on the limiter to run the final part; would have woken the kids, the neighbours, the in-laws...

Anyhow results were (from memory):
Idle: 10mBar (50mBar permitted)
2000rpm: 40mBar (160mBar permitted)
So, well within spec.

I will check the wiring and plumbing to the sensors though, when I get 10 mins. Just in case there's a small leak in the pressure sensor line or something.

Another idea did just pop into my head; I replaced the intake manifold with a Febi branded one a couple of years ago. Pretty soon after, it popped the MAP sensor out of the manifold - the grommet had split. Got a new genuine grommet and it's been fine since...but maybe it's splitting again/leaking a bit now? I need to have a look. I do have a spare grommet here. I looked at expected vs actual charge pressure - looked to me like actual was lagging a bit; around idle expected would be ~1020mBar, but actual was ~980. A bit above idle expected was ~1060, but actual 1000~1020. Obviously would be handy to see these numbers with some load on the engine, but I can't do that right now.

While I had the computer plugged in, I also ran INPA and had a look at the injection quantity adjustment or whatever it's called. All looks fine, and well within the green region for every cylinder. That said, cyl1 was higher than the rest; most were around +/-0.1 ~ +0.2, but cyl1 was consistently +0.3 ~ +0.5. If I held the revs around 2000rpm, it would sometimes peak at about +0.7 where the others were all pretty stable. I guess injector 1 may be getting a bit weak, but not need replacement yet?

Also read 'information memory' on the DDE in INPA - came up with 4CE0; particle filter system. It listed a bunch of conditions; 1850rpm, 60mph, 86degC coolant temp, 410Bar fuel pressure, 0 throttle input.....49.23mBar differential pressure - all looks perfectly fine to me?? And some more notes about it (from google translate):
Engine protection regeneration was activated (particulate filter heavily loaded)
No errors have occurred yet
The error did not cause a warning light to illuminate
Error entered in the shadow
Environmental conditions 1st block valid (error only occurred once)
Environmental conditions 2nd block invalid (error only occurred once)

Sorry about the wall of text.

[Tambohamilton]

Had a look at things under the bonnet and engine cover today - couldn't find anything out of place.

I think I'll treat it to a tank of premium and see if that cheers it up. Should help clear the dpf, if that is the issue...won't do any harm.

[ptpending]

check also if any of your rims are warm or hot after driving
the brakes can also begin to lock a little at a such mileage

[Tambohamilton]

Checked that, all seemed ok - I could touch all 4 discs and they all felt about the same temperature.

Thanks for the input

[Tambohamilton]

I think I've got a slow vacuum leak - sometimes I get in the car and remember to try the brake pedal before starting the engine (6mt), and it's firm. Feels fine with the engine running though. No automatic start/stop, so I don't have vac sensor on the brake booster. Would that cause any noticeable symptoms, if vac was weak? Turbo control is electronic, but egr and swirl flaps are vacuum actuated.

[Tambohamilton]

Originally Posted by Tambohamilton

Had a look at things under the bonnet and engine cover today - couldn't find anything out of place.

I think I'll treat it to a tank of premium and see if that cheers it up. Should help clear the dpf, if that is the issue...won't do any harm.

Seems back to normal with a tank of premium diesel. Roughness and hesitation all gone, and has returned 37mpg on this tank which is guess fits with the multiple short journeys I've done on it.

I think I'm blaming a new fuel additive that I was using - claimed to do all of the good things and none of the bad things...but I should have known better because I couldn't find the ingredients anywhere. Back to Millers ecomax once I'm off premium again.