2008 GL320 Non-Bluetec.

The issue I'm having is a stumble or hesitation when the engine is warm and I go to pull away from a stop at throttle tip-in. It stumbles for a split second then takes off. Similar to a slight misfire and its very noticeable. No other symptoms from that point on until I stop again.

I have DAS and have checked everything related to the high pressure rail system in attempt to find a smoking gun with little resolution. Zero codes. So far heres what I've done or tested:

1. Checked fuel rail pressure control Y74 - OUT OF SPEC on the 300bar test. Acceptable range is 370-507mV and mines at 520mV. High test is normal. I tried 3 other rails with the same result.
2. Checked "fuel injector quantity correction adjustments at idle +-5mm" - all within spec
3. Checked "fuel injector quantity correction adjustments at 1500rpm 1500bar +-5mm"- all within spec
4. Checked "fuel injector quantitiy correction adjustments across several pressure levels +3mm" - all within spec until you reach 1600bar, then it bucks and misfires. 2 injectors out of spec.
5. Replaced the injectors that showed out of spec adjustment and coded - Reran #4 and showed 2 different injectors out of spec. I can rerun this test over and over and it show different injectors out of spec.
6. Ran a injector leak off test - All within spec.
7. Replaced the Y94 quantity control valve - No difference.
8. Replaced the in tank fuel pump thinking it could be a low pressure fuel delivery problem. Pump was at the low side of normal (58PSI) - No difference.
9. Replaced the air filters (oem) and reset adaptation - No difference.
10. Replaced the fuel filter (oem) - No difference.
11. Replaced the MAP sensor (oem) - No difference.
12. Replaced the boost sensor (oem) - No difference.
13. Removed and cleaned the EGR - No difference and it tested within spec.
14. Replaced the upstream O2 sensor - No difference.
15. Pulled both cats/DPF and cleaned - No difference.
16. Bypassed the swirl motor with a resistor - No difference.
17. Replaced the CCV - No difference.
18. MAF and Rail pressure sensors test in-spec.
19. No turbo leaks.
20. Intakes were removed and de-carboned a year ago when I did the oil cooler seals.
21. Cascade overflow valve replaced - No difference.

One thing I will note is that I can reset all of the engine adaptation values and it will go away for a bit, but ALWAYS comes back.

Being that I have issues with tests #1 and #5, I'm starting to wonder if it's a problem with the high pressure pump. I dont know of a way to test it by itself. Has no problem putting out 23kPSI. Really trying to figure out if the Y74 issues is a side effect of something further upstream or downstream.

Below 1500rpm, the Y74 sensor controls fuel regulation and above 1500, the Y94 controls it. It seems like the issue lies in the hand off or switching point that takes place at that RPM.

Any ideas?

 

Keep driving until it throws a code?
Nothing saved in the canbus modules I presume?
At what MAP reading does it stumble?
Since you have DAS, can you also watch what your o2 sensors are doing or the fuel correction levels?

Just to confirm it DOES NOT happen with the engine cold? If this is the case I have an idea what it is.

 

I will need to get back with you on the MAP stumble and o2. I have investigated them before but need to retest. I can monitor fuel correction while in motion, but DAS is not quick enough to capture the split second stumble. Its like the air/fuel is not kosher.

Yes, it only happens when warm/hot. If it were a gasser, I would say its related to closed loop only. I can gently ease in to the throttle and it does not do it. What is your suspecion?

 

In my experience it's been a partially failed sensor. Typically either cam or crank, or a leak between the maf and the intake manifold. Which I tend to lean towards becuase 1) it only happens in closed loop. 2) when you reset the adaptations it goes away for a bit. I reccommend checking all the darn o rings, 2 on the outlet pipe, 1 on the hose to the intercooler, 1 on the resonator past the throttle body. And probably some on the TB itself. Also, have you cleaned the short egr pipe that goes to the TB area?

 

Yes on cleaning the EGR tube as well as intakes. Kind of a new development. For grins, this morning I unplugged both MAF sensors and took it for a drive - drove brilliant. Although I could not get full boost (stopped at 19psi, but fuel was 23k), it drove brilliantly. The power band was much much more smooth and predictable and no limp mode. Injectors were quieter as well. I think we're working in the right direction.

With this experience, I may go ahead a replace the air intake assembly if there are no cracks or leaks between the turbo and air boxes. Just wish it wasnt so damn expensive ($350). Both MAF's did pass the simple DAS test last week.

I do know unplugging the MAF's shuts off the feedback from other sensors (open loop - AFR and Lambda were 0 on this trip) so I wonder if the issue is truely with one of the MAF's or if it is another sensor being cancelled out. MAF does make sense.

 

Well you could always try cleaning them... anyway I'm happy to provide some mass air flow readings from my good om642. On 164 section maj has the mas air flow diag procedure so you could always try following that and see if it tests manually correctly before spending the money.

 

To give an update, I replaced the mass airflow sensors (HFM SFI) and intake housing. $350 (ouch) but i feel it was necessary to rule it out due to mismatched MAF values from left to right and a hairline crack where the clasp clamps to the turbo.

At the same time I followed the procedure to reset adaptations when you replace the HFM.
-Reset quantity mean adaptation
-Reset HFM SFI drift values
-Reset air filter soiling.

The MAF now reads way more air than before and a smoother transition to higher values. The MAP also has a smoother transition and reading vacuum when there is no boost demanded. Previously it would just read 14.1 psi (ambient) no matter what until boost is applied.

It is driving great with a lot more power down low, however, time will tell if this fixes it for good. Fingers crossed.

 

Thanks for the update with the fix (maybe) hopefully it sticks.

 

No dice. Right back to square one.

I've discovered that when certain adaptations are reset, the DPF does a regen. Car drives like a dream when this is taking place. As soon as its done, its right back to stumbling. This explains why it drives awesome for a little while and then goes back. DPF is at 10% load and 0 grams of ash with a max of 35hPa restriction. The extra fuel being dumped is somehow helping.

I reran the "injector correction over several pressure levels" test. The test reference level is 0 to +3mm*hub3 with any injector reporting above 3mm*hub3 needs to be replaced. Injectors 4 and 6 were at +3.0 and +3.5 respectively at the 1400bar and 1600bar levels. Smoking gun, but no so fast. I can run this same test and it will be different numbers and even injectors. The two injectors that are new show -3mm*hub3 to -5mm*hub3. There is no reference range for minus values on this test. I also reran the injector leak back test and there was no issue.

Just for grins I swapped out one of the new injectors with an old one and it runs worse even after recoding. Symptoms are exaggerated. Being that putting an old injector in there made it worse, I'm thinking of replacing the other 4. Car has 200k on it.

This thing is going to drive me nuts.

 

I admire your tenacity. Good luck.

 

Im at 186k and have had to replace one, with another close by. 200,000mi for those injectors seems to be it. There is a place called Becs Performance in Socal that has a bosch test bench if you really want to see how they perform.

 

I ended up replacing one injector and it made a world of difference. Apparently when you replace an injector, you're supposed to code them but not reset any quantity mean adaptations or teach in zero quantity calibration. The injector adjustment coding does that on its own and resetting quantity mean or zero quantity afterwards defeats the purpose of coding. I'm still skeptical to call it fixed but it runs much much better in town and on the highway. I will call it a fix after 4-500 more miles.

I'm in the Eastern Kansas area and have a trip planned to tow our camper to Colorado Springs in early Nov and would love nothing more than to have this fixed.

 

I had similar issues to what was described by PO during acceleration that turned out to be turbo VNT actuator intermittently losing a solder contact once engine warm but It would set a code in CDI control unit about VNT implausability also.

 

Update. It appears that the issue has been resolved. It took a while to iron out, but I believe the true issue was simply patience and tool education .

I did have two bad injectors, but I would reset adaptations in DAS -after- recoding the injector. After doing some digging, I found this is not advised. A simple recoding eliminates the need to reset adaptations and doing the latter nulls coding. Resetting adaptations made the CDI4 lose all injector pressure level adaptations.

What seems to have done the trick was to re-enter all injector codes as if they were new, save, and drive. It took longer to recalibrate zero quantity injection over all fuel pressure levels than I anticipated. The levels are 250bar, 600bar, 800bar, 1200bar. The higher levels adapt first.

In my case it took approx 500 miles to adapt the 800 and 1200bar levels with another 3-400 miles to adapt the 250 and 600bar levels.

 

In Xentry simulation for my car (2007 E320 bluetec CDI/ WDB211022) I can run injectors "Quantity correction values for smooth running over several pressure levels", just as you can on your car. This test only comes up in simulation for me when I set the region to "rest of the world". But when I try to run xentry on my car, I can only get values for idle.
Is this test specific to VIN or were you able to configure your xentry somehow to run this test over several pressure levels?

 

I believe the test is found under CDI4 > Troubleshoot by means of complaints > engine knocks and clatters (i think) in driving mode > quantity correction over several pressure levels

 

For some reason, i can't choose cdi4. My xentry selects both: cdi4 and cdi5