2.7 CRD high 1.500rpm idle when engine warm (only in 4Hi)

[OffroadSpike]

Originally Posted by JeanLuke

I had the same experience as RTB.

OffroadSpike, to prove this issue try giving it a rev in N or P with the transfer case in low range. It should drop to idle quickly. The ECU uses a different fuel map in low range with zeroed injection quantities.

Yes, I posted a video demostrating no issue with 4Lo. I noticed this "feature" since more than a year ago and spent a lot of time trying to know what was causing it. I tried finding air leaks, cleaning sensors, testing solenoids,... never would have imagined it's actually a factory setting.

[Deezelweazel]

Originally Posted by JeanLuke

The ECU uses a different fuel map in low range with zeroed injection quantities.

Really?

I do use the W5A580 Transmission from the Merc C30 with the Original Mercedes TCM. Which is not intended for 4 low.
No difference at all. Of course in conjunction with the ECU from the C30. And I do still have 4 low with only a minor problem. The torque generated could grenade my drive shafts, if hitting the trottle too hard (of course I calculated the values only, just to stay save).

Normally a slow speed drop is a sign of bad chip tuning when requested fuel is not following up desired fuel. This was a problem with VP pumps.
I would pressure test the fuel regulator of the rail and the overpressure release rail valve. This delay is not normal.

Is the transmission gear oil level correct? Maybe it is slipping?

[RTB]

In 4Lo the revs drop instantly.
In 4Hi the revs float for a bit.
The only difference here is the transfer case sensor.

If it was a mechanical problem then it would be there all the time. But it is not. Anyone at all out there with a CRD can run this very basic test.

The two different fueling maps have been clearly shown. These maps live in the ECU, not TCU. Transfer case sensor goes to the ECU as can be seen in WJDiagPro as it reads the voltage here and is used for the fuel map selection. The signal is then sent over the comms bus to the dash and TCU. TCU only knows indent selection, not voltage which can again be seen in WJDiagPro.

From the manual "The PCM continually monitors the transfer case
switch to determine the driveline operating mode."

At least three people here have modified their 4Hi maps and have either reduced this idle float, or removed it completely by changing the 4Hi maps in the zero % throttle range.

[JeanLuke]

Originally Posted by Deezelweazel

Really?

I do use the W5A580 Transmission from the Merc C30 with the Original Mercedes TCM. Which is not intended for 4 low.
No difference at all.

Yes, really. A few of us here have collectively picked the mapping apart and have a good understanding of most of it. (Note, I still have not figured out the fan map relationship to the AC pressure.)

Your setup is highly customised, particularly having a different ECU and a different TCU.

The standard fuel map has non-zero IQ's at zero TPS in 4Hi at RPM a little above idle. This is what causes the RPM hang-up in neutral. It is also non-linear. In 4Lo it is linear and, more importantly, zero IQ at zero TPS.

[Adrian D]

Originally Posted by Deezelweazel

Really?

I do use the W5A580 Transmission from the Merc C30 with the Original Mercedes TCM. Which is not intended for 4 low.
No difference at all. Of course in conjunction with the ECU from the C30. And I do still have 4 low with only a minor problem. The torque generated could grenade my drive shafts, if hitting the trottle too hard (of course I calculated the values only, just to stay save).

Normally a slow speed drop is a sign of bad chip tuning when requested fuel is not following up desired fuel. This was a problem with VP pumps.
I would pressure test the fuel regulator of the rail and the overpressure release rail valve. This delay is not normal.

Is the transmission gear oil level correct? Maybe it is slipping?

Good thing the guys in Israel running NP241ORs don't think about grenading their drivelines when rock-crawling on 33 and 35" tires

[Adrian D]

Originally Posted by JeanLuke

Yes, really. A few of us here have collectively picked the mapping apart and have a good understanding of most of it. (Note, I still have not figured out the fan map relationship to the AC pressure.)

Your setup is highly customised, particularly having a different ECU and a different TCU.

The standard fuel map has non-zero IQ's at zero TPS in 4Hi at RPM a little above idle. This is what causes the RPM hang-up in neutral. It is also non-linear. In 4Lo it is linear and, more importantly, zero IQ at zero TPS.

I can only imagine the complication of running the Merc ECU and TCU with the rest of the Jeep electriconics.

All when the C30 maps exist, the Jeep maps are documented and main difference in TCU calibration vs the AMG is the solenoid current map.

[Deezelweazel]

Thanks for the input and explanation, Gents!

I guess I'm lucky that it works- I do have to admit that I do use piggyback units PL 1000 to adopt values.
ECM is all the same as Jeep-There is no difference in the layout.
I was referring to the drive shaft U-joints- they can't handle that torque load.