CFD

Hello friends!

I am having some transmission quirks.

In Standard mode:

- Floor the car, it seems to rev up to a soft limiter around 6k rpm and never shift (definitely pulls timing over 5k rpm)
- Kick down works just fine
- Part throttle hard acceleration (up to 75%-80% throttle) it does just fine (does not pull timing, supercharger remains engaged)

In Manual Mode

- Floor the car and shift before ~4500rpm, trans shifts quickly and engages the next gear in a nice firm manor.
- Floor the car and shift between ~4500rpm and 5000rpm, trans engages next gear but pulls a lot of timing (or supercharger is disengaged)
- Floor the car and shift over 5000rpm, car acts just as it does in standard mode. Does not shift out of that gear despite driver commands until you let off of the throttle.



I am stumped. I was thinking maybe the 13-pin connector let ATF leak into the TCU, causing weird things to happen, but I would think that would cause a consistent problem across the entire rev range and throttle positioning.

Any ideas?

E42AMG???

I'd start by checking the fluid level and then pull the tcu out it's on the passenger side under the hood in the fuse box closest to the fender.

GrepAwk

My guess is the fluid is slightly low. I suggest not flooring it any more until you check. Do you have a dipstick to check it?

I had one occurrence which was similar. Fluid had been oozing out of the connector for months and I kept thinking "I'll get to that someday". Then one day while in Sport/automatic mode it didn't finish the shift from 1st to 2nd on a hard pull from a stop light. I suspect it sipped some bubbles and didn't have enough fluid to feed the 1-2 circuit to complete the shift. It slipped and rev'd up. I pulled over and turned car off/on and it reset. I babied it home (didn't go into Limp Mode). Tried a gentle test of manual mode paddle shifts and they worked. But I didn't hammer it, so I'm not sure if that matches with your experience. Got home and measured it while still hot and found it was low. Left it parked until I could get a replacement connector ring/full fluid/filter change a month later.

Hasn't happened since then.

CFD

I will give it a look in the morning. I just went out in the car and successfully got it to pull strong up to ~5500rpm a couple of times and manually shift into the next gear without pulling any timing or turning the supercharger off. The P/O told me that it had a tune and pulley. I only logged 180kPa @ ~5600rpm. This seems to fall right in line with the data I have sourced from the interwebz for what a stock pulley will produce (11.6lbs). After a couple of solid pulls, it seemed to become more finicky, not wanting to give me the beans over 5000rpm.

This makes me wonder. I was logging iATs, and saw a peak of ~130F under load with a quick recovery down to ~75F when cruising afterwards. Water temps were stagnant at ~200F. Tonight is definitely the strongest its ever ran, and the coldest its been since I've owned it (about 60-65 ambient temps).
Deductively, my initial thoughts are that it is iAT related, however the symptoms I have do not coincide with this hypothesis (car doesnt shift on its own under WOT in standard mode, car pulls timing in manual mode when shifting over 5000rpm.

Is confused...

E42AMG???

Iat pulls time like so

95 degrees F. Retards 3.5 degrees
113 degrees F. Retards 6.3 degrees
149 degrees F. Retards 9.5 degrees

this is why timing is being pulled.

you may have a conservative tune that either only allows for the extra boost down low and keeps the same up top by opening the bypass valve slightly.
or once it sees higher iat it bypasses the extra boost back to stock.

i would check the trans fluid first and go from there.

CFD

Thank you for that.

I finally scanned the whole car. The only trans code that populated was "p2221 y3/6b1". I just placed an order for a new conductor plate and 13-pin connector. I'll try that first as there were no other codes in the TCU.

I will update this thread with the results of a new conductor plate in case anyone else has these symptoms/lone code.

CFD

UPDATE

So I just flushed the trans, changed the filter and replaced the conductor plate. The transmission definitely shifts smoother with a more firm lock up. However, it is still doing the same thing where it will not shift out of any gear in Standard mode under full load @ high RPM. It seems to be opening up the bypass valve/turning the supercharger off then lingering around 6,000rpm.

Truly stumped at this point. Any ideas?

CFD

Went out and logged tonight. It is NOT pulling any timing. It is dropping boost instantaneously then adds timing to compensate. It is not belt slip. Any ideas on what could cause it to divert boost under load at higher rpm?

CFD

Car has been down due to paint work. Before handing it off to the body shop, I changed the fuel filter and connected a mechanical pressure gauge to the fuel rail. Rail pressure is as rock steady as a return-less system can be. As I was logging rail pressures, I sometimes noticed smoke coming from the back of the car that I traced back to an ATF leak. I have yet to figure out the exact location of the leak, but It appears to leak much worse under high load/rpm. I am not familiar at all with the NAG1 transmissions, but I am sure if the TCM is reading a sudden drop in line pressures (due to the leak) it would cut boost. However, prior to the transmission service, I was experiencing the issues without any ATF leaks. As soon as I get the car back I will diagnose and fix the trans issue, but I am leaning more and more towards it being a TCM hardware issue.

Any thoughts?

CFD

Next thing on my list to try is throwing some unleaded 110 in the car to see if it is knocking...

nwjames1231

@CFD, Hey bud did you resolve the transmission shift problem? I have the same issue. C240 2004 173k miles. It shifts hard, and jerks and skips in lower gears. Gears 2-3 really rough.

CFD

Sure did. It's been a while, but I believe it was fluid level. I remember it being HYPER sensitive to the fluid level. It had to be perfect.

Sorry for not having anything better. I dealt with a whole host of issues since that have left my memory of these symptoms and their cause a little fuzzy.