4.8is transmission journey from broke to ballin'

[SigBoi]

Originally Posted by PropellerHead

Trip 1:
Drop the tranny, replace a gasket that frequently fails and causes rough shifting. Gasket not obviously damaged. Transmission fluid flush and fill. Same filter- replaced ~25k ago. Agree to replace filter and fluid at next interval- ~90k miles.

Mark off driveshaft to look for slippage. None found.

Diagnose rough idle through codes. Replace engine module that handles the same items as faulted in codes.

Diagnose air suspension. I heard audible air leakage while parked. Turns out this was a wheel problem. Found some leaking stems. Leveled the suspension.

Cost: $700

Result: No rough idle! No more rough 1-2 shifts when cold! Sport auto mode WORKS without hanging on to a gear like a freshman virgin does a senior suitor. It was SO nice! I was happy! But could I be MORE happy?

What was the engine module that was replaced that fixed the rough idle? I heard the IVM could affect this, and I've replaced mine with no effect to cold rough idle.

[bcredliner]

Originally Posted by SigBoi

What was the engine module that was replaced that fixed the rough idle? I heard the IVM could affect this, and I've replaced mine with no effect to cold rough idle.

There are several potential causes of rough idle. Some of them are--secondary air pump, spark plugs, failing coil, vacuum leak etc. Troubleshoot rather trying to solve it with new parts that may or may not be the cause.

[SigBoi]

For sure, the IVM I replaced to fix the other issues it was causing, like weird shifting and random rough starting, which it did. I also heard it affected cold start rough idle, but it didn't do anything for me there.

OP said this module that he replaced cured his cold start rough idle, which I'm experiencing now. Would not hurt to know what module this is while investigating root cause. I'm going to get a smoke test done next to see if there are any vacuum leaks, then onto the next check.

[amancuso]

Originally Posted by SigBoi

For sure, the IVM I replaced to fix the other issues it was causing, like weird shifting and random rough starting, which it did. I also heard it affected cold start rough idle, but it didn't do anything for me there.

OP said this module that he replaced cured his cold start rough idle, which I'm experiencing now. Would not hurt to know what module this is while investigating root cause. I'm going to get a smoke test done next to see if there are any vacuum leaks, then onto the next check.

I'm wondering if I have an IVM issue as well. I noticed sometimes the car idles a little weird when first starting it, also the way the transmission shifts is weird, like it shifts too early leaving the car with no power, which makes me have to push the accelerator further for it to downshift again.

[twinspool]

Originally Posted by amancuso

My 4.8is has the cold 1-2 shift bump issue as well as strange quick shifting when in D mode. No error messages, etc. If I let the car warm up for 3 minutes before driving, there is no 1-2 bump. I plan on having the fluid drained and filled as well as the sealing sleeve and "adapter" changed in a week or 2. I'll also have the transmission programming checked as well. Does anyone know what the proper up to date file for the transmission programming should be?

hey bud, if you dont mind, please let me know what indie you plan on using.. I'm experiencing the same every now and then and would love to have this done. I would appreciate it.

Jae

[amancuso]

Originally Posted by twinspool

hey bud, if you dont mind, please let me know what indie you plan on using.. I'm experiencing the same every now and then and would love to have this done. I would appreciate it.

Jae

Jae, I use Southampton Imported Cars in Southampton NJ.


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[amancuso]

Here's some further info on the weird behaviour of my transmission...

"My new to me 4.8is w/ 83k miles seems like it shifts too quickly on moderate throttle (speed limit of 35-45) and to make it actually go it has to downshift. It also does something weird very rarely but has done it about 10 times over the past 3k miles. When traveling at lower speed, say 40, and I try to accelerate gingerly without stomping the pedal, it feels like the transmission shifts halfway, makes a whooshing sound then bumps into gear, almost like it's sliding before actually shifting into gear. I am getting the fluid changed along with that square adaptor, 4 small hoses and the electrical plug gasket changed, also checking the transmission programming and adaptations reset this weds. I guess my next step if this doesn't work is the solenoids or even whole mechatronics unit change?"

[twinspool]

Originally Posted by amancuso

Here's some further info on the weird behaviour of my transmission...

"My new to me 4.8is w/ 83k miles seems like it shifts too quickly on moderate throttle (speed limit of 35-45) and to make it actually go it has to downshift. It also does something weird very rarely but has done it about 10 times over the past 3k miles. When traveling at lower speed, say 40, and I try to accelerate gingerly without stomping the pedal, it feels like the transmission shifts halfway, makes a whooshing sound then bumps into gear, almost like it's sliding before actually shifting into gear. I am getting the fluid changed along with that square adaptor, 4 small hoses and the electrical plug gasket changed, also checking the transmission programming and adaptations reset this weds. I guess my next step if this doesn't work is the solenoids or even whole mechatronics unit change?"

I dont have much to add however, being that you are in there already, I would also change out the solenoids while you're in there..

[upallnight]

Instead of changing the whole mechatronic unit, I would send it to Gary to have him rebuild the one you have now. He will send the solenoid out for testing and if they are bad he will have them replaced.

Here's a video of him overhauling a ZH6hp26 valve body.

https://www.youtube.com/watch?v=MlDVqH9VEgQ

Dealers in his area send their cars to him to overhaul the trans.

[bcredliner]

I suggest that you take it to a well recommended transmission shop that does work on BMW transmissions for a complete diagnosis before doing anything.