2002 M1123 4L80E Strange Shifting

[badger_610889]

Thanks Mogman,
I suspect something around the TPS, I’ll check the voltage indeed, thanks. I have a gut feeling some adjustment in that area will happen, though I don’t see what has changed to make the transmission behave differently.

While I was doing the high-level check (I had less than an hour so had to pick my battle) the 4L80E Transmission troubleshooting supplement was extremely helpful. All connectors are pristine, I was hoping to find an easy root cause! I wish I had a diag tool that can connect to the hmmwv at hand.
Also I had time to adjust the brake sensor which had gone off a bit, as a consequence the brake light stayed off until I’d really hit the brakes. Something we should have in mind to check annually!

 

[Mogman]

I prefer to use an analog meter (Simpson 260) this way you can watch the voltage and see of there is any "noise" coming out of the potentiometer (TPS)
If the voltage rises smoothly (edit while moving the throttle) without any jerky needle movement the pot is good, if the needle jerks around then the pot is noisy and will not work correctly, this can be seen on a digital meter but it is much easier to see on an analog meter.

 

[badger_610889]

Thanks to your advice I took a look at the TPS today and realized that while it looked solidly tightened, it’s actually easy to rotate by a few degrees in both directions. It was getting late and dark, so I couldn’t get to the bottom of it but that seems to be the issue for my high shifting.
I’ll know tomorrow!

 

[Hummer Guy]

Interesting thread, I’ve experienced some off shifting issues with the M1123 for the past couple weeks, I checked all connectors by the TPS, checked the TPS impedance which looks fine (from 5k idling to 2k ohms full throttle) checked the connectors on the transmission and all looked fine as well, but I didn’t know about the brakes! Will check it tonight.

The truck drives nicely but shifts high, as if it was full throttle all the time. Well it feels normal in full throttle, but feels painful when the engine is cold as it will stay in 1st until 3000 rpm+ making me unwilling to drive it.

Mines just don't want to lock/unlock the torque converter when it gets up to highway speed which makes the RPMs be around 2,500-2600 at 60Mph and for some reason it loses overdrive if Im in heavy stop/go traffic after driving for about an hour, I think that probably has something to do with the cooling, I'm planning on going to a better and bigger transmission cooler and hopefully changing the internal wiring harness would fix the torque converter lock up issue, I notice there was a small leak around the wiring harness, maybe that shorted the wires, I'm not sure

 

[Mogman]

Mines just don't want to lock/unlock the torque converter when it gets up to highway speed which makes the RPMs be around 2,500-2600 at 60Mph and for some reason it loses overdrive if Im in heavy stop/go traffic after driving for about an hour, I think that probably has something to do with the cooling, I'm planning on going to a better and bigger transmission cooler and hopefully changing the internal wiring harness would fix the torque converter lock up issue, I notice there was a small leak around the wiring harness, maybe that shorted the wires, I'm not sure

The cooler is big enough on the HMMWV, do you have a working trans light?, have you pulled the codes? There are several issues that can cause the transmission to act differently when warmed up than when cold.

 

[badger_610889]

Just to confirm: the loose TPS was the cause of the odd and high shifting on the m1123!

For once, I got an easy fix on a hmmwv ahahah

I just rotated the TPS to the max toward the rear / against the throttle opening direction, which took literally a minute, took it for a spin, and could enjoy smooth virgin shifting velvety and where it should be. The m1123 made me happy again!

 

[badger_610889]

The cooler is big enough on the HMMWV, do you have a working trans light?, have you pulled the codes? There are several issues that can cause the transmission to act differently when warmed up than when cold.

Yeah according to the literature, heat is well handled by the control unit and overheat should lead to errors flashed on the trans light in diag mode.
I'm glad I've read this stuff and won't need it in the end (hopefully)

 

[Mogman]

Just to confirm: the loose TPS was the cause of the odd and high shifting on the m1123!

For once, I got an easy fix on a hmmwv ahahah

I just rotated the TPS to the max toward the rear / against the throttle opening direction, which took literally a minute, took it for a spin, and could enjoy smooth virgin shifting velvety and where it should be. The m1123 made me happy again!

You still have not said if you have a working trans light, this is VERY important, being able to see a trans light and then being able to read codes is extremely important to keep you from frying your transmission.........
Not all issues cause a trans light so being able to read codes any time your trans is not working correctly is as important as having a working trans light.

 

[Hummer Guy]

I've finally made my way back to this, it ended up being the external wiring harness, the whole wiring was a hack job, the wire that controls the torque converter had come out the crimp.

 

[Loose Boots]

hey guys, just got a new stynadyne fuel injection pump, but my old TPS wont work, its got a big knob instead of the flat-head peg. Ive seen images of the type I need but cant find it anywhere. any help would be greatly appreciated.

 

[Retiredwarhorses]

hey guys, just got a new stynadyne fuel injection pump, but my old TPS wont work, its got a big knob instead of the flat-head peg. Ive seen images of the type I need but cant find it anywhere. any help would be greatly appreciated.

wrong pump….but it helps to know the truck model and pump part number.

 

[Mogman]

hey guys, just got a new stynadyne fuel injection pump, but my old TPS wont work, its got a big knob instead of the flat-head peg. Ive seen images of the type I need but cant find it anywhere. any help would be greatly appreciated.

Welcome to the SS forums, there are many here willing to help.
Please start a new thread on this subject as it has nothing to do with this threads subject matter.

 

[Loose Boots]

wrong pump….but it helps to know the truck model and pump part number.

1097r1 had engine swap dont know when but its 6.5 4 spd.
part no. m3 d32831-6278. Got it from stynadyne distributor.

 

[Mogman]

That would be DB2831-6278

1097r1 had engine swap dont know when but its 6.5 4 spd.
part no. m3 d32831-6278. Got it from stynadyne distributor.

AGAIN, start a new thread. it is not polite to hijack someone else's thread.

 

[Loose Boots]

Again? this is my first time posting on here. I just figured a post about TPS somebody might know something. There's no need to be rude about it. I'm not hijacking anything, just had a quick question so I asked in a thread with a similar topic. I don't see any reason why that should be an issue. Obviously, the people responding to this thread have knowledge on the subject, and answering my question does not prevent them from being able to continue assisting the person who started the thread.

 

[Mogman]

Again? this is my first time posting on here. I just figured a post about TPS somebody might know something. There's no need to be rude about it. I'm not hijacking anything, just had a quick question so I asked in a thread with a similar topic. I don't see any reason why that should be an issue. Obviously, the people responding to this thread have knowledge on the subject, and answering my question does not prevent them from being able to continue assisting the person who started the thread.

I asked you in post #32 to start another thread, that is why I said again.
But to answer your question that is an IP for a 6.5L with a 3 speed transmission, you could remove the plastic cam and use it on a 6.5L with a 4 speed but unless you got a super good deal on it you should return it and get the correct IP.
The part number of that IP is actually DB2831-6278

 

[Loose Boots]

I asked you in post #32 to start another thread, that is why I said again.
But to answer your question that is an IP for a 6.5L with a 3 speed transmission, you could remove the plastic cam and use it on a 6.5L with a 4 speed but unless you got a super good deal on it you should return it and get the correct IP.
The part number of that IP is actually DB2831-6278

My apologies, i didnt see that post. Thank you for the info and in the future I will try to be better at where I ask questions.