2003 1078a1 will not shift to 7th gear

[infinitymotors]

The truck is new to me. I feel like I am running form gears 1-5. The mode button is not on and I am not showing any codes. I can only achieve about 38mph. any suggestions would be appreciated .

 

[Khann]

The truck is new to me. I feel like I am running form gears 1-5. The mode button is not on and I am not showing any codes. I can only achieve about 38mph. any suggestions would be appreciated .

This may sound dumb but When i first got my 96 model i had they same type of issues I couldn’t get any speed what so ever and transmission wouldn’t go into 6 gear some of the time and never 7th
So after banging my head against the wall because I couldn’t open the cab do to a leaking Oring on the cab lock i fixed the cab lock allowing me to raise the cab and try to see what may or may not be happening
And the first thing i saw was my Air to Air boot missing one clamp so the turbo was not doing its job resulting in no power to get the truck up too speed. Replaced the missing clamp and She now runs great

Oh if you haven’t read yet Get your Drive shaft balanced

 

[Blairg]

The truck is new to me. I feel like I am running form gears 1-5. The mode button is not on and I am not showing any codes. I can only achieve about 38mph. any suggestions would be appreciated .

While 38 mph is not correct. Trucks without the mode switch engaged starts in 3 gear and top out in 7th. What does the readout display when driving?

Blair

 

[Ronmar]

They start in 2nd and go to 7th. When you turn on the switch the control should show N N When you select D it should show 7 2 after it shifts into gear.

So holding both up and down arrows simultaneously showed no error codes in D1-D5...

A possibility is that the throttle is not rotating the governor linkage all the way to the high speed stop screw. On a mechanical diesel that governor linkage position = engine RPM, and if it cannot reach the high speed stop with pedal input it won’t upshift properly.

Another possibility is the throttle position sensor on top of the engine is out of cal and isn’t relaying accurate throttle position information to the TCU.

There is a procedure in the manual to tell the TCU to re-learn the sensor limits, but you want to make sure the pedal is fully rotating the governor linkage to touch the high speed stop screw before you run it.

 

[infinitymotors]

This is a 1078a1 with a 3126. It’s all electronic engine. The shift display shows either a 7 in normal mode and a 5 with mode button on. This shifter does not display your current gear. It’s just the way it is.


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[Coffey1]

I would say hose off no power.
They will act super crazy with that hose loose or off.

 

[infinitymotors]

I checked all hoses and has tons of power in other gears. When I put it in mode it seems no different except I can tell the transfer case is splitting the power. It starts out in a low gear. I assume it’s starting in 1st. The check engine light is on.


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[Blairg]

This is a 1078a1 with a 3126. It’s all electronic engine. The shift display shows either a 7 in normal mode and a 5 with mode button on. This shifter does not display your current gear. It’s just the way it is.


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Crap...missed the A1 part.

 

[Ronmar]

Crap...missed the A1 part.

Yea, me too...

Infinity, you need to read the transmission codes, and also see why it has a check engine light. It should still be starting out in 2nd gear in mode though...

 

[infinitymotors]

There are no codes. I do need to get to cat and scan the codes.


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[Coffey1]

Injection actuation pressure sensor or regulator
Just a guess.

 

[infinitymotors]

Yes I think I need to put it on a trailer and take it to catapillar

 

[Coffey1]