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I have a 1999truck 3126 cat engine. cant get it to go over

Customer Question
20 mph. is there problem...
I have a 1999truck 3126 cat engine. cant get it to go over 20 mph. is there problem with throttle position sensor?
Submitted: 2 years ago.Category: Medium and Heavy Trucks
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5/3/2015
Technician: Cat Man, Cat Engine Expert replied 2 years ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 9,034
Experience: I am ASE Master Truck Certified.
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Thanks for asking your question and requesting me. I will try and help you out.It's very possible there is a problem with the TPS.Does the yellow or red engine light come on while driving?
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Customer reply replied 2 years ago

no

Customer reply replied 2 years ago

No. can't get out of second gear. and speedometer doesn't work.

it's a 1999 8500GMC Allison automatic MT 653

very urgent. need help now

Technician: Cat Man, Cat Engine Expert replied 2 years ago
Thanks for the information Since the light does not come on I would first suspect a low fuel pressure problem. I have seen this many times. The engine light will not come on when pressure is low and the engine will have low power. There are three things that can cause this. The first is clogged filters. Inwould change them first Second is a failed fuel pressure regulator on the back of the head Lasty is a weak fuel pump. Please reply back if you need more help or have more questions. I am happy to assist.
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Customer reply replied 2 years ago

wont get out of 2nd gear and speedometer wont work.

It seems like an electrical problem.

when speedometer works everything works and shift

Customer reply replied 2 years ago

it seems electrical problem. Is there a sensor that would prevent the transmission from shifting over 2nd gear.

urgent/ broke down on highway

Technician: Cat Man, Cat Engine Expert replied 2 years ago
I see. Thanks for the information.I the speedometer does not work when the truck is doing this, you may have a faulty vehicle speed sensor in the transmission, or faulty wiring that connects to the vehicle speed sensor. When the vehicle speed signal is lost, the trans will not shift correctly as the engine RPM may be limited. When the engine ECM does not know the speed the truck is going, it will limit the engine RPM and speed.
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Customer reply replied 2 years ago

where is location of transmission speed sensor?

Technician: Cat Man, Cat Engine Expert replied 2 years ago
The vehicle speed sensor is located on the tail end of the transmission. It screws into the transmission. It has 2 wires on it.
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Customer reply replied 2 years ago

will tapping on it help?

wires look ok.

Technician: Cat Man, Cat Engine Expert replied 2 years ago
Its worth a try. Normally when they are failing they will need to be replaced.
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Customer reply replied 2 years ago

hard to find replacement stuck on highway, middle of no where, and no tools.

how long does a senor usually last? is this a come problem?

Technician: Cat Man, Cat Engine Expert replied 2 years ago
I hate you are stuck on the highway. I know how frustrating it can be. Sensors do fail from time to time. Normally they last for 5-7 years.
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Customer reply replied 2 years ago

at one point it came out of it and shifted fine. Transmission sounds great. But when we stopped for fueling, stopped engine. We started it up and again the same thing.... cant get out of 2nd gear.

Does this sound like sensor problem?

Technician: Cat Man, Cat Engine Expert replied 2 years ago
I see. Thanks for the information. If the sensors fails like that the trans will not shift correctly. I wish you had a way to get a sensor to put in.
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Customer reply replied 2 years ago

any chance you know any parts store I can get one on a Sunday outside Toledo?

Need a special dealer right?

Technician: Cat Man, Cat Engine Expert replied 2 years ago
Unfortunately I do not. Sorry. But you will need to get it from a GM dealer. Nornally they are not open on sundays.
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Customer reply replied 2 years ago
Thought as much
Technician: Cat Man, Cat Engine Expert replied 2 years ago
Yeah sorry. Most all parts places are closed on Sunday's.
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Technician: Cat Man, Cat Engine Expert replied 2 years ago

Hey.

I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks!

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Cat Man
Cat Man
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