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1995 Hummer H1 throttle position sensor

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pitsingerk

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Hummer is 1995 H1 6.5 non turbo diesel. It is shifting hard between 1st and second (4L80E). Took it to a trans shop and they said it doesn't seem like a trans problem, said the throttle position sensor may need to be adjusted. Has anyone on here had any experience adjusting the sensor. I have the manual for the truck. They state you need a gauge block to do the adjustments and such. Is this as simple as loosening the bolts of the sensor and giving a tweek and driving the truck to see if it cured the issue, or can I really screw something up here.
 
Typically if the computer doesn't have a code in it leave it alone. Make sure you understand what it is and how to adjust it before you even try. Otherwise you can limp the transmission. Limp means 2nd gear only! Then you have to adjust it properly to be able to shift normally again.

There is no Service Engine Soon light for a maladjusted TPS just a stored code as shifting is NOT an "Emissions" problem. So you will have to paperclip and read the codes or read the codes out of the computer to be sure.

Idle speed adjustments tend to throw the TPS adjustment off.

A Scanner can read TPS% and look for flat spots. So can back probing the sensor wires and opening and closing the throttle with the engine off.

Lets get a picture of the Injection Pump and see of it is a mechanical or electronic pump. Just because the year means electronic for civilian stuff doesn't mean military used it. :rolleyes5:

Normally a DB2, mechanical IP, has the TPS sensor on it and a throttle cable going to the pump.

We adjust the sensor on a 1993 without the gauge block by voltage. You have 5v source, output voltage, and ground. You want 0.5v at the output voltage, engine off, cold start solenoid that moves the throttle open disconnected: Throttle closed. Your 1995 HUMMER may be different - I don't know for sure.
 
The TPS is the most common problem with shifting issues on the mechanical 6.5L and a 4L80E trans, and it is common for them to fail. I couldn't tell you how many TPS's I've replaced on various vehicles with no codes, yet the TPS was the problem. Normally though when the TPS messes up on a 6.5L, you lose OD or won't go into lock-up. I know there is a guage block you use which I believe is .646 according to what I could find, but it should be in the .45 or so at idle and above 4.5 volts at WOT. A harsh 1-2 shift only though doesn't really sound like a TPS issue, but the known issue with the sealing rings in the early pre 97 4L80E's. They had problems with the sealing rings for the 1-2 shift accumulator sticking which would cause a harsh or delayed 1-2 shift. The 1-2 accumulator is basically a shock absorber for the 1-2 shift, and if it sticks you lose that shock absorber and get a banging shift. I know the TRANSGO shift kit address's this issue by updating it to new style sealing rings.
 
An update on the Hummer. We took it to R&R Engine in Akron to have them test / put on a new TPS. They tested it and ended up tracing the wiring down to the transmission to find a connector loose. They cleaned it up, reconnected it, and all is back up to par now. Shifting like it should. Simple solution to a complicated problem.
 
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