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Discussion Starter #1
Hi,
I am new here and am having some tranny problems. I have an idea where I'm going with the tranny but I'm having problems finding how to test and adjust the throttle position sensor. My chilton manual and ATSG tranny manual don't have anything other than "make sure the resistance moves smoothly". I have read that you are supposed to put some kind of block in and set to a certain resistance.

Can someone please point me in the right direction?

Thanks in advance!

93 K2500 6.5TD 4L80E (DB2 Mechanical injection)
 

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What kind of problems are you having? Mine was losing the TPS signal sometimes when I started it. It was caused by it's resting position sometimes being 'dead'. I simply loosened and turned the TPS ever so slightly to a new resting position and I was good to go.
 

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Turn the key on, don't start the engine.
With a voltmeter, check the voltage across the dark blue and black
wires of the TPS.
It should be .5 to .75 volt at idle and 4.2 to 4.5 volts at full throttle.
If the readings are off loosen the screws and adjust the TPS until you get
it in range.
If it will not set in those ranges you may need a new one.
 

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Turn the key on, don't start the engine.
With a voltmeter, check the voltage across the dark blue and black
wires of the TPS.
It should be .5 to .75 volt at idle and 4.2 to 4.5 volts at full throttle.
If the readings are off loosen the screws and adjust the TPS until you get
it in range.
If it will not set in those ranges you may need a new one.
Added to FAQs :thumb:
 

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Thanks glagulator. Please download your brain to diesel place
 

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I had the TCM go bad in my 92. It would loose the TPS signal after 5 miles. The transmission would go to full pressure[very hard shifts] no lock up and no overdrive. The way I figured out what was happening was driving with a scan tool connected in order to see what the TCM [computer] was seeing. It was a bad connection in the TCM that would heat up and loose connection. Stopping the engine and restarting would make it work again. A scan tool and trans pressure gauge is essential to diagnose a 4L80E. You really need to know what the TCM/ECM is seeing from the sensors.
The inputs the TCM uses are : throttle position, engine RPM, input RPM,and output RPM. There is a internal temp sensor in the transmission that can cause limp/self preservation mode also. It is part of the internal wiring harness.
The main wiring connector on the 92-93 4L80Es were troublesome and were replaced by a somewhat better connector in 94. The older trans can be updated to the newer style connectors.
 

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Discussion Starter #7
Turn the key on, don't start the engine.
With a voltmeter, check the voltage across the dark blue and black
wires of the TPS.
It should be .5 to .75 volt at idle and 4.2 to 4.5 volts at full throttle.
If the readings are off loosen the screws and adjust the TPS until you get
it in range.
If it will not set in those ranges you may need a new one.
I will try this next, thanks.

I am having problems with no OD, no TCC lockup when cold. It will try for OD and lockup right away but it will slip and go into limp mode. Once warm (10-15 miles in 3rd) it will go into OD with lockup if I hit the key off and back on. I have installed a line pressure gauge, and I am getting a full 175 PSI brake standing in P N and OD (2 secs max, per ATSG service manual) and 325 in R. I have the updated harness because my screw in type has leaked fluid into the contacts and I have heard about a whole set of random problems that that can cause. I am hoping to get that installed along with a drain plug and a second fluid change (first was w/ filter 1500 miles ago) this weekend if all goes well. My suspicion of the TPS comes from my line pressure and shift patterns. At 60 MPH if I nail it to the floor it will not downshift and it will just lug in OD with lockup. If I am going about 55 and nail it it will usually shift but not always. And my line pressure stays at idle pressure (50-75 PSI) unless I am over half or 2/3 throttle.

I suspect that someone adjusted the TPS to make it run in a higher gear to get better mpg or something, but overlooked the fact that throttle position also controls line pressure and the transmission's ability to hold the additional power.

Please correct me if I'm wrong on anything, I am not claiming to be an expert.
 

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Discussion Starter #8
Another possible issue could be that one of the TPS wires melted onto the intake manifold and had shorted out and threw a code a few months ago. I moved it away and taped up the wire. Do you guys think the short could have burned something else up or will it protect itself? IIRC it was the dark blue wire.
 

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Another possible issue could be that one of the TPS wires melted onto the intake manifold and had shorted out and threw a code a few months ago. I moved it away and taped up the wire. Do you guys think the short could have burned something else up or will it protect itself? IIRC it was the dark blue wire.
Jim, Did you get this sorted? It is similar in many ways to a problem I am having.
 
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