1995 Chevy Truck Premature upshifts, no throttle response

Tiny
VEXTRON
  • MEMBER
  • 1995 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
Truck is a one owner, given to a grandson upon the owners passing. Has 5.7l, 4l60e, and manual transfer case. Transmission rebuilt. Have done regular tune up, including fuel filter. No check engine light. No broken wires. Tried unplugging ABS fuse, and checked temp switch as advised. Seems no one else has a clue. Not taking to an $80/hr garage for diagnosis unless absolutely necessary. Anyway, this is an intermittent problem. Premature upshifts (will go into OD at 20mph), no throttle response at 55+ (acceleration, downshifting, nothing), cycles from OD to 3rd on it's own. Torque converter is locking up as it should though. As soon as you pull it into 4WD, it runs perfectly. No problems except the front actuator doesn't engage and the 4WD indicator light isn't on. To put it into 4WD, you have to stop, turn it off, put it in 4WD and restart it. Again, only when it's acting up. If it's acting up and you just turn the key on(not started) the actuator does nothing or it cycles in and out. Actuator is new. Any thoughts? I don't want to go on a replacing 'skeet shoot' on this thing. There has to be a common denominator in there somewhere between two and four wheel.
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Tuesday, February 3rd, 2009 AT 3:24 PM

5 Replies

Tiny
MASTERTECHTIM
  • MEMBER
Are you losing your gauges when this problem happens? What is the battery voltage gauge reading when its acting up? Is the check engine light on?
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Tuesday, February 3rd, 2009 AT 3:36 PM
Tiny
VEXTRON
  • MEMBER
Nope, not losing gauges. I pulled all the grounds and cleaned everything. Battery is new. Voltage runs about 12-14 according to the dash gauge.
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Tuesday, February 3rd, 2009 AT 3:40 PM
Tiny
MASTERTECHTIM
  • MEMBER
Ok we have to start someplace and hope the rest falls into place. You say the front diff wont engage unless you stop and shut off vehicle and restart, intermittently and sometimes it shifts ok. Your problem must be in the power source to the transfercase switch, which basically has ignition voltage from the ignition key and sends power to the front diff actuatopr when in 4wd and if this works when you turn key off and then on again I would assume that your problem is the ignition switch. And when you turn key off and on you make ignition contact again. This would also cause shift problems too because you would lose power to the transmission shift solenoids. I bet if you scanned the computer you would find a lot of transmission solenoid trouble codes.
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Wednesday, February 4th, 2009 AT 5:35 AM
Tiny
VEXTRON
  • MEMBER
What you are saying makes sense. Never thought of the ignition switch, but it has never given any trouble before. There are 3 wires running to the transfer case switch; 1 is hot, 1 is ground, the last is hot when 4WD is engaged. Correct? Working backward, the hot wire goes from the TC switch to the fuse box (4WD fuse?), Then to the ignition switch I assume. If there is a bad spot in the ignition switch, perhaps the feed for the transmissions is in there too. I bought a Haynes manual for the truck but the electrical diagrams are rubbish. They don't tell you squat. I'll tap into the wire running to the TC switch and put a light in the cab. It should be on while the ignition is on, then if it loses power it should go out. The truck is a daily driver for a 17y/o so I don't always have it here to look at. But I'll let you know what I come up with. Thanks.
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Wednesday, February 4th, 2009 AT 11:34 AM
Tiny
MASTERTECHTIM
  • MEMBER
Your right on track
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Wednesday, February 4th, 2009 AT 1:35 PM

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