'91 G20 v8 5.7 shifting


Old 11-07-12, 06:35 AM
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Join Date: Nov 2012
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'91 G20 v8 5.7 shifting

Bought a Chevy g20 2 months ago that had been sitting for ~2 years. receipt showed a tranny rebuild 2.5 years ago.

Van will shift into reverse, first, and second without hesitation however, when it goes to shift into third or higher it will revert to neutral w/ high RPM. If you goose the throttle, it will sometimes go into 3rd/4th etc but unreliably.

Replaced the Inline & tank fuel filter, just did a transmission fluid drain & refill with new filter.

Ordered the cable to chk computer codes.

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Old 11-07-12, 09:22 AM
Join Date: Oct 2010
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I wonder if a solenoid in the transmission is stuck.
Old 11-07-12, 01:14 PM
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You don't need a cable for that, just a paperclip, unless your '91 is different from my '94 GM product:


The tranny codes can be hard to find as they are not always listed in manuals; they'll be in the 70' & 80' range. Let me know if you need to decipher one, I have a complte list in the shop manual for my wrecker.

Do you know what tranny is in it?
Old 11-08-12, 07:33 AM
Join Date: Jan 2007
Location: North Central Indiana
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If its been sitting for that long you may have something sticking. I have had very good luck with a product called "Lube Gard" for situations like this. Keep us informed.
Old 11-15-12, 11:59 AM
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Tried the Lube Gard, no change in reaction while driving so far after a week.

Transmission model is: 700r4

incidentally: The radio does not turn on, power antenna stays down, the cruise control does not work, and the fan speed lever on the console only works in Off and High. Just in case this points to a cluster issue?
Old 11-16-12, 07:30 AM
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Any chance some wiring was gnawed on by rodents while stored? You didn't mention codes. Here are tranny-related codes as per my manual. Note this is for a 4L80E tranny, but I think the codes are GM generic.

14 - Engine coolant temperature high
15 - Engine coolant temperature low
21 - Throttle position high
22 - Throttle position low
24 - Vehicle speed low
28 - Fluid pressure switch assembly
39 - TCC stuck "off"
53 - System voltage high
58 - Fluid temperature high
59 - Fluid temperature low
68 - Overdrive ratio error
73 - Pressure control solenoid current
75 - System voltage low
81 - Shift solenoid circuit failure, 2-3
82 - Shift solenoid circuit failure, 1-2
83 - TCC solenoid circuit fault
85 - Undefined ratio
86 - Low ratio
87 - High ratio

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