Question about Cars & Trucks
Posted by Anonymous on
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Posted on Jan 02, 2017
The vacuum shift solenoids have power to one side of them at all times.
The GEM applies ground to them, to activate them, after the shift on the fly position confirm from the trans case.
The power to both should be on the White w/ Light Blue stripe wire.
Ground to them ( from the GEM ) is
2WD : Gray w/ Black stripe wire
4WD : Red.
The only TSB I know of is for the 04-06 MY trucks, for the IWE solenoids ( the kind without the water shield ).
Did you jack up the front end ( and support correctly ) turn the key to the run position ( do not start ), and shift into 4WD, and check the front drive shaft ?
If the shaft still turns, the problem is in the transfer case, if not you are looking in the correct place.
The GEM will not signal a vacuum solenoid until the transfer case has shifted into 4L or 4H ( 4 switches that are the return signal to the GEM ). Could be a problem with the connector on the transfer case ( think it is a 8 or 10 pin connector ) to the contact plate position switches in the trans case.
There is a manual front ale cable, but I would think you would want to confirm why the GEM is not signalling the shift solenoids, prior to replacing them
Posilock make a kit for the F-150
Posted on Dec 12, 2009
GMC S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual
VACUUM DIAGRAMS (See Figures 1 through 85)
Below is a listing of vacuum diagrams for most of the engine and emissions package combinations covered by this manual. Because vacuum circuits will vary based on various engine and vehicle options, always refer first to the vehicle emission control information label, if present. Should the label be missing, or should vehicle be equipped with a different engine from the car's original equipment, refer to the diagrams below for the same or similar configuration.
Check the link autozone.com (free register), select the year ('91 sample), Brand, Model, Sub-Model, Engine Size and make the next root...
1991 GMC TRUCK S15 4WD 4.3L TBI 6CYL REPAIR GUIDE >> EMISSION CONTROLS >> VACUUM DIAGRAMS
I really hope helps with this (remember rated this help). Good luck.
Posted on Jan 07, 2010
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