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Automotive/1991 Chevy Silverado,no 4 wheel drive

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Expert: - 11/21/2010


Question
Hello Ernie and thank you.
my 1991 Chevy K1500 has no 4 wheel drive,replaced front actuator,checked all 4 bulbs in 4 drive indicator at lever(all Good),put in 4 low waited 5 min while moving in driveway both forward and backwards(same process in 4 Hi)I do not know if I have a switch under the shift lever for 4 wheel drive or  not also Not shure of color code if any on actuator wiring and what voltage it should have.4 wheel drive worked exelent last winter but this year actuator quit and was replaced by my mechanic at my request.it was stuck.I am a disabled Vietnam Marine but I know how to use a VOM,any help will be appreciated.
Bob Lathim
USMC Ret.

Answer
I wish I could help, but I have absolutely NO data on 4x4 systems, never having had one of these.  In regard to the vehicles I DO have or have had, I have made a point to get any and all documentation I could find, and that is the one recommendation I CAN make.  Beyond that, I can offer some general thoughts

First, I would wonder if the previous actuator, found to be stuck or seized when it was removed for replacement, may have opened a fuse that was not replaced or a circuit breaker that was not reset or which did not automatically reset.

That would be plausible because actuators of this type would be expected to draw a large amount of current but only for the short amount of time it takes to do its job, after which it would shut itself off via a limit switch at the end of its mechanism's travel.  The short burst of current needed by an actuator working normally would be below the let-through energy required to open its fuse or breaker by a comfortable margin, and would pass uninterrupted.  A seized actuator, on the other hand, would not shut itself off, and thus would open the overcurrent protection.  Task 1 then would be to find the overcurrent protective device and check it out.

Another possibility is that the wiring or a connector which feeds the actuator may have been damaged by an UNinterrupted overcurrent caused by a seized actuator.  The task in this case would be to check the feed harness and the connectors, nearest the actuator at first, but then working back from the actuator to the control circuit which enables it and finally back to its connection at the main bus if necessary.  Look for signs of corrosion and/or pitting in the connectors and sections of insulation that show the effects of excess heat, ie: discolouration, melting or carbonising.

Finally, it is possible that a corroded connection or section of damaged wire caused the ORIGINAL actuator to fail in the first place.  This could happen if the resultant excess resistance in the feed applied too low a voltage at the actuator to move it and, since it then would not shut off either, the solenoid in the actuator may have "slow-cooked" over extended minutes - or even hours - until the likely distortion of the solenoid and its actuator seized the mechanism.

IF you can get an original shop manual for your 1991, get it.  If not, it is possible that you could get an auto-electric shop to pull you some wiring diagrams from their Mitchell on-line database.

Good luck and best regards ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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