91.5 OD problem

[KOG]

This is the sometimes it does, sometimes it doesn't OD. Flashes water in fuel and wait to start lights, but it's not the OD solenoid on this one. Does the same thing with the solenoid unplugged. And I cut the wire from solenoid about 6 inches from computer just to make sure it wasn't a wiring harness problem. Flashes lights also with water sensor and TPS unplugged. Lights will flash when truck goes over a good sized bump which indicates some mechanical connector failure, but I haven't been able to relate any other condition to light flashing. It will drop OD when lights flash if it has gone into OD to begin with.

This is making me think I've got a bad engine computer. This truck doesn't have a check engine light so I can't pull trouble codes that way. How does one pull trouble codes on this model? '92 FSM hasn't helped with that. It lists codes, but doesn't tell how to get them other than check engine light.

Any idea if '92-'93 engine computers interchange? I'd think that they probably would and those will apparently feed a check engine light among other things. '93 replacements also seem to be a lot lower priced.

 

[dpuckett]

My 91. 5 had a check engine light, as did my early 91, and my current 92. I'd say if you are having all these issues, it could be the computer. But, it seems my late 91 had an external voltage regulator, so it may not interchange. I know the 92 and 93 will interchange, BTDT.



Daniel

 

[cerberusiam]

You either have a bad ground somewhere, a broken wire, or possibly the SBC connector/board is cracked. I assume you have checked, scraped, greased all grounds, battery connections and fusible links.



Other model year computers may work, or not. Even in the years there are discrepencies. Its a $300 roll of the dice.



Pulling codes SHOULD work the same way as the later trucks. Key on-off on-off on-off then on and leave it. The CEL will flash a series of times that represent digits with a short pause between digits and a longer pause between codes.

 

[1stgen4evr]

I don't have an answer but I do have a truck with similar symptoms. I installed a switch on the OD whereby I can engage it at my choice. I don't however drive this truck now. I remember a post on the problem that someone said was cured by ensureing (scrape, sand, clean and apply dielectric grease) the small ground from the negative terminal that attaches on the radiator core support.



James