joker_800watts

Ok my truck is driving me nuts ! Anyone have a wire diagram of the engine /alt/tach/pcm .

i would love to just bypass the PCM for charging but i have an Auto and might as well get it all working correctly.
changed engine speed sensor all ready. GAP at .010
i have no tach reading, no charge from Alt. and the trans does not shift correctly.

here is what happened drove in very heavy rain storm the night before.
next day every thing is fine get about 10 miles from the house and poof the check engine light is on the GEN light on tach jumping up and down then it would smooth out for a second and go right back to acting wild again then the tach dumped to zero the alt quit charging and the trans has no OD or lock up.

anyone have a wire diagram so i can trace this wonderful stuff ?
or anyone had the same fun i am having and know where to look ??
a wire diagram would help for lots of things to come i am sure

CTD2001

Bad ECM/PCM Had a 93 with same symptoms and new computer took care of the problem. Go through the engine compartment and check over all connections and make sure connections are clean and tight. Make sure the harness is clean and tight where it plugs into the computer. I spent better part of two days going through the enitre wiring system in the 93 i have making sure all connnections were good.

red70ragtop

Check your fuses, too.

patdaly

Try gapping it at .049/.051, thats the factory spec.

You may well have it too close.

infidel

The Diagnostic Manual available here has about 60 pages of PCM tests that can be done without a scanner to pinpoint problems. They are about $20
https://techauthority.gltghosting.co...atalogId=10051

joker_800watts

ok swapped pcm's still the same . changed the engine speed sensor the same results. but codes in computer are . Cam sensor , cooltemp input to high
purge valve c fault ??

infidel

As I said on on another forum, problem is most always a bad connection.
Next step is very time consuming, unplug the pcm connector and use a pin or needle to make sure all the female connectors are making a tight fit. Some might even be broken.

The internal circuit breaker might be tripping due to short at one of the sensors. Unplug them all and check resistance.

I've had nightmares about what happens when it seems the PCM is bad, very difficult to trace it down but it can be done.

joker_800watts

sounds like a long task that i have little time to fool with. but i guess i will spend the day again trying to find the problem

joker_800watts

ok here is where we stand now. the PCM did smoke because i get signal from the new one the old does nothing won't even light the check engine light when key is first turned on. any how i still get no tach no charge and as soon as i turn the key it throws a code coolant sensor out put to high. any guess's
i have found the culprit that shorted the PCM but still no luck

infidel

I would guess short to the coolant sensor or a bad sensor. Try unplugging the sensor and see what happens.

It also could be that you have an intermittent connection problem at the PCM and just the act of swapping PCMs corrects it partially. I've seen this a few times when a person swaps in a new PCM, they think they cured the problem but in a short while it's back.

You said you went though deep water when the problem first started, could have caused a short inside one of the wiring looms. There is either a 5 or 10 volts supply that goes to various sensors, some of these branch out to the various sensors with spices inside the wire looms. There are also ground splices inside the loom, a perfect situation for a short. Maybe just lifting up the low points in the looms to drain water might correct this.

What I've found the problem usually boils down to is the female connectors at the PCM are extremely flimsy, almost like it was designed to be plugged in only once.

joker_800watts

ok well i will keep on my task and search ! it was not deep water just one Bad A#$ rain storm very heavy rain. i felt the truck stumble that night and since i was watching the road it was one of those hum what was that? then the next day truck ran fine but like a said about 10 miles from home it went nuts and so here we are now with every meter and test light looking for the mystery wire that is at fault.

joker_800watts

Thank you Infidel for the link on repair books.
https://techauthority.gltghosting.co...atalogId=10051
this has got to be one of the best repair manuals i have seen in years.
and cheap 21 bucks for a 900 page book .

Oh i have still not located my problem yet but i have had little to no time to work on the truck and so it will probably be the 22nd before i have a day off and can check this stuff.

Any one need a repair manual i would suggest going to the above link to order one.

12VRoush

i have the same exact problem on my 96! and im hoping i dont have to replace the pcm! i have to wait to start or water in fuel or tans temp, and no tach movement and tans has no overdrive and starts in second gear.... i trace the wire diagram and the vehicle speed sensor,engine speed sensor,water in fuel sensor,intake heat sensor,tps,battery temp sensor?,and coolant temp sensor are all hooked together..... your engine speed snesor controls your tach ? the way i look at it is if one sensor goes bad, the other will malfuction and cause more problems because the rely on each other...

Shanehanna