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1993 6.5 automatic 4wheel drive long bed

the ECM is basically a TCM. code might be stored and reason it's stuck in 2nd. does the speedo work?
 
remove the electrical connection on the trans. should be a small screw holding it in place. if there is trans fluid in it then there is an O-Ring leak. sometimes this will cause connectivity problems for the signals.
 
It shorts out in the tranny fluid is why.

Other possibilities: the harness inside the he pan can be pinched. I did a fitler change, then about 1500 miles later, same thing happened.

Another time I had a bad speed sensor causing it. Same thing, but iirc had a code for sesnor also.
 
I've had the fuel canister off and am familiar with the plug. The tranny guys want it tomorrow for a free inspection. I might delay cause it could be more electrical than mechanical.
 
Not real familiar with 93 but on the newer ones when the fuel heater shorted it would blow one of the ECM fuses. I would think if the fuse is blown it would be in limp mode which is 2nd gear IIRC.
 
The 1993's have lots of "sneak circuits" on the fuses completely unrelated to the label. I forget what fuse, maybe the gauge cluster, that was blowing as a dead short. Turned out to be the cold advance switch internally shorted to ground.

Adding to the advice above for electrical: Look for the speed sensors, (2) of them, and inspect the wiring harness, 6" or so, all the way back to where it joins and especially where it joins the main harness. I find the insulation cracks and falls off in this area shorting out the sensors. Replacement connectors with the wires are expensive, but, appear to last.

Yes, two sensors. Identical plugs so don't mix them up. One is the input shaft speed sensor on the front of the transmission and the second on the rear is the output speed sensor.

Inspect all wiring in the area for rubbing through. Do a wiggle test on the harness and listen for the fuse to pop or use a meter that makes noise when shorted. You are just looking to see if a wire shorts when things move during a shift.
 
I just had the PCM fuse issue happen; also had the lift pump fuse blow at the same time.

If the 93 shares the same PCM wire routing as other 6.5's, there are 2 likely candidates:
- Ground wires at the passenger side rear of the block / valve cover might need cleaning.

- OPS is going bad (it shares the same ground location as the lift pump and PCM).

Fortunately for me that I also had the lift pump fuse blow as it gave me enough information to get good results from a search. And fortunately for all of us, our good buddy Ferm identified this on another forum.


My approach was to address all the variables so I:
- had the OPS replaced with a new AC Delco part.
- had the grounds cleaned (shop reported that they were a bit crudded).
- added a ground from the battery to where the PCM / OPS / LP ground on the block.
 
The fuel heater is almost always on a seperate fuse from any ecm feeds. If it is blowing the fuse when it shifts, then I would look for any chafed wires rubbing when they get moved like during a shift. Next I would be checking for shorts to the trans. Then finally shift solenoids. Since you say it happens when it shifts, look for things that get power during a shift. 93 is most likely the new style plug already. As to atf causing things to short out, I've never bought that. Every solenoid ans psm connection inside the pan is immersed in atf all the time already, and that doesn't cause any issues. The problem with the old plugs was they leaked, and the oil would attract dirt and dust, and the dirt/dust getting into the plug is what caused the issues, not the oil itself.

Try and narrow the problem down and exactly how to replicate it, then go from there. If you find it only happens on a specific shift, then you can start checking the circuits used for just that shift. This way you can narrow the problem down instead of checking everything.
 
nealpellecchia said:
Yes. Code said gear ratio.
Click to expand...

Only code?

Whatever happened is likely an inability to shift due to the fuse blowing short. Blown fuse is a short somewhere as outlined above. The manual will tell you what circuits to troubleshoot, but, you do not have enough information to make use of it.

Again visual inspection of wiring harness with wiggle test is not fun, but, the best use of your time. Eliminate the external wiring best you can.

Replace fuse. Put test light across fuse. Manually shift from 1 to 2 to 3 to OD (4th whatever you want to call high gear). Note what shift causes the fuse to pop: aka the light comes on when the fuse blows. Then you can look closely at the solenoids and circuits involved for that shift.

If you probe the transmission for a short be aware that the solenoids likely have suppression diodes built in. You put full power to them with reversed polarity I guarantee the diodes will impressively blow their magic smoke out, taking the TCM out in the near future, or simply short causing more problems. Did I mention a voltmeter and being aware of the voltmeter's polarity for useful safe readings? (There are other old school ways to test like: test lights and full power 'did it click'... But not the easiest choice when reading the manual to probe the trans connector esp. with the risk I mentioned. )
 
WarWagon said:
Only code?

Whatever happened is likely an inability to shift due to the fuse blowing short. Blown fuse is a short somewhere as outlined above. The manual will tell you what circuits to troubleshoot, but, you do not have enough information to make use of it.

Again visual inspection of wiring harness with wiggle test is not fun, but, the best use of your time. Eliminate the external wiring best you can.

Replace fuse. Put test light across fuse. Manually shift from 1 to 2 to 3 to OD (4th whatever you want to call high gear). Note what shift causes the fuse to pop: aka the light comes on when the fuse blows. Then you can look closely at the solenoids and circuits involved for that shift.

If you probe the transmission for a short be aware that the solenoids likely have suppression diodes built in. You put full power to them with reversed polarity I guarantee the diodes will impressively blow their magic smoke out, taking the TCM out in the near future, or simply short causing more problems. Did I mention a voltmeter and being aware of the voltmeter's polarity for useful safe readings? (There are other old school ways to test like: test lights and full power 'did it click'... But not the easiest choice when reading the manual to probe the trans connector esp. with the risk I mentioned. )
Click to expand...
I unplugged the cold advance fast idle circuit cranked the engine..did not stary...and it blew the ECM fuse 10Amp.
 
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