Overdrive problem

[ZGardulski]

I have been having problems with my OD. about two weeks ago I completely lost OD on my 93 W350. I also noticed that the switch on the dash wouldn't light either. I have already checked the TPS and it is working fine. Wondering if I have a wiring problem somewhere, but I can't find and schematics for the switch/TPS/solenoid. I did try replacing the switch, no change. Any help please, 50 MPH back and forth to work 40 miles is getting old quick. Thanks.

 

[cerberusiam]

Check for power on the larger wire in the 2 wire harness on the transmission. It sounds like either the power supply for the OD solenoid is bad or the PCM is having issues. Check all your grounds also.

 

[dpuckett]

Unless you have 4. 10 gears, you can go 60 in 3rd with no problem, except a little more fuel consumption.



DP

 

[AndrewKing]

HI,

I have the same problem occasionally (except my switch will light up and go off when I push the button).

I was wondering if it would be possible to install a 3 position switch in place of the facotry unit... . Position #1 being " OD off" , Position #2 being "factory OD on" and Position #3 being "forced OD on" by somehow applying the needed voltage / current needed to turn the OD on and keep it on until manually switched off. (this would have really helped me on my trip to Ohio when the OD kept switching on and off at speeds of 70 MPH (I was only carrying 700 lbs)... . It was a long and slow and noisy trip without OD!



Thanks for any ideas on how to make this work.



Andrew

 

[KOG]

A three position switch is probably not a good idea. The factory dash switch is a momentary on. Push once to toggle OD off, push again to toggle OD back on. The real switch (relay) is on the engine controller board.

 

[cerberusiam]

HI,

I have the same problem occasionally (except my switch will light up and go off when I push the button).

I was wondering if it would be possible to install a 3 position switch in place of the facotry unit... . Position #1 being " OD off" , Position #2 being "factory OD on" and Position #3 being "forced OD on" by somehow applying the needed voltage / current needed to turn the OD on and keep it on until manually switched off. (this would have really helped me on my trip to Ohio when the OD kept switching on and off at speeds of 70 MPH (I was only carrying 700 lbs)... . It was a long and slow and noisy trip without OD!



Thanks for any ideas on how to make this work.



Andrew

Yep, works like a charm. Single Pull/Double Pole switch with center off is what you need. Cut the signal wire between the trans and PCM, add enough wire to each end to run to switch in cab, wire the switch for center off, one end position pass thru for normal, the other end position run a wire to a good ground for OD engage over ride.



A simpler version is just tap the OD signal wire and run to a switch with the other end run to ground.



NOTE: With the "mystery" switch on OD is engaged at all times. Makes for a slow launch. :-laf

 

[Philip]

If your TPS checks good. Remove the plug from the PCM and check the teminals.



The female terminals in the plug are round. Over time mine had spread out and were not making contact. The TPS signal is in the middle row third one from the left side looking into the plug.



It takes a 10MM to remove the PCM plug. Any terminals you see out of round take a very small common blade screw driver and bend the terminal back to a round shape.

 

[ZGardulski]

PCM is new(good ol' regulator issue, but doesn't mean just because it's new it is good), grounds are good(reverified after the reg prob). looks like there is another broken wire somewhere. I'm gonna try the bypass switch and hope for the best. Thanks for the inputs on keepin the beast on the road where it belongs!

 

[cerberusiam]

PCM is new(good ol' regulator issue, but doesn't mean just because it's new it is good), grounds are good(reverified after the reg prob). looks like there is another broken wire somewhere. I'm gonna try the bypass switch and hope for the best. Thanks for the inputs on keepin the beast on the road where it belongs!

Or the OD solenoid is bad. Try the switch with a tap first and see if that solves the problem.





Good luck.

 

[Greenleaf]

I also lost OD gear while in the Shilo Battlefield. I sure wish I had installed my by-pass switch. I'm ready now. (If/when the speedo quits, it's generally the VSS. ) My next stop was Nashville with the OD in/out.

 

[MotleyCrueCab]

Im not positive, but i think the od also reads off of the crank position sensor (rmp, th one by the balancer). Could be an issue.

 

[cerberusiam]

Im not positive, but i think the od also reads off of the crank position sensor (rmp, th one by the balancer). Could be an issue.

I tested this on my 92, no difference with CPS plugged in or not. CC and charging quit but OD worked fine.



Is it this way on every PCM, well... .....

 

[JSpecht]

I have the same problem with the one I have to, If you hold the swith in the OD works but the light don't light up. I used a scanner the tps,vss all works ok. Is the OD switch a momentary switch? if so mine works ok I was watching the pids in the scaner and can see it come off and on.



Is there any why to get into the pcm to fix the internal relay?????



And if you use a togle switch will the OD be ingaged all the time ???? unless switched off of course.

 

[cerberusiam]

I have the same problem with the one I have to, If you hold the swith in the OD works but the light don't light up. I used a scanner the tps,vss all works ok. Is the OD switch a momentary switch? if so mine works ok I was watching the pids in the scaner and can see it come off and on.



Is there any why to get into the pcm to fix the internal relay?????



And if you use a togle switch will the OD be ingaged all the time ???? unless switched off of course.

In order of your questions:





Yes.





No.





Yes.

 

[JSpecht]

So if I'm reading this right if I do the togle switch fix . You will have to switch the switch off when slowing down to a stop and back on after up to around 45-50mph??? Will it stall it out if it is left on????

 

[cerberusiam]

So if I'm reading this right if I do the togle switch fix . You will have to switch the switch off when slowing down to a stop and back on after up to around 45-50mph??? Will it stall it out if it is left on????

Yes.



No stall, just a sloooowwwww launch. However, if you have a lockup TC like I do and a lockup switch ... ... ... yeah, they are called a "mystery" switch for a reason. :-laf

 

[HRDROKN]

I tested this on my 92, no difference with CPS plugged in or not. CC and charging quit but OD worked fine.



Is it this way on every PCM, well... .....

This is interesting... I have had problems with my OD going in and out (have a manual activation switch also), but after I installed a speed correction box I had no more problems... . Then it started acting up again So I ignored it and just used my switch to engage OD.



Around or about this time I was having intermittent charging and finally traced the problem to a bad wire in the CPS harness. I repaired the harness and my charging problem was solved... AND my OD problem went away!

 

[cerberusiam]

This is interesting... I have had problems with my OD going in and out (have a manual activation switch also), but after I installed a speed correction box I had no more problems... . Then it started acting up again So I ignored it and just used my switch to engage OD.



Around or about this time I was having intermittent charging and finally traced the problem to a bad wire in the CPS harness. I repaired the harness and my charging problem was solved... AND my OD problem went away!

I think "charging problem" is the key here. If the battery is not fully charged and the alternator maintaining a steady output all bets are off. The fluctuations in the voltage will cause many weird gremlins, about the same as a bad ground.



I did it with a fully charged battery and a short test run and there were no shifting issues.

 

[HRDROKN]

I think "charging problem" is the key here. If the battery is not fully charged and the alternator maintaining a steady output all bets are off. The fluctuations in the voltage will cause many weird gremlins, about the same as a bad ground.



I did it with a fully charged battery and a short test run and there were no shifting issues.

I wonder then... . if my voltage was low, this may have effected my speed correction box? Are they that sensitive to input voltage?

 

[ZGardulski]

Well I finally got around to putting a switch in the old rig. Working fine now. As a few have asked, YES you have to turn it on and off manually. I just put a push on/push off button switch on the dash and it is working great. Thanks for the help all!!! One more thing is which wire was it that was broken in the harness? I would like to eventually get around to fixing that right. Thanks again.