Speedometer proplem
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Other than that you need to put a O-scope on the signal from the rear end with the wheels off the ground and on jack stands. It could also be the VSS gap or bad wiring.
You may also want to read the pdf below:
http://www.wellsve.com/sft503/Counterpoint4_2.pdf
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Posting Guru
Joined: Aug 2004
Posts: 2,417
Likes: 4
From: Braham MN
My '97 was giving me problems like that. Abs light would come on, od off light would flash and it shifted like crap. Turned out it was the plug for the tail lights above the bumper. The plug slowly filled up with road grime and dust, the contacts finally got so dirty it wouldn't make good contact. Even with the lights off these trucks send a signal through the tail lights something about the converter unlock signal coming from the tail lights. I suggest pulling that plug apart and giving it a good blast of brake cleaner to shine it up.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
A shorted brake lamp wire to marker lamp wire or shorted bulb will disengage the TC clutch and turn off the speed control the same as stepping on the brake (BOO switch).
But I do not see how it would flash the OD lamp or the RABS lamp or cause bad shifting.
It would be the same as riding the brakes with the brake lights on.
But I do not see how it would flash the OD lamp or the RABS lamp or cause bad shifting.
It would be the same as riding the brakes with the brake lights on.
Posting Guru
Joined: Aug 2004
Posts: 2,417
Likes: 4
From: Braham MN
All I can tell ya is it was in the plug. I could tell the second I started it, the abs light would be on and the od light was flashing. So I had to reach in and wiggle that plug then it would go out and shift fine.
Elder User
Joined: Apr 2011
Posts: 881
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i have a similar problem i have a 89 f150 and the spedo quit working for me i took the gear out of the tranfer case it doesnt apear to be damaged and i havnt been able to turn the cable inner portion and look at the speedo at the same time to confirm oporation is there any other tricks you guys would suggest for checking this?
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
i have a similar problem i have a 89 f150 and the spedo quit working for me i took the gear out of the tranfer case it doesnt apear to be damaged and i havnt been able to turn the cable inner portion and look at the speedo at the same time to confirm oporation is there any other tricks you guys would suggest for checking this?
Elder User
Joined: Apr 2011
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Cargo Master
Joined: Mar 2007
Posts: 2,935
Likes: 34
From: Arcadia, Fla
While we are on wierd PSOM problems.... I got one now with my 95 E350. Its the same setup as the F-series so all problems would be the same between them.
Few years ago I had the capacitor leak acid out on the PSOM circut board and caused the OD to flash and hard shifting tranny, cruse not working. I got that all fixed till now. I have keeped track of my MPG and noticed a drop for the last few fill ups. Normally that bus gives 8.5 MPG now its 6 mpg and dropping! What I found out was the PSOM is not saving the mileage into the EEPROM!! Any thoughs about this? Speed and miles are good till you turn off the ignition so the calibrations are good.
I can give this suggestion to the OP about his issue. Even though you replaced the PSOM, VSS ect. Check that bulkhead connector on the firewall. I had seen few problems with that connector not making a good contact. I found one on my 89 F250 today which was causing a cruse control issue on it.
Few years ago I had the capacitor leak acid out on the PSOM circut board and caused the OD to flash and hard shifting tranny, cruse not working. I got that all fixed till now. I have keeped track of my MPG and noticed a drop for the last few fill ups. Normally that bus gives 8.5 MPG now its 6 mpg and dropping! What I found out was the PSOM is not saving the mileage into the EEPROM!! Any thoughs about this? Speed and miles are good till you turn off the ignition so the calibrations are good.
I can give this suggestion to the OP about his issue. Even though you replaced the PSOM, VSS ect. Check that bulkhead connector on the firewall. I had seen few problems with that connector not making a good contact. I found one on my 89 F250 today which was causing a cruse control issue on it.
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