Erattic Shifting:(

[SewperDrewper]

So I have read that a bad tachometer sensor can lead to shifting that is erratic and harsh, but you can diagnose that by seeing if the Tach bounces. In my truck, my tach is spot on, but my Speedometer bounces all over the place or just stays at zero. I was told by the previous owner that it was a bad speedo cable. Is this true? If so, how hard/expensive to replace? Thanks, Drew.

P.S.- It's a 1991 F350 Crew Cab 4x4 7.3IDI E4OD w/95K Miles

 

[snicklas]

Drew,

That new of a truck will not have a "speedometer cable" from the transmission. There is a VSS (Vehicle Speed Sensor) in the top of the read diff housing. It should be on the drivers side of the pinion... (at that is where it is on my 03). It is a hall effect sensor that reads from the tone ring on the ring gear. This sensor can get dirty from particals in the oil since this is a magnetic sensor. If the truck can not read a steady speed it can throw the E4OD into limp mode, with harsh shifts. When it is in limp mode, the O/D Off light should flash. It is not hard to replace, one 10mm bolt and I believe the sensor is around $20...

 

[icanfixall]

Get under the truck and find the cable where it enters the trans. There is speed sensor there. Replace it and your problems are gone. You can test the function of the cable by lifting the truck off the ground and disconnecting the speedo cable from the cruise control. Put the truck in gear and watch how it spins. Then hook it up and disconnect the cable leading from the cruise control to the dash. Put in gear and watch again for it spinning. Even if the dash speedo head is broken but the cable is spinning you will be able to run the truck with no problems. Nothing feeds off the dash speedo head. Its off the trans. The E4OD trans gets a message from the injection pump as to how much pressure it should be making depending on how much throttle you are using. Push deeper to the floor and the trans makes more line pressure. This switch is called the tps and the voltage going to the computer must be .96 to 1.2 volts with a digital voltmeter. The high voltage makes for a fimer shify but not higher than 1.2 volts at idle setting engine off. If the computer sees 5 volts wide open throttle it will shut down and put you in limp home mode... Only 2nd and reverse with neck breaking shifts...

 

[82F100SWB]

Just for clarification, the 91 trucks are still the old body, and do have a cable drive speedo, it's the 92+ trucks that are electronic off the diff.

 

[SewperDrewper]

Thanks for all the help guys. To Snicklas: I do have my O/D light flashing. Thanks for the quick Diagnostic.
To icanfixall: You are more help than I thought I would ever get. This site rocks. I take it that the reason my cruise control is also very erratic is for the same reason since the sensor for the speedo is linked to the C/C? Thanks again guys, I'll go home and take a look at it and let you know how it goes.

 

[snicklas]

Just for clarification, the 91 trucks are still the old body, and do have a cable drive speedo, it's the 92+ trucks that are electronic off the diff.

Thanks, I did not realize the early E4OD has the output on the transmission. I had thought with the electronic trans, came the rear sensor.

 

[SewperDrewper]

Alright guys...stupid question time! I got home late and didn't have much time to look, but the only sensor I could find was the one that was attached to the transfer case. There is only one other one that I could find, and it was attached to the arm of the lever that actuates the transfer case I believe. If anyone can steer my naive a$$ in a closer direction it would be appreciated. Thanks again.

 

[rjjp]

It's on the tailhousing of the transfercase

 

[icanfixall]

Yes... Just follow the speedo cable. Its kinda acts like a generater when it works. I replaced mine and just had to "take it apart" to find out just whats inside. Really simple too. There actually is two switches on these transmissions. One is the speedo cable generater and the other is the neutral safety switch on the shift arm. Then we have the main trans electrical plug behind the exhaust heat shield on the passenger rear of the trans. If you ever remove the heat shield remember to put it back.... Otherwise you will burn up the plug from the radiant exhaust heat...

 

[SewperDrewper]

DAAAMMMMNNNN! Haha. Bought the sensor and replaced it (which by the way was a huge pain in the ass since the tolerances between the body of the sensor and the transfer case was so tight. I ended up have to sand it down a fraction for it to finally go home) However, same issue. I played with the cable a bit, and it spins nice and free. Wife was in the truck and said it was spinning the speedo as well. Any other ideas? Maybe bad wiring in the plug?!

 

[SewperDrewper]

Anybody?

 

[SewperDrewper]

So after asking a few more questions, someone told me the speedo sensor has to be VIN matched. Could this possibly be my problem since I trusted the "experts" at good 'ol Autozone when they looked it up by year and motor?

 

[Goofyexponent]

How is your FIPL voltage?

I am fighting with my truck now, It is saying the FIPL voltage is off, but I KNOW it's not. I checked it. There are no flat spots in teh voltage, and it goes in and out of limp mode by itself. I just went all week with no limp mode, on the way home tonight it just went in again.

 

[SewperDrewper]

I could always google it...but what does FIPL stand for?

 

[Goofyexponent]

Fuel Injection Pump Lever.

While adjusted correctly, it should be no less than about 1 volt at idle (when warmed up, or the high idle solenoid dis connected) and no more than 4.5 volts at WOT.