O/D light flashing...firm shifts, jumpy speedo

[clp13294]

hey guys i was driving my truck yesterday and i noticed when i started the truck to leave the track the O/D light was flashing and continued to flash the entire way home and the truck was shifting late and very hard. i started it again about 3 hours later and its still flashing. the speedo is a little jumpy but its been like that since i bought the truck last year. what could it be?

 

['94IDITurbo7.3]

VSS sensor in the rear diff. it is used for ABS funtions and also speedo. i would start with that. get the codes pulled to.

 

[flareside_thun]

x2 It may be as simple as just pulling the VSS and cleaning the magnet, they tend to collect metal fragment on them and that can play hell with everything.

 

[clp13294]

ok i will start there. how do i go about pulling codes from the truck? i have a code reader from my old foxbody mustang which i believe is OBD1, will this code reader work?

 

[LSOSGT1109]

Your reader should work just fine. You will probably get a code 29 ( insufficient info from VSS). Your VSS may just need cleaned off. If it needs replaced, it is very simple to do and they're only about 20-30 bucks.

 

['94IDITurbo7.3]

Do all OBD 1 ford's have the same connector?

 

[clp13294]

ok i replaced the VSS sensor because it was cheap enough and easy enough to replace. light is still flashing at idle, havent driven it yet. will i have to log a few miles on the truck for it to notice the sensor is replaced? have not pulled codes yet either. will do that soon. i pulled my groin muscle so i can only work in short bursts otherwise my leg stiffens up and i cant walk haha. thankyou so much for the help guys.

 

[franklin2]

Don't be scared of the computer. It knows something is wrong, and it wants to tell you, that's why it's flashing the light. Put your code reader on it and see what it's trying to tell you. Much easier than crawling under the truck to replace the vss sensor.

 

[clp13294]

before i go out to pull codes, where is the diagnostic port on these trucks? iicrc the mustang diagnostic port was under the hood on the drivers side on the firewall, will this one be in the same general area?

 

[OLDBULL8]

If you continue to drive the truck, it will ruin the transmission. When the OD lite is flashing, it's telling you something is wrong. When the OD is flashing the tranny has gone into limp mode, the harsh shifts is because you only have 2nd and reverse. On a 94 the VSS is only for the ABS. The MLSP on the tranny is what operates the speedo, along with the tach sensor on the engine. Check the connector on the tranny, could have bare wires shorting to ground or loose.

 

[Compu Doc]

before i go out to pull codes, where is the diagnostic port on these trucks? iicrc the mustang diagnostic port was under the hood on the drivers side on the firewall, will this one be in the same general area?

On my truck it is on the passenger side near the passenger side battery but mine is an E350. I think the F series have to computer on the drivers side under the dash so look under the hood on the drivers side for the connector. It may have a past plug on the end that you need to remove in order to plug your computer in and it may say diagnostic connector.

Here is a good guide.

http://www.troublecodes.net/Ford/

 

['94IDITurbo7.3]

before i go out to pull codes, where is the diagnostic port on these trucks? iicrc the mustang diagnostic port was under the hood on the drivers side on the firewall, will this one be in the same general area?

Yes.

 

[rjjp]

When the OD is flashing the tranny has gone into limp mode, the harsh shifts is because you only have 2nd and reverse.

Bet it's in high pressure mode, all gears but shift at maximum line pressure, same reason I can't cruise over 80 for extended periods... My bet is the PSM, because of the bouncing needle.
But pull the codes and post them here.

 

[flareside_thun]

Yes, all OBD1 Fords have the same connector. The MLPS has NOTHING to do with the speedo. It's job is to sense what gear the trans is in and it also engages and disengages the reverse lights, hence the reason the MLPS needs to be adjusted when replaced. Definitely pull codes. I would have done that before spending the money on the VSS. Of course, I'm a firm believer in NOT throwing parts at something to fix an issue.

 

[Kevin 007]

X2 for checking the big harness plug on the passenger side of the trans for broken or bare wires or a dirty connection. It can play games with EVERYTHING as well. It was the main issue relating to the terrible trans issues I had at one time. I have installed a harness repair kit which are easyt to find on ebay.