we just bought a used 97 ford f350 7.3 powerstroke diesel. took it to have brake work done last week. seemed fine. then a few days ago, the speedometer would go all crazy back and forth when we go over rough spots in the roads and over bumps. but seemingly only when the rear tires would go over the bumps. this has been going on for a few days now. then today, the speedometer pegged to the max and stayed there. and the abs light came on and stayed on. also the overdrive was flashing. we got to where we were going and shut the truck off. after getting back in it and restarting the speedometer started working again but was all over the place like it has been for the last few days. we were almost back to town when it started running really rough. like no power. it sounded bad. after leaving it sit a few hours we went back to start it again. it started but sounds really horrible. anyone have any ideas?

 

check the plug on the veichel speed sensor (vss) on the rear axle
the vss may need replaced

 

I had a very similar issue and the plug and a length(3') of wire had to be replaced. I found the plug and harness at my local wrecker for 0.00!

 

The first part sounds like a vss issue but the vss while not cause the motor to run bad. With the OD flashing it should be shifting hard (its in limp mode) don't drive it much in limp mode it can cause major problems.

The vss is on top of the rearend. Check the plug and wiring to it and pull the vss out and clean the end of it and see if that helps

 

would this cause the truck to shift hard as well?

 

We post at the same time read my other post

 

did your truck loose power and sound bad as well?

 

thank you for your input.

 

I did not have a running issue as a result. I would suspect a few things went at the same time. I have only owned manual trans trucks so I am not sure if it is related.

 

where would the abs sensor be?

 

The vss and abs is the same

 

ok. thanks.

 

ok. thank you very much.

 

Btw welcome to FTE!

 

what would cause the overdrive light to flash? or what is causing the transmission to be in limp mode?