95 F150, 4.9, 5 speed stalls
 

My 95 F150 2WD with the 300 and 5 speed stalls when taking off. If I rev it up and slip the clutch, it will usually get moving and run okay. It is also getting pretty bad mileage, like between 12 and 14 mpg.

It doesn't do it all the time, but it is getting worse. When I pulled codes a few weeks ago, the only thing showing was the fuel pump relay and the O2 sensor. I have replaced both of these, with no improvement on the stalling front. The O2 sensor did help the mileage, it is up to 15.2 highway, but this truck used to get 18+.

I have replaced several vacuum lines; I cannot find any vacuum leaks with starting fluid.

The negative battery cable insulation was cracked, so I replaced it and cleaned both terminals. All the factory ground straps are in place, and seem to be making good contact.

When it is acting up, the speedometer will bounce about 5-10 mph. When the truck is running right, the speedometer is steady. I did pull the VSS to clean it, no metal whiskers were on it.

It just dies like the key was shut off, before the vehicle has a chance to move; the engine doesn't even get a chance to pull down from the clutch engaging. This is a real pain when pulling a boat out of the water.

I have good flow through the fuel filter, but haven't been able to check the fuel pressure (I think I loaned my guage to my cousin). Moving wiring harnesses hasn't made a difference, even though the engine harness is covered in oil that leaked from the valve cover.

It wil do it in either forward or reverse gears.

Using the search function; from what I have been able to find, it seem s like either the VSS or the speedometer itslef is going bad. Does this make sense?

The truck has 183K on it.

I really can't afford to just throw money at the problem, and a new to me truck isn't in the budget either. If I could afford the gas; I would put my 77 F250 4WD back on the road, at least it runs right.

Thanks for the help,

Robert

The [PSOM], Programable Speedometer Odometer Module has been known to cause drivability issues. The speedometer fluctuating is a good sign your headed in the right direction. Fuse 8 and 18 interior fuse panel feeds the PSOM, If you can duplicate the concern, try removing these fuses and see if it eliminates your issue.

So the next time it stalls, pull both fuse #8 and #18?

If I understand what you are telling me, this will cut power to the PSOM adn if it sllows the truck to run right; the next step is to replace the PSOM with one from a junkyard, right?

I will try this tomorrow, it is getting dark and raining a bit here now.

Thanks,

Robert

Yes 8 and 18, you will loose some accessories, shift lock, courtesy lamps, power windows, etc. But nothing I can see you can't work around. Test not entirely conclusive but it definately would point at the Speedometer.

Okay, thanks. If the Speedometer prroves bad, I forsee a trip to the junkyard tomorrow.

RObert

If it is necessary to replace the speedometer you will want to determine the conversion constant in the original speedometer and transfer it to the new one to keep the speedometer accurate. Search the thread under conversion constant or speedometer calibration. There is a post under Bronco MPG page 2 on the procedure.

Well it is looking more and more like the PSOM, I pulled both fuses #8 and 18 and the truck ran better than it has in a year. Put he fuses back in and it died on takeoff again. Then I tried just pulling one fuse, #8 made no difference, with #18 out it works fine.

I tired a new VSS, since it was raining today and I really didn't want to drive the 65 miles to the junkyard and pull parts in the rain. The new VSS had no noticeable effect, so tomorrow I go to the junkyard.

There is supposed to be a 95 there, so hopefully I won't have to recalibrate the PSOM. Before puling my old one, I plan to see what it is set at; when I run by the radar trailers the flashing numbers agree with what is being displayed on the dash.

Robert

Sounds good. Couldn't remember, it's been a long time, so I did some research. If you only need to read the conversion constant it's pretty straight forward.
Press and hold down the reset button while turning the key to run.
The pointer will prove out, codes will appear and an E on left side for English.
Press and release the reset again. The conversion constant and [CAL] will appear in the display.

The "new" PSOM cured the driveability issues.

One bad thing and one sorta bad thing though. The bad part is that the new odometer has roughly 46,000 more miles on it than the truck actually has; I plan to keep this truck and drive it until it falls apart, I will make a note of this replacement to keep with the truck.

The sorta bad is that I got in a hurry and forgot to get the constant from the original PSOM, the new one has a constant of 972, and the way I read the chart in the article I need a constant of 914 for my 31x10.50 R15 tires. I will check the original tomorrow.

Speicher thanks for all your help.

Robert

Your welcome.

did your speedo bob while moving because mine does? by the way my truck is 94 f150 I6 5 speed 4x4

rusty, these old speedos were bad for failing.. mine doesn't work it just likes to jump from 10 mph to 85mph no matter the speed, when i shift it will hit what speed i am at for about 2 seconds then start jumping around again.. and almost all of them that i have seen or worked on are like this or they are just not working..

well mine works it just bobs a little i dont think im gunna worry about it till it goes out

yeah.. when i'm in 4th and at 2k i'm going about 45 mph.. when i'm in 5th and at 2k i'm going 55mph.. thats all i know and all i need to know.. so i haven't replaced mine yet.. money down the drain for me.. but maybe i'll get around to upgrading the entire dash

What is the year range for when the PSOM was used? Do they all interchange? (i.e. same electrical connection). Lastly, where is it located?