Recently bought a 91 B250 (5.2) conversion van with minor problems here and there. One of the issues though is that it will not kick into overdrive. It has no issues shifting from 1-2-3, but once I hit the highway and do any speed above 55, it revs pretty high, which I'm sure is killing a bit of gas mileage (not to mention it's pretty loud too).


Did a "key dance" code pull to see if I could pinpoint the issue, but the problem is, it appears to say 36 (then ends with 55), but there's a small delay from 35 to 36, so I'm not really sure if it's one or the other.

I've never done this before, but I've uploaded a video and wanted to see if someone could tell me which code it is. I'm probably just reading it incorrectly.

http://www.youtube.com/watch?v=jbUs2-H46gQ

Thanks,
Nat

 

you have a code 51.

Oxygen sensor stuck at lean position.
May be tripped by a bad MAP sensor system causing a rich condition, and the O2 sensor trying to compensate. The O2 sensor may still be good. The MAP assembly consists of two pieces, the valve and the vacuum transducer (round plastic unit with cylinder on top and both electrical and vacuum connections) - If you get hot rough idle and stalling, especially on deceleration, accompanied by flooded engine and difficulty restarting, that can be a bad MAP sensor causing the O2 sensor to try to compensate. If you get poor cold drive ability, stumbling and bucking, and acceptable warm driving with poor gas mileage (a drop of 10 mpg or more), that is usually the O2 sensor.

As for the Not going into overdrive, silly question, do you have the over drive button on or off?

 

There were 3 codes being displayed, 12, 51, and 55.

12 Battery was disconnected within the last 50 key-on cycles (normal)

51 Fuel system lean (some possible reasons given by Neutralvan above)

55 End of error messages (If you get this only, no errors were found)

 

I can tell you that it doesn't idle rough, and I've never had it stall before. But yes, back when it was cold out, it seemed a bit weaker unless I let it warm up for quite some time. The gas mileage is terrible too. I knew when I bought the thing that it'd be pretty thirsty, but dang, it seems like I'm getting 9-10 mpg with this van. Since the odo does not work, I really can't get an idea of what I'm getting, unfortunately.

With all of this, it seems like my code issue is with the o2 sensor.

As for the overdrive question, I assume I have it off. The button itself says "OD off", and pressing it while driving causes the button to light up, but no change in gears.

Thanks for the replies. I'm going to see if I can pop a new o2 sensor in and hope that does the trick.

 

Just stay away from the Bosch O2 sensors. They do not work well with our engines.