I realized that this morning. I am so glad the truck I bought to replace this one is a 96. I obviously am obd1 handicap. I will be testing tps voltage. Wish Ford put it in an easier place to get at. Thanks for the link.

 

tps checks out. ~0.9 volts at idle ~4.3 volts at wot ~4.8 volts from VREF. I spotted a rotted vacuum line. Going to replace and see if that does anything.

 

No luck. Replaced bad vacuum line. No change. Anything else I should check before I give up and take it to a shop?

 

It has to be a sensor which one i have no idea, i have an AOD hydraulic controlled transmissin and at WOT it holds gears till they wind out. My first gear goes up to 45mph second kicks in and winds out at exactly 70 mph then my third will top out at 120 mph.

 

Does this problem occur every time you go WOT or only when pulling or going up a grade? The reason I bring this up is my mother has a 1995 GMC K2500 with a 350 and the 4L80E transmission and her truck will really hold the gears at WOT but it does shift eventually. Unless you're going up a hill. In which case you put it to the wood, it will kick back a gear or two and won't shift back into the higher gears until you are over the hill. Personally I think her gears are to tall for the truck, she has 4.10 gears and the 350 has about 350,000 with no rebuild so its obviously lacking power.

Anyways if it does this when you are going up a hill or with a load it could be that is just the way the truck handles it.

 

Yea exactly when does it do it? And i think a vid for us to see would be a good idea. WOT is really supposed to hold gears if not there would be no point and motor would bog down.

 

I know you said you had a bad vacuum line did you check all vacuum lines and connections, Mine is a 95 and i had 2 bad vacuum lines a cracked plastic connector and a leaky break booster, Im not sure wich one fixed mine cause i repaced it all when i found it. shifts perfect now. ( mine would shift at wot but a severe hesitation and one heck of a hit when it went). all gone now.

 

I visually inspected the entire engine bay and saw no other obviously worn lines. I checked every connector I could find in and under truck. Doesn't mean I didn't miss anything.

It happens on flat road at wot. It doesn't wind out. It hits the shift point and bogs down. Guess I should have made that clearer in my first post.

 

So it happens on flat ground. Hmmmmm. Here's an idea, I don't know what it will prove other than that maybe second gear does work at WOT but with a little extra motivation. Go find a back road that is very long. Put the truck in first gear and stomp on it. When first gear runs out of steam MANUALLY shift the gear selector into second gear. If it shifts under this set of circumstances then you may have a bad clutch pack or plugged valvebody(I think those are the proper terms, not to sure. Someone with more knowledge please confirm).

The reason I bring this up is my very first truck was an 85 Silverado with the 355ci and TH-350 transmission. Obviously being a 16 year old kid I abused the hell out of it. One day after getting stuck and rocking the truck out of a mud pit too hard the truck lost all gears. I was new to vehicles and had no idea what the problem was so I had it towed home and it sat in my moms driveway for a month. One day for ****s and giggles I went out and started it up. I put it in reverse thinking nothing would happen then lo and behold it started backing out of the driveway. Once I was on the road I put it in drive and gave it a little gas. The engine rev'd up but the truck didn't move. I moved the selector down to second and same story. Third times the charm so I put it in first and it went into gear. Somehow I just turned my automatic Chevy into a "semi-auto". I drove it for 9 months like that, having to shift from first to second to third and back down manually. I remember a friend saying I might have burned out the clutches or valve body or something along those lines.

Anyways just something to check. Good luck.

 

I did what you suggested. Let it wind out in first and it as I was about to shift to second it bogged down. At this point I manually shifted to second and it went into gear. Wound it out in second and it bogged down again but this time it would not manually shift into 3rd. Repeated with same results. This leads me to beleive it is not the trannsmission. I am thinking it is a fuel delivery problem. I am going to start by changing the fuel filter. If that doesn't work I will test fuel pressure and go from there.

 

Ok, i agree on the codes for your cel, as everything passing,some ob1 modules do not have a Wot test though. the most common engine errors to cause tranny problems would be the tps or vaccum bad wiring, if those pass ok as you say they are would lead someone to think its a tranny problem or the electrics to it, such as the transmission control module. But what gets me is the bog down ???, wich still leads to a fuel delivery??? I have one extra idea! those years of trucks did not use the MAF sensor for the fuel mixing but lent more on other sensors. Not knowing if during your bogg down if you notice black smoke outta your tail pipe (not always present) but if your MAP sensor failed only at WOT, would indeed cause bogg, down shift errors possible black smoke do to a serious rich mixture! You can check the MAP sensor with with a volt meter and applying vaccum volts should drop as vacum applied at about 30 inch oz of vaccum should be near a WOT condition and if it is bad at the WOT position it will lose vaccum voltage on the meter will jump back, if this happens it is bad and more than likely the source of your problem. Im sure any way you look at it your sick of workin on it good luck!!!

 

That sentence has soooooooo much truth behind it.

 

LOL, been there

 

bog down huh, this is really interesting... if you had slippage the motor would just rev up even more not bog down. I am starting to believe it is not the transmission as well, this seems to be an up front problem which seems like fuel cutting off for a second. How are these trucks governed for top speed? Is it in the transmission programming and read from the VSS? My truck isn't governed so I wouldn't know... hope someone chimes in!

 

Sounds like the bog down could be the TC locking up or unlocking.
I say this cause im in the process of fixing the same problem on my 96 but my bog is the TC locking back up right before it would normally shift.