2000 f-150 4.6.....Driving to work this morning,it's about 18 degrees outside...40mins into my drive I pull into passing lane at about 55mph kick it down into passing gear & the tach goes up to 4k but the truck falls on its face,won't accelerate,makes that sound that a dirt bike does when you try to drift start it but the plug is fouled...Sounds like it is starved for fuel...If I back off the gas & slowly increase speed ,no problems..It feels like the truck is shifting but it won't speed up,the rpm's are holding steady so it doesnt seem like the tranny is slipping,(which was replaced at 70,000mi,,truck now has 76,000,warranty expired at 75,000)...Somebody suggested a gate that is involved with the catalytic conv. is stuck. Any ideas?....it runs fine as long as I don't kick it down into lower gear.

 

After some more testing it seems to be related to how far I depress the gas pedal. With the truck in park sitting in my garage,60degrees, I start to rev the engine & when the pedal gets about 2 or 3 inches from the floor board the engine sort of cuts out & starts surging at about 3k-4k. The rpm it does this at seems dependent on how fast I depress the pedal. You have to do it fairly quick to avoid over-reving the motor. It seems like it would do the same thing if it pressed the pedal slowly but at a much higher rpm,don't realy want t try that...so I think it doesn't have anything to do with rpm range. Is there somehing that monitors the position of the throttle that could be malfunctioning?...At least it is still driveable!

 

You could have a dirty MAF sensor. If you do a search on here you'll find more info on cleaning that.
You could also have a plugged fuel filter.

 

Well,I've cleaned my MAF sensor & replaced my TPS sensor,I thought for sure that was going to be the trouble... Getting same results...Only good thing now is my CEL is on,so after work it's off to autozone to get the code read. Since my warranty has expired I should probably by a code reader! Is there a right & wrong way to install the TPS sensor? After I took the old one off the new one didn't line up with the tab. I had to either actuate the throttle to get tab to line up with inside of sensor or a had to rotate sensor to line it up with tab,then rotate back to line up with bolt holes,or I had to use my finger to manually turn the inside of the sensor so it would line up. I tried all of the above & now it seems that the idle hangs up around 2k for too long then slowly comes down. Not sure if I screwed something up or if my trbl is getting worse. haven't tried putting old one back on yet. I also cleared my CEL but it came back on in about 5mins. Had neg terminal disconnected for over an hour. Anybody know anything about the TPS sensor install?

 

If you had to do that to install the TPS sensor, then it is staying too far advanced all of the time. This is why the idle is high and the MIL is lit.
I would try putting the old one back on and see what happens.
Also, try unhooking the battery for about 15 min. This should reset the PCM and maybe it will run better.

 

To install the TPS you do have to rotate the sensor to line it up and then rotate it back against it's spring pressure to get the screws in.

 

Thanks for the reply, I will try your suggestions tonight after I get off work & get back from autozone. After doing a search on the TPS sensor I think I have installed it wrong.(maybe I should have searched 1st..lol). I am wondering, if TPS is the trouble, after I install it correctly will the trouble immediately go away or will I have to drive it for awhile. The Haynes manual didn't mention anything about the reinstall of the sensor,just a plug & 2 screws that required a small amount of c4 to remove!!! I thought it was going to be simple. Do you know of any tricks on installing that sensor properly?...I hope I didn't hose myself by moving that internal drum with my finger...Afterwards I repositioned it to match the original,but it didnt change the symptoms.

 

Thanks racerguy. Didn't see your post until I finished that last one. I figured I should have done that but since I still had half a screw hanging out of bottom hole(after I cut the head off) I couldnt do that. I will get that out tonight & retry the install..I guess I'll use the old one as a reference to where it should be.

 

Went to auto zone to get code read: bad TPS sensor,,that was with the new one installed....I think I have it installed wrong & I also think I broke it. ....I am getting the same voltage readings from it as I am the original. The auto parts store is going to let me exchange it for another. So that is what I will do tonight..I got the other half bolt out so I will be able to install properly.

 

Let us know how it goes.

 

I installed the TPS properly I think,,I rotated the sensor slightly counter-clockwise if you are looking at it from the drivers side,slid it onto the tab & rotated back to line up the bolt holes,,(there is now slight tension on the sensor)...problem is when I measure the voltages according to my Haynes manual they are quite different...Haynes manual indicates I should see 1v at closed throttle & 5v at wide open from signal to ground..I see the exact opposite?! but,the haynes manual also has the 2 pictures showing this test labled different..in one picture they show the signal terminal as the top terminal & in the next picture they show it as the middle terminal,so I am wondering if the process itself is even right..I am getting the full range of voltage just backwards?..I don't believe it is possible to install the sensor in a way that would cause readings to be reversed...I now wonder if the TPS is actually my trouble..It would be nice if someone was able to measure theirs. I put the + probe in the top connection & the - probe I took to the batt. ground. I had 5v at that point & when I rotated the throttle assembly towards me it dropped to 1v. I disconnected the harness from the sensor & measured 5v at the top terminal,however the other 2 terminals had no voltage,I thought 1 of them should have had a reference voltage. I wonder if I have a problem in my harness or computer...(measurements are taken with key on,engine off)..I have a few more tests to try tonight & then when the CEL comes back on I will get it read with this new sensor installed.

 

You should be measuring voltage using the Bn/Wh wire as ground (Ford calls that signal return), Gy/Wh is the TP signal which should read 1V at closed throttle and 5V at WOT (more or less) and the Gy/Rd wire should be VREF which should be 5V any time the igniton is on.

 

I will have to look closer for the colors,Is the top terminal the siganl,though? If so ,I am getting 5v closed & 1v wide open. What should I be getting out of the harness with it unplugged from the sensor?...I am only getting 5v at the top terminal which in my Haynes manual they call the "sig" on 1 photo & "gnd" on the other...I will have to clean up the wires & try to make out those colors tonight..something tells me I am only going to verify what I already did, just for the fact that I have replaced the sensor & trbl still exists.

 

Well,here is how my harness is wired:::
The brn/wht wire is my 5v ref voltage
The grey/red wire is ground
The grey/white wire is my signal wire.
I connected my meter between the grey/red & grey/white & rotated my throttle,,,voltage went from .7v/closed to 4.98v/wot.
This all happens to match up with 1 of the 2 photos in my manual,but they don't designate colors.

Now I think that my trouble was never the TPS..I never got the code pulled when the CEL 1st lit. I cleared that code & replaced the sensor,which I broke in the process,causing me to get a fresh code that read "bad TPS"...following me on this..So now that I have another sensor installed,I will wait for the CEL to return & get the code read & hopefully that will point my in another direction. ....I keep telling myself to let this be a learning lesson in order to keep my sanity. Feel free to post your thoughts,comments or poke fun!
Will keep updating till it is fixed.

 

How old is your fuel filter?
You could also try dropping the exhaust off the manifolds and go for a spin to see if it's any better in case you have a plugged convertor.