Bucking on acceleration when warm

eldonderino

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I've been having this problem for a while now. I've never noticed the problem when the truck is cold, after driving for a couple hours or so it starts to buck when I accelerate from stopped especially going up hill. I've tried feathering the clutch in different ways, if i give it more throttle it helps but still occurs. On occasion, especially when backing up i have heard a clunk.

I usually occurs towards the end of a trip I'm wondering if it's not picking up fuel properly when the tank is low. I'm going to fill up more often and see if it helps.

-New fuel filter
-Checked u-joints - couldnt find any play could one of them be seizing up? no vibration at high speed.
-Clutch was replaced maybe 15000 miles ago with a heavy duty clutch (previous owner)
-I'm going to bleed the clutch soon - It's a bit hard to shift, and on one occasion lost pressure in the pedal and got stuck in between gears.

Any advice on what to look at? I've read lots of posts some have pointed to throwout bearing, u-joints, bell housing bolts
 

eldonderino

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I'd say it's a fuel supply issue. Clogged filter, maybe air intrusion.
Thanks. I'm gonna start with filling up the tank after it starts and see if that gets rid of it, and run a gauge so I can watch the fuel pressure. i'll start reading up more about air intrusion.
 

Big Bart

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Two thoughts

1) The fuel tank sensors in our trucks are old and failing. Usually true then die. But perhaps yours is dying a slow inaccurate death.
2) The last 3-4 inches of the fuel pickup line is a big plastic thing referred to as a shower head. They fall/break off and all the sudden at 1/4 tank you can start to run out of fuel because the fuel is or sloshes below what is left of the fuel pick up line. Thus sucking air into the fuel line.

Start keeping your truck above half full and see if the symptoms go away. If not start looking for air intrusion.

FYI “Bucking“ is generally a sign of a lack of fuel getting to the IP.
 

eldonderino

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Could very well be. I'm down to one tank because the tank selector failed, and the sending unit has completely failed in the tank I'm using. I'll have to drop the tank one of these days.
 

ROCK HARVEY

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I’m in the middle of replacing my front fuel tank sender and fixing the “shower head” issue right now. The whole assembly isn’t available from anywhere I could find, but the actual sender itself is on Amazon here:

3mirrors Fuel Level Sensor Fuel Pump Sending Unit https://a.co/d/exJ0Hnx

It’s not exactly plug and play, because the old sender is welded to the pickup tube. I cut away the parts of the old sender backing plate that I thought might interfere with the new one, then used pop rivets to mount the new backing plate to what’s left of the old one. I had hoped that I could just transfer the new plastic part onto the old backing plate, but it didn’t work. I also had to bend the wire for the float to get it to the corect “full” and “empty” positions.

The shower head is available both from ford and off-brand, but definitely read the reviews before you buy an aftermarket one. Lots of people have them break apart in just a couple weeks. I just extended my pickup tube to the bottom of the tank and eliminated the shower head altogether. Good luck and let us know if that solves your problem!
 

Kalmanto

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I had bucking like you explained. Side of the road I cut the tubes up to waterseperater and put a piece of fuel line across.
That was my side of road fast fix.
 

KGIA103

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I had not used my front tank for a while because I wasn't confident in my selector switch and needed to make a long trip. I can easily get 250 miles out of the rear tank and fill up with 12 gallons or so which is what I did on my trip. Now that I'm at home base, I switched to the front tank and after about 140 miles it started to buck up hill. I immediately switched back to rear tank because I figured the pickup tube, shower head, had been compromised in the front tank. The bucking stopped as soon as I made the switch and hasn't happened since. I have drained the front tank and will drop it for inspection and repair soon.
Moral of the story: keep your tank topped off and use your trip odometer between fill ups.
 

Old Goat

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I’m in the middle of replacing my front fuel tank sender and fixing the “shower head” issue right now. The whole assembly isn’t available from anywhere I could find, but the actual sender itself is on Amazon here:

3mirrors Fuel Level Sensor Fuel Pump Sending Unit https://a.co/d/exJ0Hnx

It’s not exactly plug and play, because the old sender is welded to the pickup tube. I cut away the parts of the old sender backing plate that I thought might interfere with the new one, then used pop rivets to mount the new backing plate to what’s left of the old one. I had hoped that I could just transfer the new plastic part onto the old backing plate, but it didn’t work. I also had to bend the wire for the float to get it to the corect “full” and “empty” positions.

The shower head is available both from ford and off-brand, but definitely read the reviews before you buy an aftermarket one. Lots of people have them break apart in just a couple weeks. I just extended my pickup tube to the bottom of the tank and eliminated the shower head altogether. Good luck and let us know if that solves your problem!
It does not give the OHM`s for the sender.
I know 85/86 is one reading then jump to 87+ it jumps to another ohm.

Goat
 

Old Goat

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I had not used my front tank for a while because I wasn't confident in my selector switch and needed to make a long trip. I can easily get 250 miles out of the rear tank and fill up with 12 gallons or so which is what I did on my trip. Now that I'm at home base, I switched to the front tank and after about 140 miles it started to buck up hill. I immediately switched back to rear tank because I figured the pickup tube, shower head, had been compromised in the front tank. The bucking stopped as soon as I made the switch and hasn't happened since. I have drained the front tank and will drop it for inspection and repair soon.
Moral of the story: keep your tank topped off and use your trip odometer between fill ups.

I went through this after my front tank sender suddenly quit. I use a sharpie and wrote on the Wing Glass when I filled up. Think I went every 300 miles and filled up.

Didn`t use the rear tank as the PO didn`t, and didn`t know if it worked. After 5 years I pulled the bed and replaced the rear with a 38 Gal tank, new senders on both tanks as well as Shower Heads.

Front tank, the Float developed a hole and sank.
I kept both old senders...Just because you can`t have too much old stuff that might come in handy later on.
Both Shower heads were in pieces in the tank. But after 30 years what do you expect?

I see all this talk about not letting the tanks get too low or you will suck all the gunk from the bottom of the tank> Just where do you think the fuel is is pulled from?
When you are driving the fuel is getting slosched around.
The SH Sits on the bottom of the tank. Both tanks were squeeky clean.

Here are a couple links where to buy senders and SD`s.



Goat
 

ROCK HARVEY

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It does not give the OHM`s for the sender.
I know 85/86 is one reading then jump to 87+ it jumps to another ohm.

Goat
The one I bought reads 15 ohms at empty, and 160 at full. This works in my 89. I think the gauge is supposed to be 16-158. I didn’t realize it was different before 87.
 

Old Goat

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83 - 84
85 - 86
Rear/Front Full 8.5 - 10.5 Empty 63 - 85

87 - 89
90 - 91
92 - 93
94 - 97
Rear/Front Full155 - 165 Empty 5 - 15

The senders on the year groupings are probably a little different in design, IDK.

Just look at the links I posted above, all info there.
Probably not a bad idea to buy one of each to have on hand in case the supply dries up. I have 2 new one`s on the shelf in the shop.


Goat
 

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