Weird hesitation during acceleration
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Weird hesitation during acceleration
Hey guys, I'm back with an old issue I've been chasing for a while. Here's the best I can describe it:
My truck (read sig.) occasionally hesitates at low speed take offs. Only occurs when it warms up. How it happens is usually, from a stop I will accelerate, RPMs up to 1100 and it will suddenly bog down to 900-1000 for half a second and then rev normally and shift. It's not consistent, sometimes it never does it, other times it will bog twice or three times in a row from stopping.
Here's what I know so far: The IAC is a new Borg Warner unit from a few months ago. It's got sufficient power and ground. The TP sensor is original. Checked VREF at 5 volts, SIGRTN at .9 - 1 volts and when unplugged, the sensor has a normal ohms sweep when you go from rest to WOT. I have just scrubbed the throttle body and reset the KAM so the computer could relearn if necessary.
There are no codes stored in the computer. Truck has around 184k miles and runs good aside from this issue. I'm stumped, I need suggestions on what to check next. I work for Ford and will have my fellow techs look too but I want to know what you guys think.
My truck (read sig.) occasionally hesitates at low speed take offs. Only occurs when it warms up. How it happens is usually, from a stop I will accelerate, RPMs up to 1100 and it will suddenly bog down to 900-1000 for half a second and then rev normally and shift. It's not consistent, sometimes it never does it, other times it will bog twice or three times in a row from stopping.
Here's what I know so far: The IAC is a new Borg Warner unit from a few months ago. It's got sufficient power and ground. The TP sensor is original. Checked VREF at 5 volts, SIGRTN at .9 - 1 volts and when unplugged, the sensor has a normal ohms sweep when you go from rest to WOT. I have just scrubbed the throttle body and reset the KAM so the computer could relearn if necessary.
There are no codes stored in the computer. Truck has around 184k miles and runs good aside from this issue. I'm stumped, I need suggestions on what to check next. I work for Ford and will have my fellow techs look too but I want to know what you guys think.
Senior User
Joined: Jan 2017
Posts: 146
Likes: 0
From: Dallas-Ft Worth
Hey guys, I'm back with an old issue I've been chasing for a while. Here's the best I can describe it:
My truck (read sig.) occasionally hesitates at low speed take offs. Only occurs when it warms up. How it happens is usually, from a stop I will accelerate, RPMs up to 1100 and it will suddenly bog down to 900-1000 for half a second and then rev normally and shift. It's not consistent, sometimes it never does it, other times it will bog twice or three times in a row from stopping.
Here's what I know so far: The IAC is a new Borg Warner unit from a few months ago. It's got sufficient power and ground. The TP sensor is original. Checked VREF at 5 volts, SIGRTN at .9 - 1 volts and when unplugged, the sensor has a normal ohms sweep when you go from rest to WOT. I have just scrubbed the throttle body and reset the KAM so the computer could relearn if necessary.
There are no codes stored in the computer. Truck has around 184k miles and runs good aside from this issue. I'm stumped, I need suggestions on what to check next. I work for Ford and will have my fellow techs look too but I want to know what you guys think.
My truck (read sig.) occasionally hesitates at low speed take offs. Only occurs when it warms up. How it happens is usually, from a stop I will accelerate, RPMs up to 1100 and it will suddenly bog down to 900-1000 for half a second and then rev normally and shift. It's not consistent, sometimes it never does it, other times it will bog twice or three times in a row from stopping.
Here's what I know so far: The IAC is a new Borg Warner unit from a few months ago. It's got sufficient power and ground. The TP sensor is original. Checked VREF at 5 volts, SIGRTN at .9 - 1 volts and when unplugged, the sensor has a normal ohms sweep when you go from rest to WOT. I have just scrubbed the throttle body and reset the KAM so the computer could relearn if necessary.
There are no codes stored in the computer. Truck has around 184k miles and runs good aside from this issue. I'm stumped, I need suggestions on what to check next. I work for Ford and will have my fellow techs look too but I want to know what you guys think.
Expect lots of white smoke for a bit. Remove the shim and take her for about a 10 min drive. What you're effectively doing is steam cleaning the engine.
Don't know that this will help your problem, but it won't hurt.
Trailering
Joined: Feb 2006
Posts: 23
Likes: 0
I have had this exact problem on my 93 F150 351w. I replaced my emissions vacuum lines last week with new silicone rubber lines (I posted a thread on it about a week ago) because the original nylon lines had become brittle and starting to break. I have not driven enough since that job to be completely certain, but I think it might have corrected my hesitation problem.
Senior User
Joined: May 2014
Posts: 287
Likes: 1
From: Cedar Lake, IN
I had an issue similar to that and it turned out the fuel pump was going out and not pumping enough fuel when I hit the throttle. That's the first thing I'd check. It could also possibly be the throttle sticking a bit and not properly opening.
Senior User
Joined: Jan 2017
Posts: 146
Likes: 0
From: Dallas-Ft Worth
That's actually a really good thought; I'd bet you might be onto something.
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