Please someone help! Bad hesitation while accelerating!
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New User
Joined: Aug 2010
Posts: 18
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Please someone help! Bad hesitation while accelerating!
Have a 1991 Ford E350 with the 460 (7.5L). Van has been running great up until 2 days ago. Out of nowhere it started hesitating and bucking during acceleration. Had no idea what could be wrong so I decided to start shotgunning parts at it.
Changed:
Fuel Filter
Plugs
Wires
Cap and rotor
Coil
PCV Valve
Did Not fix the problem!
While I was at it, I pulled off the Idle Air Control valve and cleaned it. Also pulled vacuum on the EGR valve to insure the diaphragm wasn't bad and the valve wasn't stuck.
Still Nothing!
Fuel pump in the tank is 4 months old and cat is about a year. Don't think it's either of those.
Don't know how old the frame rail fuel pump is, but I can hear it turning on. Also pulled vacuum on the fuel pressure regulator to check for a torn diaphragm. Seem fine but don't know for sure it's not stuck.
Put in a bottle of fuel system cleaner and some 91 octane fuel. Seemed like it got just a hair worse.
This is our business vehicle and I really need to get it fixed. Please if anyone has any idea let me know.
Thanks!
Changed:
Fuel Filter
Plugs
Wires
Cap and rotor
Coil
PCV Valve
Did Not fix the problem!
While I was at it, I pulled off the Idle Air Control valve and cleaned it. Also pulled vacuum on the EGR valve to insure the diaphragm wasn't bad and the valve wasn't stuck.
Still Nothing!
Fuel pump in the tank is 4 months old and cat is about a year. Don't think it's either of those.
Don't know how old the frame rail fuel pump is, but I can hear it turning on. Also pulled vacuum on the fuel pressure regulator to check for a torn diaphragm. Seem fine but don't know for sure it's not stuck.
Put in a bottle of fuel system cleaner and some 91 octane fuel. Seemed like it got just a hair worse.
This is our business vehicle and I really need to get it fixed. Please if anyone has any idea let me know.
Thanks!
New User
Joined: Dec 2009
Posts: 14
Likes: 0
fuel issue?
Did the bucking start within 10 minutes of having refueled? If so, it could be water in the gas that you just bought.
I am not familiar with a 91 model, so I am wondering if the engine is computer controlled, and so will provide diagnostic engine codes. If so, pulling the codes is the next thing you should do to learn what is really the problem. Auto parts stores like Autozone and Advance Auto parts, and others, will give you a free code pull with their reader in the store parking lot. Call them first before driving to the store.
I am not familiar with a 91 model, so I am wondering if the engine is computer controlled, and so will provide diagnostic engine codes. If so, pulling the codes is the next thing you should do to learn what is really the problem. Auto parts stores like Autozone and Advance Auto parts, and others, will give you a free code pull with their reader in the store parking lot. Call them first before driving to the store.
Thread Starter
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New User
Joined: Aug 2010
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Thanks for the reply rooster. You could be on to something. It did happen the same day it had gas put into it. I would be a little surprised if it was water though, since I'm in California and it's summer time. I checked fuel pressure today and it's right within spec. 35 PSI at Idle and 40 under load. Also tried a new MAP sensor just for fun.
As for codes, I check it but nothing was in there.
I'm thinking its time to give up and let someone else figure it out! Please if anyone has any ideas, let me know. I'm ready to burn the truck to the ground!
As for codes, I check it but nothing was in there.
I'm thinking its time to give up and let someone else figure it out! Please if anyone has any ideas, let me know. I'm ready to burn the truck to the ground!
2nd Gear
Joined: Jan 2026
Posts: 2
Likes: 0
Thanks for the reply rooster. You could be on to something. It did happen the same day it had gas put into it. I would be a little surprised if it was water though, since I'm in California and it's summer time. I checked fuel pressure today and it's right within spec. 35 PSI at Idle and 40 under load. Also tried a new MAP sensor just for fun.
As for codes, I check it but nothing was in there.
I'm thinking its time to give up and let someone else figure it out! Please if anyone has any ideas, let me know. I'm ready to burn the truck to the ground!
As for codes, I check it but nothing was in there.
I'm thinking its time to give up and let someone else figure it out! Please if anyone has any ideas, let me know. I'm ready to burn the truck to the ground!
5th Gear
Joined: May 2024
Posts: 5
Likes: 0
From: San Diego CA
So it was the in tank pump , high pressure pump or fuel pressure regulator? I have changed all but the in tank punp for obvious reasons. Although that was the first guess at want the problem is. Figures the last thing I am replacing.
Hotshot
Joined: Jul 2020
Posts: 10,543
Likes: 2,668
From: Near Salt Lake City
I am assuming your pump is shot
* That is the reason for me wanting you to drive it around with a pressure gauge taped to the windshield
A few other things in case it has a ton of miles on it
1) TP voltage sweep (throttle position) needs to be smooth and no cut outs from idle to WOT, that voltage needs to go up smoothly
Check that with a scan tool using the TP PID
2) Vacuum test the exhaust for restriction (vacuum gauge on the intake, brief WOT and retest vacuum number)
3) Spark plug condition (worn spark plugs are a common cause of lack of power / slow acceleration complaints)
* That is the reason for me wanting you to drive it around with a pressure gauge taped to the windshield
A few other things in case it has a ton of miles on it
1) TP voltage sweep (throttle position) needs to be smooth and no cut outs from idle to WOT, that voltage needs to go up smoothly
Check that with a scan tool using the TP PID
2) Vacuum test the exhaust for restriction (vacuum gauge on the intake, brief WOT and retest vacuum number)
3) Spark plug condition (worn spark plugs are a common cause of lack of power / slow acceleration complaints)
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