Please someone help! Engine stumbling and bucking
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New User
Joined: Aug 2010
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Please someone help! Engine stumbling and bucking
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:
Map Sensor
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. Checked fuel pressure after the filter and I'm getting 35 PSI at idle and 40 under load.
Put in a bottle of fuel system cleaner and some 91 octane fuel. Seemed like it got just a hair worse.
Also check for code and got nothing!
This is our business vehicle and I really need to get it fixed. Please if anyone has any idea let me know.
Thanks!
Changed:
Map Sensor
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. Checked fuel pressure after the filter and I'm getting 35 PSI at idle and 40 under load.
Put in a bottle of fuel system cleaner and some 91 octane fuel. Seemed like it got just a hair worse.
Also check for code and got nothing!
This is our business vehicle and I really need to get it fixed. Please if anyone has any idea let me know.
Thanks!
Senior User
Joined: Jul 2010
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for a quick question, the fuel pressure should rise when given throttle? i only ask because im having issues with my truck under load, my pressure goes like so, EO about 38psi ER 30psi if i throttle it it drops to about 28 then boosts to 32 or so, and relevels at 30sorry i know better than to hijack a thread.
Der Postmeister
Joined: Sep 2006
Posts: 6,859
Likes: 560
From: Long Beach, Calimexiforia
If the MAP was left dysfunctional for a while, that sensor input may have been locked out by the ECU. Disconnect the battery for a minimum of 5 minutes to clear the KAM (Keep alive memory).
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Yes so you have a problem.. weak pump/s or clogged filter.
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Thanks for the input guys! I'll check for any leaks in the air injection lines. The truck is actually driven daily as a work vehicle so it never sat for any period of time. I did suspect the map could be the problem so I tried a new one and disconnected the battery for 5+ Min.
I should have mentioned to that I had taken the truck to the dealer when this happened and they said all it needs is plugs and wires. They wanted to charge me $550 so I said no way and did it myself. I think I would have burned the place down if I would have paid them $550 for plugs and wires and it didn't fix it!
If anyone else had had this same issue, please chime in! I'm about ready to park the truck on the train tracks!
I should have mentioned to that I had taken the truck to the dealer when this happened and they said all it needs is plugs and wires. They wanted to charge me $550 so I said no way and did it myself. I think I would have burned the place down if I would have paid them $550 for plugs and wires and it didn't fix it!
If anyone else had had this same issue, please chime in! I'm about ready to park the truck on the train tracks!
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Cargo Master
Joined: Jul 2009
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From: Des Moines
Don't forget vacuum leaks! Bucking and stumbling are classic symptoms of a vac leak.
There's several different methods for checking for them. What I've done in the past is unhooked every vac line from it's apparatus [such as the EGR or vac canister], plugged them, and then, with the engine running, hook them back up one by one. If a particular component is bad, the engine will start the bucking and stumbling. Granted, your problem is under acceleration so this may not work, but you might get lucky.
Also check the TPS. You may not have an error code for it but that doesn't mean it's not bad.
There's several different methods for checking for them. What I've done in the past is unhooked every vac line from it's apparatus [such as the EGR or vac canister], plugged them, and then, with the engine running, hook them back up one by one. If a particular component is bad, the engine will start the bucking and stumbling. Granted, your problem is under acceleration so this may not work, but you might get lucky.
Also check the TPS. You may not have an error code for it but that doesn't mean it's not bad.
Der Postmeister
Joined: Sep 2006
Posts: 6,859
Likes: 560
From: Long Beach, Calimexiforia
No such thing as no codes. Codes #11 of #111 for system passed, or your not in scan mode.
Der Postmeister
Joined: Sep 2006
Posts: 6,859
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From: Long Beach, Calimexiforia
Check plug wire routing against your routing diagram for cross fire.
Senior User
Joined: Oct 2009
Posts: 177
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From: ct
i would start with some of the basics. put a spark tester on each cyl. one at a time. the type that allows you to view the spark intensity. check for consistency and brightness of each cyl.Next i would pull each plug wire while the truck is running(with a quality plug wire puller)one at a time to check that the consistency of the drop is equal. Then pull each plug to compare the burn pattern of the cly. Next do a compression test of each cyl. to confirm all cyl. are within 10 pnds of each other and are within the normal specs.Next put a noid light on each of the injectors to see if the signal is good from the pcm.
This is a good start for your diagnosis and should only take about an hour.
This is a good start for your diagnosis and should only take about an hour.