EFI 460 lacks power
New User
Joined: Jul 2005
Posts: 4
Likes: 0
From: Minnesota
Sounds like I have the same truck, same problem.
I have a 96 F350, 4x4, crew cab, long box, 7.5L, 183,000 miles. Underpowered.
I've done most of the same checks and replacements. New O2 sensor, plugs, K&N air filter, checked fuel pressures, checked fuel injector flows individually, no bad codes, checked flow through the exhaust, and I just don't have the power that it should have. I had a weak fuel pump in the rear tank and had less power when on that tank, but I finally replaced it and now the front and rear tanks/pumps perform the same. I suspect we could have a common problem, but I'm also at a loss as to what it could be.
I have a 96 F350, 4x4, crew cab, long box, 7.5L, 183,000 miles. Underpowered.
I've done most of the same checks and replacements. New O2 sensor, plugs, K&N air filter, checked fuel pressures, checked fuel injector flows individually, no bad codes, checked flow through the exhaust, and I just don't have the power that it should have. I had a weak fuel pump in the rear tank and had less power when on that tank, but I finally replaced it and now the front and rear tanks/pumps perform the same. I suspect we could have a common problem, but I'm also at a loss as to what it could be.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
So when I'm testing the pressure while the engine is running I need to have the vacuum hose off the fuel pressure regulator?
Today I found a new issue; or maybe it's the same issue? Normally when I fill my gas tank I don't fill it to the point where the tank is so full that it backs up into the filler neck. Today I did that and noticed gas was leaking from a gap on the top of the filler hose. There is a gap where the metal part of the filler neck and hose meet and it poored out quite rapidly. The gap is at the top of the hose so when filling it, naturally the gas flows on the bottom of the hose and therefor, no leak was detected. Not until the entire hose started filling with gas did I notice I had an issue.
Aside from letting debris into my tank, what other issue would this create for the way my truck runs? Could this be the culprit for the lack of power?
Today I found a new issue; or maybe it's the same issue? Normally when I fill my gas tank I don't fill it to the point where the tank is so full that it backs up into the filler neck. Today I did that and noticed gas was leaking from a gap on the top of the filler hose. There is a gap where the metal part of the filler neck and hose meet and it poored out quite rapidly. The gap is at the top of the hose so when filling it, naturally the gas flows on the bottom of the hose and therefor, no leak was detected. Not until the entire hose started filling with gas did I notice I had an issue.
Aside from letting debris into my tank, what other issue would this create for the way my truck runs? Could this be the culprit for the lack of power?
Yes the high pressure test procedure for both Engine On and the High Speed Test call for removing and blocking the vac at the regulator.
The leak at the filler could be introducing vent/pressure problems ......and you might already have some debris up in the "screen" on your pump assembly causing issues........
Good luck getting her fixed and back running to your satisfaction.......
Junior User
Joined: May 2011
Posts: 51
Likes: 0
From: NAVARRE FLORIDA
guttless 460
Well let me join the club 96 F250 4x4 460 and it sounds like we are driving the same truck. I've been thru 6 fuel pumps last one replaced the entire tank sending unit and pump on rear tank it went out about 3 weeks ago and now I'm sitting in my driveway at work with the 3rd dead pump in the front tank. scheduled to go to the shop for tune up, fix exaust leak from passenger side manifold, rear pump and now front pump, new pcm, coil, injectors, fuel regulator, im sure im leaving things out but all this because it runs great until u put ur foot in it and then it feels like you've got a cruise ship hooked to your bumper and it cant get out of its own way. Pitiful, I know I won't get great mileage out of it n I don't mind stoppin for gas every day cuz I drive ALOT OF MILES but damn it it ought to at least be fun to drive since I'm droppin $100 bill a day on gas. I love my truck n I'm going to figure this out. But im probably not going to be of any help with what finally fixed it since im doin it all at the same time. But I will definitely post everything I do and maybe by the process of elimination yall can figure out yours assuming the pile of benjamins I'm throwing at it fixes it. It's got just under 220k miles on it and alot of the parts I'm replacing are original so they need to go. I will add an 02 sensor to the list tho. Thanx for all the info and good luck! God bless!
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
Even the most seasoned pro would be proud of the care that I take when removing or installing parts. There are no kinks in the fuel flow and whether or not there is currently a clog in the pump screen, it was running like crap before and after the new tank and pump was installed. ??
Senior User
Joined: Feb 2012
Posts: 223
Likes: 3
From: Baltimore MD
Probably not a weak rear pump... The rear fills the front issue means that you lose fuel pressure when on the rear tank because the pump's work is half going to fill the front tank. That would sound like the multifunction reservoir.
More Turbo
Joined: Dec 2007
Posts: 641
Likes: 3
From: Umicorn UtopiaFantasyLand
What kind of long tube headers are you running? I have 96F350 std cab lb also with 460.About same mileage.
I scanned the trucks computer and not one single code came up. I even double and triple checked it to be sure; still nothing.
I don't know what could be causing my engine to be lugging so bad. I jacked the rear tires off the ground and ran it to get the tires spinning to see and hear if the brakes are dragging but everything is fine. The rear LSD is working fine as well I might add.
A while back I was thinking I had a dead cylinder or two but all the header primary tubes were hot and all were close in temperature.
Does anyone have a clue what could be causing the engine to be down on power?
For the record, stats are as follows:
-1996 F350 4x4 Regular Cab, Long Bed (actually a '95 but sold as the
'96 model year so it's OBD1 and does not have a MAF sensor)
-'95 460 7.5L V8 (90,000 miles)
-ZF S5-42 5-speed transmission, swapped from '93 F350 (78,000 miles)
-New clutch and clutch related items (about 2000 miles on them)
-Borg-Warner 4407 transfer case (same miles as engine)
-3.55 axle gear ratios
-Long tube headers
-Gutted Catalytic converter (O2 sensor is before CAT so no thrown codes)
-Y-pipe after cat. converter, dual pipes exit our rear with resonator tips
-New O2 sensor
-New gas tank, fuel pump, fuel filter
The O2 sensor is rather new but maybe it's slowly dying? I have noticed a lot of soot coming out the tailpipe. I've owned another EFI 460 with no Cat. Converter and it wasn't hardly sooty at all out the tailpipe.
I don't know what could be causing my engine to be lugging so bad. I jacked the rear tires off the ground and ran it to get the tires spinning to see and hear if the brakes are dragging but everything is fine. The rear LSD is working fine as well I might add.
A while back I was thinking I had a dead cylinder or two but all the header primary tubes were hot and all were close in temperature.
Does anyone have a clue what could be causing the engine to be down on power?
For the record, stats are as follows:
-1996 F350 4x4 Regular Cab, Long Bed (actually a '95 but sold as the
'96 model year so it's OBD1 and does not have a MAF sensor)
-'95 460 7.5L V8 (90,000 miles)
-ZF S5-42 5-speed transmission, swapped from '93 F350 (78,000 miles)
-New clutch and clutch related items (about 2000 miles on them)
-Borg-Warner 4407 transfer case (same miles as engine)
-3.55 axle gear ratios
-Long tube headers
-Gutted Catalytic converter (O2 sensor is before CAT so no thrown codes)
-Y-pipe after cat. converter, dual pipes exit our rear with resonator tips
-New O2 sensor
-New gas tank, fuel pump, fuel filter
The O2 sensor is rather new but maybe it's slowly dying? I have noticed a lot of soot coming out the tailpipe. I've owned another EFI 460 with no Cat. Converter and it wasn't hardly sooty at all out the tailpipe.
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
Some say that is so, others disagree. I've seen the insides of many engines that had been driving around with much worse exhaust manifold leaks than mine for hundreds of thousands of miles with no affect on the valves.
I don't even have a hundred thousand miles on my truck so I think I'm safe. It's not that I don't want to fix the issue, I will. It's just that I will have to remove the cylinder head and either machine it or replace it to fix the warpage at the exhaust port.
Anyway, as I said, it's had a leak forever and just recently lost power. I'm thinking it might have something to do with the fuel system. I've been too busy to recheck the fuel pressure but something tells me the root of my problem has been the gap in the fuel filler hose at the gas tank that has most likely been letting debris in; that plus I've been losing fuel to evaporation. I was getting about 8-9MPG with the C6 3-speed trans and after swapping over to a ZF 5-speed, I have had a few tanks where I got worse mileage than with the 3-speed.
I only use the front fuel tank and have never used the rear so I should fix the filler hose on the one I use, replace the fuel filter, and recheck the fuel pressure. If that doesn't fix the problem then I may need to drop the tank and see what kind of debris(if any) is in there clogging up the system.
Then after power has been restored I'll try once again, ANOTHER new O2 sensor and see about finding some new cylinder heads to fix my exhaust leak issue. I've tried many of the best exhaust manifold gaskets on the market and I'm forced to believe there is no such quick fix for my leak.
I don't even have a hundred thousand miles on my truck so I think I'm safe. It's not that I don't want to fix the issue, I will. It's just that I will have to remove the cylinder head and either machine it or replace it to fix the warpage at the exhaust port.
Anyway, as I said, it's had a leak forever and just recently lost power. I'm thinking it might have something to do with the fuel system. I've been too busy to recheck the fuel pressure but something tells me the root of my problem has been the gap in the fuel filler hose at the gas tank that has most likely been letting debris in; that plus I've been losing fuel to evaporation. I was getting about 8-9MPG with the C6 3-speed trans and after swapping over to a ZF 5-speed, I have had a few tanks where I got worse mileage than with the 3-speed.
I only use the front fuel tank and have never used the rear so I should fix the filler hose on the one I use, replace the fuel filter, and recheck the fuel pressure. If that doesn't fix the problem then I may need to drop the tank and see what kind of debris(if any) is in there clogging up the system.
Then after power has been restored I'll try once again, ANOTHER new O2 sensor and see about finding some new cylinder heads to fix my exhaust leak issue. I've tried many of the best exhaust manifold gaskets on the market and I'm forced to believe there is no such quick fix for my leak.
Senior User
Joined: May 2011
Posts: 184
Likes: 0
From: Garden City
Are you sure it doesn't have a MAF sensor? I have a 93 T-bird that is OBD1 and it has a MAF sensor.
Just checking because of your statement earlier
"96 model year so it's OBD1 and does not have a MAF sensor".
Just checking because of your statement earlier
"96 model year so it's OBD1 and does not have a MAF sensor".
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
My engine has never once ran anywhere near the red on the temp gauge yet the coating still burnt off and rusted shortly after buying them. I will never buy Hedman headers again.
Post Fiend
Joined: Nov 2008
Posts: 23,849
Likes: 20
From: McKenzie River
When did the truck start running poorly?...........After or before the modifications that were done?
I have seen plenty of rigs with exhaust leaks that had no effect on performance........just nerves.
My 93 460 F-250 2wd with the E4OD has only headers and a timing bump to 13* as a departure from stock and all emissions controls are still active, I can pull a 6% grade at 6,000ft at 70mph with ease carrying a 9.5ft cab-over camper and 2,500 lb boat in tow, so I know the power is there...........I suspect something has gone bad on one of your modifications or as stated above, fuel press. is failing at high demand.
I have seen plenty of rigs with exhaust leaks that had no effect on performance........just nerves.
My 93 460 F-250 2wd with the E4OD has only headers and a timing bump to 13* as a departure from stock and all emissions controls are still active, I can pull a 6% grade at 6,000ft at 70mph with ease carrying a 9.5ft cab-over camper and 2,500 lb boat in tow, so I know the power is there...........I suspect something has gone bad on one of your modifications or as stated above, fuel press. is failing at high demand.
Laughing Gas
Joined: Aug 2002
Posts: 1,069
Likes: 19
From: Central Wisconsin
I have chased a similar complaint with my old '96 F150… turned out to be two stuck brake calipers on the front wheels. 10 MPG with a 5.8 was disgusting… the brakes never really seemed to get hot.
Then one day I had the truck on my lift and I couldn't turn a front wheel…hmmmm.
Then one day I had the truck on my lift and I couldn't turn a front wheel…hmmmm.
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
I have chased a similar complaint with my old '96 F150… turned out to be two stuck brake calipers on the front wheels. 10 MPG with a 5.8 was disgusting… the brakes never really seemed to get hot.
Then one day I had the truck on my lift and I couldn't turn a front wheel…hmmmm.
Then one day I had the truck on my lift and I couldn't turn a front wheel…hmmmm.
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
When did the truck start running poorly?...........After or before the modifications that were done?
I have seen plenty of rigs with exhaust leaks that had no effect on performance........just nerves.
My 93 460 F-250 2wd with the E4OD has only headers and a timing bump to 13* as a departure from stock and all emissions controls are still active, I can pull a 6% grade at 6,000ft at 70mph with ease carrying a 9.5ft cab-over camper and 2,500 lb boat in tow, so I know the power is there...........I suspect something has gone bad on one of your modifications or as stated above, fuel press. is failing at high demand.
I have seen plenty of rigs with exhaust leaks that had no effect on performance........just nerves.
My 93 460 F-250 2wd with the E4OD has only headers and a timing bump to 13* as a departure from stock and all emissions controls are still active, I can pull a 6% grade at 6,000ft at 70mph with ease carrying a 9.5ft cab-over camper and 2,500 lb boat in tow, so I know the power is there...........I suspect something has gone bad on one of your modifications or as stated above, fuel press. is failing at high demand.
Thread Starter
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Junior User
Joined: Sep 2013
Posts: 93
Likes: 1
The only years to get MAF in an EFI 460 pickup was '96 and '97. My truck is a '95 leftover sold as a '96; and yes, I'm sure it doesn't have an MAF sensor.