7.5L Hesitations under load
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Joined: Aug 2007
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From: New Hampshire
7.5L Hesitations under load
We have a 96 Motorhome on a F53 460FI. On Memorial Day it broke down. I replaced the fuel filter and got us to our destination and home. It still didn’t run right and our fuel gauge didn’t work, so I dropped the tank and replaced the fuel pump. Now I have a sputter / hesitation after the vehicle warms up. This happens more often when accelerating or when coming to a stop.
If I let off the gas to coast a little and then give it a little gas- I get the sputter or when I stop at red light it feels like it is going to stall.
I picked up a cheap fuel pressure test gauge from Harbor Freight. The pressure jumps up to ~45psi (KOEO) which is correct; however when I check the pressure with the engine running the needle bounces. I am not talking about a little bounce, but a very erratic flutter. Is this normal?
I would expect some movement, but thought it would be minimal. This is difficult to get an accurate reading. Would a bad injector cause this?
I changed the plugs and wires about 2 years ago and ohm’d them out to make sure I don’t have a bad wire. The plugs look fine and there is no indication of anything abnormal. I replaced the cap and rotor do to arcing on the caps. This is OBD-I and there is no codes being logged.
I am usually pretty good at troublshooting, but this one has got me stumped and I don't want to keeping changing parts.
If I let off the gas to coast a little and then give it a little gas- I get the sputter or when I stop at red light it feels like it is going to stall.
I picked up a cheap fuel pressure test gauge from Harbor Freight. The pressure jumps up to ~45psi (KOEO) which is correct; however when I check the pressure with the engine running the needle bounces. I am not talking about a little bounce, but a very erratic flutter. Is this normal?
I would expect some movement, but thought it would be minimal. This is difficult to get an accurate reading. Would a bad injector cause this?
I changed the plugs and wires about 2 years ago and ohm’d them out to make sure I don’t have a bad wire. The plugs look fine and there is no indication of anything abnormal. I replaced the cap and rotor do to arcing on the caps. This is OBD-I and there is no codes being logged.
I am usually pretty good at troublshooting, but this one has got me stumped and I don't want to keeping changing parts.
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
You've done a pretty good job, lots of the right information. Welcome.
Good initial fuel pressure, but fluctuates while running plus stalling/hesitation kind of makes me think a vacuum issue is futzing with fuel pressure regulator. A simple vacuum check would be a good place to start, get a can of starting fluid or WD40 and with the engine running spray around the hoses. If the engine rev's up, then you've sprayed near a vacuum leak.
If no leaks, then I would pull and cap the vac line into the regulator and check fuel pressure again. If the fuel pressure fluctuates without vac, the way the system works either you are not getting enough pressure from the pump or you have a high volume leak. They typical fuel system runs fuel up from the pump to fuel rail, around the injectors and to the regulator. Once it reaches the regulator, the regulator closes the return line until it has too much pressure and it opens up and lets the excess flow off.
Good initial fuel pressure, but fluctuates while running plus stalling/hesitation kind of makes me think a vacuum issue is futzing with fuel pressure regulator. A simple vacuum check would be a good place to start, get a can of starting fluid or WD40 and with the engine running spray around the hoses. If the engine rev's up, then you've sprayed near a vacuum leak.
If no leaks, then I would pull and cap the vac line into the regulator and check fuel pressure again. If the fuel pressure fluctuates without vac, the way the system works either you are not getting enough pressure from the pump or you have a high volume leak. They typical fuel system runs fuel up from the pump to fuel rail, around the injectors and to the regulator. Once it reaches the regulator, the regulator closes the return line until it has too much pressure and it opens up and lets the excess flow off.
Cargo Master
Joined: Nov 2005
Posts: 2,051
Likes: 10
From: TEXAS
You may also want to go over to a more RV related site and ask the same question. I may not be correct on this, but I was thinking that this was a problem that was not uncommon with some of the Ford powered Class A motorhomes. And for some reason I am thinking it had to do with the gas cap and vapor lock of the fuel line....but again I am not sure on this.
You may want to try www.rv.net/forum/
You may want to try www.rv.net/forum/
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