Fuel Pump bad?
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Senior User
Joined: Mar 2004
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From: Alabama
Fuel Pump bad?
My 302 with a 570cfm Holley seems to act up when cruising at RPM's over 2000. When I say act up, I hear what seems like a miss or sputter, or backfire out the exhaust. I can hear but not feel it. I pulled my plugs and I think it's running lean (they were whiteish color).
The reason I'm asking about the fuel pump is, I have an in-line clear filter and a fuel pressure gauge and my fuel pressure is all over place. Sometimes I can see air bubbles flowing through the filter. The pressure will be 9psi one minute and 2 the next. It's not erratic though. The pump is fairly new as well as all the rubber lines between it and the sending unit which is new and all clamps trippled checked. The specs on the pump are supposed to be a maximum of 8 and minimum of 6.5. I thought if a mechanical pump was bad it would either not work or dump fuel in the oil/ leak so I'm looking for advice.
The carb has been tuned and retuned and tuned again and the timing doesn't really affect it unless it's at like 16* or higher than it's worse.
It runs great but it's just annoying when cruising. What do you think?
The reason I'm asking about the fuel pump is, I have an in-line clear filter and a fuel pressure gauge and my fuel pressure is all over place. Sometimes I can see air bubbles flowing through the filter. The pressure will be 9psi one minute and 2 the next. It's not erratic though. The pump is fairly new as well as all the rubber lines between it and the sending unit which is new and all clamps trippled checked. The specs on the pump are supposed to be a maximum of 8 and minimum of 6.5. I thought if a mechanical pump was bad it would either not work or dump fuel in the oil/ leak so I'm looking for advice.
The carb has been tuned and retuned and tuned again and the timing doesn't really affect it unless it's at like 16* or higher than it's worse.
It runs great but it's just annoying when cruising. What do you think?
Cargo Master
Joined: Jun 2007
Posts: 2,723
Likes: 5
From: Roseburg, OR
You are right on about the pump. If you are seeing bubbles in the filter check for any loose connections, loosen and spin hose clamps a quarter of a turn and re-tighten. Check the pick-up in the tank for any holes, somehow air must be getting in.
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
Agreed with checking the connections.
With today's lousy gas, I'd be a bit leery of running all rubber gas lines instead of a hard line....rubber where needed, hard line for long runs.
Try not to over tighten the hose clamps - the rubber could pinch out between the gear slots causing problems. Fuel injection clamps work well here.
Do you have a clear filter between the pump and carb?
With today's lousy gas, I'd be a bit leery of running all rubber gas lines instead of a hard line....rubber where needed, hard line for long runs.
Try not to over tighten the hose clamps - the rubber could pinch out between the gear slots causing problems. Fuel injection clamps work well here.
Do you have a clear filter between the pump and carb?
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From: Alabama
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Lead Driver
Joined: Mar 2004
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If the pump is seeing a fluxuation then either it's bad or the line is leaking somewhere. If there is any steel line look it over real close, anywhere it comes in contact with anything steel can rub a pin hole in it and thats all it takes to make it not work right. An engine will run on just a few pounds but when you put a load on it, it will start missing.
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Cargo Master
Joined: Jun 2007
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From: Roseburg, OR
Secondaries will not be open at 2k rpm cruising. You could have an issue with timing which would typically cause a ping. The air bubbles in your fuel filter are a dead giveaway that somehow air is entering the system. You might have more than one problem, but fix this one first, then move to the next.
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Senior User
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From: Alabama
Lets just assume the air bubbles are not the issue here since the sending unit is new, the rubber portion of the lines are new to include the clamps that have been tightened and re-tightened and add that the in-line clear fuel filter between the pump and carb stays full even after the truck has sat for a couple of days which leads me to believe that if there was a pin hole in the metal line that it would leak at some point. Given the facts that it idles fine, no hesitations, no off idle stumble. and has no issues at WOT, is it conceivable that maybe the transfer slot (cruise circuit) in the carb needs adjusted to cure the sputtering/miss at cruising speed or while holding the throttle at 2500 rpm (for example)? When I pulled the plugs they indicated a lean condition (white). I'll try and post a video tomorrow that will hopefully visualize what I'm talking about as far the sputter or whatever it is...
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Ok, let's toss the fuel lines/bubbles for the moment...and I'll offer some random thoughts.
Does the coil (if you're running one) ohm out to specs? Plug wires ohm out good?
Plugs - Autolite? Motorcraft? Other? Have you tried switching plug brands?
No fuel pressure regulator, correct? Have you tried running it with the fuel pressure gauge disconnected? (air leaks within the gauge?)
No excessive play in the distributor?
No foreign particles in the carb?
No excessive play in throttle shaft (side to side, up & down) causing a vacuum leak?
That's all I have for randomness at the moment.......
Does the coil (if you're running one) ohm out to specs? Plug wires ohm out good?
Plugs - Autolite? Motorcraft? Other? Have you tried switching plug brands?
No fuel pressure regulator, correct? Have you tried running it with the fuel pressure gauge disconnected? (air leaks within the gauge?)
No excessive play in the distributor?
No foreign particles in the carb?
No excessive play in throttle shaft (side to side, up & down) causing a vacuum leak?
That's all I have for randomness at the moment.......
Thread Starter
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Senior User
Joined: Mar 2004
Posts: 280
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From: Alabama
Ok, let's toss the fuel lines/bubbles for the moment...and I'll offer some random thoughts.
Does the coil (if you're running one) ohm out to specs? I have fairly new MSD coil: What are the OHM specs? Plug wires ohm out good? Fairly new Summit Racing 8mm: Specs?
Plugs - Autolite? Motorcraft? Other? Have you tried switching plug brands? I had Autolite Platinum and just switched them out to Autolite Coppers, gapped to .044
No fuel pressure regulator, correct? Correct Have you tried running it with the fuel pressure gauge disconnected? (air leaks within the gauge?) No I haven't.
No excessive play in the distributor? No
No foreign particles in the carb? No
No excessive play in throttle shaft (side to side, up & down) causing a vacuum leak? No.
That's all I have for randomness at the moment.......
Does the coil (if you're running one) ohm out to specs? I have fairly new MSD coil: What are the OHM specs? Plug wires ohm out good? Fairly new Summit Racing 8mm: Specs?
Plugs - Autolite? Motorcraft? Other? Have you tried switching plug brands? I had Autolite Platinum and just switched them out to Autolite Coppers, gapped to .044
No fuel pressure regulator, correct? Correct Have you tried running it with the fuel pressure gauge disconnected? (air leaks within the gauge?) No I haven't.
No excessive play in the distributor? No
No foreign particles in the carb? No
No excessive play in throttle shaft (side to side, up & down) causing a vacuum leak? No.
That's all I have for randomness at the moment.......
New User
Joined: Mar 2005
Posts: 14
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Put fuel pressure regulators on your lines... steal them off an old Ranger (83 thru 87 Six Fuel injected) and keep them away from heat. I know you're carb'd but not all fuel pumps are the same... it might be pushing in more than jet level and just squirting at some point... Might be a junkyard fix, I hope.
I have an '86 Fuel Injected Ranger, and when my fuel rail heats up, it causes issues. After putting some Kevlar under the little UFO-looking *******s and the rail, I've had way less problems in 90 degree heat.
I have an '86 Fuel Injected Ranger, and when my fuel rail heats up, it causes issues. After putting some Kevlar under the little UFO-looking *******s and the rail, I've had way less problems in 90 degree heat.
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Senior User
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From: Alabama
<iframe width="420" height="315" src="http://www.youtube.com/embed/1oHHEwipRrY" frameborder="0" allowfullscreen></iframe>
I replaced the fuel filter and no more bubbles. I took the Carb off and checked the secondaries and closed them a little. So I either have an ignition issue or worse. I did have the valve covers off and checked what I could and everything look fine. Hopefully you can hear in the video what I was trying to explain.<iframe width="420" height="315" src="http://www.youtube.com/embed/vunrU73wdbE" frameborder="0" allowfullscreen></iframe>
I replaced the fuel filter and no more bubbles. I took the Carb off and checked the secondaries and closed them a little. So I either have an ignition issue or worse. I did have the valve covers off and checked what I could and everything look fine. Hopefully you can hear in the video what I was trying to explain.<iframe width="420" height="315" src="http://www.youtube.com/embed/vunrU73wdbE" frameborder="0" allowfullscreen></iframe>