74 390 fuel delivery problem
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More Turbo
Joined: Jun 2001
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74 390 fuel delivery problem
On my 74 390 with a MC 2100 carb I am having some type of fuel delivery problem. After going about 1/4 mile down the road the truck will hiccup a time or two then just try to die. I can always start it again, but as soon as I touch the gas it attempts to die. I have to sit there and let it idle for a minute or so before I can take off again. (possibly to refill the fuel bowl?)
I thought that the float might be hung so I limped back into the garage and checked the float. It was fine, although the level was kinda low, so I adjusted it to the highest I could and took it back on the road. Did the exact same thing.
This time I took the entire float/seat assembly off and looked for an obstruction. There was none. I also took the filter off the card, it was fine.
Next I checked to make sure the fuel pump was pumping. I put the line into a container and turned the engine over and it pumped every 2nd rotation like it should.
Any suggestions on what this might be or something else to check?
I thought that the float might be hung so I limped back into the garage and checked the float. It was fine, although the level was kinda low, so I adjusted it to the highest I could and took it back on the road. Did the exact same thing.
This time I took the entire float/seat assembly off and looked for an obstruction. There was none. I also took the filter off the card, it was fine.
Next I checked to make sure the fuel pump was pumping. I put the line into a container and turned the engine over and it pumped every 2nd rotation like it should.
Any suggestions on what this might be or something else to check?
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 785
From: Simi Valley, CA
As original these trucks had a fuel filter in the fuel pump. Look at the pump...is there a serrated metal can (about the size tomato juice can) on it? That can unscrews, and inside is a cartridge type fuel filter. Most ppl aren't aware there's a filter there, so they rarely get changed.
Inside the gas tank, on the pickup tube is a plastic mesh filter screen. They never get changed, same reason, no one knows they are there.
C4AZ-9365-A .. Cartridge Fuel Filter (Motorcraft FG-1)
D1AZ-9A011-A .. Fuel Tank Pickup Filter Screen-LARGE I.D.
C0AF-9276-A .. Fuel Tank Sender Gasket
These parts are available from Ford and NAPA.
EDIT: Behind the acc pump diaphram is a check valve, that should be replaced when the diaphram is. C4AZ-9576-A .. (Motorcraft CM-825)
Inside the gas tank, on the pickup tube is a plastic mesh filter screen. They never get changed, same reason, no one knows they are there.
C4AZ-9365-A .. Cartridge Fuel Filter (Motorcraft FG-1)
D1AZ-9A011-A .. Fuel Tank Pickup Filter Screen-LARGE I.D.
C0AF-9276-A .. Fuel Tank Sender Gasket
These parts are available from Ford and NAPA.
EDIT: Behind the acc pump diaphram is a check valve, that should be replaced when the diaphram is. C4AZ-9576-A .. (Motorcraft CM-825)
Last edited by NumberDummy; May 24, 2007 at 02:29 PM.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The power valve is on the bottom of the fuel bowl. You can't see it with the carb bolted to the engine. When vacuum gets low (when the throttle is open wide) it opens and lets some fuel bypass the jets so that you've got more fuel going into the throat of the carb.
If your power valve was blown, you would know. You'd be shooting out black smoke and soot, and the engine would barely run at all. I don't think your problem is the power valve. If your float height is set to spec, and you have two nice streams of gas shooting at the venturis when you hit the throttle, then I'm going to guess you have a vacuum leak. Does this happen after you start the truck cold? If so, that would point to a choke-related problem.
If your power valve was blown, you would know. You'd be shooting out black smoke and soot, and the engine would barely run at all. I don't think your problem is the power valve. If your float height is set to spec, and you have two nice streams of gas shooting at the venturis when you hit the throttle, then I'm going to guess you have a vacuum leak. Does this happen after you start the truck cold? If so, that would point to a choke-related problem.
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More Turbo
Joined: Jun 2001
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well it does it regardless of temp. I have tried it both hot and cold. As for the choke it seems to be working properly, (or close enough so for my needs).
I might take it out tomm. and then after it dies pull over and take the top of the card off and check the fuel level in the bowl.
I might take it out tomm. and then after it dies pull over and take the top of the card off and check the fuel level in the bowl.
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Thread Starter
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More Turbo
Joined: Jun 2001
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Yes unfortunately it does has points, but it doesn't just suddenly die, it just kinda putters out. it is classic fuel starvation symptoms. I can drive the truck cross-country in 1st gear at idle speeds, but as soon as I get it up and going she putters out on me.
Posting Guru
Joined: Aug 2005
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A vacuum gauge is what u need. You could check the manifold vacuum and the ported vacuum coming from carb to dist. vac. You can check dist vac by (ugh) sucking on the line. Leave rubber hose on dizzy side. Shouldn't be able to suck air and with dist cap off the vac linkage passing thru from vac on outside will move( ergo vac. advance)
