[middlevillePS]

Hello everyone. New member here but I’ve used the info on this forum for years and love it.

I am looking for the specs on the cam lobe that runs the mechanical lift pump. Ideally I would like to be able to measure the difference between the max lift and “no” lift by spinning the motor around (using dial indicator). If somebody knows the spec for that I would be very grateful!

 

[Patrick Feeley]

I've never seen it in any of my factory service manuals or literature. Not sure if you could find an international dealer or Ford dealer (or other) that would have a new stock camshaft that could be measured to get the difference between the pump lobe base circle and the lobe. Cheers!

 

[middlevillePS]

I've never seen it in any of my factory service manuals or literature. Not sure if you could find an international dealer or Ford dealer (or other) that would have a new stock camshaft that could be measured to get the difference between the pump lobe base circle and the lobe. Cheers!

Thanks. That was my next move. Just got to find one…

 

[Steve83]

...measure the difference between the max lift and “no” lift by spinning the motor around (using dial indicator).

Why not just do that? Presumably, you already have a 7.3L engine with a camshaft installed, and a dial indicator; right?

 

[Patrick Feeley]

I'm presuming he wants to know what the spec is so he can tell if his is worn. I haven't ever seen mention of someone having a worn fuel pump cam lobe though. Cheers!

 

[middlevillePS]

Why not just do that? Presumably, you already have a 7.3L engine with a camshaft installed, and a dial indicator; right?

I do. However, that doesn’t tell me if it’s in spec. I know that the lobe is there because it drives the fuel pump. However, I am 99% convinced that it is worn to the point it cannot make the pump make enough pressure. Before I get into a camshaft or go electric, I was hoping to verify this is the problem.

I do not want to get into the “have you checked this or that”, but it makes only 10PSI at idle and while driving. I have gone to the point of feeding the fuel directly into the pump (so everything between tank and pump is eliminated as the problem); clamping off the return line right off the fuel bowl (so FPR is not the problem); two different Napa pumps; and three different quality gauges. There is no fuel in the oil, so not losing it through injectors. The lobe looks a little worn, so I suspect that is the problem as above. At this point I’m just going to go electric. Appreciate the help though.

 

[middlevillePS]

I'm presuming he wants to know what the spec is so he can tell if his is worn. I haven't ever seen mention of someone having a worn fuel pump cam lobe though. Cheers!

That is correct. I feel I have eliminated everything else, so it’s two bad pumps in a row or the cam.

 

[Steve83]

I haven't ever seen mention of someone having a worn fuel pump cam lobe though.

That's my point: unless it's visibly worn all the way across the lobe, some part of it will be the original profile. But probably the whole thing.

...it cannot make the pump make enough pressure.

Then all you really need to do is see how far the pump follower has to travel to make pressure, and compare it to your cam's lobe. Other engines' cams' lobes aren't really relevant.

 

[middlevillePS]

That's my point: unless it's visibly worn all the way across the lobe, some part of it will be the original profile. But probably the whole thing.Then all you really need to do is see how far the pump follower has to travel to make pressure, and compare it to your cam's lobe. Other engines' cams' lobes aren't really relevant.

I have talked to a couple of different reputable shops and they have run into worn lobes, but I would be happy to be wrong here. Assuming the lobe is fine, then what would your recommendation be to figure out what is going on? As I mentioned above, everything from the tank to the fuel bowl inlet has been eliminated, and the return has been physically blocked. Two new pumps have been tried. I am measuring at the Schrader valve (and I have swapped that in and out with another as well). What am I missing? TIA

 

[Big Horn]

As I mentioned above, everything from the tank to the fuel bowl inlet has been eliminated, and the return has been physically blocked.

Was wondering if it could be a venting issue for either the pump or fuel tank vent?

 

[bugman]

A member on another forum was having a very low fuel pressure problem and he found that the filter wasn't completely seated in the housing. Possibly his first problem was with the fuel pump that he replaced but then compounded the problem down the road with other things that he did.

 

[Steve83]

...everything from the tank to the fuel bowl inlet has been eliminated...

Then it must be something between the inlet & outlet, like all the other loops & orifices & valves inside the filter bowl assembly. Try eliminating the bowl by feeding fuel directly to the pump's high-pressure inlet, and see how much pressure comes from the outlet during cranking. You'll have to come up with some way to connect the pressure gauge to the dead-headed outlet. Remember (as bugman mentioined) there's a valve inside the filter's stand-pipe NOT indicated on this diagram:

1997 Ford F-250 Technical Info picture | SuperMotors.net

fuelflow.jpg 7.3L PSTD Fuel Flow Schematic [url=https://www.supermotors.net/registry/media/1161710][img]https://www.supermotors.net/getfile/1161710/thumbnail/ffbowl.jpg[/img][/url] ...

www.supermotors.net

 

[middlevillePS]

Was wondering if it could be a venting issue for either the pump or fuel tank vent?

The tank has been eliminated as a possible problem because I am feeding fuel from a fuel can directly into the fuel bowl inlet. Not sure what you mean by pump vent. Can you elaborate?

Then it must be something between the inlet & outlet, like all the other loops & orifices & valves inside the filter bowl assembly. Try eliminating the bowl by feeding fuel directly to the pump's high-pressure inlet, and see how much pressure comes from the outlet during cranking. You'll have to come up with some way to connect the pressure gauge to the dead-headed outlet. Remember (as bugman mentioined) there's a valve inside the filter's stand-pipe NOT indicated on this diagram:

1997 Ford F-250 Technical Info picture | SuperMotors.net

fuelflow.jpg 7.3L PSTD Fuel Flow Schematic [url=https://www.supermotors.net/registry/media/1161710][img]https://www.supermotors.net/getfile/1161710/thumbnail/ffbowl.jpg[/img][/url] ...

www.supermotors.net

steve. I have always loved your supermotors site with all the disagrams. Used it for years on broncos. I do need some help here though—where is the standpipe? Are you talking about the little screen that you get to after removing the FPR?

I’ll work onbypassing the bowl. Good idea thanks.

 

[Steve83]

IDK the real name, but it's the plastic tube in the center of the filter bowl. I found out almost the hard way that it's left-hand-threaded into the bowl, with the heater plate held between. But there's a spring-loaded valve in the top of the plastic tube.

It leaks a little fuel when it's closed, but it's an obvious restriction.

Glad to hear someone is still getting some use from SMN.

 

[middlevillePS]

IDK the real name, but it's the plastic tube in the center of the filter bowl. I found out almost the hard way that it's left-hand-threaded into the bowl, with the heater plate held between. But there's a spring-loaded valve in the top of the plastic tube.

View attachment 186823

It leaks a little fuel when it's closed, but it's an obvious restriction.

View attachment 186824

Glad to hear someone is still getting some use from SMN.

I don’t know what it’s called either, so standpipe it is. I’ll check that out. Thanks.

 

[middlevillePS]

I don’t know what it’s called either, so standpipe it is. I’ll check that out. Thanks.

IDK the real name, but it's the plastic tube in the center of the filter bowl. I found out almost the hard way that it's left-hand-threaded into the bowl, with the heater plate held between. But there's a spring-loaded valve in the top of the plastic tube.

View attachment 186823

It leaks a little fuel when it's closed, but it's an obvious restriction.

View attachment 186824

Glad to hear someone is still getting some use from SMN.

Well gents, good news and bad news. I took the fuel bowl out, ran fuel directly from a five gallon jug of diesel into the input of the low pressure side. I then ran the output of the low pressure side directly into the high pressure inlet. Then I took both fuel returns on the front of the heads and teed them with the fuel pressure gauge. I cranked the truck with start disabled and got about 30 psi dead headed into the gauge. Then I got brave and started the truck. I’m getting about 40 psi at idle while running. So, good news is that you were both right and there is nothing wrong with the pump! Thanks a ton for your help so far.
The bad news is that I was using an NOS fuel bowl, so there is something in there causing the problem. I have used two different FPRs on it but I still get the 10 psi at idle. Even when I pinch off the return (outlet from the FPR) I still get 10 psi at idle. Has to be something in that bowl as Steve indicated. I don’t think it can be the filter not being seated all the way because it is the factory Ford that is attached to the cap.

I guess the next step is to swap out the fuel bowl and see what happens…unless you have other thoughts.

 

[Steve83]

I don’t think it can be the filter not being seated all the way because it is the factory Ford that is attached to the cap.

Uuuhhh...

Amazon.com: Ford Cap : Automotive

Amazon.com: Motorcraft FD4595 Fuel Filter : Automotive

Buy Motorcraft FD4595 Fuel Filter: Fuel Filters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[middlevillePS]

IDK the real name, but it's the plastic tube in the center of the filter bowl. I found out almost the hard way that it's left-hand-threaded into the bowl, with the heater plate held between. But there's a spring-loaded valve in the top of the plastic tube.

View attachment 186823

It leaks a little fuel when it's closed, but it's an obvious restriction.

View attachment 186824

Glad to hear someone is still getting some use from SMN.

Uuuhhh...

Amazon.com: Ford Cap : Automotive

Amazon.com: Motorcraft FD4595 Fuel Filter : Automotive

Buy Motorcraft FD4595 Fuel Filter: Fuel Filters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

i am hoping you just found the problem. A new filter and cap came with the NOS fuel bowl and I didn’t even think about it. I cannot get that filter to separate from the cap. Hoping it’s defective.

 

[bugman]

If the filter and lid are a Racor, and Ford there should be just a couple of plastic clips holding them together. But there are aftermarket filters that the lid is attached to it and you cannot remove it.

You should be able to just use it, but don't get rid of the old cap. I actually carry a spare cap with me along with a new filter and gasket.

Sent from my SM-A426U using Tapatalk

 

[middlevillePS]

i am hoping you just found the problem. A new filter and cap came with the NOS fuel bowl and I didn’t even think about it. I cannot get that filter to separate from the cap. Hoping it’s defective.

Gents, just following up here with the conclusion. Bottom line is that it confirms what we all know—when all other possibilities have been eliminated, what remains is the truth, however improbable it might be (or whateve mr the quote is). Anyway, it was the damn fuel pump. TWO brand new Napa pumps and all this other tail chasing. Finally gave up and took it to a shop. They ran through some other stuff and then bought a FORD pump. Runs beautifully now with 50+ Psi at the Schrader valve. I guess it’s gotten to the point that you can’t even buy good $#*+ from a store like Napa. Thank you for all the help.