The Diesel Stop banner
1 - 9 of 9 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
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!
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #3 ·
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…
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #6 ·
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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #9 ·
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
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #13 ·
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:

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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #15 ·
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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #16 ·
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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #18 ·
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

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.
 
1 - 9 of 9 Posts
Top