gmctd wrote:
At this point, you still do not know what is causing the problem, or it would not be a problem, at this point - is my point - simple testing can point to the culprit
I look at it this way: I
have a gauge. it is crude, but it works for the test I am doing. It consists of a clear tube coming off the bleeder with some liquid in it. If there is pressure, the liquid pushes out. If there is vacuum, it gets sucked in. I still have a problem, as you put it, because I haven't fitted a different fuel pump. I knew the fuel pump was the issue. I didn't need an additional pointer to the culprit.
gmctd wrote:
if others with lift pumps were having this problem, they would be posting about the problem, which they are not, so asking if others have vacuum at the bleeder after adding a lift pump is not a good test procedure, and could possibly result in yours not being resolved for any number of days - or weeks.
You say that nobody else has reported an issue and therefore my issue is unique, but others may not be reporting problems with lift pumps because they haven't looked for them. After all, my engine seemed to run fine with the 74029 pump in spite of what I found. No symptoms and most people wouldn't bother to check for vacuum. But this pump clearly would not have solved the air in the filter head problem when I installed the self bleeding circuit, because there was still vacuum there.
NAPA called Federal-Mogul for me (since FM won't let mere laymen like me call and ask questions), and they were told that the 74029 pump (or any of their solenoid pumps) should
not be used with the CP3 pump because it flows a maximum of 22gph at free flow, much less at any pressure. This is far away from the 72gph that NAPA quoted me initially. If it were the case that the CP3 used all fuel that flowed into it to feed injectors, 22gph would be ample...after all, 25mpg at 50mph = 2gph fuel usage. But the CP3 returns a lot of fuel to the tank. So according to Carter even 22gph isn't enough to keep up with the demands of the CP3 inlet and maintain positive pressure, and there may be enough of a restriction to full flow at high power that the CP3 may be starved for lubrication. According to Carter via NAPA, trying to pull through a working solenoid pump is actually harder than trying to pull through one that has failed. The flow-through design was compared to the failure mode of automotive thermostats in that they are designed to fail open rather than closed. (Joe, this bit of info is something you may want to be aware of.)
Instead, they recommend a rotary vane pump such as they recommend for use in Cummins trucks. They initially recommended the P4070, but web searches make it look like it is not rated for diesel. NAPA called them back on that, and they are rated for diesel and regularly installed in diesel rigs such as Cummins, Fords, etc. It is also not much more expensive than the 74029: $78 versus $43.
It sounds to me like the in-tank solution you came up with is the elegant way to go. For me, since I already started down this path, finding a suitable external pump is the simplest solution.