First, yes I am a loyal Captain Hook fan for a couple years and have re-read his sticky on fuel leakdwon several times though I can recite the fuel leakdown test in my sleep.

My problem is something seems to be telling the fuel pump not to exceed 55psi and then it immidately drops to 50 when the pump shuts off and holds there. The only thing that I can think of is there is some electrical issue and that I'm not super sharp on (resistors, ohm readings and all that happy junk)?

What I described above happened with the old injector system so I figured I had a leaking poppet or a faulty regulator and didn't think much of it because I had a new updated spider on the shelf just waiting for the time for me to install it. I figured the issue would be solved once I installed the updated spider assembly.

So last week, I installed it. Took it for a drive, drove better but I could feel slight surges. So I started the leakdown test and got the same exact results as I had with the old system. Dead ended the test at the filter and got 90 psi and still holding above 80psi after 10 minutes. I even took off the fuel pipes in the engine compartment and dead ended the feed line to see if there were any leaks in the new fuel lines I installed last year. Got similar results that I did at the filter.

I then re-attached the pipes and dead-end tested the feed line where they plug into the spider assembly. Again 90 psi with little leakdown after 10 minutes.

So my pump seems to be fine, the lines are fine, the fuel regulator came brand new on the spider assembly as you know but yet I get the same low pressure when the pump activates (55 dropping to 50 immediately) as when the old spider was installed.

By process of elimination all I can wonder is if there is some type of electrical issue that is causing the low pressure. HELP!

 

If you have >90psi dead-ended, does not leak down, and you have switched spiders/pressure regulators then it looks like the fuel pressure gauge you are using is probably off. Get a different one from different place and recheck please.

FYI AC/Delco upgrade MPFI spiders go to 58psi after the initial pulse, (with the engine not running) - as does mine, which I replaced because old one was 58 psi. Captain's 60 psi minimum is not critical with MPFI upgrade, but 50 is certainly a low reading. Bet it's the fuel pressure gauge.

 

Thanks for the reply, but the gauge being off was my first thought also. I went and got another one and performed all the checks with both gauges and they both ran the same numbers. I should have added that point to my original post.

Before I stopped working on it the other night, thinking it might be a command or electrical issue, I discovered I had a .67 amp parasitic draw at the battery. I haven't located the culprit yet or even know if it would have an effect on the fuel pump acting the way I described.

 

Does anyone know what the correct amps the fuel pump should be drawing are? I've seen two answers: normal is 8-10; and the other was 1 am per 10psi of pressure. Attached is a snapshot of a fuel current test I did on my fuel pump using my Snap On scope and low amp clamp probe. As you can see my pump doesn't get above 6.77 amps. As stated before I believe I'm trying to locate an electronic gremlin.

 

All, I wanted pass along some things I've found that may or may not help others with similar issues. First, since I first began this thread back in August I have been pretty much been giving myself a crash course on automotive electronics. I'm 100 times more proficient than I was when this thread began. I also purchased some new tools that I wish I had long ago (an oscilloscope; a Load Pro; Power Probe IV and short/open finding kit (PP ECT2000)). I'm a little bit of a tool junkie.

So here's what I wanted to share: The first image below shows the ramp of my fuel pump with the truck idling. It looks like I might have to replace the fuel pump. But before I do that I will be load testing all the wires and coming up with some way to pressure test the fuel pipes end to end. Hopefully in the near future I will drop the tank to do all of this. I've read many other threads where a poster is frustrated because their fuel leakdown test passes, but they still have poor performance, even after putting in new AC Delco secondary ignition parts, etc. Below are a couple other things I did last night that very much improved my fuel trims. But getting back to the pump and what the scope is showing...

If you look at where the "1" cursor line is you will see that peak and the two peaks before it are in the 7.6 amp range then the next 7 peaks drop to the 6.6 amp range. Then it repeats itself. This tells me that the pump motor has 10 commutators and with a little math the speed of the pump is ~7,566rpm (the scope is set at 10ms...divide 60,000 by the time is takes for the pump to complete one full revolution (7.93ms)). Two unknowns to me are what is the correct rpm for the pump and as stated in the above post, what should be the correct amp draw. However, from the research I've been able to dig up, it looks like the pump should be drawing over 8 amps, actually closer to 10 (which mine is not). But I'm not dead certain on that.

One thing I am dead certain of (from the research I have done), is that waveform definitely shows a problem with the pump of some type. The humps are supposed to be close to level...not dropping as much as a full amp for 7 of the 10 commutators. Is it a voltage drop problem in the wires or grounds, etc...or is it the pump itself? Don't know, but when I drop the tank I'll figure it out.

I went into detail in the previous two paragraphs to help people like me who are totally baffled as to why their fuel leakdown passes...but yet they still have a bad pump (or circuitry issue). Now I know. Just sharing new found knowledge. I also want to add that though the waveform shows surges, at idle the truck purrs like a kitten and the tach stays pretty much rock solid. So the pump is not causing the truck to surge at idle or vice-versa. By the way, I was using a Snap-on Vantage Pro Scope and low amp clamp probe on the feed wire to the pump.

Now for a couple things that helped me last night have the truck perform much better on it's fuel trims. First, cleaned the MAF sensor. Pic shows how it looked. Not really horrible, but needed cleaning. I've seen much worse. The other thing I did, which I think helped a lot was to make a rubber gasket for the top of the throttle body where the air intake mounts. If your truck is like mine, inlet duct is held on by the one long black plastic thumbscrew and a spring steel clip with two prongs.

If you push down on the clip side of the inlet duct you might notice that there is a little gap between the duct and the mating surface of the throttle body. I had about a 1/16" gap. It was tight on the thumbscrew side but had a small gap on the other. Even though the inlet duct has a gasket on it, I believe un-metered air was getting into the throttle body thru this gap causing my fuel trims to constantly be rich in response to lean condition measured at the O2 sensors. So I added the rubber gasket I made from 1/16" rubber I had laying around. Together, those two things felt like the truck had just had a tune up. It was a little better cleaning the MAF, but it was quite a bit better with the clean MAF AND the rubber gasket. Truck is still lacking the power under load it should have from the pump issue, but it daily drives just fine (city or hwy).

More to follow when I drop the tank, and if anyone sees anything in that waveform they want to point out...or knows what the correct amp draw or rpm is for the fuel pump...please share.