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Thread: 10 PSI and 35.7 A/F Ratio

  1. #1

    Default 10 PSI and 35.7 A/F Ratio

    I need some help! The fuel pump cavitated last night and ever since then I have been reading a 35.4 lean as hell air fuel ratio and the pump is not building pressure like it should! someone please help me!

  2. #2

    Default 10 PSI and 35.7 A/F Ratio


    I believe you are running saddle tanks. Correct me if I'm wrong, but I dare say you have the pump closer to one tank than the other. If this is true, the distance from the most distant tank to the pump, combined with high ambient temperatures, may be placing undue stress (best guess) on the pump internals. You've expressed in another post that you have already experienced cavitation (CAV code?). I'm also assuming your pump is plumbed downstream of the solenoid. If this is the case, I have to wonder if the pump is attempting to pull fuel more so than push it.

    Without really knowing what I'm talking about, I'm guessing that the pump may have incurred some type of internal damage based on your comments about less pressure and the extremely lean reading you are getting off of the hand held. I'm not sure how the pump is constructed, but if the pump, (in theory) experienced cavitation/heat and damaged [one or more impellers?], the pump may very well run but would certainly loose efficiency. I'd start by pulling the pump and filter and checking for debris.

    I have another idea, but it requires, first of all, using a return fuel system (for each tank) and plumbing a separate pump/filter for each tank and ditching the solenoid. You could route fuel pump power from the Atomic controller to the saddle tank selector switch and simply use this switch to select which system (pump) you want the Atomic to power depending on which tank you want to feed from. It's a solution that's a bit more expensive, but one that may end up averting quite a few headaches in the long run.

    However, first of all find out if the pump has incurred damage.

  3. #3

    Default 10 PSI and 35.7 A/F Ratio

    That i my biggest fear right now is that from the pump cavitating and overheating, it may have damaged a brand new pump. That is a very good theory on why I am having problems, yes I do have dual tanks with a solenoid and the pump may infact be pulling the fuel instead of simply pushing it! One of my ideas that I am contending with is putting a 31 gal blazer tank in the back of the truck between the frame rails. I think that the blazer and k10 frame are the similar if not the same and I have a guy that can fab up some brackets for me. If I go this route then I will put the pump in the tank and I will be running a return style system as well. I have read that the system works very well when the fuel cools the pump.

    Just fooling around under the truck today, I realized that I have a hard line run to the front of the truck as a return line, and in fact that return line comes to a tee and splits into a feed for both tanks, i am considering getting a new pump and hooking up a return system first with the dual tanks hooked up and then if I still have issues, then I will pursue a full on swap of the onboard fuel storage! What do you think "xcarguy"? i need to get something figured out fast because this is my daily driver and I am heading back to school in the fall to Boise ID. Its a 10 hour drive that I was planning on taking the truck on, but if it is not done, don't really know what I will do. What do you think about the walbro pumps, are they more dependable than the MSD pump as far as longevity of the pump!?

    Thanks so much for your great Ideas!


  4. #4

    Default 10 PSI and 35.7 A/F Ratio

    Does the pump make any noise at all when the system is powered on?

    If it is attempting to prime, try running a fuel line from the pump to a gas can (bypassing the existing fuel tank system). If the pump is able to prime the system the pump is OK. It's possible the fuel tank solenoid is not working right or restricted in some way.

  5. #5

    Default 10 PSI and 35.7 A/F Ratio


    I certainly like MSD tech's idea of checking that solenoid first. Being the lesser of all evils, it would be great if it turned out to be the culprit. I've ran Walbro pumps in the past with great success, but I really can't say how they compare to the MSD pump as the MSD pump per my application (return system) also performs very well. More importantly, if you plan on an in-tank application/returnless system, I would think your pump would need to be of the type compatible for pulse width modulation (anyone feel free to correct me on this if I'm mistaken).

    You say you are headed back to school and want/need to take your truck. I'm not sure how large your saddle tanks are, but have you considered (just as a temporary fix--maybe quickest fix) of simply running one saddle tank with an external pump/return system? Long-term, I'd go with the single tank in the rear with the in-take pump and returnless system. On my application, I was forced to mount my pump externally due to my tank having a depth of only seven inches. However, if I had the option for an in-take application, that's the way I'd go.

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