Advice needed. Altitude VS fuel pressure readings.

Discussion in 'Open Discussion' started by nickb2, Mar 24, 2017.

  1. nickb2

    nickb2 Wrench. I help when I can

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    Hello all.

    I was talking to my co-worker about some weird findings I was getting when diagnosing an intermittent fuel pump.

    The readings I was getting were about 30psi for a so called spec of 55-60psi.

    I said to my co-worker, I tried three different fuel gauges and came up with same readings every-time. Reason why, the fuel pressure kit is very sloppy and has been very abused by flaky hands.

    So after three gauges, I determined that the fuel pressure is exact.

    The vehicle in question is a E350 with a 5.4l year 2012.

    Client tells me he can cold start it only if he cycles the key 10 times. I have told time repeatedly the fuel pump is on it's last legs.

    Here is where I get skeptic. My co-worker tells me the fuel pump is fine and it is normal that I am getting readings like that so far up north and in altitude. So I went and got another e series truck with same fuel pump in it. Got 50psi. I accounted for maybe a drop or two seeping from a looses Schreader valve whilst taking readings. Truck started fine @ -37c. I can see that a drop of 5psi may account for altitude, but not 25psi.

    Who is right? Can altitude vary THAT much psi readings, or is my co-worker just not getting it?
     
  2. nickb2

    nickb2 Wrench. I help when I can

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    I know for a fact this is a returnless type and pressure regulator is integral to fuel pump assembly.

    So anyway, I went and ordered a new assembly, as the client also stated the fuel level has been sporadic for some time. I told him we will kill two birds with one stone.

    But I can't for the life of me understand the logic of my co-worker who says that altitude will vary that much on a fuel pressure gauge. I think he is nuts to think that. But since I always like to make sure, I wanted some knowledgeable answers to give him before I school him.

    In my understanding, a fuel pressure gauge reads psi regardless of altitude. So if my logic works here, shouldn't my readings be higher?

    I read this on the net. This is also how my man brains sees things.

    However, as altitude increases, atmospheric pressure decreases. ... Those measured at the 5,000-foot level (where an atmospheric pressure of only 12.2 pounds per square inch is the ambient pressure) would indicate about 2-3 psi higher than at sea level
     
  3. nickb2

    nickb2 Wrench. I help when I can

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    We are at an altitude of 1709ft. So my readings should only be off of 1 or so PSI. Not 25psi.
     
  4. billr

    billr wrench Staff Member

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    I don't think altitude (barometric pressure) will have any effect on a gauge reading psig, as most fuel-pressure gauges do. As to how baro affects an FPR, whether it is referenced to MAP or not, I would have to think about more than I care to right now. However, I feel quite certain baro could never have a 25 psi effect on FP. Maybe a few psi, like you suggested, maybe none...
     
  5. JackC

    JackC wrench

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    Seems to me that in a closed environment (such as your fuel pump situation), altitude would have little or no effect.
     
  6. nickb2

    nickb2 Wrench. I help when I can

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    Thx guy's, that pretty much confirms my thoughts. I was thinking I was dense for a minute there.

    BTW, I ordered new shreader valves for ford and the common one that does GM and Mopar. I hate it when I have to work with sloppy tooling. I do not find myself anal or anything, I think it is a matter of principle. Good tools in proper working condition equals faster and accurate diagnostic times and less grief for the tech using them.

    But I have come to an understanding that many so called techs have come up here before me, many could not tuff the work conditions. I have seen this before. When ppl don't give a crap, the tools usually take a beating.

    On a less than funny note, the packs of husky's up here are getting hungry, I was bringing home a pizza last night from the restaurant, I had to kick one of them in the snout with my steel toe boot, he was getting a bit to aggressive for my taste.There were six of them circling around me. I must admit, I was scared. They probably sensed that.

    There are posters being put up for the Innu nation to properly leash their dogs and also to get them neutered. Well, it will be a cold day in hell before they ever change their way. So I have my winchester buck knife on me at all times now. If I have to gut one, I will without hesitation.

    There have been a few attacks of late and the locals are getting nervous. The Innu's just laugh. Thing is, the poster does state that legal measures will be taken, and shooting on site will be done as a last resort by the local police force. There are after all a lot of young kids wandering around without supervision up here. It would not be funny for something to happen to a young one for lack of just plain giving a damn about how to safely restrain your pet.
     

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