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  • Confirmation of Diagnosis

    Hello,

    I have been trouble shooting my fantastic compuvalve on my 1999 f250 bi-fuel. My diagnosis leads me to low-flow injector issues based on the following:
    1) alt light stays lit
    2) car runs on cng pretty good at high rpm
    3) car shuts off very fast when take foot off of gas
    4) fuel gauge reads fuel when car is off, once when in running at high rpm. otherwise it records no fuel, yet i know it has fuel and it keeps running at high rpm
    5) however, i have not been able to tell if there is a vacuum leak in vacuum to compuvalve, the whitish vacuum line has a very tiny hole in it, but will easily come out of the nipple on the compuvalve (it is just zip tied on, have not been able to get clamps that small at my auto parts store)

    I have filled the coalescent filter housing twice with alcohol, once with sea foam (alcohol to flush sea foam), car went from barely running on cng in any capacity to it's current state where it runs fairly well at a consistent high rpm. The running at idle has not improved at all.

    Does this seem right to you?

    David

  • #2
    Re: Confirmation of Diagnosis

    I see that you say that you say the fuel gage reads empty when there is fuel in the tank. I have a 2004 and the fuel gage is read at the high pressure transducer. I think the older f150 had a tank sensor that also reads high pressure. I would look for something restricting the fuel flow. Find where the high pressure transducer is, check for line restriction or voltage at transducer. Just my suggestion hope it helps.

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    • #3
      Re: Confirmation of Diagnosis

      Thanks for the info. I have traced the lines until they disappear above the transmission and have seen no kinks, etc. I will need to figure out what the transducer looks like and where it is located first, :-) then I can check the voltage.

      Oh, btw. It reads 'low fuel' a most of the time, but twice now when idling at high rpm (where it runs smooth), it has shown that I have full tanks. If I had a restriction, wouldnt that make it run better a low rpm and worse at high rpm? My experience has been just the opposite. It stalls almost immediately at low rpm but at high rpm will run quite nicely...

      David

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      • #4
        Re: Confirmation of Diagnosis

        @davlun - I have seen instances where NG has been 'flooding' the system, leading to stalling at low RPM (idle) and rev'ing fine at higher RPM's. Two specific issues come to mind, the most curable came in the form of dirty injectors (sticking partly open and seeping NG constantly into one or more cylinders). The other issue was a bit more obscure, but an defect in the regulator allowed NG to backflow through the vacuum line into the air intake causing all of the cylinders to have excess fuel and not enough air at idle. The ECU response would be to call for more air, not ecxpecting that the air it was calling for contained more fuel.
        '11 Fusion Bi Fuel & FMQ2-36 VRA
        (Former owner '09 Civic GX)

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        • #5
          Re: Confirmation of Diagnosis

          The best thing you could do is to get a service manual "SERVICE MANUAL BI-FUEL POWERTRAIN CONTROL/EMISSIONS DIAGNOSIS" I seen one in ebay for $20.00 The transducer will have a voltage of 0 to 5 volts. It could be on your tank if you have more than one connection. in my manual, if i am right the voltage for most of the alt fuel electrical comes from alt fuel relay. It could be as simple as a bad relay ? You might be able to get an electrical print from ford. I hope you find it.

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          • #6
            Re: Confirmation of Diagnosis

            @gap and @raskell - Thanks for the suggestions, I will check those, when I get up to speed on them. Just ordered a 2000 manual, could not find a 1999, so hope they are close.

            Two more flushes and what sounded like a chirping sound went away when first started with alcohol in the filter housing. Now it pretty consistently shows a fuel level, runs a bit better at high rpm, not much change at low rpm, maybe some better. I am beginning to think that I am hearing a bit of a chirping sound when first started with alcohol flush, that seems to go away as it runs for a bit. Is that it cleaning or is it a sign of a bad injector?

            Thanks for the continued help. I am in southern california, gas is sky high right now, sure wish this was running.

            David

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            • #7
              Re: Confirmation of Diagnosis

              The chirping sound that goes away may also be sings of a vacuum leak. A dried, split or loose vacuum hose would cause the rough running. There should be a vac line attached somewhere on the compuvalve going to the system vac (at or near the air intake). May be a combination of hard plastic/rubber lines that can get brittle or loose with age and heat. The cost to replace the vac lines should be minimal and it wouldn't hurt to do it, even as preventive, to see if it cleans up your issues.
              '11 Fusion Bi Fuel & FMQ2-36 VRA
              (Former owner '09 Civic GX)

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