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  1. #21
    Super Star Member LD1's Avatar
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    Kubota l3400

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    I dont think there is any cheap way to test an injector short of having an expensive o-scope.

    but if you are carrying proper fuel pressure TO the fuel rail, it is possible that some of them arent firing??

    I think we are to the point where this is going to be a tough one to figure out in person, let alone over the web.
    ".........there is only one way to find out."
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  2. #22
    Elite Member dodge man's Avatar
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    West central Illinois
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    Kubota BX2350

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    I'm not sure, just going by memory, but it seems like every vehicle I've owned the fuel pump shut off after a few seconds without the engine running. I'm really bad at this stuff and knowing the correct terms, but I will throw out a couple of ideas. An injector could be leaking causing the pump to run all the time. I doubt this, but could be possible. It also seems like there might be some sort of valve, sensor etc that sends fuel back to the tank when the rail reaches a certain pressure. Maybe this is bad, so its sending fuel back to the tank and thats why the pumps run all the time. This could also explain the no start since you would have low rail pressure. It seems like knowing your rail pressure would be important. Thats a wild guess also and may only apply to diesels. I'd say for sure its fuel related since its starting on ether.
    Dave,
    BX2350

  3. #23
    Bronze Member
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    East Texas

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    You mentioned that this truck is rarely used. Fuel will loose its potency over time. I have a mower that wont even try to start after the gas is about a month old. Since you verified your fuel preasure is good, and it will start and run on its own with either, I supect the fuel itself.

  4. #24
    Elite Member SPIKER's Avatar
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    Ohio, Jeromesville, Ashland County
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    Jinma 284

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    Hey Guys:

    Keep it coming, sooner or later it has to be found (by SOMEBODY) maybe not me lol...

    The Fuel Injectors MAYBE are only half firing, no good way to test this I have an OLD O-Scope no leads and not sure it would work anymore as I've had it setting in shed for 15 yrs (it was 1980's HP unit)

    Not too worried about the fuel in it as pretty much all new cars will run on pretty bad gas.
    Mark
    I may remember why I went to the other end of the shop, I'm just afraid once I get there I'll forget how to get back!

  5. #25
    Veteran Member deerefan's Avatar
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    louisiana
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    1952 8N, 2005 JD 5103

    Default

    Check your timing and/or wear on the distributor gear. Also, check your egr valve/system. A bad egr valve (or dirty one) can cause fuel issues, cause it to run rich.

  6. #26
    Elite Member Tig's Avatar
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    Kubota, B7100HST-D

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    Well here's a long shot that might not make complete sense at first glance, but it's a reasonably quick check.
    Find and inspect the fuel cut off (crash) sensor on the firewall. Bypass it with a jumper (paper clip). This sensor shuts off the fuel pump when impact is detected. It's probably near the passengers feet. A bad connection there will give you no end of grief. My 96 would just gag, puff black smoke, struggle and often die, refusing to start until the passenger happened to step on the sensor just right. The connector on mine was visibly damaged (overheated). While trouble shooting that bug I did not detect any fuel pressure problems. I finally resorted to jumpering out relays and sensors while trying to get home with the Christmas tree. It was the absolute last thing I looked for and checked. Once I found it, I jumpered it with a paper clip and had no further trouble. Replaced the sensor a month later.

    I agree with the comments on the fuel pump shutting off if the engine is not running. Turn the key on and it runs for three seconds then stops. My 86 2.9L, 92 4.0L Rangers were like that. Oddly I can't really say about my current Ranger, an 08 because I've never had to check.

    Also the NOID light, previously mentioned, is used to test injector signals.
    You can check each fuel injector's electrical continuity with an ohmmeter.

    Finally, back to fuel. How does the fuel smell when you pull an injector line? Any whiff of turpentine? I've had gas go so bad that it would not even burn with a match. Tank smelled fine, but the fuel in the lines stank.

    Question, How many miles on this engine?
    Steve

    The best things in life are not things.

  7. #27
    Elite Member SPIKER's Avatar
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    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    Quote Originally Posted by Tig View Post
    I agree with the comments on the fuel pump shutting off if the engine is not running. Turn the key on and it runs for three seconds then stops. My 86 2.9L, 92 4.0L Rangers were like that. Oddly I can't really say about my current Ranger, an 08 because I've never had to check.

    Also the NOID light, previously mentioned, is used to test injector signals.
    You can check each fuel injector's electrical continuity with an ohmmeter.

    Finally, back to fuel. How does the fuel smell when you pull an injector line? Any whiff of turpentine? I've had gas go so bad that it would not even burn with a match. Tank smelled fine, but the fuel in the lines stank.

    Question, How many miles on this engine?
    Steve: Thanks for the reply, the Fuel I do believe is fine it DOES RUN but have to start it with a shot of ether to get it going. I (THOUGHT) the pumps used to STOP after a few seconds which now they are not so second guessing if they ran continuously or not. The Pumps dont run if the Impact Switch is bad, and I am getting full fuel pressure on the rail so even partly damaged impact switch would cause fuel pressure or no fuel pump operation.

    Engine only has 118,000 miles or so. will be looking at timing tomorrow and pulling the CAP and making sure there is no slop in the distributor.


    Thanks for help so far... still wondering got some Kerosene for my turbo-heater so will be able to work in cold better tomorrow...
    I may remember why I went to the other end of the shop, I'm just afraid once I get there I'll forget how to get back!

  8. #28
    Veteran Member mostly_gas's Avatar
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    in-between tractors

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    If the plugs are dry after several attempts to start your problem is with the injectors. Try unplugging them on at a time to see if anything changes (shorted injector can "kill" the rest). If you get a NOID light you can see if the injectors are having their signal cut after cranking (flashing initially, then stops). You will need to check the wiring between the PCM and injectors for shorts or breaks.
    If wiring is good, you will need a very good scan tool to figure out why PCM is not "firing" the injectors

  9. #29
    Platinum Member
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    Oliver 1855, Case 1840, Cub 1550

    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    Sounds like you may have a bad computer ground problem, at battery neg cable there are 2 smaller wires, these go to a gray plastic connector near the battery. these tend to corrode, if bad, cut out connector and use 2 Yellow heatshrink butt connectors. Check and clean all grounds and battery cables at both ends. Could also be a bad fuel pump relay(green and black) or PCM power relay(gray and black). Also check the innertia switch for corosion. The fuel pump should run 3 sec when key is turned on.Check for mice damaged wiring.

    Also it is common for the distibuter gear to spin on the shaft, to check, remove the cap and try to rotate the rotor.

    Dave

  10. #30
    Platinum Member
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    Default Re: help troubleshootinf pickup, 91 f150 6cyl

    Also if the above items check out ok, try unpluging the spout connector, inline on yellow wire near the distributorand try starting. I have had TFI modules on the distributor were the timing control circuit malfuntioned, remove and have tested at a parts store, check stator and see if rubber is crumbling. Ford PCMs hardly ever fail, I have replace less than 10 in 26 years as a drivability tech at a Ford dealer. I would tend to think this is a wiring or ground isue, due to pump run time isue and PCM not testing.

    Dave

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