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Thread: Auto mechanics?

  1. #1

    Auto mechanics?

    For you shade tree mechanics out there, how can you be sure, if a fuel injected engine, is actually getting any fuel?



    Thanks Greg

  2. #2
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    Is it still running?

    Having never messed with fuel injection, this can only be related as something read years ago in a book troubleshooting VW fuel injectors.

    The author suggested removing the fuel injector and then watching to see if it produced a spray into a can (to catch the fuel). It should be a fine spray and not a stream.

    You would have to have someone help to turn the key or rig up some wiring to get the fuel pump working. The engine might need to be turned over to get the injector(s) to work.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  3. #3
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    Many fuel rails have a schrader valve on them that you can hook a pressure gauge to. I found a air conditioning gauge set will hook up. Not sure about leaving fuel vapors in the ac line set to contaminate the freon.
    Low fuel pressure will cause the engine to run rough with raw gas smell out the tailpipe. high pressure will cause the same thing.
    First baby test is engine off then turn key to on. Listen for the fuel pump to come on and build pressure then shut off in about 3-5 seconds.
    Look for vacuum hose to manifold pressure sensor or gasoline pressure regualtor. Is that hose secure and not cracked?
    Bill D
    Bill D

  4. #4
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    There are probably multiple youtube videos with your particular vehicle that show what to do, and what tools to use. There are lots of variations in different fuel systems, so best to find something specific about yours.

    I had trouble with a diesel tractor fuel system, and ended up hooking up an electric fuel pump to eventually find a tiny leak in the injector pump that was Very hard to find. It would run for a few minutes, and die. The extra pump kept it running long enough for the leak to show up.

  5. #5
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    Not shade tree, retired 41 year pro.
    Find the schrader valve on the fuel rail and use a small punch to depress the pin while someone cranks the engine. If you get fuel spraying out, the pump and relay are probably OK. Wear eye protection and an old shirt for that test and don't smoke or do the test near a lighted BBQ grill.
    If the pump tests good, use a mechanic's stethoscope placed against a fuel injector. When cranking the engine you should hear a rhythmic ticking from the injector.
    BillL

  6. #6
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    Why do you think the cylinder is NOT getting fuel?

    How old is the car? Is it new enough to have an ODBII port? Any codes?

    If it is running rough and you think it is not getting fuel pull one sparkplug wire at a time. If it runs worse then that cylinder is most likely good. If there is no change in how the engine runs then there is something wrong on that cylinder... spark, fuel or compression. If you think the problem is fuel then change that fuel injector, they generally aren't all that expensive.

    We were working on my daughters 2003 Maxima which was running rough and had a code indicating a problem in cylinder one. We pulled apart the upper intake to get to the back three plugs and fuel injectors then put in 6 new plugs, 6 new COP (coil on plug) coils and a new fuel injector on cylinder 1. It has been running great ever sense. It probably didn't need everything we put in it but it was very easy to do with the intake all apart so might as well do them all. At $120 each for OEM injectors is wasn't worth putting in 6 new injectors so we just did the 1. We have no idea what the actual problem was but it is definitely gone now at a fraction of what a repair shop would have charged us... and my 17yo daughter got to try her hand at doing a bit of wrenching.
    Last edited by Michael Schuch; 09-27-2022 at 2:33 AM.

  7. #7
    Quote Originally Posted by William Lessenberry View Post
    Not shade tree, retired 41 year pro.
    Find the schrader valve on the fuel rail and use a small punch to depress the pin while someone cranks the engine. If you get fuel spraying out, the pump and relay are probably OK. Wear eye protection and an old shirt for that test and don't smoke or do the test near a lighted BBQ grill.
    If the pump tests good, use a mechanic's stethoscope placed against a fuel injector. When cranking the engine you should hear a rhythmic ticking from the injector.
    BillL
    I'd like to amend this just a tad -- First, do what William suggests, but DO NOT turn the ignition on, and DO NOT crank the engine! If the fuel system is in order, there WILL BE fuel pressure at the Schrader valve indefinitely- If there's no pressure initially, this indicates an injector is leaking down, or somewhere else down the line that's leaking, or a junk fuel pump--

    IF there's no pressure, THEN turn the ignition key on ONLY. This will activate the fuel pump for a few seconds. Turn the key OFF, then check the valve again...

    If you get fuel, then the pump is at least working...
    If you get AIR coming out, that indicates the pump is trying to fill the fuel lines, and air is in the way.

    If YES to fuel and/or air, fuel pump is okay- if YES to air, you may have an injector leaking, either into a cylinder OR on top of the engine! (not good)

    If NO, then crank the engine for 4-5 seconds, then check for fuel or air-

    If YES, finally, then the pump could be bad- even a bad pump may pump fuel, but may not build up the high-pressure needed for injectors to flow properly. This is when you need to check the pressure at the rail...

    If NO thru all this, the pump is junk, or not getting power- and not getting power is a whole nuther can o' worms!

    FWIW, I've had 2 pumps on FI vehicles go bad, one on my old Buick Ttype, which pumped gobs of fuel still but would only build about 4psi pressure, not even close to enough- the other was the one in my '02 F250 that went out about 9 years old, and it just up and died, no pumping, no noise, no nothing; shut it off, went to bed, next day the pump was toast...
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  8. #8
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    I put a small fuel pressure gauge on the fuel rail of my LS powered '84 CJ7. https://www.summitracing.com/parts/sum-800138

    NOW you tell me...

  9. #9
    I disassembled the manifold to access the fuel rail. The problem is, there is no schrader valve to found. That's what has me stumped.

  10. #10
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    One quick and dirty test is to spray some starting fluid into the air cleaner and immediately crank it over. If the engine fires you know that you're getting spark, but not fuel. If the engine does not fire, odds are you have an electrical problem.

    This isn't 100%, but it's an easy troubleshooting tool.

  11. #11
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    Firstly a heads up, most modern fuel systems both petrol and diesel run over 20 BAR and that will cause a serious injury if you get hit by it, trust me you do not want that to happen. If working on a fuel injected car it is best to know what the rail pressure is.

    Now to fault finding for the average person, an Infra Red temp gun is one of the quickest ways to find if a cylinder is down fire the gun at the exhaust manifold runner for each cylinder and if the temp on one is down significantly then that cylinder has a problem and you have a starting point which can be multiple things or a single thing.
    Chris

    Everything I like is either illegal, immoral or fattening

  12. #12
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    That ir gun is about $20 at Horrible Fright on sale.
    Bill D

  13. #13
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    Quote Originally Posted by Greg Wieskamp View Post
    I disassembled the manifold to access the fuel rail. The problem is, there is no schrader valve to found. That's what has me stumped.

    Year, make, model, and engine displacement. Without that info any diagnostics is a WAG. :-)
    BillL

  14. #14
    2007 Dodge Nitro 4.0

    I finally found a video showing how to check pressure without a schrader valve. Now I have to find a place in the fuel line to tap in.
    Last edited by Greg Wieskamp; 09-28-2022 at 6:50 AM.

  15. #15
    So, we had fuel pressure. So far on this car he has replaced the fuel pump, alternator, TIPM, Battery, cables, spark plugs, and a host of other things. On a whim, I decided to check ALL the fuses in the TIPM. Found a blown 25amp fuse. Replaced it. Started right up.

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