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Rich in one bank, lean in the other, equal on load

Discussion in '1994-2004 V6 Mustang Tech' started by kitsune1324, Aug 7, 2019.

  1. Pete fender

    Pete fender Pete Fender

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    Plug, wire, or coil.
    You have good spark, so unplug #4 spark plug, at the plug.
    If still no change, the plug.

    If not that, I would say a bad valve, most likely #4 intake.
    Did you run a compression test?
     
  2. Sam36

    Sam36 Active Member

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    A valve problem would certainly show up on a compression test though...
     
  3. Pete fender

    Pete fender Pete Fender

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  4. kitsune1324

    kitsune1324 Active Member

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    Ran a compression test and leakdown test. For the compression test, the method was 5 strokes total, record the first and last stroke.
    Cylinder 1
    First hit 130psi
    195psi
    4% leak - crankcase

    Cylinder 2
    First hit 130psi
    190psi
    8% leak - crankcase

    Cylinder 3
    First hit 135psi
    211psi
    10% leak - crankcase

    Cylinder 4
    First hit 90psi
    162psi
    6% leak - crankcase

    Cylinder 5
    First hit *not recorded
    182psi
    8% leak - crankcase

    Cylinder 6
    First hit 105psi
    168psi
    9% leak - crankcase
     
  5. kitsune1324

    kitsune1324 Active Member

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    Just throwing it out there, if the valves/etc are fine, what if it's something like a broken RR or a bent pushrod?
     
  6. billegoat

    billegoat Member

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    A bent push rod, any kind of damage to the rocker arm will cause compressions like that....also remember you have Hyd roller lifters that can have an issue to, I've seen on Ls motors have valve to piston strikes and damage lifters and nothing else.
     
  7. Pete fender

    Pete fender Pete Fender

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    A bent push-rod or damaged rocker arm would cause tapping or knocking.
    I'm thinking since your chain tensioner was broken, it would be a bent valve or push-rod.
    Most commonly a bent valve or two, intake.
     
  8. kitsune1324

    kitsune1324 Active Member

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    Also, I ran the compression/leakdown tests on two separate days. I did bank 2 first when it was warm, I did bank 1 the day after when it was cool..the internals are also forged so keep that in mind.

    Other than that, today I changed the cam synchronizer and guess what!! Nothing. Absolutely nothing. We'll see how difficult it is to pull the rockers and everything off so I can check out the pushrods and possibly valves. One thing my uncle (gm mechanic) thinks could be wrong is the computer. I did a few tests today and with the injector unplugged there's little to no difference in how the car runs, however, when I hit the exhaust with a laser thermometer cylinder 4 was colder than it usually is. So maybe there is slight combustion? Maybe the combustion is just happening too later or the fuel injector really is putting in too much fuel, even though I just changed the damn thing.
     
  9. Sam36

    Sam36 Active Member

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    The more I think about it, the more I don't like these numbers. You say there is only 15k miles on this motor? My 3.8 that is stock and has 220k miles on it does 150 psi on a compression test (was 190 when new I think). I'd think for a motor that has been bored and stroked, you'd be getting above 200psi on every cylinder... unless there is a lot of "track" time on the motor.

    But that said, 160 psi on a cylinder will not cause a miss. I once had an old Datsun with a straight 6 that was quite wore out. It had 30psi on 2 cylinders, 10 psi on another, and I think the rest were like 80psi and it ran "pretty good", though it had no power.

    Would be nice if you had an oscilloscope so we'd be able to see what waveform is being sent to each injector.... Perhaps its firing at the wrong time, or not enough. You could try to manually activate it.

    I also find it weird that nearly everyone on here that has a "miss", usually has it on cylinder #4 ...
     
  10. Sam36

    Sam36 Active Member

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    The factory service manual states that the cam synchronizer is only used during engine start up to find TDC of cylinder #1. After that, the sensor is not watched any more by the computer. I state that so you won't continue to "fiddle" with it like so many here do, thinking that it is like moving the distributor on an older car... it is not.

    I dug up the most resent posts from the other guy that was having "cylinder #4" troubles: Intermittent Misfire After Throttle? He seems to state that changing the coil fixed it... note that he had already changed the coil 2 or 3 other times previously...
     
  11. Pete fender

    Pete fender Pete Fender

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    The cam position sensor is needed to start EACH sequence of injector firing.
    Not just startup, but the entire time the engine is running.
    You misunderstood what you read.
    Compression test...
    Warm motor, pull fuel pump fuse, crank it with all the plugs out and throttle body wide open. All cylinders should be within 25% of each other. about 100 psi on a worn engine, 160 new.
    You source of info is suspect.
     
    Last edited: Aug 30, 2019
  12. Sam36

    Sam36 Active Member

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    I swear in some book "somewhere" there was some "theory of operation" of the 3.8 engine start-up sequence which stated what I said. In the diag book, the only mention of cranking and cam position is for coil on plug applications. Perhaps I somehow conflated the two. But by turning the cam sensor, am I actually changing the timing of the injectors? That actually makes me want to go play with it now :D But certainly seems redundant as when you know #1 is at TDC, everything can be timed by crank alone hence why my original statement made sense, though I guess it is just a theory now...

    20190830_180723.jpg 20190830_180743.jpg 20190830_180812.jpg 20190830_180902.jpg
     
  13. Pete fender

    Pete fender Pete Fender

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    Turning the Cam position Sensor, will advance or retard the opening and closing (Dwell) of the injectors.
    If it was only there to start the engine, you could pull the wires off once started, but it has to constantly "tell" the PCM when #1 is at top dead center in order to keep the injectors in time.
    The crank sensor is set to tell the PCM when it is at TDC, so the tach works, and cam and crank's relative positions are in a running state.
    If the opening is too soon or too late, the injection of fuel also is out of time, and your engine will loose power, the mixture will be either too lean or rich, and the engine can be damaged by knocking or flooding.
    The PCM also relys on the two sensors giving a signal to the PCM in order to fire the plug at a predetermined instant. (Ignition timing is also controlled by PCM.)
    The faster or slower the engine turns, the dwell of both is increased or decreased by the PCM.
    It's not just 3.8's. it all injection systems.
    Coil on plug, single multi-coil packs,(3.8) and dual coils,(4.6 and 2.3 eight plug) are not tied to the injectors, but are timed by the same cam sensor/crank sensor triggers, using the PCM.
    The fuel and ignition systems are separate, but co-ordinated with by the PCM.
    I am tired of typing PCM, but it literally runs the car, it's the brain telling the organs what to do, so to speak.
     
    Last edited: Aug 30, 2019
    Sam36 likes this.
  14. kitsune1324

    kitsune1324 Active Member

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    I double checked the cam synchronizer and it was centered with the tool (as it should be) at TDC.
    I smoked the intake again with a LOT more pressure than previously, there were no leaks except out the new EGR valve. From what I could find, this is normal under high pressure and the valve opens up under vacuum, so I doubt that the EGR would still be the issue. I traced the O2 wires all the way back to the ECU and it's working as it should. Anyways, I'm still lost as to what the problem could be. This week I'm going to try another new coil pack and a new (used) matching computer. The tune has PATS disabled so I shouldn't run into any issues.
     
  15. Pete fender

    Pete fender Pete Fender

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    The PCM (What you call the ECU) may be why #4 has a problem.
     
  16. kitsune1324

    kitsune1324 Active Member

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    Well the new ecm came in today, thankfully it has the same ecm code and strategy so I was able to flash the tune on it and try running the car. Unfortunately it ran exactly the same as before.. I'll try to get a long log of this ecm if anybody wants one, but I feel like I'm sol at this point.
     
  17. Pete fender

    Pete fender Pete Fender

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    Here is another shot in the dark...
    Check the vacuum hose that is on the bottom of the throttle body.
    Mine, stack, had a slice , then it went to the vapor recovery system.
    The hose was collapsing and the car was running badly.
    When I replaced that, @ 144.000 miles, it not only cured it, but in handling it, my hands looked like charcoal from handling the hose.
    The evap main components are behind the passenger side inner fender.
    Funny thing is, I had no codes.
     
  18. fasterthanyou

    fasterthanyou Active Member

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    I haven't read in detail all of the responses to this thread but here's my worthless 2 cents:

    I had a truck come in the shop the 3 days ago. Although it was a ford 4.0l the issue was the same. Lean bank 1 rich bank 2. Ran like crap.

    I unplugged maf to force it into the failed maf table which helps to rule out maf and o2 sensors as the source of the problem.

    Still the same thing. ran bad, lean bank 1 rich bank 2. Removed the vacuum line to the egr valve and the engine immediately ran smooth. The egr solenoid was stuck open causing the egr valve to be open at all times that the intake manifold was under vacuum.

    Just to verify that the ground circuit wasn't the issue causing the solenoid to stay open I unplugged the electrical connector at the solenoid but the solenoid was still open.

    Replaced the solenoid, and all was well after that.
     
  19. fasterthanyou

    fasterthanyou Active Member

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    You can unplug the cam sensor on these engines and the engine will run as if nothing changed. Really seems silly that they even use a cam sensor, at least in my opinion.

    Seems like the only use for the sensor is to drive the oil pump.
     
  20. kitsune1324

    kitsune1324 Active Member

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    Pete, that's a good question. That line was initially leaking when I did a smoke test so I used hose clamps to hold it together. I can't seem to find that line anywhere for purchase, would you happen to know the exact name or part number?

    Fasterthanyou, that's something I actually haven't checked at all, I'll give that a shot tomorrow! If it doesn't work I'm probably going to end up taking the mustang in to be looked at unless anyone can think of anything else.