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Ford 4.6 Misfire

Discussion in 'Non-Mopar Tech Support' started by neoncrazy101, Aug 17, 2015.

  1. neoncrazy101

    neoncrazy101 Member

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    Hey guys, so I was all ready to sell our 2004 Grand Marquis (172k) and then she decided to wanted to start to misfire, I swear cars have a soul of some sort lol. I was/am getting code P0306 (misfire cyl. 6) and P0316 (Misfire detected within the first 1000 cycles). I've moved the plugs, coils, and injectors around to other cylinders and the problem did not move. Plugs have 15k on them and look fine. After running out of idea's a few days ago I decided to put in a new plug and coil boot (These have a C.O.P setup) and it didn't change anything but hey, it was super cheap lol. I've taken voltages and ohms and compared them to the cylinder 5. I've also ran compression tests and all cylinders were good, (mid 160s-mid 170s).

    Cyl. 6: .8ohms primary and 5.5ohms at the secondary. Voltages at the connector fluctuated from 2-2.7v, randomly would zero out or dip down to around 1v but always came back up to the 2-2.7v range

    Cyl. 5: 1.1ohms at primary and 5.5ohms at secondary. Voltages were between 2.1-2.3 volts. No random dips or anything.

    Also checked the ohms between the connector and where it connects to the main harness (under the brake master cylinder) and it was 1.2ohms, that was for cylinder 5 and 6.

    I have no idea why cyl. 6 would randomly zero out or dip down so low before returning. I suck at figuring out electrical problems so any help would be great. I've asked around on Crown Vic forums but they are of no help.
     
  2. ImperialCrown

    Level III Supporter

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    Do you feel the misfire 'shake' at idle and higher engine speeds? Is the misfire only at idle or all the time?
    Follow the basics: spark, fuel, compression. Can you start the car with a plug in the #6 cylinder, but have the COP with a spark plug plugged into it laying on its side on top of the valve cover to watch the actual spark across the gap?
    Were the plugs that were in #6 a different color or appearance than the rest of the plugs?
     
  3. neoncrazy101

    neoncrazy101 Member

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    When you first start the car, you can feel the car shaking a little bit, once you put it into gear the shake gets a lot worse (actually seeing the hood vibrate and such). At that point though even if I put it back into Park or Neutral, she still shakes a lot more than when I first start her up but not as bad as when she's in gear.

    I've done compression and her compression is good, that cylinder actually has one of the higher numbers when compared to the rest. (~170psi range) I have not tried it with an actual plug but I have tried to check the spark with a tester. I could not see the spark with the tester but I could hear it and it would randomly ground, the tester did not like staying in the coil boot, hooray.

    The plugs all looked the exact same. I even tried replacing that single plug just for kicks with an OEM Motorcraft and nothing changed.
     
  4. Locodave

    Locodave Member

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    On the 4.6. I'm thinking you know that pass side, front to back are cyl's 1-2-3-4 and driver side front to back are cyl's 5-6-7-8. So the 2nd one back on the driver side is the one with issues.

    I would, key on, test for voltage at the coils connector. The ECM controls ground. Probe a few coil connectors to see matching voltage. Ground the test meter neg probe to a good ground. Don't bother to use the other wire at the connector to use as a ground. One will be hot and the other is the ground. If you try to use the other wire as ground. You are going thru the ECM and it might not show a ground.

    Do a wiggle test at the connector as it might be a prob inside the connector. Battery volts go to the ECM, then output to each coil, from the ECM. not shure if you would see battery volts or reduced volts @ the coil.

    I would then, key off. Start pulling connectors off an injector, do one at a time. Set the meter @ ohms. Probe the 2 terminals on the injector. Compare with others for ohm values. You might have a bad injector if the ohms reading on # 6 are way off than the others.

    Key on, then test for battery voltage at the injector connector. Red wire is the hot, feed @ each injector.

    I was hunting diagrams to see if supply volts to the coil and injector are on the same feed. If a bad injector, on #6 when operated to ground, would pull volts down at the coil? Used close at the same time.

    Fuse F1 19, 15 amp does feed power to both. Goes thru the PCM power relay in key on to get energized, then to splits to the ECM for the coils, and splits directly, not going thru the ECM to the red wire @ the injectors.
     
    #4 Locodave, Aug 23, 2015
    Last edited: Aug 23, 2015

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