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Thread: Random misfire (P0300 & others + sometimes no AC)

  1. #1

    Angry Random misfire (P0300 & others + sometimes no AC)


    2004 Marauder, approx 180K, well maintained. She uses some oil, but not terrible.

    I have been battling this for a while in my spare time which is slim. I’ve had my mechanic friend with the uber expensive Snap-On computer look when it’s been happening too. Car could be great for a few weeks then occasionally and randomly I’ll get a P0300 (Random Misfire) along with some stumbling on acceleration and idle. Sometimes this is combined with other codes. Sometimes not. SOMETIMES when it’s misfiring I have no AC.


    My diagnostic ability is limited because it will usually "fix" itself before I get back home and I can't find the problem if it's running great in my driveway.

    At random, my symptoms are, and in various combinations:

    • Drive great, misfire a little, get worse, then smooth out and be fine
    • Instant light on startup and drive like poop, or light on startup and drive like eh, but drivable
    • Driving fine for a while and suddenly misfire with light immediately
    • Driving fine for a while and a light and misfire many miles later or no misfire at all
    • Driving fine, misfire, park it, shut off, start up, and it’s all better…or not
    • Misfire, AC will blow hot for a while, magically come back
    Fortunately I've never stalled out or been stranded because she always comes back like a Phoenix.

    Over the last few months some codes that I recall have been:

    • P0352 – Ignition Coil B primary/secondary circuit
    • P0356 - Ignition Coil F primary/secondary circuit
    • P0305 – Cylinder 5 misfire detected
    • P0316 – Continuous misfire detected on startup first 1000 revolutions (Showed up a few times over a few days but not before)
    ….Replaced crank position sensor, then later got…
    • P0315 – Crankshaft position system variation not learned (This one has not come back since shortly after the new CPS)
    This past weekend when I was replacing the coils and adding Granatelli connectors, I noticed a little oil in #6 hole so I did the cover gasket. In retrospect I realize I didn’t pull the plugs. Oops! But after I did the coils, it has some issues finding a good idle, but eventually settled down. Took it for a spin and drove AMAZING like it got a shot of adrenaline and I loudly whooped “She’s BACK!” Drove it for a couple days and all good. Big smiles. Happy dance. Then this morning, 5 min down the road, light, misfire, flipped it around and drove the Jeep to work with my head down in shame.

    So to recap, replaced plugs, factory coils, few COP connectors had exposed/green wires so soldered and replaced and replaced cam cover gasket on PS, new PCV and hose. (The PCV to cam cover detents where the PCV turns and locks into the ‘grommet’ are a little worn so the PCV is possibly cocked a tad. Can’t find replacement ‘grommet’ part that bolts into the cam cover). Cleaned MAF & air filter. Did injectors a while ago when this first started. Techron a couple times in the past. With my mechanic's Snap-On, he's actuated/tested all the stuff he can like EGR, etc.


    As my last act, I’m going to pull the plugs this weekend, again, and put in a new set of XP104’s. That way I can be 100% sure it’s not the COP/plug. Again. Kind of.

    I haven’t ruled out things like the PCM or an intermittently broken wire somewhere and i
    f this were persistent it’d be a different story, but it’s RANDOM, and goes away on its own. And coupled with the AC issue, I just don’t know. I've been playing with my various 4.6L's for something like 18 years so I know my way around the platform. This has me stumped. After years of fiddling with a seriously annoying problem, I’m about ready to call it quits. I trust my Jeep and Suburban more and I know FAR less about those vehicles.

    Thoughts?
    Last edited by Rob; 08-24-2018 at 01:40 PM.

  2. #2
    Join Date
    Jun 2017
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    Age and brand of battery? If it's not a Motorcraft and if it is 2 years old or older, then....these days it is highly suspect....

    Bad ground is the other idea.....

  3. #3
    Diehard (Platinum?) and I'm not certain of the age. Few years. Terminals are clean and tight.

    The obvious chassis grounds are good. Removed, cleaned, and re-bolted. Does anyone have a map of all of them? I don't think I missed any though.

    I considered the battery but I have noticed no voltage drop, dim lights, or startup issues ever. Alternator is new as of maybe 4 or 5 years. I suppose I can have my mechanic put his tester on next week for giggles.

    Also, I had a chuckle when I read this thread about batteries. They are all largely made by the same company, but I respect where you are coming from.

    https://www.mercurymarauder.net/foru...hlight=battery

  4. #4
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    Sounds like you already replaced the usual suspects. Dont spend another dollar till you do a compression or leak down test.

  5. #5
    Join Date
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    Lightbulb

    Quote Originally Posted by Agent2006 View Post

    Bad ground is the other idea.....
    With phantom electrical issues I also locate and clean every ground - always use dielectric grease afterwards. Unplug and replug electrical connectors and pack with dielectric grease. Intermittent tells me it isn’t a major failure (obviously). When was the last time the OP pulled the negative cable off of the battery for several minutes? (pcm reset). Always negative first - positive last and reattach in reverse order (negative last). Basics first, especially with a 15yo car.
    Current Garage:

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    “You've gotta dance like there's nobody watching,
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    And live like it's heaven on earth.”
    William W. Purkey

  6. #6
    Right, it's not a major catastrophic failure because it will drive for weeks just fine, the not.

    Compression was done last year with no findings.

    When I did the driver side cam cover I had to disconnect the three main harness connectors. I checked for anything untoward and they were good. I was going to do a dab of dielectric grease but it slipped my mind.

    Battery has been disconnected and let sit, I dunno, hundreds of times over this whole diagnosis period. Every time I made a change. The last time was when I did the COPs this past weekend.

  7. #7
    Join Date
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    how much does a cam sensor cost for one of these?

    All those previous codes are a wash once you correctly installed the new coils, replace the plugs and lets see how it drives once you have new plugs and coils, new cam and crank sensor.

    I would look at the ground wire on the passenger front timing cover, make sure its grounded well.

    Report back and we can try and help out. Do you have anyway to log this experience?
    The twins2.3 whipple/aluminatorVortech V-2 lots of goodies

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  8. #8
    Tomorrow (Sat) is supposed to be a nice day so it's plugs and recheck grounds. Timing cover is first in the list.

    Cam sensor is under $30 and I'll have one before the end of the week.

    I did have a documentation plan. My cheapo Innova 3130 is only so good so I wanted the AutoEnginuity scan tool and Enhanced Interface for Ford-family (EI01). Yummy mode 6 data. My plan was to start to log data on my laptop literally every time I started the engine. I don't mind the investment in diagnostic tools, but phantom issues are not really scan tool level. Better than nothing though, unless anyone has a 100+ channel lab scope I can borrow for a few months.

    Thanks everyone. You people are a very fine bunch.

  9. #9
    Join Date
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    Vaccum leak?
    Could be dirty or sticking IAC or EGR.
    Rubbed harness behind heads?
    This is interesting, please keep us updated.

  10. #10
    My findings on Saturday:
    • Tore into wire loom starting from PCM and moved outward. To my delight, all the connectors looked clean and wires were good. However, found totally sliced slightly larger red wire going to cruise control. Don't use cruise so not surprised I didn't notice. Soldered, heat shrinked and rewrapped it all. Why is there a black pin hole test plug on the cruise and another random wire? Plus an epoxied shut one from the PCM? Didn't get to the harness towards the back of the DS head but it looked ok with no chafing. I hate chafing, but there are creams for that.
    • Re-checked COP connectors for more bare wires. They all looked good.
    • Re-seated the Granatelli connectors to the COPs. Anyone else notice they like to pull out and remain firmly seated on the plug necessitating retrieval via needle nose pliers, and require heroic efforts and just the right angle to seat?
    • AGSF32WM plugs looked OK. New as of maybe 10K miles ago. No unusual fouling or red flags. Replaced with XP104 just because. Gaps carefully verified as identical.
    • PS timing cover ground admittedly looked rough. I was sure I checked it before, but clearly I didn't. The rest were removed and again re-cleaned for due diligence.
    • Found two slightly cracked rubber hoses. One was the ~4" rubber piece that goes from the intake to the hard plastic tube that goes to the purge solenoid. I couldn't read the numbers on the label to order a new one and the parts diagrams were vague. Anyone have that PN? Also the hose from the intake tube to the DS PCV grommet had a few little cracks where it slipped over the nipple. I didn't have the appropriate tubing in my stash of goodies so I wrapped some electrical tape around the offending areas. Neither hose looked particularly bad and it's more likely me manhandling them caused them to actually crack.
    Started up. Ignition circuit H insta-light. Rough idle. Re-seated COP. Disconnected battery for a while.

    Started up again. Better idle, still not smooth. Inspected COPs. Thought I was having a plug blow out. #3 COP appeared to be pushing up and out and I had to push it back in like a hernia. Commenced to freak out. Shut off car. Cry in corner.

    Saturday night:
    • Get super stressed thinking I'm having a blow out and look into Time-Sert. Held off clicking the 'checkout' button.
    Sunday:
    • Caffeinate
    • Re-re-inspect all components. Clean the snot out of the plug holes and threads. (Anyone have a clever method of doing that besides a bottle brush and paper towel taped to a dowel?)
    • #3...I think it was the pressure of the squeezing bulging gasket that fooled me. When I got the car I noticed the PS valve cover has a couple bulging plug gaskets (2, 3, 4). Hack before me probably over tightened. Why?! They don't leak so I'm leaving them be for now. Makes changing plugs interesting because my plug socket sometimes gets stuck on them. Also, my PS plug cover has a mostly stripped bolt so it's not holding the COPs in/down tight. That was my fault on Saturday. Really annoying since that's the side with the migrating COPs. I will be retapping and getting that secured. I think it's the only thing holding in my COPs on the PS. Yikes...
    • Drove about 20 min to Dunks and back and Hallelujah! I don't think she's ever driven as smooth. No codes, smooth idle. Code scanner showed only the EGR and CAT left to learn. I had other things to do so I didn't want to be out too long.
    • Started car few hours later and....maybe little rough idle. No codes but didn't feel as smooth as before. Hung head in shame and put my tools away.
    • De-stressed by petting one of my hens that loves to roost on humans. She's like a lap dog.
    I drove the Towncar to work this morning. Yeah a 4.6 that doesn't give me constant grief. Before I rely on her to actually get me from point A to B, I want to thoroughly test close to home and make sure its actually a problem and not me being neurotic and way too sensitive to normal still-learning PCM weirdness. And I want to make sure that cover bolt is re tapped because that's really stressing me the way the cop wanted to wiggle out.

    So, my take away is, I'm just not sure. The questionable vacuum hoses could have been a factor, but that it would ride great, take a dump, then go back to business as usual all in the same drive makes me think it was something else. I discovered a few issues that may be causing me grief NOW (bulging plug gaskets, moving COPs, and unfortunately stripped bolt that should be holding my COPs in that sort of isn't). But those threads were damaged on Saturday so the cover should have held those COPs down firmly all this time, thus a non issue? Yes, I want to replace the cover gaskets on the PS at some point, but I really don't want to because it's a super pain. Plus, it wasn't just the PS that was misfiring originally, unless a few occasionally misfiring COPs would cause a cascade even on the DS side? I don't know how sensitive the ignition system is but I always thought if one failed, then only ONE failed.

    Also, can someone please tell me why my AC would sometimes blow warm when I was having a misfire? Is there some emergency system that causes the compressor to shut off thus alleviating additional engine stress when there is a misfire?

    I realize I fired birdshot at the paper and hit the 10 ring, but I've had this kind of semi success before. I think everything's great for a few days, then not. I'm reserving judgment until the weekend when I can do some meaningful cruising and highway runs.

    I suppose I could replace the EGR but I am not looking forward to that EGR nut and she misfires as much at idle as driving so I believe the IAC is a non-issue at the moment.


    In the meantime, any other suggestions?

  11. #11
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    You might have a burned exhaust valve. If there is carbon buildup on the edge of the valve ( or the chrome / silver on the valve is blackened), when it goes down, it's not seating properly.
    Those codes can come up because of this. I would get a leak down test on your engine. it may pinpoint the problem. My Silver had a burnt exhaust valve on #6.

  12. #12
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    Your compressor will shut off during a misfire FYI. Ac will temporarily shut down

  13. #13
    Ok good, so it is going into a protection mode and I don't have mysterious cascading electrical failures.

  14. #14
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    Suggestion: take the battery out of the Town Car and install it in the Marauder.

    I don't have long distance diagnostic powers, in fact the ones for my own heaps in my driveway are pretty lame, but when I first got my LS1 Firebird, after a short time the thing would run fine, then run rough...then OK...like it was possessed. The car became that fun but crazy chick we all knew in high school, couldn't say goodbye ...

    Replaced the battery ---purred like a kitten. Must have a been a loose cell plate, or something, could never get a bad battery reading from it, seemed to start just fine, but going down the road....

    Would be interested to hear the compression test results if you do that test...
    Last edited by Agent2006; 08-28-2018 at 04:54 PM.

  15. #15
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    I'm not the smartest guy ever, but I don't think a compression issue would be intermittent.
    In my personal experience, intermittent means electrical.
    Could still be vacuum related. May be worth getting a smoke test.
    Your friend with the scanner should be able to actuate the iac and egr in functional tests.
    If you're lucky, the misfire counter will point to a specific cylinder. If not, try a contribution test.
    May be worth trying to back probe the cops and checking voltage under load.
    If you want to get really fancy and have access to the equipment, can back probe the cam and crank sensors and check that they are triggering correctly.
    Kinda want to get my hands on it, but I'm at least 3hrs away.

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