Results 1 to 6 of 6

Thread: Misfire cyl 1

  1. #1
    4X4V8 Guest

    Misfire cyl 1

    About a week ago I noticed on cold start up an irregular engine misfire. I hooked up the Nanocom and it showed a misfire on cyl 1. I have used the vehicle more than usual since then, about 5-6 times from cold. At each cold start, it misfires anything from only about 3 times to 10 times before running normally. Or not misfiring at all.

    I swapped cyl1 plug with cyl 7.
    See attached pic. I think cyl 1 plug is the one with the white-ish electrode. My concern is the colour of the electrode on cyl 1 compared to cyl 7. Does it mean anything? Lean? Corrosion?

    RR P38 plugs.jpg

    It still has the misfire, only cyl 1. Only when cold. Not every cold start up. When warm, idle is not perfectly smooth; almost like failing engine mounts, a slight vibration at idle in gear. That has been like that for a while (months). This is possibly unrelated to the misfire. I don't know.

    The coolant reservoir looks like it is down a little on coolant, but I did have a leak at the manifold pre-heat hose a few months ago (since fixed). I can't remember if I topped up the reservoir or not. Anyway, I topped it up last night with approx 300-400ml to bring it to the 'cold' low marker.

    There are no Motronic fault codes showing on the Nanocom; I have checked this a few times in the last week.

    Plugs were allegedly fresh when I bought the car, so only perhaps 1yr/3000km or so old. Plug wires look fresh also.

    There was a thread I found on here a few pages back about nanocom ign output readings that indicate a normal range. I'll print that out and then see what readings I get from my car.

    My gut feeling however is that I have a head gasket leak, coolant into cyl 1. But it could also be plugs, plug wires or ign modules.

    I don't seem to have any external coolant leaks from head gaskets (or anywhere else).

    What do you guys reckon?

  2. #2
    Join Date
    Oct 2007
    Location
    Williamstown, Victoria
    Posts
    726
    Total Downloaded
    0
    The fact that only cylinder 1 is affected, even after swapping plugs, indicates it is something unique to that cylinder.

    I would try swapping cylinder 1 lead over with another lead to see if the problem moves as a first step.
    Make sure all leads are securely plugged into all plugs and coil pack.

    If you are not certain about the age of the plugs, it might be a good idea to replace them, unless you are confident they are not that old.

    Head gasket leaks can let coolant into the cylinder, effectively steam cleaning the plug, where your plug is showing whitish deposits, which can indicate it is running hot or lean, which might be a partially blocked injector on cylinder one or possibly the injector seal on cylinder one leaking.
    You could try spraying some carby cleaner on injector 1, to see if that changes anything.
    If you look behind the A/C compressor you can see injector 1, I would do that with cold engine idling so you are not spraying a solvent on a hot engine.
    I don't think it would be MAF or 02 sensor related, as that would affect more than one plug.

    Are you seeing any air bubbles entering the expansion tank from the return hose while the engine is running?
    I would keep an eye on the coolant over a few days, check the coolant level every morning while it is cold to see if there is any coolant loss which might indicate a coolant leak or head gasket issues.
    Hope that is of some help or at least a start.

  3. #3
    4X4V8 Guest
    Quote Originally Posted by PeterH View Post

    Are you seeing any air bubbles entering the expansion tank from the return hose while the engine is running?
    I would keep an eye on the coolant over a few days, check the coolant level evey morning while it is cold to see if there is any coolant loss which might indicate a coolant leak or head gasket issues.
    Hope that is of some help or at least a start.
    Well some good news -- maybe. When I checked the coolant this morning it was down a little on yesterday's top-up, but then I had topped it up when the engine was warm. So that is inconclusive. I need to top up when cold and check when cold.

    However I took off the coolant overflow cap and checked on cold start-up if there were any bubbles coming from the return line (seems obvious to me, but you did mean that I should check when engine is cold, right?). It was a constant, steady flow of coolant. Watched it for about 30sec, all good, no bubbles.

    The other thing I noticed this morning on a 30min drive was that it perhaps misfired once when cold, and a few more times randomly at operating temperature. I forgot to hook up the Nanocom before I left for the drive; did that back home and while it showed no misfires I could feel the engine miss like a slight misfire, randomly. Idle is generally not what I would call perfectly smooth either.

    So there is something going on here, not quite sure what yet. Will continue with your suggestions of swapping leads first, and doing a cold top-up of coolant and subsequent cold check a few days later to see if coolant is actually dropping in the reservoir. Then injector.

    I just hope it is not head gaskets. Could the Land Rover gods give me at least another six months before that happens please? Have other things to fix first!

  4. #4
    Join Date
    Oct 2007
    Location
    Williamstown, Victoria
    Posts
    726
    Total Downloaded
    0
    I have been experiencing a slight random missfire myself, I replaced my plugs (NGK Platinum PFR5g-11 on a 2001 4.6 Thor) and the missfire has gone.
    Might be worth a shot!

  5. #5
    4X4V8 Guest
    Quote Originally Posted by PeterH View Post
    I have been experiencing a slight random missfire myself, I replaced my plugs (NGK Platinum PFR5g-11 on a 2001 4.6 Thor) and the missfire has gone.
    Might be worth a shot!
    I have read volumes of P38 info over the years that sometimes it's hard to remember what is what .... but I thought I've heard somewhere that the platinum plugs are not worth bothering with or can cause misfiring... is that right? Obviously you think they're worth a go. I can still feel a very slight misfire. Maybe I'll try new plugs too.

    I've been using the car every day this week and the obvious cyl 1 misfire has gone.
    All I have done after swapping plugs earlier (1 for 7) is get a pair of pliers on cyl1 ign boot, as it didn't feel like a positive fit to me on the plug. Just a fairly gentle squeeze with the pliers. I haven't had time to try swapping leads yet, but I may have found the problem anyway.
    I will leave the car for a few days to see if the misfire returns. The fix seems too easy...
    .

  6. #6
    Join Date
    Oct 2007
    Location
    Williamstown, Victoria
    Posts
    726
    Total Downloaded
    0
    Hey you never know, you may have just solved the problem!
    As P38 owners we are always listening for little sounds or clues as to what might be going on, sometimes I wonder if I'm imagining things!
    With things like plugs, everyone seems to have a different opinnion on what's best, I've been using those for quite a few years now with no problems, but I'm always open to trying a different type if they run well in a P38.

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!