306XT misbehaviour
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  1. #1
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    Icon9 306XT misbehaviour

    Hi All,

    Time for another "what the hell is going on" post, regarding my 98 306xt. She's been running nicely for a bit now, but as of last night has begun behaving oddly. Driving home, the engine started almost missing - I'm not sure that it IS actually missing, but for no apparent reason revs would suddenly drop then pickup, drop then pickup.. rinse, repeat

    Seems to happen particularly when I'm only feeding it a little bit of throttle - cruising along at 60 in fourth, for instance, at around 2300 revs. I've just been playing with it in my driveway to see if I can replicate it, and with it sitting on 3000 revs after about 10 seconds it'll drop to ~2650 then pickup, drop and pickup... you get the idea.

    Could this be a fuel-delivery issue? I did have a slight fuel leak from the fueltank rollover valve (which was bodged up with some putty by my friendly mechanic) that I _think_ has been fixed (only had one tank of fuel since then, so it's a bit hard to tell).

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    What else could be causing this sort of misbehavior? Having flicked through the archives, the words "head gasket" seem to be associated with similar issues....

    So - any hints?

    Thanks all....

  2. #2
    Moderator Alan S's Avatar
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    It's a common one in Citroens often caused by spark plugs & leads showing their age & arcing out on the head or conductive crap on the coil allowing the high voltage side to ground out on the LT plug.
    In both these cases it is most noticeable when you are cruising usually in top or 4th gear, foot set in one place on the accellerator and car sitting on a costant speed. If you back off it will sometimes jerk for a second and if you flatten it sometimes it will miss like shit & then take off whilst on other occasions you'd swear there's nothing wrong with it.
    More likely in this region than fuel unless the injectors are in bad need of a clean but then it doesn't usually start suddentl but progressivly gets worse over a few days or weeks.
    Spray a bit of WD40 around the coil for starters & see if it makes any difference and wipe your plug leads & check the plugs for gap & condition.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
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    Quote Originally Posted by Alan S
    Spray a bit of WD40 around the coil for starters & see if it makes any difference and wipe your plug leads & check the plugs for gap & condition.

    Alan S
    Thanks Alan. Unfortunately, being a complete mechanical novice I'm buggered if I can even figure out where the sparkplugs _are_ (although I think they're under the long black thing on top of de engine). My haynes manual is, of course, utterly flippin' useless, as it doesn't cover the 16v engines.

    ARGH!

    Is replacing the sparkplugs actually very difficult? Or is it something that I should be able to do with a quick trip to supercheap?

  4. #4
    Banned orestes's Avatar
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    Thanks Alan. Unfortunately, being a complete mechanical novice I'm buggered if I can even figure out where the sparkplugs _are_ (although I think they're under the long black thing on top of de engine). My haynes manual is, of course, utterly flippin' useless, as it doesn't cover the 16v engines.

    ARGH!

    Is replacing the sparkplugs actually very difficult? Or is it something that I should be able to do with a quick trip to supercheap?


    spark plugs should be under the long black leads on top of da engine and shouldn't be to dificult to change your self

  5. #5
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    Quote Originally Posted by orestes

    spark plugs should be under the long black leads on top of da engine and shouldn't be to dificult to change your self
    Now, that's what I thought too... and I'd take a piccie to show ya but the lil' lady nicked it so I'll just have to state - there are no overly obvious spark-pluggy leads (such as I've seen on ALL MY OTHER CARS) leading to anything. I've found the four most likely candidates, but they appear to be attached in some fashion to a long, thin, black cylinder that runs across all of them.

    Looks like I'd have to take something off first before getting close to them. The probable-plugs have wires leading into them, but they aren't solid blackrubber deals - I can see two distinct red wires towards the top of the plugs. Should this be the case, or has someone done a dodgy on me?

  6. #6
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    306 motors don't have spark plug leads, which is why you can' t find them You are right, the plugs are underneath the "black thing" on top of the engine. That black thing is the cover over the coil packs - pull that off, and you'll in find the spark plugs.

    That leads me to the next thing, missing in 306's as you describe tends to be coil packs. It's a very well known problem on the S16, and is less common on other models. Search for 306 coil pack and you'll find some answers, assuming I'm right of couse.

    Derek.

  7. #7
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    Quote Originally Posted by DeKa
    306 motors don't have spark plug leads, which is why you can' t find them You are right, the plugs are underneath the "black thing" on top of the engine. That black thing is the cover over the coil packs - pull that off, and you'll in find the spark plugs.

    That leads me to the next thing, missing in 306's as you describe tends to be coil packs. It's a very well known problem on the S16, and is less common on other models. Search for 306 coil pack and you'll find some answers, assuming I'm right of couse.

    Derek.
    Hooray! Now I don't feel like quite so much of a doofus.. thanks Deka What's a replacement coil pack worth? And how often do they tend to fail? A quick flick through archives indicates that they cost $190 a pop... *weep*

  8. #8
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    Quote Originally Posted by sysiphus
    Hooray! Now I don't feel like quite so much of a doofus.. thanks Deka What's a replacement coil pack worth? And how often do they tend to fail? A quick flick through archives indicates that they cost $190 a pop... *weep*
    Have to say I don't know the answer to the $$ question, as I've never had a problem with them (fingers crossed). I also don't know how they're tested, but it's probably only 1 faulty one causing it to run on 3 cylinders momentarily.

    Derek.

  9. #9
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    Allrighty, just got my baby back from Stuart at Peugotech (thanks Stu!) $360-odd dollars later, and one small bit of plastic, and she seems much healthier.

    Turns out that the map sensor (manifold pressure sensor) was on the blink, which meant that vaccuum's weren't being reported properly, yadda yadda yadda (i.e. tech talk I didn't really follow). I have to say, for $250 this lil' bastard bit of plastic doesn't look overly fancy!

    Kinda expected gold-plating, or a compartment to store foi gras!



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