CX turbo idling
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Thread: CX turbo idling

  1. #1
    Fellow Frogger! marc61's Avatar
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    Default CX turbo idling

    I've got a very slight miss when the engine is warm and idling. Couldn't describe it as a misfire, I can feel it and its enough to make the rev counter flicker by 100 rpm or so and the oil pressure gauge flicker too in sync. Not perceptible on cold start, but always there once warmed up. Otherwise engine performs very well.

    Have checked the air circuit for leaks, checked the aux air valve is opening and closing, cleaned out the mixture screw on the AFM, plugs are good. What to try next? Change the HT leads maybe? Any suggestions welcome - its an 87 Turbo 2.

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    Cheers

    Marc
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  2. #2
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    Quote Originally Posted by marc61 View Post
    I've got a very slight miss when the engine is warm and idling. Couldn't describe it as a misfire, I can feel it and its enough to make the rev counter flicker by 100 rpm or so and the oil pressure gauge flicker too in sync. Not perceptible on cold start, but always there once warmed up. Otherwise engine performs very well.

    Have checked the air circuit for leaks, checked the aux air valve is opening and closing, cleaned out the mixture screw on the AFM, plugs are good. What to try next? Change the HT leads maybe? Any suggestions welcome - its an 87 Turbo 2.

    Cheers

    Marc
    Hi Mark,

    Just bought a 87 25GTI last Saturday and drove home beautifully. On Sunday felt like a slight miss and seemed to be holding back a little. When I opened the lid I heard a 'clicking' noise, looked over and could see one of the HT leads shorting through the spare tyre! Took the spare wheel out and she went up the road like the clappers. Must have been shorting through the steel radial belts. I'll have a good look at the plug this weekend. Could be worth checking before you start spending any money. Good luck with the car.

    Danny

  3. #3
    Real cars have hydraulics DoubleChevron's Avatar
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    The AFM isn't a part of the idle settings. While the idle switch on the throttle spindle in shut, the AFM is ignored (that why if you pop one of the hoses off the intercooler or AFM, the motor will idle ..... but cut out as soon as you try to rev it).

    You know ... I rekcon I'd be doing a compression test first to rule out the mechanical side first. I haven't experienced this sort of miss myself. Usually stuff either works ... or intermittently doesn't ....

    don't worry about the tacho/oil pressure gauges moving ... that's just electrical load ... they'll all flash in unison with the indicators too.

    seeya,
    Shane L.
    'Cit' homepage:
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    Yay ... No Slugomatics


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  4. #4
    Fellow Frogger! marc61's Avatar
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    I did a compression test and all were good, within a few psi of each other. The HT leads seem good, I've grouped them with a tie wrap near the coils to keep them away from shorting to metal anywhere if they are leaky. Also checked the coil resistances and they are about right, but one terminal was rusty so cleaned that up. But the problem remains.

    It seems like taking it for a good blast helps, but within a couple of seconds of stopping at a traffic light I get like a very slight misfire. Was wondering whether a fuel injector can dribble when the engine is idling, or the mixture can go wrong in one cylinder because the injector isn't happy at idle? Plugs are clean, car performs well, economy is normal, but its just not happy idling!

    Cheers

    Marc
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  5. #5
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by marc61 View Post
    I did a compression test and all were good, within a few psi of each other. The HT leads seem good, I've grouped them with a tie wrap near the coils to keep them away from shorting to metal anywhere if they are leaky. Also checked the coil resistances and they are about right, but one terminal was rusty so cleaned that up. But the problem remains.

    It seems like taking it for a good blast helps, but within a couple of seconds of stopping at a traffic light I get like a very slight misfire. Was wondering whether a fuel injector can dribble when the engine is idling, or the mixture can go wrong in one cylinder because the injector isn't happy at idle? Plugs are clean, car performs well, economy is normal, but its just not happy idling!

    Cheers

    Marc
    has someone messed iwth the idle bypass screw? The brass screw in the hose across the back of the rocker cover. Open it a turn and then put it back where it was and see if it's happy then (I've moved it a couple of times, and just hte act of moving it seems to clear the idle up).

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  6. #6
    Fellow Frogger! marc61's Avatar
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    Thanks Shane. I took the idle screw out, cleaned it and put it back, but no change.

    Idle is fine when cold but not steady when engine is warm, sometimes just a very slight miss then at other times it's not happy with rev counter flickering about by 100-200 rpm. Then if I drive it for a few minutes it's goes back to just having the very slight miss.

    Have been looking for vacuum leaks, spraying carb cleaner at each joint, but can't find any. Can't figure out if it's missing a spark somehow or if it's a fuelling issue.

    How far off bottom is the mixture screw in the AFM supposed to be? Mine is 2.5 turns off bottom but I don't have CO meter to check exhaust.

    Cheers

    Marc
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  7. #7
    Too many posts! JohnW's Avatar
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    Plugs or injectors?
    JohnW

    Renault 4CV 1951
    Renault R8 1965
    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Renault Scenic 2006 (daughter's)
    CitroŽn CX Pallas 1980

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  8. #8
    Fellow Frogger! IE23's Avatar
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    This might be totally unrelated but my car used to hunt in the revs at cursing speed until I replaced the AFM with a new one.


    Adrian

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    Too many posts! JohnW's Avatar
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    At what speed does bad language start?

    Seriously, I'm finding this interesting, so thanks all.
    GreenBlood likes this.
    JohnW

    Renault 4CV 1951
    Renault R8 1965
    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Renault Scenic 2006 (daughter's)
    CitroŽn CX Pallas 1980

    National Co-ordinator, Renault 4CV Register of Australia

  10. #10
    Fellow Frogger! marc61's Avatar
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    Problem occurs at idle only, around 900 rpm, foot off pedal. About 50% of the time it idles steadily but there's what feels like a very slight misfire/unevenness, but not as bad as a misfire. Then the rest of the time it gets the shakes and the idle is rough flicking about by 100rpm or more. It doesn't conk out and if I touch the throttle it picks up fine, it drives fine, economy/performance is normal.

    I've cleaned the AFM, taken out the mixture screw and cleaned the passageway, checked for vacuum leaks, checked and cleaned the air valve, the plugs are good and consistent no obvious signs of weakness/richness, the coil resistances are right, the leads look good.

    Running out of ideas. Can an injector behave strange at idle conditions only?
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  11. #11
    Member mork63ukCGAT's Avatar
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    pull the injector leads off one at a time to see if the rev drop if the same for each cylinder, and if it smooths out.

    Check the auxiliary air idle valve on the block, loose hose there can cause issue.

    Pull the fuel ECU and open it up, look for a burnt track (really obvious) this can happen if the car has run with a dodgy battery connection.

    Track on the AFM worn, can cause the revs to lift and fall as the demand for air changes, as it hunts for fuel.

    Intercooler end caps intergrity failing.

    Valve clearances 'cam wear' only as you mention a few psi difference in cylinders.

  12. #12
    Fellow Frogger! marc61's Avatar
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    Quote Originally Posted by mork63ukCGAT View Post
    pull the injector leads off one at a time to see if the rev drop if the same for each cylinder, and if it smooths out.

    Check the auxiliary air idle valve on the block, loose hose there can cause issue.

    Pull the fuel ECU and open it up, look for a burnt track (really obvious) this can happen if the car has run with a dodgy battery connection.

    Track on the AFM worn, can cause the revs to lift and fall as the demand for air changes, as it hunts for fuel.

    Intercooler end caps intergrity failing.

    Valve clearances 'cam wear' only as you mention a few psi difference in cylinders.
    Thanks for the advice. Rain has stopped play for the time being - the throttle cable snapped last night, near the pedal.

    Came home by tow truck. Driver said to me half way back what car is that, I've never seen one of those before! I told him they don't break down often (!).

    Waiting for replacement cable to arrive, then will carry on investigating.
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  13. #13
    Fellow Frogger! marc61's Avatar
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    Just completing the story here.....I managed to find a NOS AFM and fitted it about 6 weeks ago. Oh boy what a transformation, smooth idle, clean pick up at low revs, almost no jerkiness! I guess the old one must have been well worn - car has done 141000 miles.

    I'm also staggered by the improvement in fuel economy, the last 3 tankfuls have averaged 28mpg which is about 5mpg more than before. Almost too good to be true but I filled up today and the last 312 miles consumed only 48.7 litres (29mpg).

    Cheers

    Marc
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  14. #14
    Member mork63ukCGAT's Avatar
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    Quote Originally Posted by marc61 View Post
    Just completing the story here.....I managed to find a NOS AFM and fitted it about 6 weeks ago. Oh boy what a transformation, smooth idle, clean pick up at low revs, almost no jerkiness! I guess the old one must have been well worn - car has done 141000 miles.

    I'm also staggered by the improvement in fuel economy, the last 3 tankfuls have averaged 28mpg which is about 5mpg more than before. Almost too good to be true but I filled up today and the last 312 miles consumed only 48.7 litres (29mpg).

    Cheers

    Marc

    Mine does 27mpg @100 leave you to guess kph or the other one

  15. #15
    Too many posts! JohnW's Avatar
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    For the record, my 2.0i, 8 valve Xantia does about 9.5 L/100 km around town (29-30 mpg in the old units) and probably around 8-8.5 (32-34 mpg) cruising out of town. Here, cruising means no more than 110 kph.

    The carburetor CX C-matic does 20-25 mpg at best. Too depressing to work it out in detail or regularly! Still, I hardly bought it for the fuel economy.
    JohnW

    Renault 4CV 1951
    Renault R8 1965
    Renault Scenic 2005 (wife's)
    Renault Scenic 2007 (mine)
    Renault Scenic 2006 (daughter's)
    CitroŽn CX Pallas 1980

    National Co-ordinator, Renault 4CV Register of Australia

  16. #16
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by mork63ukCGAT View Post
    Mine does 27mpg @100 leave you to guess kph or the other one
    mine used to consistantly do 34mpg on a country run ..... It hasn't in years though.... If it does ever leave town it's generally dragging something big and heavy from it's towbar

    I towed a big walk in coolroom up from Geelong a few years back. I used 60litres of fuel in about 150km

    seeya,
    Shane L.
    mork63ukCGAT likes this.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  17. #17
    Member mork63ukCGAT's Avatar
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    Quote Originally Posted by marc61 View Post
    Just completing the story here.....I managed to find a NOS AFM and fitted it about 6 weeks ago. Oh boy what a transformation, smooth idle, clean pick up at low revs, almost no jerkiness! I guess the old one must have been well worn - car has done 141000 miles.

    I'm also staggered by the improvement in fuel economy, the last 3 tankfuls have averaged 28mpg which is about 5mpg more than before. Almost too good to be true but I filled up today and the last 312 miles consumed only 48.7 litres (29mpg).

    Cheers

    Marc
    I had a pair of AFMs reworked and balanced a few years back... still on the car for show, not bothered about the slight restriction the cause; even though it is now running on the KDFI. they worked a treat.

  18. #18
    Fellow Frogger! marc61's Avatar
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    Yes I reckon I'd have a chance of getting 27mpg @ 100 now. Just goes to show there's a tremendous efficiency benefit from a turboed engine provided the air fuel mixture is right.

  19. #19
    Fellow Frogger! marc61's Avatar
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    Couple of questions re idling. How should a CX turbo idle after a cold start?

    I've noticed mine needs to be cranked over a bit longer lately to get ignition, then it starts and idles poorly for a few seconds below 1000rpm as the suspension rises up. If I drive it a few metres and dump the clutch it idles at about 1100-1200 rpm steadily until it's warmed up. I think it should be idling at 1100-1200 rpm from the outset of a cold start, then settle down to about 900rpm once it's warm.

    Am trying to figure out what's changed to cause this at a cold start. Might it be the air temp sensor?

    Cheers

    Marc

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