R26 Revs dropping during hard acceleration

Discussion in 'Mechanical - Engine, Gearbox, Exhaust etc' started by richlowndes, Dec 20, 2016.

  1. I have a stage 1 remapped R26 which is driving really well apart from the following problem which has become apparent a few days ago.
    On hard acceleration the revs seem to fluctuate a little as they go through the upper end of the rev range. The engine note seems to rise and fall a little. On occasion I have even seen the rev counter needle drop a little during acceleration before then going up again. It seems a little bit like the clutch is slipping but there are no issues at all changing gear, pulling away, or any at other time other than during full acceleration. This seems to happen in third, fourth and fifth gears but it doesn't always happen and is sometimes difficult to detect. I'm pretty sure it didn't used to do this!

    Any ideas would be most welcome.

    Many thanks

  2. Clutch slip. So clutch is on its way out. Will get worse over time.
  3. OK thanks for this. I just can't understand why it is only it then and not at low revs on pulling away.
  4. It'll be at certain high torque moments. If you drive away in 1st reasonably gently the clutch doesn't need to translate that much torque.

    It'll be worst in 3rd gear or higher flooring the car at low revs.
  5. Hmm. Thanks for this. It's definitely only noticeable at around 4 to 5k rpm. I'll keep an eye on it. I guess if it's the clutch it will only get worse I'll know soon enough.
    If I need to replace it, should I get the flywheel done at the same time and if so, should I go for the k-tec lightened single mass flywheel?
  6. To me clutch would mean the revs go up but speed doesn't increase - Rev's wouldn't actually drop.

    To test the clutch head to a hill and try flooring it up it in a high gear (5th) and then when the cars at full torque that's when it'll slip.
  7. Duh! Yes, of course.
    Reading too fast on stupid mobile.

    5k seems quite high for slip OP.
    Would expect that closer to 3k or so (whenever max torque is).

    That said, if the clutch & transmission is ok, revs cannot drop, as that would mean deceleration.
  8. You're noticing it more at them revs because that's roughly where the engine produces the most torque.

    Flywheel is usually done at the same time, yes. I'd do some research on the pros and cons of changing to a single mass flywheel and go from there.

    Are you aware that this could leave you stranded, broken-down if it gets really bad? I'd be looking at getting this done sooner rather than later tbh.
  9. Yes I would like to get it sorted, but not convinced it's the clutch. As others have said, I would expect clutch problems to a) be more noticeable at lower revs, and b) cause an increase in revs for a set speed, rather than a drop in revs (though it is of course possible that the decrease is simply a result of an earlier increase in revs).

    Also, rather difficult to get it sorted at this time of year. :worried:
  10. I would say that if the revs are fluctuating at high loads and rpm's, it may be worth checking your fuel filters it sounds like a lack of fuel at the highest demand.
    BEEFTEC likes this.
  11. Sounds sensible. Any idea how to do this?
  12. As above, to me seems like it could be fuel related.

    What does your exhaust sound like at idle? Any 'chuffing' or misfire kind of noises?

    Could be that the injectors are getting a bit clogged. You can remove them and get them cleaned or replace if so.
  13. I had an issue like this with my 250, where planting the throttle in higher gears. Eventually my thermostat went and since that was done, it hasnt done it since.
  14. Thermostat or coolant temp sensor related I suppose could cause the cold limiter to kick in or fuel mix to change to a cold start mix, but this would be a harsh dip in power - Is this what you're getting?
  15. Hi all. Thanks for all your replies.
    In answer to these questions:
    It sounds ok at idle. No weird noises though perhaps hunts a little, but nothing untoward.
    There is certainly no harsh dip in power. It's a fairly subtle wobble, both in terms of sound and needle movement.

    Anyway, I don't drive the car on long journeys very often, so I wonder whether the injectors have got a bit clogged up or something. So today I did a 140 mile journey. At the start of the journey I filled up with fuel and bunged a bottle of Redex into it and and during the second half of the journey I pushed it quite hard. I don't want to speak too soon, but by the end of he journey it certainly seemed a lot better- better, smoother power deliver, no noticeable wobble in the rpm, and seemed faster (quite scary watching the rev counter intently at 4000 to 5000 rpm in 4th and 5th!). The improvment might simply be because the engine was fully warm, but I'll find out tomorrow.

    Strangely, and probably coincidentally, the clutch pedal has become really squeaky. (Sort of a low pitched squeaky scrapey noise). I've sprayed loads of WD40 silicone onto the spring, which hasn't helped at all. There's a sort of piston thing connected to the pedal- is this what's called the slave cylinder or am I getting confused. I think the noise is coming from there. Any ideas?

    Many thanks for all the help.
  16. Sorry- posted the same thing twice so have deleted this post
  17. The redex will be a cheap fix if that sorts it!

    What sort of fuel do you run it on out of interest?
  18. matt e

    matt e South East RSM Area Rep

    im betting the clutch slipping, mine did it before going along the motorway and put your foot down and when it was accelerating it was dipping then it caught up again. abit like a auto changing gear
  19. Thanks both.
    It definitely seems to have improved. Not completely, but much better. The redex seemed worth a try for the cost.
    I run it on premium. I might try super for a while and see what happens.

    I agree with Matt- it sounds a little bit like a torque converter auto.

    Thanks all
  20. That being said, i also put new plugs in mine around the same time as having the stat done and regapped them down from preset (mk3 being a particler with its gap) and found the car generally ran better. So maybe check the plugs and regapped them to suit?
  21. Just to follow up on this...I haven't done anything to the car since I last posted. It has been absolutely fine since putting the redex in (and the last time I filled up I put a tank of super unleaded in).
    I'll return to this post if anything changes.
  22. Well, unsurprisingly, the issue has returned. I am getting erratic rev changes when accelerating hard in gear. It's more pronounced than it was when I originally posted. I'm getting a rev drop during hard acceleration but it seems to follow a rather quick increase in revs (which would be expected if the clutch were slipping). It's a bit like the engine is overrevving, and then wheels are catching up, and so the revs are dropping back down again momentarily, before then increasing again.

    So, assuming the clutch is slipping... can I adjust it at all?
    If not, then I guess it's new clutch time. Do I replace the clutch, DMF and slave cylinder all at the same time? I realise I may be able to change the clutch for an R26R one, and replace the DMF with an SMF. The car is running a stage one remap at 267bhp and I have no plans to change that. Can anyone offer advice as to what I should replace, and whether I should stay standard or switch to different parts?

    For info, it's an R26 with 86k on the clock.

    It's probably worth mentioning that pulling away, and going uphill in his gear etc does not present any problems, which seems a bit odd.

    Many thanks for any info,
  23. Did you sort this my megane 250 is doing the same in higher gears and rpm the revs fluctuate as you describe ?

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