i bought my megane rs250 a few weeks back and it hesitated/jerked under boost, it would sound like running on 3 cylinders and go into in limp mode, check injection would appear on the display. id turn the car off then back on and it was fine. the garage took it and changed all 4 plugs and ignition coils. it is alot better now nad hasnt gone into limp mode since or shown the warning sign but i still get a missfire or boost cut every now and again if i floor it in 3rd or 4th. the garage are happy to pay for parts/labour to get it fixed but are struggling to identify the issue, no fault codes are present and the problem isnt consistant for them to find. the car has just ticked over 65000miles and the only mod is a dump valve with recirc blanking plate, which i intend to remove asap. could this be caiusing an issue? ie boost leak causing bad AFR's etc iv read the injectors themselves or the n75 valve could be the problem too? Basically what im asking is what should i go about checking replacing first? as i dont want the garage to get fed up throwing money at my car then just give up with me. thnaks,
Haven't they plugged the car in? Spark plugs on these cars are a good guess as they're a fussy bugger (So make sure they've fitted the correct plug). Boost levels are easy enough to monitor/graph to see if you've got a boost creep or loss. Sounds to me like you need a better garage TBH
Thanks for the quick replies. I dont think its mapped, is there an easy way to tell? it wass plugged into a snap-on diagnosticks tool, he seemed pretty knowlageble, Ill check the plugs gap tonight, 0.7mm rings ab bell, is this correct?
it's not just the gap that's important but the plug model number. I believe for the RS250 it takes NGK plugs but i forgot what part number. It's not used by any other vehicle manufacturer..
it has the plugs mentioned above, all gapped at 0.7mm, Its in at renault preston atm, they believe its the dump valve leaking pressure which is a possibilty so theyr putting satndard parts on to see if the problem is fixed, hopfully thats all it is.
You bought the car with the knowledge of this happening? Anyways, it sounds like it may be related to boost pressure regulation, so either related to keeping the pressure down (wastegate actuator stuck, leaking actuator, N75 valve malfunctioning, leaking vacuum lines), or related to not being able to keep the pressure up enough (leaking recirc/dumpvalve, bad MAP sensor). One thing that may be occuring is that it builds up too much boost pressure, causing the pressure measured right at the turbo to be too high compared to the intake manifold (as boost pressure in the intake manifold is also regulated by the intake valve position, regulating boost as a secondary mechanism). A too large differential between the two causes a fuel cut and dashboard warnings. A leaking recirc valve won't cause these kinds of cuts and warnings, it'll just be incredibly down on power. Edit: It may also be down to a bad mapping, if it has been mapped (Renault can check this). Another issue might be injectors that sometimes get a bit annoying and cause stutter. Happened to me before, went away after a few days (it happens, may be due to some very small dirt in the injectors).
I test drove (had a blast up the duel carridgeway and potter arroun) bought it since all was/seemed ok at the time. A few days later when i got the chance to realy put my foot down the problems started. Credit the seller he seems to be doing his best to sort it. iv been given a Leon FR as a courtesy car whilst they sort everything
sorry to bring this old post back up, did you ever manage to find the problem? My rs250 does the same thing
