Megane stalling at 4000rpm and hard acceleration

Fist double check the cam timing. Your symptoms are like those of a blocked exhaust.

Thanks for the advice.. I`ll check the cam timing tomorrow.

One other thing I had noticed is the idle control stepper motor is constantly being avtivated at idle - sounding vaguely like a geiger counter! Maybe it always does this but it could be more useful info?

Its meant to do this- thats how the ECU regulates the idle.

I am unable to understand how it can stall from 4000rpm?!?!

Tim..

Sorry - my post was not that clear. If I`m in 1st and going slow (under say 10mph) and depress the accelerator hard it will lurch several times to a stall. In the higher gears when it hits 4000RPM it will similarly lurch until I depress the clutch and more often than not the engine will not be turning until I either bump it or turn the key.

Good to know the idle motor should be like that, puts my mind at rest

- thanks.

The trouble I have with checking the timing marks is that the crank shaft does not have the mark indicated it should have in the manual!! I`ve cleaned it up well but still cant see anything. The Haynes manual suggests there should be a TDC timing mark on an inspection hole at the fly wheel end but not helpfully does not include a picture - hmm I think another post is call for...

UPDATE:- Good news and bad news.

Thanks to MrCheerful - I rechecked the cam timing. this time counting

15 teeth on the flywheel to find TDC (as mentioned in the Renault manual). It appears I was indeed TWO teeth out on the cam. Dont think this has done any valve damage.

With this sorted it has lost the 4000RPM jumping and bucking but still has the slow speed, hard acceleration problem.

One thing that did make it slightly less likely to send it haywire was to remove the air filter. Still not drivable but maybe this could provide a clue to someone that knows??

Cheers!

I presume you've double checked everything is plugged in and all hoses are in good, connected order?

For those familiar with Renaults it would be helpful if you gave them your year and engine info. It wouldn't help *me* much without knowing the exact fuel control system employed, but I'll make a wild, off-the- wall suggestion anyway...

If there is some provision for the ECM to "relearn" crankshaft to camshaft timing (typically monitored by two discrete sensors on modern FI systems), then it is possible that upon original completion of the repair, the incorrect cam and crank relationship was "memorized" by the ECM --- and once you corrected the mechanical cam/crank relationship, the ECM would need to have a relearn performed. Many US domestic models have a provision for this with a scantool. Like I implied, I have no experience with French Renault at all.

Your symptoms sound an awful lot like a torn air flow meter intake tube, but I read that you checked that.

Toyota MDT in MO

Update - Still not working :-(

Thanks to everyone who replied. Its still not working and I have tried the following:

1) Replaced MAP sensor and checked pipework (second hand ones) 2) Changed lambda sensor (for second hand one) 3) Replaced plugs (new ones) 4) Attempted to run with main exhaust disconnected (proving exhaust is not blocked) 5) Double checked cam timing

The engine is a 1.6l petrol and the engine is a K7M multi point injection.

Can anyone offer any more suggestions of things to try? I am considering replacing the TDC sensor but as the engine starts and runs fine at idle I cant believe its this.

Could it be the fuel pressure regulator starving the engine under heavy acceleration? If the valve clearances were mal-adjusted could it exhibit this nasty bunny hopping?

Cheers!

Very slightly bent inlet valves can cause this, you get a build up of combustion blowing back into the manifold and it runs really badly at higher speeds. A similar effect is caused by a blow between two cylinders. In view of the mal timing that had occurred, if I was working on it, the next thing I would check is if any valves are bent, I would do this by putting the engine at TDC no.1 and blowing compressed air into the cylinder, ideally there should be almost no loss, but any bent valves, even a tiny bit would be shown up as a leak out of the exhaust or inlet. Obviously repeat the exercise with other cylinders. This test will also show up a blow between cylinders. You need to jam the engine at the tdc point or the air pressure will turn the engine over.

Mrcheerful

& get the fault codes read.

Thanks MrCheerful - I`m building up a DIY leak down tester as discovered on this useful looking website:

I sure hope I haven't bent any of the valves! But I guess its all good learning, I mean where else do you learn the intimacies of a FI closed loop system while bunny hopping down the road!

Regards..

Hi everyone!

Firstly thanks to everyone that has suggested things to help out with this problem. I`ll shortly write a summary post to describe my experiences and findings - hopefully to assist someone else in a similar position.

Picking up from my previous post I did a leak down test and did find that I had several mal adjusted valves. Seems that when I initially put the cam back on it was pushing down hard most of the valves which may have made the adjustment inaccurate? Maybe that or probably I messed up. However this did not solve the problem.

The problem was finally narrowed down to me failing to do up a bolt that holds two thinner earth wires to the head. This is located behind the dip stick and below the main earth strap. Doh! I guess it's the simple things that gets ya! I`m very happy to say the car feels stronger than ever.

Best regards...

Thanks for the update and glad you go it sorted out. Looks like those were EFI grounds.

Toyota MDT in MO