Megane stalling at 4000rpm and hard acceleration

Having just completed a DIY head gasket and timing belt change I took
the car for a spin.

I found it lurched violently when I accelerated hard (foot to the
floor) in 1st gear and also did the same in any gear when it hit
4000rpm. Some of the lurches resulted in a dead stall, which were easy
to re-start after.

Idle sounds fine and power is fine so I am hopeful I have got the cam
belt on correctly. I`ve checked the air flow sensor pipe and seems
fine - no cracks etc. Compression is OK on all cylinders too.

Can anyone help please?

> wrote in message
oups.com...
> Having just completed a DIY head gasket and timing belt change I took
> the car for a spin.
>
> I found it lurched violently when I accelerated hard (foot to the
> floor) in 1st gear and also did the same in any gear when it hit
> 4000rpm. Some of the lurches resulted in a dead stall, which were easy
> to re-start after.
>
> Idle sounds fine and power is fine so I am hopeful I have got the cam
> belt on correctly. I`ve checked the air flow sensor pipe and seems
> fine - no cracks etc. Compression is OK on all cylinders too.
>
> Can anyone help please?
>

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

On 16 Jun, 15:00, "MrCheerful" > wrote:

> 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?

> wrote in message
oups.com...
> On 16 Jun, 15:00, "MrCheerful" > wrote:
>
>> 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..

On 16 Jun, 23:53, "Tim.." > wrote:
> > wrote in message
>
> oups.com...
>
> > On 16 Jun, 15:00, "MrCheerful" > wrote:
>
> >> 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 canstallfrom4000rpm?!?!
>
> 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!

> wrote in message
oups.com...
> 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??

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

On Jun 17, 2:42 pm, wrote:
> 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!

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!

> wrote in message
ups.com...
><> 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