Engine Stutter

[roy666]

Hi Guys – my engine seems to have developed a sort of power loss at high revs. At first I thought it was the ECU kicking in to stop over-boost, but that is usually like hitting a brick wall (ish). It happens around 4k-5k revs, accelerator flat down, and then a stutter develops and the revs stop. Its like a high-pace stutter and it continues unless I come off the revs a bit, then if I push hard again, the stutter starts once more. I can recreate it as many time as I like. What the hell is this? M

[Rambo]

Sounds like it might be the ignition coils and/or leads breaking down ?????

[HJ2]

I’d start with the good ole wastegate wiggle if I were you and take it from there.

[alan e]

Worth checking the timing to

[lotusflasherman]

I’d start with the good ole wastegate wiggle if I were you and take it from there.

What's showing on the Boost Gauge? Does it feel like a rev-limiter operating too early?

The ECU switches off the fuel pump when it detects overboost for over 1/2 second , so boost drops pump comes back, boost goes high switches off again = end result is what you might call a high speed stutter that feels like a rev-limiter.
The 'brick wall' syndrome is usually when it's high enough to generate a CEL and then enters limp mode for several seconds - that seem like several minutes...

I check my wastegate by connecting an electric tyre pump directly to the wastegate capsule - then I can see if it moves and at what pressure. Should be open at 6 psi (0.4 bar) so almost any pump will work.
(Higher boost pressures are produced by the Boost Control Frequency Valve controlling the 'leakage' in the tube to the wastegate capsule.)

[Danevansgolf]

Sounds like to me it’s a cracked spark plug. Hairline crack in the ceramics. Good luck finding the source.

[Giniw]

Maybe you should check the secondary throttle too?
https://www.youtube.com/watch?v=7afM8kVtR8k

[HJ2]

Hahahaha! Poor Roy!
Wastegate wiggle: the only one with 2 votes

[alan e]

Buy a new car that will fix it in the end it will be the easy way out

[HJ2]

Where’s the fun in that?

[Simon_P]

HT - probably a coil pack.
To test when it happens change up a gear and see if it happens at lower revs - you should be able to make it happen or recover by playing the throttle.

As mentioned above, always check the basic settings first.

[roy666]

So i started the checks.... wastegate wiggle...no probs; leads..no probs... and then the spark plugs. Took off the centrecover to find that the number 3 spark plug connector was very slightly high.. about half a centimeter. Took them all off, good clean up, back on. Engine sweet.. no stutter at all. Dan, you get the coconut. thanks all. M

[V8vroom]

I still have this problem.... so far:

spark plugs all changed - made no difference

wastegate wiggle - no difference

Spydercars have added a manual boost control valve to turbo to stop over boost (currently Everest Chip but limited to .75 bar) - no difference

so next step is changing coils and leads with mate later in November when time... fingers crossed as not sure where to go after this.....all ECU diagnostics normal apparently....

Rupert

[roy666]

Rupes - my "stutter" only manifested itself under load at high revs around 5K... felt like she just would not accelerate smoothly. Otherwise the engine sounded and started normally...a single spark cap not connected properly made all the difference. sounds like yours a bit more problematical... can't be spark plugs. M

[HJ2]

You changed the spark plugs... but did you check if they are gapped 0.8mm and not 1.1mm?

[roy666]

Bummer - I did not check.... not 0.8 then... is that a mistake?

[Simon_P]

1.1 gap is an option so it is unlikely to make a difference.

[HJ2]

Is 1.1 an option? Perhaps for the N/A ?

[John_W]

31 thou is the correct gap for the turbo. That’s just under 0.8mm. 1.1mm is too wide fot the turbo (especially if running high boost) and will cause a misfire at high revs. Michael Werkman visited us on his Scottish odyssey and complained of a misfire at high revs - we solved it just by resetting the gap correctly.

John

[HJ2]

I had the same problem after fitting new plugs, many moons ago. Re-gapping the plugs cured the problem instantly.