Shuddering after 0.7 bar

[GrahamS2]

My stock '96 S2 has developed a very strange problem. If I go to WOT in any gear, the boost builds as the revs go up, but once it reaches 0.7 bar at around 2700rpm the car develops a strange shuddering / stuttering - like it can't get past that point

If I hold WOT the boost will eventually get to 0.9 but nothing more. It really doesn't feel happy.

I thought it might be fuel related but I'm really not sure.

Other than that she is running smoothly, provided I don't floor it!

Any ideas?

[S2 Ant]

are the temps high? mine does something similar sometimes if the water temp is at or just over 90 when the fan is due to cut in.

or perhaps a boost leak.
Possibly some other sensor that isnt happy so is preventing more boost, i know what im thinkin but cant think how to put it in to words

[rotoryboy]

Is that not overboost protection??

[S2 Ant]

overboost protection feels like your about to be put thru the windscreen, is the boost cut severe?

[Doug_RS2]

Is it a misfire? If so, could be a coilpack that is going bad.

[shadquattro]

just had a similar problem on mine,felt like fuel depravation turned out to be lambda sensor not working between 2200 and 2700 rpm

[Kodiak]

Sounds exactly like my problem:

http://www.s2forum.com/forum/showthread.php?t=6780

The quick summary: I cleaned my MAF with a moderate improvement. A boost leak seems to be the most likely cause, so I've ordered a leak test kit.

If you solve the problem, please let me know. You've described it a bit differently than I have, but I'm pretty sure we're experiencing the same thing. It seems to be a common problem, with various possible causes.

[GrahamS2]

Ah!!!!

Thanks a million for the feedback guys!! Kodiak, this is exactly what I'm experiencing. The boost streaks quickly up to 0.7 bar and then stutters / hold back from there to 0.9.

I definitely suspect a bad tank of fuel (it has only done it on this tank so far) as Doug's description of the knock sensors was spot on to what is happening. Also the fact that the car runs perfectly unti EXACTLY 0.7 bar would point to that. Right?

I will clean the lamda and MAF sensors this wekeend just to be sure I will also fill up with othet fuel tonight and see if that helps.

What exactly happens when the knock sensors come into action? What else could cause engine knock?

[s2driveruk]

if its a really severe stutter then i'd say it was a boost leak, i had this a few days after i bought the car and i wondered what the hell was going on. I think the WGFV was replaced too when it went into quattrosports (now QST). However knowing what i know now i wonder if it actually had anything to do with the WGFV

[Kodiak]

Thanks a million for the feedback guys!! Kodiak, this is exactly what I'm experiencing. The boost streaks quickly up to 0.7 bar and then stutters / hold back from there to 0.9.

I definitely suspect a bad tank of fuel (it has only done it on this tank so far) as Doug's description of the knock sensors was spot on to what is happening. Also the fact that the car runs perfectly unti EXACTLY 0.7 bar would point to that. Right?

I will clean the lamda and MAF sensors this wekeend just to be sure I will also fill up with othet fuel tonight and see if that helps.

What exactly happens when the knock sensors come into action? What else could cause engine knock?

I suspected bad fuel at first, too, but after a few tanks of Optimax I've ruled that out.

My car also runs perfectly up until the point where it starts stuttering.

As I said, I cleaned the MAF which has made the stutters less violent, but they are still there.

Where is the Lamda probe, what does it do, and how do I clean it? Is cleaning recommended?

I'm waiting for my boost leak test kit to arrive. I'll let you know the results of the test when it does.

Incidentally, I've pulled code 2413 from my car. It would be interesting to see if your car has the same code, Graham.

[GrahamS2]

Fixed!!

Well, after spending a fair part of Saturday morning looking for a non-existant boost leak, I decided to call a mate of mine who has done a LOT of turbo work on his VR6 - a very knowledgeable chap. After a long discussion around the effects that boost pressure has on the ability of a spark plug under different pressures (still trying to get my head around some of this stuff!), the anwer came in the form of 2 simple words...

SPARK PLUGS

The fool that I bought the car from had assured me that it was running the correct Bosch Platinums (he even gave me an extra set with the car!). After pulling the plugs, they turned out to be Champion EONS... Lying prick!! The middle plug had a big arc scar down the side and was thus the cause of my problem.

So I fitted the correct plugs and she is running better that ever before. The boost progression is so much smoother and it now holds 1.1 bar well into the rev range. Lovely stuff! The chap in the Alfa 156 GTA feels that she is running pretty well too (especially after the hiding I gave him...)

[Kodiak]

Great news! I'll add that to my list of possible culprits if my boost leak test doesn't turn up anything. I'm pretty sure my car's running OEM plugs, though. I'll check it out.

Mmmmm, 156 GTA.

[GandalfS6]

Hey Graham - I thought you sold the S2!

I had the exact same problem but in my case I was the idiot! I had fitted supposedly fancy NGK Iridium plugs - got a huge misfire at boost. I was actually at the Phakisa race track at the time and had to disconnect the WGFV just to be able to put in some laps! BTW on the Gtech my car made a huge 92 KW at the wheels with the WGFV unplugged! Changed the plugs to OE Bosch plugs and the car ran perfectly!