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shudder under boost

1K views 7 replies 5 participants last post by  FruitLooPs 
#1 ·
Hi guys, i'm just wondering whats up with this.

I dont think my car is boosting properly, it goes fine at like 60km/hr and just driving around and the gauge moves into the yellow etc. But at highway speeds if i put my foot down it drops a gear accelerates and if i put it right down the boost just hits the yellow-red section and the car lurch/shudders as if the front was losing grip but it's obviously not.

I drop off the gas a little bit and it smooths out and goes fine, the previous owner thought it was hitting boost cut but i dont see why, especially since its not going into the full red on the gauge.

Somethings up, but where to start? I also thought i was getting a check light sometimes - didn't get a chance to see it at first, came back on i glanced down and it was the gas light ;):p Does the same thing even with gas though.
 
#3 ·
i had that problem and it turned out just too be a bad set of bosch spark plugs that werent gapped right

(from the previous owner)

i changed to ngk and it ran pefectly though bosch did enough damagae methinks so i replaced the di cassete totally anyway...those things arent as expensive as i though but damn it still sucked almost 500 bucks... :evil:
 
#6 ·
Well changed plug for a new one, added dielec grease to all boots and now its fine :D Sweet

the old plug was cracked down the plastic in two places, i might put up an image - what causes this, arcing in the di unit? the electrodes were kinda brick/rust coloured so i'm not sure what that means, temp too high maybe but thats white yeah?
 
#7 ·
Do you Kiwis use unleaded fuel and if so is MMT still legal in NZ? When we had MMT in our unleaded fuel here in Canada we got reddish brown plugs all the time. Now that MMT is gone and they are using ethanol (mostly) as an octane booster our plugs have gone back to light tan.

The white insulator part of the plug is ceramic rather than plastic and it is a bit fragile. Usually, cracking results from installation errors, if the plug socket isn't held perfectly straight up and down on the hex part of the plug body (many have a rubber insert to assist in lining the socket up) then you can inadvertantly torque the insulator a bit sideways which will lead to stress fractures possibly right away and also perhaps later in the plug life.

I have never experienced a plug insulator cracking in over 30 years so you can be sure it is rare.

If you have a bad plug the conventional wisdom is to replace it asap as a misfire is rumoured to be hard on the DI cassette.
 
#8 · (Edited)
Yeah unleaded no idea about MMT? never heard of it. I dont think someone has screwed up teh installation of that spark plug, at least it doesn't look like it. I'll get a pic for you guys. :D

Its def boosting properly now though, which is a big relief since a DI cassette is a whole lot more than some grease and a plug.

Soz bout quality cam phone doesn't do macro, and size limit uploading didn't help. The two cracks are nearly 180 degrees off from each other, and at the hex base have brown/black kinda burn type discolouring.
 

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