Missing Problem

[flutterpast]

just wondering if anyone can help me... most of the time after ive done a burnout, the motor runs rough for about 2 minutes and sounds like its missing 2 or 3 cylinders and then fixes its self. the other day it got so bad that it stalled and wouldnt start up straight away. has anyone heard of this before? my car is running 15 psi

[XR6TWolf]

Sounds remarkably like valve springs. They have a habit in BAs of being pretty weak and allowing valve float at high revs. End result is that lifters pump up and you end up with a rough running engine which usually sorts itself out after a minute or two.

[dule]

You'd hope they were replaced if it's a BA running 15 PSI

[XR6TWolf]

You would hope so but the way it is described as "fixing itself after a couple of minutes" sounds very much like pumped up lifters.

[flutterpast]

its a ba mk II and nah they havent been replaced. but yeah youre probably right. just that I read a heap of other problems similar to this and there were soooo many different causes. I forgot to mention that when the engine stalled, the oil light flashed and beeped at me a couple of times. this is odd considering I just changed my oil to a 15 weight and changed the filter

[flutterpast]

cheers guys. turned out to be bleeding lifters. 50 bucks a lifter and 3 hours labour :(

[ratter]

Lifters are not normally a problem on these motors, and if a lifter is a problem and they bleed down they tick but do not cause the engine to run rough and then clear up, valve springs are a problem with a bit of added boost to the motor, I hope not for your sake, but I think your problem will return

[flutterpast]

really? glad you said that because I havent had the work done yet, that was just a quote. would it be worth getting the springs changed to heavier ones first to see if that fixes it? thanks heaps for your help

[Sasha]

Although ratter is correct, it sounds like you have an honest mechanic there (labour wise), might pay you to ask for a quote to replace the valve springs anyway as it sounds like its the best price you will get.

You wont realise the need for heavier valve springs until high rpm sign-off anyways, in most cases where valve float would occur the rev limiter is well before this anyways, and the only other time you would need them is if they were piss weak and they were overcome by boost and the valve raised of its seat due to extremely high manifold pressure, neither of which would cause the symptoms you have described.

Edited 10/08/09 01:30 PM by Sasha

[XR6TWolf]

Sorry Sasha I disagree. BA's were infamous for valve float and it for just this reason that the multitude of options for valve springs (Nispro, Atomic etc) and special tools for fitment are so easily obtained.

I have heard numerous tuners discuss the weaknesses and several of the more reputed ones here in NZ dont even want to waste the money tuning unless the springs have been done.