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Still not fixed, but more information.
'96 Aero (manual)
JT 3" turbo-back exhaust system
K&N drop-in filter
Problem:
The car occasionally gives low boost, only ever in 2nd gear and when flooring it suddenly, usually after tame driving at say 30mph. Often, it snaps back up to full boost suddenly. I never see boost problems in any other gear.
The original post is at the link below.
The story so far:
I have tried replacing the bypass valve with a new one, to no avail. Then, following Kyle's suggestion, I reversed the direction of the valve in case it was being blown open. No improvement.
The next thing to try was Bob Davis's suggestion of a substitute solenoid valve, kindly lent by Bill Davies (you should have it back by now, Bill - many thanks). This was not quite the same as mine. The "W" outlet on mine had a larger inside diameter and the body is stamped "XF", Bill's (from his '93 CSE auto?) was stamped "XK". Bill's valve performed quite differently. I got full boost, but spool-up was much slower and I never saw the problem with this valve. Perhaps the different valve matches the different turbo/wastegate?
Refitting my own valve, fast spool-up was back, and so was the problem.
I've been told that too fast a spool-up can cause Trionic to "panic" and limit boost, because it thinks things might be happening in a way it can't control (e.g. stuck wastegate) and anticipates trouble. One cause of this, I'm told, is too high a base boost pressure. Indeed, base boost looks quite high on my boost gauge, being quite near the broken red.
I fitted a graduated boost gauge (it's small and hard to read, so I am not confident in quoting at a precision less than 0.05 bar) and found that my base boost is still around 0.45 bar, where I set it (I believe '96 manual Aero spec. is 0.42-0.48 bar). So much for that theory.
Leaving the boost gauge connected, I was able to reproduce the problem. When the boost "sticks" in 2nd gear, it sticks at about 0.55 bar - not much above base boost, but definitely above it. On one occasion, I saw it step up a bit after a short while, to around 0.6 bar, then sit there.
One thing I have definitely noticed recently is that spool-up is very brisk compared to a few months ago, and naturally it is quickest in 2nd gear (I never notice what happens in 1st as it's over too quick and I don't do "drag starts" anyway). I'll check my plugs today - I have a feeling that low-speed running is improving as the gaps increase towards 1.1mm (I gapped them at 0.9mm when I fitted them). Could this, along with the JT system, be making spool-up too fast for Trionic to be comfortable with? The nature of the problem is much less "occasional" recently, which helps with troubleshooting, if I regard it optimistically.
Has anyone else seen this problem with a car fitted with the JT system?
Any other suggestions?
Many thanks to all those who have helped so far. I know I've rambled a bit, but I think it helps to show my train of thought throughout the problem-solving process.
posted by 62.253....
Occasional boost problem in 2nd gear
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