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Thread: No boost control with Boost Button lm 22 S-IV tune

  1. #1
    Mitsu booster
    Join Date
    Aug 2009
    Location
    Joliet, il
    Posts
    15

    No boost control with Boost Button lm 22 S-IV tune

    So it seems my lm doesn't control boost at all anymore. Lot of variables though as several things have been changed.

    Car is an 87 shelby z with +40's and a 3 bar.

    First off is the turbo. I bought it off ebay mostly for the 2 1/2 swingvalve and when it arrived I found it to be a fresh rebuild with a large compressor wheel (no step in the inlet). I also noticed that the waste gate puck got hung up because the was hole was ported too big. So I welded up the side of the hole and made the waste gate hole "D" shaped so the puck wouldn't hang up.

    Then there is the waste gate actuator. This worked fine on my other turbo and controlled boost just fine with the stock lm and with several different boost button cal's. First time out with the new turbo and very little boost. Shimmed the actuator out and hit over boost with and unmodified recently downloaded S-IV cal. I bypassed the solenoid (manifold pres/vac straight to actuator can) and it holds boost around 7-8 psi. So it would seem the actuator is cable of controling boost to some extent. I upped over boost to 22psi and found that it would swing high and the regulat boost around 18psi, finally thought I was getting somewhere but it seems this is just drive pressure unseating the puck and not the solenoid controlling boost. Set boost/rpm to 10psi across and it still goes right to 18 psi.

    The solenoid and wiring seem to function just fine. Has power key on and when grounded at the lm connector the solenoid switches. It has verified manifold vac/boost going to the top of the solenoid, w/g actuator to the middle and the bottom vented. I haven't tried to monitor the w/g solenoid signal since my hand held scope/graphing meter is at work and I'm on vacation this week. But the driver in the lm module worked fine before and I'm confident the the circuits are ok.

    Since I didn't have a good way to look at the signal out of the lm I thought I would swap the stock lm and 2 bar map back in. Ran very rich off course with the +40's but actually controlled part throttle boost fine. At wot it would just hit what felt like a rev limiter hold boost around 12psi with almost no power not the usual overboost shutdown. Let off a little and it goes right back to normal 10psi and pulls fine.

    Any thoughts on this? I would like to shim the can a little more to get some more boost out of it and hopefully reduce lag to full boost but I need to be able to actually control boost.

    I understand there are three different ways to control boost depending upon cal and hose routing.
    Manifold directly to w/g and the solenoid as a bleed.
    Manifold to normally closed solenoid to w/g (the way it is right now)
    Manifold to normally open solenoid to w/g (fail safe)
    Looking at the w/g pulse width to the solenoid in the ca it looks like the S-IV cal may actually be set up for normally open. Pulse width goes down as pressure goes up, is this right? Should I try switching manifold hose to the bottom of the solenoid?

    Actually, I think I am going to out now to try and switch the hose, if the solenoid is not doing anything it should be 7-8psi at wot anything else will at least show the solenoid is doing something.

  2. #2
    Mitsu booster
    Join Date
    Aug 2009
    Location
    Joliet, il
    Posts
    15

    Re: No boost control with Boost Button lm 22 S-IV tune

    I switched the manifold hose to the bottom of the solenoid and it has 7-8psi max.

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