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too much boost

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  • too much boost

    Please excuse the daft questions but I'm used to carbs, nitrous and na engines. Ive repaired a broken vacuum line, sorted out the timing and fitted my new turbotweeks 3 bar chip with a 3 bar map sensor. Previous to this it was apparently a stock truck and i could only hit about 12psi on my boost gauge now i am seeing the gauge creep up to 20psi and so far i haven't hit more than about 2/3 throttle! i have 20in hg vacuum on tickover so I'm assuming i dont have a broken hose or leak anywhere? i have an aftermarket afr gauge fitted and throughout the accellaration I'm seeing about 12 on the afr gauge even when boost hits 20 psi, the knock sensor alert included in the chip where the check engine light flashes isn't flashing and clearly I'm a little concerned about damaging the engine, any words or wisdom greatly appreciated ?

  • #2
    Turn it rich. Should be around 10.5 afr @ full throttle (WOT)


    • #3
      thanks, I haven't hit wot throttle yet as i need to sort this boost issue out , sitting on top of the turbo looking down towards it is a small solenoid(boost solenoid?)? with two 3mm vacuum hose ports on it, the top port has a hose that goes down to the turbo (actuator?) which had the brittle hose i replaced a part of, should the bottom nipple have a hose attached as its just open to atmosphere atm ? am i right in thinking that hitting 20psi is going to do damage even if the fuelling is rich? i do have a chiltons manual to refer to but tbh its a bit of a nightmare as it covers so many models , ive found several basic things wrong so far under the hood and it was originally a Japanese import so I'm unsure who or how many people have tinkered so far and what may be incorrect or stock, I'm in the uk so there isn't anyone i can take it to who would be familiar with these for advice, there's probably only a doz or so ty's in the country and in 49 years of life and visiting car shows i have never seen another


      • #4
        Does the truck have a stock turbo? Stock downpipe? Cat? Exhaust?


        • #5
          The small solenoid on top of the turbo is the boost solenoid. It should be plumbed with new hoses. One side to the port on the front of the turbo, and the other side to the port on the wastegate actuator. Use this link below. The turbo port sticks straight out the front of the turbo housing and connects to the passenger side of the solenoid. The wastegate actuator sits below the turbo and the port sticks straight up, and connects to the driver side of the solenoid.

          You should not be seeing 20psi of boost, unless the chip is set for that much. I assume you are using an aftermarket gauge. Your AFRs should me mid 11s to be safe, high 10s to be extra safe.

          If you can reach your hand down behind the actuator, there should be a rod sticking out of the back. Try to wiggle it front to back. The rod opens the internal wastegate and sometimes freezes up. Just make sure it moves front to back, so you know its opening properly.
          Vacuum hoses on the GMC Syclone and Typhoon are not only unique to these vehicles, but very brittle and aging quickly. Years ago, mine we're starting to deteriorate so badly that I decided to replace them, and write up instructions on how to do so. That work turned into the original SyTyArchive's Silicone Vacuum Hose kits that Sportsmachines sells today. These kits are pretty easy to install once you have the right parts. Many people find it much easier to buy a kit, but you could gather the parts yourself. Though, it's very hard to find top-quality parts in small quantities (I learned a lot about glass-filled nylon, check valve diaphragms, and silicone hose).
          Last edited by Aeroking; 10-16-2018, 06:25 AM.

          Why is EVERYBODY racing on low boost?


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