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Old 01-04-2013, 04:40 PM   #1
Boost pulls back to 5psi under full throttle HELP  
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Here's the problem with my '86 GLHS. Basically at any throttle position past about 80% it pulls boost back to exactly 5psi. Anything from 0-80% throttle responds normally and gets normal boost levels up to about 14psi (Mopar Stage II ECM) depending on load. However even if I'm getting full boost at say 75% throttle, once I go past that 80% throttle threshold it instantly pulls boost back to 5psi. It will hold 5psi unless I let off some on the throttle, then it will quickly build boost back to normal.

I'm not sure what is taking control of boost at heavier throttle, but it's not right. I have to assume it's an adjustment, maybe of the TPS? Let me know what you think.
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Old 01-05-2013, 06:13 AM   #2
Re: Boost pulls back to 5psi under full throttle HELP  
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I am not an expert on turbo's but...
Does the 86 have an adjustable wastegate arm???

Tee a vacuum/pressure gauge inline between the wastegate solenoid and wastegate and see what pressure is in that line before and after 80% throttle.
You may not be seeing anything before 80% throttle.

BTW...TPS is not adjustable but the controller has to see above 3.50 volts to recognize WOT.
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Old 01-05-2013, 10:58 AM   #3
Re: Boost pulls back to 5psi under full throttle HELP  
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Hmmm, do you have the orifice fitting in line between the actuator and the solenoid, if not you may need to install one.

Check to see that the actuator has that little brace rod between the center section and the actuator bracket.
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Old 01-05-2013, 01:59 PM   #4
Re: Boost pulls back to 5psi under full throttle HELP  
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ECU pulling back the boost because of detonation? Need a scanner on it to see. One thing to check out would be the SoCal SDAC meet at applebee's in LaHabra the 1st thursday of every month.
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Old 01-07-2013, 02:00 PM   #5
Re: Boost pulls back to 5psi under full throttle HELP  
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ECU pulling back the boost because of detonation? Need a scanner on it to see. One thing to check out would be the SoCal SDAC meet at applebee's in LaHabra the 1st thursday of every month.
Thanks for the tip in the SDAC meet, I'll probably try to go next month. I live less than 15 minutes from there.

As far as detonation, I don't think that's it. Seems directly related to throttle position and I definitely don't hear even a little ping.

FWIW, the car recently had the cyl head rebuilt and all the hoses were replaced as well as the TPS at that time, this issue stared afterwards. I'm leaning towards the suggestion that ChargedDust made regarding the orifice fitting. I haven't looked for it yet, but if that could cause such a problem then that's likely the culprit.

I will be back here if the problem persists after checking for the orifice fitting.
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Old 01-07-2013, 07:41 PM   #6
Re: Boost pulls back to 5psi under full throttle HELP  
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Quote:
Originally Posted by GLHNSLHT2 View Post
ECU pulling back the boost because of detonation? Need a scanner on it to see. One thing to check out would be the SoCal SDAC meet at applebee's in LaHabra the 1st thursday of every month.
That meeting is every month?? I thought it was like once a year or somethin
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Old 01-07-2013, 08:10 PM   #7
Re: Boost pulls back to 5psi under full throttle HELP  
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yep every month, 1st thursday. There's an on-going thread over on Turbo-mopar.com about it.
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