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| 3800SC series 2 lost boost (Page 1/1) |
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RichLo1
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APR 11, 02:55 PM
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Hey, I have a relatively stock 3800SC series 2 out of a 1999 GTP in my 88 Fiero. It just has a 3.5 pulley instead of stock and headers with mandrel bent exhaust. It was running fine but then after some spirited driving it lost boost... No supercharger whine and way low on power. Same thing after sitting overnight to cool down. The belt is fine, the pulley is spinning. What could cause this? I have a scanner that I can data log sensors if needed but I'm not sure which ones to look at?
Also, I was only getting around 4 PSI of boost before this happened, is this normal for this pulley size? That seemed low but being a positive displacement blower with free flowing exhaust it may be normal?
Thanks in advance!
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Raydar
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APR 11, 05:07 PM
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Not a 3800 person, but I'll venture a guess. 3800s have a boost bypass valve(?) that is supposed to kick in at low RPM/throttle position. Could that be stuck open?
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sanderson231
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APR 12, 07:49 PM
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| quote | Originally posted by Raydar:
Not a 3800 person, but I'll venture a guess. 3800s have a boost bypass valve(?) that is supposed to kick in at low RPM/throttle position. Could that be stuck open? |
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and it's controlled by a solenoid------------------
formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged
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RichLo1
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APR 14, 10:48 AM
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I data logged boost and confirmed it wouldnt get above 0psi when revving. I looked at the solenoid mentioned above and saw that it wasnt moving much so I pushed the lever down all the way with my finger and it hit 5psi when revving. So I ordered a new solenoid to see if that fixes it. I will also delete the computer controlled actuator while I'm in there.
I'll post results good or bad when its replaced.
Just a question, has anybody ever attached a cable to that lever and run it inside the cab as a manual over ride of that vacuum solenoid? It seems like you could get more boost sooner if you know your going to be at a track or something that day then go back to vac operated when on the street.
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sanderson231
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APR 14, 12:53 PM
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Here's is how the boost control solenoid should work:
"As engine load increases, reduced vacuum acts upon the spring tension in the bypass valve actuator, causing the bypass valve to close and increasing boost pressure. When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle (OFF). This opens the solenoid valve and allows boost pressure from the intake manifold to counteract the spring tension in the bypass valve actuator, opening the bypass valve and recirculating excess boost pressure back into the supercharger inlet. With reverse gear selected, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle (OFF) at all times."
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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged
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