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Old 11-19-2005, 07:38 PM   #1
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Default Series I overboost

I've been thinking about it, and I don't think Series I L67 PCMs have built in overboost protection. It'* been found that they only got MAP sensors if they had a boost guage, which would show that the PCM doesn't take boost into account for anything. The only thing the PCM knows is that there should be boost under certain throttle angles, and under what conditions (other than overboost) it should try to dump some.

Those are my recent thoughts on it.
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Old 11-19-2005, 08:58 PM   #2
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Hmmmm......you have a good point there.

Unless it detects it by an overly-lean condition?

Or by certain MAF readings?
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Old 11-19-2005, 09:02 PM   #3
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I had this thought because after I leaned out my mixture (by lowering the setting on my AFC 2.2) my boost dump in third problem decreased by a couple pounds.
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Old 11-19-2005, 09:06 PM   #4
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So maybe it only dumps boost based on KR data?

Edit.
That'* not the case. I'm still battling KR due to my increased top-end flow. And I still achieve 11psi.
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Old 11-19-2005, 09:17 PM   #5
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I thought about this too once I started having this boost problem and then the news about only having a MAP if you have a boost gauge cane out.

Not sure how/when the PCM decides to dump the boost but I do know that if you bypass the BBV then it will stop. Kinda like having a dirty bandaid on a cut but I don't know what else to do. It can't be by a lean condition because I'm pig rich with 0 KR each time I run my 2" pulley and it still happens. It has to be MAF based...
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Old 11-19-2005, 09:30 PM   #6
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Careful. If you hit fuel cutoff and the boost doesn't dump..........
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Old 11-20-2005, 02:14 AM   #7
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Quote:
Originally Posted by willwren
Careful. If you hit fuel cutoff and the boost doesn't dump..........
I know that is why I dont like it.
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Old 11-21-2005, 09:57 AM   #8
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Need OP. Hmmmm Interesting thoughts. Anyone searched the manual to see if it'* anywhere in there how the PCM is programmed to dump?
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Old 11-27-2005, 06:15 PM   #9
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From the book:

Boost Control System

Purpose

The boost control system regulates induction boost pressure during rapid decelearation, under very high engine load situations and anytime reverse gear is selected.

Operation

Under most conditions, the PCM commands the boost control solenoid to operate at 100% duty cycle ("ON"), keeping the solenoid valve closed and allowing only inlet vacuum to control the position of the bypass valve. At idle, full inlet vacuum applied to one side of the bypass valve actuator diaphragm counteracts spring tension to hold bypass valve open. 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 0% duty cycle ("OFF"). This opens the solenoid valve and allows boost presure from the intake manifold to counteract the spring tension in the bypass valve actuator, opening the bypass valve and recirculating excess boost pressure back to the supercharger inlet. With reverse gear selected, the PCM commands the boost control solenoid to operate at 0% duty cycle ("OFF") at all times.

Results of incorrect operation

An open CKT 922 or boost control solenoid valve stuck open will cause reduced engine power, especially during wide open throttle operation.

CKT 922 shorted to ground, boost control solenoid valve stuck closed or a restriction in the boost source or signal hoses will cause full boost to be commanded at all times and a possible overboost condition during high engine load situations.

A restriction in the vacuum signal hose to the bypass valve actuator will cause a rough idle and reduced fuel economy.
----

Now we're all on the same page. I'm curious what exactly it considers very high engine load...
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Old 12-01-2005, 06:09 PM   #10
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hummm.... Other then J Wikoff and me who is having this problem? are you DrJay?
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