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Overboost Woes... thoughts, anyone?
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=88918		 Page 1 of 1
Author:  acuboy [ Wed Jun 20, 2018 11:47 pm ]
Post subject:  Overboost Woes... thoughts, anyone?
Hey Guys,

I'm sort of at a loss. I have 160k miles and GDE Eco tune. So, I'm throwing a CEL p0234 overboost whenever I'm accelerating onto the freeway. The Jeep will then "limp" and not exceed 70mph. If I clear the code without shutting down it doesn't recur and the jeep seems to run fine. I've replaced the MAP, boost solenoid, boost modulator and filter with no change. The actuator arm seems to move with no problem. The vanes seem to turn ok and I don't feel play in the spindle, but honestly I don't entirely know what normal feels like. I haven't replaced the vacuum lines, but there's vacuum at the solenoid. I'm kind of at a loss. I'm in Oakland, CA, and have been having trouble finding any reputable shop that even wants to touch it. Am I forgetting something obvious? Some of you may have seen me post on the facebook group and all the input I've received there has been greatly appreciated. Just want to enjoy the summer!

thanks
duncan
Author:  WWDiesel [ Thu Jun 21, 2018 11:31 am ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
Has your EGR been removed or blanked off?

I would suspect the MAP sensor is the culprit.
The overboost code and subquence limp mode is caused when the MAP sensor runs out of range on the top end. [3 bar (20 kPa @ 0.4V , 300 kPa @ 4.65V)]
Either your turbo is producing too much boost, which I doubt very seriously, or the MAP is defective and is reporting out of range on the high end of the boost pressure signal to the ECM.

Installing a boost gauge will allow you to see exactly how much boost is being produced during hard acceleration and help diagnose the problem.

:SOMBRERO:
Author:  acuboy [ Thu Jun 21, 2018 1:07 pm ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
Thanks for your reply. I have an EGR delete through the GDE tune. When the overboost problem first occurred the first thing I swapped out was the MAP. I've heard people mention shortening the range of the actuator arm to prevent overboost, but this seems like a bandaid and also seems like it would effect the performance. If there's too much play in the travel of the actuator arm can this cause overboost? Does that mechanism start to develop too much pay over time? I'm installing a boost gauge tomorrow, so I should have more info then. I believe you can see boost through the Torque Lite app, which I'm assuming would be the same info the brain is seeing. Anyway, all thoughts or input are appreciated. This has been a tricky troubleshoot for me.

thanks
d
Author:  WWDiesel [ Thu Jun 21, 2018 2:24 pm ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
acuboy wrote:
Thanks for your reply. I have an EGR delete through the GDE tune. When the overboost problem first occurred the first thing I swapped out was the MAP. I've heard people mention shortening the range of the actuator arm to prevent overboost, but this seems like a bandaid and also seems like it would effect the performance. If there's too much play in the travel of the actuator arm can this cause overboost? Does that mechanism start to develop too much pay over time? I'm installing a boost gauge tomorrow, so I should have more info then. I believe you can see boost through the Torque Lite app, which I'm assuming would be the same info the brain is seeing. Anyway, all thoughts or input are appreciated. This has been a tricky troubleshoot for me.
thanksd

Please note: NO TUNE can completely guarantee that no leakby takes place in the EGR valve. Only by totally removing the entire system (Weeks Elbow Kit) or installing a blank-off plate in the exhaust feed line to the EGR valve can you totally eliminate any possibility of leakby.
I believe to much play in the linkage for the variable vanes would actually cause underboost, not overboost. Being you stated it only happens when doing a hard for fast acceleration leads me to believe either the turbo is actually producing too much boost, or the MAP sensor is defective and giving the ECM false information during full boost operation. I really believe the problem is the latter.
Good for you on installing a boost gauge, that will tell you a bunch. If you don't see actual boost greater than 24 psig peak during full boost acceleration, then the problem is not your turbo or linkage.
First thing I would do is install a new MAP sensor and see if it fixes your problem.

You can purchase online a GM MAP sensor PN GM 55206797 for ~$20 bucks. :google:
*actually it is a BOSCH part, PN 0 281 002 845
Many on LOST including myself are using this GM/Bosch sensor in place of the much higher priced OEM sensor. :wink:
Author:  GordnadoCRD [ Fri Jun 22, 2018 12:22 am ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
Hopefully you are installing a mechanical boost gauge rather than an electronic one. It will give you true boost, whereas the electronic one will only show you what the ECM is seeing, and that could be incorrect.
Author:  WWDiesel [ Fri Jun 22, 2018 2:15 pm ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
GordnadoCRD wrote:
Hopefully you are installing a mechanical boost gauge rather than an electronic one. It will give you true boost, whereas the electronic one will only show you what the ECM is seeing, and that could be incorrect.

X2, very true!
Author:  acuboy [ Fri Jun 22, 2018 4:19 pm ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
Does anyone know if there's a difference in MAP sensors on the market. The one i installed in trouble shooting this problem was the one from ID for $22.50. I thought I remembered reading that there might be some inferior ones on the market. The reason I'm scratching my head is that the P0234 is being triggered when the boost being measured by my Torque Ap (which I believe is what the ecm is seeing) is between 18 - 20 and my understanding is that it's not supposed to trip a fault until 27. Maybe I installed a faulty sensor?

thanks!
Author:  GordnadoCRD [ Fri Jun 22, 2018 5:13 pm ]
Post subject:  Re: Overboost Woes... thoughts, anyone?
To know for sure, it has to be compared to the boost level the ECM is demanding at that instant, and that changes constantly depending on all the current sensor inputs moment to moment.
Author:  jsrmonster [ Sat Jun 23, 2018 10:45 am ]
Post subject:  Overboost Woes... thoughts, anyone?
Your vnt actuator needs to have some preload on it. Adjust /lengthen so it takes 5” vacuum to begin moving. It should finish moving at 18” Vac.
The actuator must have more authority over the exhaust back pressure to allow the vane to position towards axis for venting exhaust (wastegate). If the exhaust back pressure force on the backside of the vanes is greater than the actuator spring force it will creep the vane position into boosting insteading of venting regardless of commanded signal to actuator solenoid. Very simple closed loop control when vnt actuator is adjusted properly, but goes open loop easily when not - resulting in overboost and limp after exceeding pressure limit and fault time-constant.
Jeff ;-))
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