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No boost this morning? Fixed!
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=85590		 Page 1 of 1
Author:  flash7210 [ Wed Nov 16, 2016 9:07 am ]
Post subject:  No boost this morning? Fixed!
As soon as I pulled out of my driveway I could hear that the exhaust note was different. Thought maybe it was just a cold engine. But as soon as I got out on the road it certainly didn't feel right.
It felt like limp mode. :x
So I stopped and checked for codes. P0299 underboost was the only new code.
I was only getting 4-5 psi boost under acceleration.
Checked boost hoses. All were tight and I couldn't hear any air leaks while driving.
So I cleared the codes and tried to drive again. Same problem.
Stopped, checked vacuum lines and solenoids. All were good.
Only thing left to do was bypass the small vacuum solenoid.
Sure enough, the solenoid bypass fixed it.
Boost levels are now back to normal. :D
Author:  lacabrera [ Wed Nov 16, 2016 11:52 am ]
Post subject:  Re: No boost this morning? Fixed!
flash7210 wrote:
As soon as I pulled out of my driveway I could hear that the exhaust note was different. Thought maybe it was just a cold engine. But as soon as I got out on the road it certainly didn't feel right.
It felt like limp mode. :x
So I stopped and checked for codes. P0299 underboost was the only new code.
I was only getting 4-5 psi boost under acceleration.
Checked boost hoses. All were tight and I couldn't hear any air leaks while driving.
So I cleared the codes and tried to drive again. Same problem.
Stopped, checked vacuum lines and solenoids. All were good.
Only thing left to do was bypass the small vacuum solenoid.
Sure enough, the solenoid bypass fixed it.
Boost levels are now back to normal. :D


Hi, With the vacuum solenoid bypassed do you get an over boost and limp mode, asking because I recon I have a faulty solenoid that's causing an over boost. Only happens in the same area of my journey to work, steep drive down to a river and on the climb up the opposite side triggers an over boost and limp mode. Happens every time but only on this part of the journey.
Author:  flash7210 [ Wed Nov 16, 2016 1:18 pm ]
Post subject:  Re: No boost this morning? Fixed!
The small vacuum solenoid is just a simple on/off valve for the vacuum supply.
If its stuck in the off position, no vacuum will be supplied to vacuum actuator on the turbo, resulting in a underboost condition.
Bypassing it means that vacuum supply is always on.

The large vacuum solenoid modulates vacuum to the turbo actuator in order to maintain whatever boost level the ECM wants to see (by way of the MAP sensor).
Bypassing the large solenoid would make it so that the vacuum to the actuator is always high. Which means that boost level will also always be high. Which will result in a overboost condition.
If the large solenoid were faulty, this could result in a overboost condition OR a underboost condition, depending on which position its stuck in.

Generally, when diagnosing a boost problem, I start with the MAP sensor.
Make sure its clean and reading the proper boost level.
If not, then check the vacuum system.
Author:  WWDiesel [ Wed Nov 16, 2016 1:43 pm ]
Post subject:  Re: No boost this morning? Fixed!
lacabrera wrote:
Hi, With the vacuum solenoid bypassed do you get an over boost and limp mode, asking because I recon I have a faulty solenoid that's causing an over boost. Only happens in the same area of my journey to work, steep drive down to a river and on the climb up the opposite side triggers an over boost and limp mode. Happens every time but only on this part of the journey.

As flash stated, more than likely a MAP sensor problem. First thing to try; replace the MAP sensor!
You can use a GM part, no. 55206797 in place of the Mopar unit and cost is only around 20 bucks on line. :wink:
Link:> http://www.gmpartsdirect.com/oe-gm/55206797
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