Inconsistent boost levels

[lq9crew]

Hey all,

I've been lurking since I bought my RS 3 years ago, now I need some help!

I bought my 2013 RS manual new. Trifecta budget tune since 14k miles, now at 38k. I have had an ultra gauge since before the tune.

Soon after tuning I noticed occasionally when in 6th gear crusing about 70mph or 3000+ rpm, if I went WOT it would not fully boost. Normal for my car is 19-23psi at that type of rpm. Once in a while it would only build to 9-11psi. It would hold that lower psi until I let completely off the throttle and coasted for a few seconds, then most times if I went back to WOT it would be normal and build to 20ish psi.

I figured it was the wastegate pin, so I had the turbo checked and replaced by the dealer last week.

It is doing the exact same thing with the new turbo, and a new coil pack/plugs as well.

Any ideas of what to look at next?

Any things I can watch on the ultra gauge to try and track it down?

I appreciate any help!

 

[RMinNJ]

Something with the tune? What do the Trifecta people say?

 

[lq9crew]

I never really considered the tune would cause this, being a canned budget tune and my car is 100% stock.

I reached out to the vendor I got tune from with an unrelated question, was put off by the response I received, maybe time will be better.

Thanks for the suggestion

 

[ScarabEpic22]

Flash back to stock. See if it still does it.

 

[JesusTheAgnostic]

Not sure if I understood your post completely, but check out my thread:

http://www.sonicownersforum.com/forum/1-4l-turbo-sonic-engine-discussion/21253-no-boost-all.html

I know it says no boost at all, but that's just how it felt, I really had about 14 lbs.

And also, don't pull in 6th gear, down shift.

Other than that is that I'm like 99% sure that the car will change the way the car performs depending on what it thinks is right.

 

[EPYON96R]

Hi, I am also Trifecta tuned. I drive a 1.4t auto. I have been Tuned for over 50k miles/2+years. Do you have the latest update from Trifecta. It is the select a tune update. If not send them an request. And as far as boost issues. I had some weird issues that started during the summer last year where I was not getting max boost. Checked the PCV valve(built into the intake manifold) and it was missing, causing boost issues, but no codes. I got a new intake manfold and was back to 19-21 psi.

 

[mja]

Any ideas of what to look at next?

Pull your intake charge tube off the throttle body. Is there oil in the TB?

 

[Eric Smit]

It may just not allow the full boost for the situation. You don't have a boost pedal, you have an available horsepower pedal.

 

[mja]

It may just not allow the full boost for the situation. You don't have a boost pedal, you have an available horsepower pedal.

The easiest fix for this situation is a computer glitch that sometimes occurs, ign off, open/shut door, ign on, and the mysterious limp mode disappears. Im guessing he did that already.

 

[WOT-Tuning]

It may just not allow the full boost for the situation. You don't have a boost pedal, you have an available horsepower pedal.

The easiest fix for this situation is a computer glitch that sometimes occurs, ign off, open/shut door, ign on, and the mysterious limp mode disappears. Im guessing he did that already.

The most likely culprit here is the PCV issue as MJA stated. If it is missing or malfunctioning you would be bleeding off compressed air through the PCV check valve.

This has been consistently documented as an issue on this engine on both Sonic's and Cruze's. Feel free to contact us for support and to get you on the latest version of the calibration if you aren't already. However, I am going to stick with you having to get the IM and valve cover looked at to have th entire PCV system checked for issues.

 

[lq9crew]

Thanks for all the replies.

Car acts perfect when flashed to stock, as in predictable power/boost levels. No surprises.

I need to check the charge tube and throttle body for oil, I have never had it off, now nearing 40k miles. I will also check for the PVC tomorrow.

It is a strange issue, when it happens I can go to WOT (70 mph in 6th, 3100 rpm) and it will build only 8-9 PSI no matter how long I hold WOT. If I let of the throttle fully for 3-5 seconds and go back to WOT, it will immediately build 20+ PSI. The new turbo last month has made ZERO difference.

I will report back when I look at the PVC. Where is the best price for a replacement manifold if I need to go that route?

Thanks all!

 

[lq9crew]

ZERO oil in the charge tube, or throttle body. The throttle body is cleaner than my 2006 Sierra with 6.0l was with similar mileage.

Orange pvc "valve" in the middle runner of the intake is present. Vacuum hose leading from pvc valve in IM to turbo inlet has a light film of oil but no heavy buildup.

Thanks guys.

Rob

 

[JesusTheAgnostic]

Best place is probably RockAuto, it's like $280, plus you can get it with Paypal Credit so it's like $50 a month. That's what I did. So, there's no oil at all in your charge tubes? or at your throttle body? I believe this oil is common and the only way I know that it reduces the amount of oil present is bypassing the bypass, at least according to the thread. I don't know what hose you're referring to from the manifold to the turbo inlet, the only hose i can think of is the BPV line to the solenoid, have you checked out my thread yet? It's not quite your issue but you might find something useful.

 

[RMinNJ]

"..will build only 8-9 PSI no matter how long I hold WOT.."

Maybe datalog when it does this and the logs will show something ?

 

[Steelmesh]

Just a thought, scan for Desired Boost and commanded Boost Control Solenoid % and compare them between your 9-10 psi low boost and the 20+ psi high boost runs. It may point towards something mechanical, otherwise it is software related as in something is preventing the computer from commanding 20+ psi.

 

[EPYON96R]

How did the pcv orange valve check go?

 

[lq9crew]

Well, the orange PVC valve was there, but just to rule out the pvc as being a possibility, I just replaced the intake manifold assembly. Still doing the same.

The rupture disk on the valve cover is intact, no oil.

No codes, or pending codes.

No vacuum leaks, or other strange behavior.

Trifecta is my next stop.

I'll keep everyone updated.

 

[RMinNJ]

Maybe that solenoid that everyone is bypassing for the bypass valve?

Does it do it untuned that the dealer could see? (probably not right..standard unable to duplicate?).

 

[lq9crew]

Does it with the bypass valve bypassed or not and the bypass valve is new with the intake.

It acts perfect on stock tune.

 

[RMinNJ]

Yeah, Sounds like you have to data log and send logs to the tuner then.