# 2018 Cruze 1.4T overboost Q



## Taxman (Aug 10, 2017)

I only logged one full throttle run before tuning my 2016.
It hit 30.3psi absolute, (15.6 boost) at 3800rpm, and the ECU closed the throttle.
After that it didn't go above 27.9, and it dropped below 25 psi by 5000rpm.


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## mean buzzen half dozen (May 13, 2018)

Thx Taxman ,

I take it seeing 15.6 psi it did not hit any overboost warning horn or indication?


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## Taxman (Aug 10, 2017)

No CEL or other warning that I noticed, just a massive loss of power. I didn't realize until I looked at the throttle position on the chart that it closed the throttle on me. I don't think it was stabilitrak, and it didn't correspond to a knock event, so I assume it was boost related.

If you only see 12psi below 4000rpm it might be due to changes between 2016 and 2018 to the stock tune to reduce LSPI.

I only floored it twice before tuning it, and that was the only one I logged. The other time was uneventful, just steady power.


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## williscu (Apr 10, 2018)

Interesting. I have a 2011 ECO @ 250,000 miles & I get 10 PSI :grim: @ 2000 rpm. Its fun to pull steep hills in 6th without shifting. I have a boost gauge. 

I exceeded 20PSI once when I had a leak behind turbo @ the clamp. That was scary, but fun!:th_SmlyROFL:

Im guessing I got a solid motor right? Eats valve covers but I can change em out in 7 mins now. Just chime right in GM powertrain engineers.


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## jblackburn (Apr 14, 2012)

williscu said:


> Interesting. I have a 2011 ECO @ 250,000 miles & I get 10 PSI :grim: @ 2000 rpm. Its fun to pull steep hills in 6th without shifting. I have a boost gauge.
> 
> I exceeded 20PSI once when I had a leak behind turbo @ the clamp. That was scary, but fun!:th_SmlyROFL:
> 
> Im guessing I got a solid motor right? Eats valve covers but I can change em out in 7 mins now. Just chime right in GM powertrain engineers.


Check the check valve in the intake manifold. 

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## jblackburn (Apr 14, 2012)

Taxman said:


> No CEL or other warning that I noticed, just a massive loss of power. I didn't realize until I looked at the throttle position on the chart that it closed the throttle on me. I don't think it was stabilitrak, and it didn't correspond to a knock event, so I assume it was boost related.
> 
> If you only see 12psi below 4000rpm it might be due to changes between 2016 and 2018 to the stock tune to reduce LSPI.
> 
> I only floored it twice before tuning it, and that was the only one I logged. The other time was uneventful, just steady power.


I wonder if this is what happened to me merging the other day. 4000 rpm and the car stuttered and then was missing about half the power. Not fun when you're trying to get up to 70. After that, it was perfectly fine again. 

I've had this happen once before in a huge rainstorm. My other theory is condensation pooling in the intercooler from lots of light throttle highway driving. 

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## Taxman (Aug 10, 2017)

Here's the data plot.
If we call it zero seconds when I punched the throttle, at 0.9 seconds the throttle is fully open (TPS is blue line in top graph). At 1.6s it begins to close. Full throttle reads 83.9%, during the event it shows as low as 52.5%. At 2.1s, it's back to 83.9%, but that half second power loss was very unsettling. During the event MAP dropped from 30.3 to 27.6. At the end of that half second it went up to 27.9 and then began to taper off as RPMs increased. At 6.3s I let off the throttle to merge with 68mph traffic. By then it was turning 5500rpm and MAP had dropped to 23.5.

In looking at it frame by frame, I'm sort of surprised that the MAP reading did not change enough to explain the engine seeming to fall on its face like it did. If I'd known it would record a half second event that I was interested in, I would have set the log rate to more than 15x per second. 

View attachment 268597


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## jblackburn (Apr 14, 2012)

Taxman said:


> Here's the data plot.
> If we call it zero seconds when I punched the throttle, at 0.9 seconds the throttle is fully open (TPS is blue line in top graph). At 1.6s it begins to close. Full throttle reads 83.9%, during the event it shows as low as 52.5%. At 2.1s, it's back to 83.9%, but that half second power loss was very unsettling. During the event MAP dropped from 30.3 to 27.6. At the end of that half second it went up to 27.9 and then began to taper off as RPMs increased. At 6.3s I let off the throttle to merge with 68mph traffic. By then it was turning 5500rpm and MAP had dropped to 23.5.
> 
> In looking at it frame by frame, I'm sort of surprised that the MAP reading did not change enough to explain the engine seeming to fall on its face like it did. If I'd known it would record a half second event that I was interested in, I would have set the log rate to more than 15x per second.
> ...


Looks like it cut power pretty severely due to a knock event?


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## Taxman (Aug 10, 2017)

Knock retard appears (4.3°, blue line in 3rd graph) at 7.9 seconds as the car shifts into 5th gear, 1.6 seconds after I got off the throttle and I think I'd already engaged the cruise.

Conditions at that frame in the data: 3260rpm, 30.6% throttle (idle is 20+%), 68mph, 4.9psi MAP (9.8psi vacuum), water temp 185°, IAT 37°, spark advance 4° but it was around 30° a few frames earlier.


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## 17Cruzer (Apr 18, 2017)

Taxman said:


> Knock retard appears (4.3°, blue line in 3rd graph) at 7.9 seconds as the car shifts into 5th gear, 1.6 seconds after I got off the throttle and I think I'd already engaged the cruise.
> 
> Conditions at that frame in the data: 3260rpm, 30.6% throttle (idle is 20+%), 68mph, 4.9psi MAP (9.8psi vacuum), water temp 185°, IAT 37°, spark advance 4° but it was around 30° a few frames earlier.


Sounds like you may have reached the limits of the MAP sensor. Try a 3 bar sensor.


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## Ma v e n (Oct 8, 2018)

mean buzzen half dozen said:


> Hey guys,
> 
> I am wondering at what psi of boost pressure does a stock 2018 1.4T Cruze get an overboost C.E.L? (Check engine light)
> 
> ...


P0234 sets when boost exceeds the expected amount for more than 3 seconds. It can occur at 5psi, or 10, or 20psi... The maximum boost the ECM expects to see is 20.1psi(240kpa)


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## Taxman (Aug 10, 2017)

Ma v e n said:


> The maximum boost the ECM expects to see is 20.1psi(240kpa)


I can't quite hit that tuned, and I haven't come close untuned. 
High boost for me is 19lb tuned or 16lb untuned. 
I expect to hit the 20s when I get my final tune.


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## Ma v e n (Oct 8, 2018)

Taxman said:


> Ma v e n said:
> 
> 
> > The maximum boost the ECM expects to see is 20.1psi(240kpa)
> ...


I don't doubt you don't see it stock. That's just max it ever expects to see.


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## gmansyz (Dec 23, 2018)

So the max seems to be about 20 psi? Perfect as I have a vacuum/boost gauge that goes to 20.


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## williscu (Apr 10, 2018)

Me too (20 psi boost guage) I wonder about pegging it out all the time at 20. But then again it'll pull 10 psi @ 2000 up steep hills in 6th so that hasnt broken it. I feel like gm neutered this motor just cause they can!

A few spins on the wastegate solenoid does wonders.


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## Ma v e n (Oct 8, 2018)

williscu said:


> Me too (20 psi boost guage) I wonder about pegging it out all the time at 20. But then again it'll pull 10 psi @ 2000 up steep hills in 6th so that hasnt broken it. I feel like gm neutered this motor just cause they can!
> 
> A few spins on the wastegate solenoid does wonders.


They neutered it so it can operate on the cheapest possible fuel and oil and still have some chance of meeting emissions and durability standards throughout it's life.


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## williscu (Apr 10, 2018)

Emissions lol. Well mine didnt set a code for that until 248k. Converters toast & rattling. But it makes great power. Since im paid to drive I just use excellent fuel & even better oil.

One time I got some really bad gas & the boost peaked at like 2 psi. I was mad. Had a full tank of it too.


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