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Boost Creep in Cold Weather
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Old 03-16-17, 03:45 AM   #1
putrio
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Default Boost Creep in Cold Weather

Hi All,

Background: Weather dropped ~40 degrees (to below freezing) since my last mod, which was an Invidia Q300 catback exhaust. I already had the Invidia catted divorced downpipe installed. Other mods are AEM CAI and Cobb AP v3.

My STI isn't my daily driver (Prius.....heh), and the last time I drove it, had no issues, was hitting the 93 octane ots map boost target of 19psi and holding. Couple of weeks later, 40 degrees colder, I noticed this morning the AP was showing a max boost pressure of 21.2 psi. What!?! Turned it from S# to S, did a pull. Let off when it hit 19psi, which is over what it should be in Sport mode. Car felt completely normal, didn't hear any funny noises, but I couldn't see if there was any smoke as it was dark out. The turbo has never passed 19.4 PSI before, so I kind of freaked out. I don't want to do break anything, so I have a few questions.

1. How slowly does boost creep up when at WOT?
2. What's the easiest way (besides my foot) to get control of the boost? Would an aftermarket boost control solenoid provide more efficient boost control, like the Perrin ECBS? I was going to upgrade the clutch as my next mod, but I feel this is way more important.
3. Can low oil level cause the wastgate to function less effectively? I....am embarrassed to say (and learned a valuable but hopefully not costly lesson) I checked the oil a week ago and ended up adding three quarts. I will do an oil change this weekend as well since I dun f'd up.
4. Not really a question, but I will do a logging session on my way home this afternoon in case someone requests that type of data.

Thanks for any advice!
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Old 03-16-17, 02:09 PM   #2
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Default Re: Boost Creep in Cold Weather

Uploaded datalog file (it's HUGE sorry), should anyone want to check it. Line 10092 is where it spikes up to 21 PSI. There's another spike above 20 PSI at line 23076. The wastegate duty around these times isn't maxed, so I would think it'd be able to control boost better. Thoughts? Lots of views, no comments yet :-(
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Old 03-16-17, 05:58 PM   #3
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Default Re: Boost Creep in Cold Weather

This sounds to me like you experienced a boost spike. Boost spike and creep are different. A boost spike can be a reaction due to suddenly going WOT or a large increase in throttle. Colder temps can also attribute to this since it is denser air and more air is going into the turbo than expected. Boost Creep is a scenario in which you are cruising at highway speeds and all of a sudden the boost starts to increase without any addition throttle input. This can also happen while driving normally and colder temps will greatly increase boost creep. The rate at which either creep or spike occur and how often vs how fast is really unpredictable. I don't think you can put a speed or time on boost creep/spike. The best way to control boost and fight again boost issues is with a boost controller and external waste gate. The ecbs gets its readings from the ECU and will control the operation of the waste gate in terms of when to limit and allow the turbo to create more boost. The external waste gate's job is to prevent the turbo from creating excessive boost by relieving exhaust gasses. Both of those components complement each other. The are not power adders but rather controllers. Both will require a tune to operate correctly and efficiently.

Low oil will not cause any of these issues. Although boosting the car on 3quarts low on oil is a bad idea and dangerous game. I would top off your oil level and keep a close eye on your oil levels. Check it every week/fill up until you feel comfortable in terms of consumption rates.
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Old 03-16-17, 06:26 PM   #4
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Default Re: Boost Creep in Cold Weather

Quote:
Originally Posted by putrio View Post
Uploaded datalog file (it's HUGE sorry), should anyone want to check it. Line 10092 is where it spikes up to 21 PSI. There's another spike above 20 PSI at line 23076. The wastegate duty around these times isn't maxed, so I would think it'd be able to control boost better. Thoughts? Lots of views, no comments yet :-(
Not a pro but just trying to help. First thing is when you installed your mods did you remove the pill restrictor in the vacuum line for the factory boost control? There is a small brass restrictor pill located in the short vacuum line coming off the turbo compressor housing and that could be restricting the wastegate causing you to overboost. I'm guessing it was because you were hitting target boost before though. If you already did that then try using the Low Wastegate map option that cobb usually gives with their maps because that will reduce boost a little. If that doesn't help then it's time for a EBCS, i suggest Grimmspeed, and an external wastegate set up to eliminate boost creep or you can get the internal wastegate ported. As for the colder weather, cold air = more dense which will help the turbo spool faster causing more boost creep at higher RPMs and that is why you're seeing higher boost when its cold outside but I'm pretty sure that COBB puts boost target and wastegate duty cycle compensation in their maps when intake temps are under 50F to reduce boost. Overall I recommend just getting a pro-tune because that map doesn't seem to be doing your car too well as you have knock all over the place especially at high load which is going to cause you to possibly crack a ringland and no one wants that.
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Old 03-16-17, 06:55 PM   #5
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Default Re: Boost Creep in Cold Weather

Looks like you have a spike and creep. Additionally, your fuel trims are pulling 15+% fuel... You need a tune.
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Old 03-20-17, 03:13 AM   #6
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Default Re: Boost Creep in Cold Weather

Thank you all. I'll try to get a tune as soon as possible. YamahaSHO, what numbers indicate the extra fuel?

Do you agree with sti26 about knock being an issue? From what I can find online fine knock learn doesn't have as much weight/importance as feedback knock.
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Old 03-26-17, 11:06 PM   #7
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Default Re: Boost Creep in Cold Weather

AF Corrections = Reactive fuel trim.
&
AF Learning = Proactive fuel trim based on trends.


These numbers get added together to determine total fuel correction at any given moment.
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Old 03-27-17, 03:55 AM   #8
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Default Re: Boost Creep in Cold Weather

Thanks Jason, I'm still learning some of this stuff. Unfortunately....I think something was damaged when I was running it so low on oil. I noticed when pulling into my subdivision a strange rattle coming from the engine compartment. Pulled into the garage and shut it off, had the neighbor come over, and started it again, and he said it sounded like a valve was damaged or a crankshaft bearing was allowing play in the shaft. It's a clatter-like sound, that increases with throttle, and has some RPM areas where it disappears.

I also checked out the OTS map I was running when I filled up with gas, and was running the non AEM stage 2 map, instead of the AEM version.

Essentially, I made all sorts of mistakes. It'll be a pretty long time before I can get it fixed probably, so for now, it's going to have to sit in the garage. Boooo.

Edit - crankshaft is what the neighbor said, not camshaft.

Last edited by putrio; 03-27-17 at 04:08 AM.
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Old 03-30-17, 10:35 AM   #9
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Default Re: Boost Creep in Cold Weather

Quote:
Originally Posted by putrio View Post
Thanks Jason, I'm still learning some of this stuff. Unfortunately....I think something was damaged when I was running it so low on oil. I noticed when pulling into my subdivision a strange rattle coming from the engine compartment. Pulled into the garage and shut it off, had the neighbor come over, and started it again, and he said it sounded like a valve was damaged or a crankshaft bearing was allowing play in the shaft. It's a clatter-like sound, that increases with throttle, and has some RPM areas where it disappears.

I also checked out the OTS map I was running when I filled up with gas, and was running the non AEM stage 2 map, instead of the AEM version.

Essentially, I made all sorts of mistakes. It'll be a pretty long time before I can get it fixed probably, so for now, it's going to have to sit in the garage. Boooo.

Edit - crankshaft is what the neighbor said, not camshaft.
That's definitely not good. My first guess would be a spun rod bearing. With these cars it is crucial that you keep a check on oil.

An aftermarket EBCS would also crucial to safety to your engine, while its not absolutely necessary its really a no brainer. Another thing is the OTS tune. The ECU in these cars are not very smart, OTS tunes work great with some cars like VWs because the ECU has the capability of adjusting the niggles in the flash. It sucks that you're learning this way but it is what it is. Once you get the engine issues sorted, i suggest a COBB ebcs(great quality) and a custom tune with a COBB accessport. Please feel free to PM me anymore questions.
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