Boost on tune seems inconsistent

[_UsUrPeR_]

Hey all. I bought this car used. It's got a remanufactured engine that was tuned with an Accessport from a reputable shop that still exists.

Last Fall, I was having some issues with boost cut where the vehicle would hit ~23 psi and chop fuel. It felt amazing up until fuel cut, but I knew something was wrong because it shouldn't be hitting fuel cut to begin with. It turns out that it was a bad MAF sensor. Since I replaced the sensor, the car is behaving normally, but it doesn't seem to go above 16PSI. I know this was tuned to 19PSI, and sometimes, for a few minutes after starting the car when it's still warm after parking for a few minutes, it will hit the tuned limit and feels amazing. After about 3 minutes of driving, it seems to settle back down to a 14~15 psi peak, and then that's all that's allowed by the ECU.

I called the original tuner to see if he could pull the tune on his end to tell me what boost was set to, and he was unable to get it on his system. I guess they changed their system since it was tuned in 2023 and he's unable to find it. To diagnose, he said he'd start by smoking the intake because it sounds like a boost leak, so I figured I'd do the same.

I ran smoke into the intake, and I couldn't see any leaks anywhere, though I couldn't get the manifold to pressurize past 3~5 psi with the smoke machine. When I pull the smoke off, a little pressure was holding, but not by a lot. I'm not sure where boost would be getting by, but when the engine's running under WOT, it will absolutely hit its metrics, because it had no problems hitting 23PSI when the MAF was malfunctioning, and it will hit 18~19 PSI when conditions are right for a few minutes.

The engine runs great, feels good under WOT, AFM reads around 10.25:1 which I feel is a good ratio under WOT, wastegate duty hits 50ish when the ECU is hitting 19PSI, and 38 when its in the 14psi range, HPFP shows fuel pressure at 1800+ Act. I just can't figure out why boost would be rolled back after a couple minutes by the ECU. If anyone has any suggestions, I'd appreciate it.

 

[Easter Bunny]

who is your tuner?

 

[_UsUrPeR_]

who is your tuner?

The vehicle was tuned by Horsepower Techs in Clinton Township, MI

 

[Easter Bunny]

can you post a log?

 

[Enki]

Seems like it probably didn't have a boost tune, but a load tune (this is good). If the MAF was replaced and the logs show similar MAF voltages before and after, this is likely your culprit.

Also, 10.25:1 AFR is NOT GOOD. Pull the negative off the battery, wait ~30 seconds and put it back on to reset trims, in case this is an issue.

To second Buns, post a log; log everything on the Accessport so you don't miss anything; start with a cold start log (start logging before you start the car and let it run until the idle comes down, then stop the log). From there, a single 3rd gear log should be fine to see what it's doing at the top end.

We also need to know what mods are on the car, especially intake.

 

[_UsUrPeR_]

Will do. Thanks. I'll be getting back with this information.

 

[_UsUrPeR_]

First, the modifications:

Corksport HPFP
Cobb cold air induction system
Cobb Turbo Inlet Hose
Cat deleted
Stock exhaust
Stock intercooler
Stock TurboAccessport, of course

I think that's it. I didn't own the vehicle when the tune was done, but I remember seeing a dyno sheet where it hit 340 horsepower around 18PSI. One thing to note: the vehicle was tuned without a cat.

I haven't been able to get a cold start logged yet, but I did manage to get a high boost log this morning. Initially I had to replace the MAF sensor because it was giving a bunch of bizarre readings, and overboosting. The car felt amazing, but it would hit ~23PSI and hit fuel cut. I knew that probably wasn't great for the car, so I tried to take it real easy.

To describe, I have been working on the suspension. I replaced a bunch of worn stuff, and the car has been sitting all weekend, except to move it around my driveway. Upon starting driving it this morning, the turbo seemed more awake, and the sound coming out of it was way different, like it was breathing better. The power also came on like a freight train, and it hit boost cut a few times in second and third gear. After 30 seconds of driving, I realized I should record this so plugged in the Accessport and managed to pull the "highboost.csv" log I am including in this post.

This seems like a common occurrence where when the car isn't fully warmed up, it feels amazing and hits high boost, but then it evens itself out and will only hit ~13 PSI at the absolute limit.

I'm also including a log from freeway driving (freeway.csv)

I'll get a 3rd gear pull tomorrow and post it then.

I have checked and re-checked the intake for leaks, and am not sure what else could be causing this issue. Further, if it was leaking, it seems like hitting ~23PSI in the highboost log wouldn't be possible. I'm used to RX-7 tuning when it comes to AFR, and if it were hitting 23 PSI, I would expect to see an AFR around 7, but in the 23PSI pull that I logged, I am seeing 9.85 at the lowest, isn't great. I am presuming that I probably have a leak before the turbo, but after the MAF sensor, if that's kind of AFR isn't where it should be...

 

[Enki]

So yeah, the stock turbo can't make much boost past 5k, and I bet that HP number was obtained from a VERY happy dyno and that HP peak was well below anywhere you'd want to shift at.

 

[_UsUrPeR_]

HP number was obtained from a VERY happy dyno

I'm sure that's the case. I wish I had the printout somewhere, or had taken a photo of it. C'est la vie.

That compressor chart makes sense. Damn, the stock turbo is already way outside of efficiency island by 20PSI. Well I guess I feel good that it's being efficient in its current settings.

I guess I need to find out why/how the ECU is hitting 23PSI. What would cause this? I just swapped out the MAF in September because it was a LOT worse because the old MAF was most likely going bad.

I'm going to be able to get behind the wheel tomorrow to get some more logs.

Thanks for your help.

 

[Enki]

The stock turbo is undersized and maxed out from the factory by design, to make it "punchier." It should have come with a GT28 sized turbo from the factory, but didn't.

 

[Crazycanadian]

In your logs the Waste gate duty cycle maxes around 38 - 40%.. This looks like a tune that would be for a boost control setup for interrupt, not the factory bleed setup. It also looks like you might have a sticky waste gate.

 

[Enki]

Hopefully a third gear log will be cleaner, but make sure to add calculated load, MAF volts, and throttle position (though this probably won't show much. You can remove Fuel injection amount, HPFP desired pressure, and mass airflow g/s. Also make sure to start between 3000 and 3500 RPM and let it wind out to 6k for best visibility on behavior.

Normally a fourth gear log would be better, but we take what we can get.

 

[_UsUrPeR_]

Per your request, I have Two 3rd & 4th runs and a cold start from ambient temp to operating temp.

I'm super interested to understand what you think. If you think it's a boost leak, I'm probably going to need to replace the charge pipes from the turbo to the IC, and the IC to the throttle body because they're still stock. This is the intercooler style that is all metal up until a 3" gap to the TB. If anyone has any recommendations for a good pipe, let me know.

Thanks for your help!

 

[Enki]

Looks like it's trying to avoid killing itself; probably time to get HPFP internals if your tuner can't get the airflow under control.



This slow regen of pressure is exactly what I'd expect to see on stock internals as the RPM climbs; I went ahead and added this row to my math spreadsheet for rough fuel calcs and got the following:


Note that the row I added (row 13) shows the HPFP flow cc (row 9) divided by the injector size (B3) times two (two injection events per revolution that overlap, but this isn't perfect).
Note also that this doesn't account for MFG tolerances, low speed/rpm leakby, and other variables (it's a rough estimate); there have been some stock internals cars that made way more flow than they ever had any right to, and got the factory freak status because of it.

If someone wants to chime in with better math, by all means, and I'll run it through the sheet.

Also keep in mind that DI injectors have half the injection window of PI injectors (can't inject fuel during combustion or exhaust) so sizing them double is a hacky way to show their true flow potential.

@Easter Bunny

 

[Crazycanadian]

I don't see a Baro reading. Where are you from? what's your typical/average baro reading?

These cars aren't tuned based on "gauge" boost numbers that everyone references.. They are tuned base on absolute MAP values. "gauge" boost numbers is absolute Map - Baro.. If you're local Baro is lets say 12 or 13 cause you are pretty high up in the mountains. There's a pretty big compensation table that reduces max boost, that might not be tuned right. The fact you don't see over 50ish % duty cycle is interesting. Is your waste gate setup in bleed or interrupt mode?

You're first post explaining the over boosting sounds like a waste gate that's sticking closed, not fully opening. It's possible later on it's starting to stick open. but...

You do have a high pressure fuel issue, I'd solve this first before getting to far into other things. You're dipping quite low when you first roll into it. All though it catches up later, this dip is a problem. In your other log the fuel pressure is solid during the pulls, but you are also at 160 deg coolant temps in that one. This one you are little warmer, so it indicates that as things get hot, you start having a problem. This goes along with your symptoms.. Not having the tune file makes this stuff muddy though since there's questions with how things have been setup that we are left without knowing.

When it comes to looking at fuel trims and AFR's you want the car up to operating temp. I get that your problem is during warm up, but there's information that can be gathered about other sensors and validating other readings when the car is being driven at operating temps during normal driving (not just WOT logs)..

 

[Easter Bunny]

@Enki what did i do?

stop going WOT

rebuild the HPFP

 

[Enki]

Nothing, just looking for input/confirmation/corrections

 

[_UsUrPeR_]

I just rebuilt the HPFP. @Enki, I think you helped me out with that here less than a year ago. It's got Corksport internals D:

On the good side, I think I found the boost leak. I replaced the worm gear hose clamps that came with the car with some t-bolt hose clamps, and I think that sorted my problem with what seemed to be a boost leak. After replacing the clamps, I was able to hit 15~16PSI no problem. So I was running with a boost leak for quite a while (3rd_4th_pull.csv).

I drove about 15 minutes on the freeway, and pulled off to go into a store for a second. I was in the store for ~15 minutes. Came out, got in my car, and of course I wasn't logging right then, but pulled onto the street and hit boost fuel in first gear, and then again in second gear. I managed to get a log as I got on the freeway for posterity, then started to just drive it like normal. I logged almost the whole drive afterward. The ECU seemed to calm everything down at some point, and wouldn't go above 16PSI which felt a lot better.

@Crazycanadian: I'm in Detroit so ~500 feet above sea level. I just upgraded the accessport firmware today. It was about three or four years old. Whenever the original tune was done. Is that a new metric that it captures? As to the wastegate setup, I have no idea. This vehicle was tuned for the previous owner, and I bought it like that. The Turbo is stock, and the wastegate is stock.

One thing I am noticing: the HPFP fuel pressure seemed to do alright when the engine was cold, but looks like shit in the second log when the vehicle was driven and parked warm, waiting ~15 minutes, and then getting back in the vehicle after it's at operating temp. The HPFP internals are less than a year old.

As to the tuner, I spoke with him. He's local to me. The dude said he'd tune it again for $1200, but I haven't made any substantive changes since I bought the car, and think that there's something I'm missing in all this. No need to get it tuned if I can't even get the HPFP pressure correct.

 

[Enki]

Lmao $1200
The fuck is he doing that takes $1200 worth of time and effort? That has to be a 'fuck off' price.

Also, the car will run like shit until it re-trims. Best to pull the negative off the battery and tap the brake to reset learned trims and whatnot.