Power Loss After 5000 RPM on 3rd Gear and Above

[bl4cksta]

Hey everyone!

I have an issue where my car noticeably accelerates slower after 5000 RPM in 3rd gear and above. I'm running a self-tuned ECU calibration, and I’ve attached logs for reference. In the logs, I noticed that the RPM and MAF readings fluctuate slightly after 5000 RPM. Could this be related?

Mazda 6 MPS, mod list:

• FMIC

• Corksport HPFP upgrade

• Custom 3-inch intake (with custom maf calibration)

• Blow-off valve

• Increased preload on the wastegate spring

Any insights would be greatly appreciated! Thanks in advance.

[mituc]

In the log you provided there are not enough parameters to draw a conclusion. I also noticed that you're overboosting slightly and the boost is pretty high for the amount of air you are getting in (at 5300rpm at 260kpa MAP you should get around 300/s of air if you are on the stock catalytic converters, and more if you have exhaust mods, and assuming you already have a decent turbo setup).
Please take another log with this dashboard preset:
https://www.dropbox.com/scl/fi/afnzjbrr ... if94d&dl=0
If possible please also share the tune.

[bl4cksta]

Thanks for your response, mituc!

I forgot to mention that I'm running a stock exhaust with straight pipes (cats and resonators removed). I also have a 3.5 bar MAP sensor (Bosch 0 281 002 456) with the corresponding calibration.

I've attached the tune file and 2 logs: one of slow city driving and one of a full-throttle pull in 2nd, 3rd, and 4th gears.

[mituc]

The tune is decently put together, I have to admit that I see this rarely. Congrats on that!

What I noticed with the first set of logs seems to stand with these newer logs as well, but it's a lot more visible now. So the boost readings are very high for the amount of air you are getting into the engine. I'm thinking that maybe the MAP sensor you have is damaged. The calibration for this sensor part number is correct, but the readings you get from your sensor in particular may not be right. Do you happen to have a spare one that you can swap in?

The MAF calibration is also a bit weird, I believe you made the calibration around some defect (a leak). By example there are areas where the LTFTs are around +10 and the STFTs correct about as much (or +16 versus -14-ish, at idle +7 versus -9.4, and so on), meaning that in some circumstances you may have a leak which makes the ECU adapt to it, and then it applies corrections to bring it back down once that leak either changes or disappears.

[bl4cksta]

Thanks, mituc, you just boosted my confidence! This tune was built in part thanks to your many invaluable replies on this forum - I really put in the effort! Thank you.

Regarding the MAP sensor: I don’t have another identical one to compare, but its readings more or less match my analog boost gauge, with a variance of about 0.1-0.2 bar. I assume this is within the margin of error and can be ignored (or is it not?).

Regarding the MAF: I tried using Versa’s calibration, and the car felt exactly the same, but in the logs, I saw slightly lower g/s readings (currently peaking at 270, while with Versa’s calibration, it was around 260). Could it be that the actual air consumption is higher than what the ECU sees? And does this affect the engine’s power output?

Anyway, thanks for the advice, I had already considered installing the stock intake and stock calibration to check the "baseline" air consumption. I’ll probably do this over the weekend and report back with the results.

[CrazyCanadian]

There's a good chance you are running into a flow restriction with the stock exhaust/stock down pipe.. This is similar to having a plugged cat.. Back pressure starts to climb forcing manifold pressure up, but total air flow goes down... It would be interesting to see how things look with the stock MAF cal and stock MAF housing.. Possibly the stock MAP sensor as well to get a better base line...

I am on the stock MAP sensor and stock MAF housing size/stock Maf call.. I run 2.1 - 2.2 load and 34psi MAP reading.. You're running 5psi more then me, but 5 lbs/m lower mass airflow.. I am basically full bolt on, FMIC, custom 3" turbo back exhaust, stock turbo ect..

You're also getting quit a bit of knock which.. high back pressure will cause extra heat in the combustion chamber increasing knock..
Part of your logs..

Massive knock.jpg (570.1 KiB) Viewed 1272 times

This is from my car for comparison..

Adam no knock.jpg (549.29 KiB) Viewed 1272 times

A few other notes I saw.. Your load based fuel cut is close to what you are running, if you start driving into different area's you might hit this as your load and boost targets shift to account for different altitudes and ambient air temps.. I ran into this problem when I did a 13,000 km road trip from Vancouver BC to Florida..

I like to run my throttle based Boost limit 2 to 3 psi lower then my hard Boost cut limits.. You're running with a 1 psi difference..

[mituc]

You're also getting quit a bit of knock which..

That's the ECU freaking out when approaching the boost limits (according to the sensor at least)...
As for the clogged cat/exhaust... usually the turbo will not build boost in such cases, but in his case the boost jumps a lot while the airflow doesn't. Even at idle there's a 3kpa difference compared to what we know the vacuum should be, and sometimes the manifold pressure would not change at all when starting driving, which is unusual. That's why I suspect it's the actual sensor and not a mechanical problem with his car (I would not rule it out, but for how this is what I think).

[CrazyCanadian]

You're also getting quit a bit of knock which..

That's the ECU freaking out when approaching the boost limits (according to the sensor at least)...
As for the clogged cat/exhaust... usually the turbo will not build boost in such cases, but in his case the boost jumps a lot while the airflow doesn't. Even at idle there's a 3kpa difference compared to what we know the vacuum should be, and sometimes the manifold pressure would not change at all when starting driving, which is unusual. That's why I suspect it's the actual sensor and not a mechanical problem with his car (I would not rule it out, but for how this is what I think).
[/quote

I've seen some interesting patterns similar to this with OEM vehicles when diagnosing odd lack of power problems.. I've also seen the effects of removing a restrictive muffler on tuned vehicles.. I don't think the exhaust is plugged, but rather a possible restriction. It takes time for the exhaust to back up in the system to a point where it becomes a problem.. so your lower/mid range stuff doesn't suffer.. but power falls off on the top end where there's a high amount exhaust volume.. I noticed he mentioned his external gauge matches is logs fairly close, which in an OEM diagnostic sense that's how you'd validate the sensor being good..

I agree with you, putting the stock MAF housing, stock MAF cal in would be a good thing to do first...I would put the stock MAP sensor back in as well.. I'd tune something safely with in those limits.. Then I'd put the other MAP sensor in, see how it goes.. Then try the intake.. If he hits a wall or some odd results, then I'd look at the exhaust as part of the problem..

I've done some stupid stuff experimenting with the tune on my car.. Setup boost cut to purposely hit, reducing Over boost throttle reduction limits to purposely limit my car to waste gate or below waste gate limits, I've used the Operating Load limits, Requested Load Limits to purposely limit my car anywhere from 1 to 2 load.. I live at sea level and watched how my BARO compensation tables really limited boost when driving up to the mountains, other stuff like this in order to get a better understanding on how the tables work and what kind of results I'd see.. Not once did I see knock freak out the way his does.. I did see the ECU pull fuel and start running lean..

[CrazyCanadian]

You're also getting quit a bit of knock which..

That's the ECU freaking out when approaching the boost limits (according to the sensor at least)...
As for the clogged cat/exhaust... usually the turbo will not build boost in such cases, but in his case the boost jumps a lot while the airflow doesn't. Even at idle there's a 3kpa difference compared to what we know the vacuum should be, and sometimes the manifold pressure would not change at all when starting driving, which is unusual. That's why I suspect it's the actual sensor and not a mechanical problem with his car (I would not rule it out, but for how this is what I think).

I've seen some interesting patterns similar to this with OEM vehicles when diagnosing odd lack of power problems.. I've also seen the effects of removing a restrictive muffler on tuned vehicles.. I don't think the exhaust is plugged, but rather a possible restriction. It takes time for the exhaust to back up in the system to a point where it becomes a problem.. so your lower/mid range stuff doesn't suffer.. but power falls off on the top end where there's a high amount exhaust volume.. I noticed he mentioned his external gauge matches is logs fairly close, which in an OEM diagnostic sense that's how you'd validate the sensor being good..

I agree with you, putting the stock MAF housing, stock MAF cal in would be a good thing to do first...I would put the stock MAP sensor back in as well.. I'd tune something safely with in those limits.. Then I'd put the other MAP sensor in, see how it goes.. Then try the intake.. If he hits a wall or some odd results, then I'd look at the exhaust as part of the problem..

I've done some stupid stuff experimenting with the tune on my car.. Setup boost cut to purposely hit, reducing Over boost throttle reduction limits to purposely limit my car to waste gate or below waste gate limits, I've used the Operating Load limits, Requested Load Limits to purposely limit my car anywhere from 1 to 2 load.. other stuff like this in order to get a better understanding on how the tables work and what kind of results I'd see.. Not once did I see knock freak out the way his does.. I did see the ECU pull fuel and start running dangerously lean..

[mituc]

That's the ECU freaking out when approaching the boost limits (according to the sensor at least)...

I totally agree with you from a hypothetical standpoint.
However, on fully stock exhaust, with both cats on, you need a pretty potent turbo to push that boost, and then at that boost the airflow would be close or above 300g/s around 5500rpm, while he is barely getting 260 which is on par with a factory turbo pushed hard, and the factory de-catted + unresonated exhaust he has.
And then at that boost and airflow running 12 degrees of timing around 5300-5500rpm will not work on pump gas unless maybe you are running 9.0:1 compression ratio pistons.
So having all these points of reference, my conclusion was that the airflow is about correct, and the boost readings are incorrect (inflated by a lot, at least 20kPa). Having to push that boost (about 23PSI boost or 260kPa MAP) and having such a low air flow would mean that the exhaust restriction is bad enough to cause misfires and bogging, while all he feels is the ECU logic kicking in and pulling timing because the reported boost values are close to or above the throttle reduction limits (there are spikes up to 317kPa MAP/31.5PSI boost on that log, ad only 250g/s of air at that boost simply doesn't cut it).