[SOLVED] Light Throttle Hesitation/Hiccups/Surging

[Brado]

Year/Make/Model: 2008 Mazdaspeed3
Mileage: ~165K chassis / ~5K motor
Location: Arizona
Concern: Acceleration feel under light throttle
DTC's: None
Modifications: Stock block, BNR S3V4, 3” intake, catless DP, 3” exhaust, etc.
ECU/Tuning Software: Cobb Accessport V3
Tuner: DramaTuned
Is the concern intermittent? Yes, but happens often.
Can you duplicate the concern? Yes
Recent Repairs: Too many to list
Correction: Newish build all together.

Hey everyone. I have a longtime issue that I want to finally poll the community on as I only recently discovered it wasn’t considered normal.

When I’m accelerating and giving the car light near constant throttle, often times I’ll hear the turbo spool up in this tiny amounts and then back off. It’s hard to explain but it feels like if I were to just blip the throttle momentarily or something.

Similarly, there are times when I shift into the next gear and give some light throttle only to feel like the car has hit a sort of wall. Similar to if I turned on the AC compressor or something.

This has been the way the car drove for as long as I can remember, and I have always chalked it up to just the drivability of the Speed3. Well I finally reached out about to my tuner about this and he said that’s not normal and it should be really smooth.

This got me curious and excited, as I’ve always wanted it to be as driveable as say an NA car under daily commuting.

So far all I’ve done is get a bunch of data logs where the hesitation happened and have tried switching my HKS SSQV to recirc as well. While recirc definitely helps with drivability, I still felt and heard the spool/intake noises fluctuate under light throttle accelerations. I swear sometimes it’s like a few psi and then with what feels like the same throttle it just spools up and I’m not even trying to get into boost. It’s not very predictable or consistent and it can be frustrating.

So I’ve ruled out it being an issue with running a VTA setup. The motor, HPFP, PRV, turbo, are all brand new so I’m left with little to really change it seems.

After doing a bunch of reading, I was thinking it could be one or more of these:

• Bad O2 sensor
• Purge valve
• Vacuum/boost leak

I have also attached two datalogs that were when the hesitation happened. Looking at the throttle position I can see it open a bit at seemingly weird times, which may be why I am feeling hiccups, but I can’t pin why. The O2 readings fluctuate but I’m told that’s normal.

I’m a bit lost on what to do next here, but I’m super excited to get this sorted!

 

[Rokusek]

Wastegate duty %, LTFT, STFT and injector duty cycle right here... Whats going on there?



Any idle issues? Without an idle issue, idk if o2 sensor, purge valve or vacuum leak would be a huge concern. Still a concern none the less.

What has your tuner said?

 

[Brado]

Wastegate duty %, LTFT, STFT and injector duty cycle right here... Whats going on there?

View attachment 22333

Any idle issues? Without an idle issue, idk if o2 sensor, purge valve or vacuum leak would be a huge concern. Still a concern none the less.

What has your tuner said?

No idle issues that I’ve noticed.

Tuner has said that he thought it was likely plug related. I had mine gapped at .026 and went down to .024 to check. No difference. He also said it could be a leaky BOV, bad or dirty O2 sensor, dirty MAF sensor, filter, etc.

I have cleaned the MAF and the filter is brand new. I haven’t tested another MAF, but that’s something additional I could try. I don’t know if the O2 sensor has ever been replaced either. I haven’t done any boost leak testing, but the BOV flange is welded and I replaced the c-clip within the last 2 years.

As for the logs, I’m not the best at making much from them. I just noticed the AFRs seem to dip intermittently and figured that was caused the car to open the throttle plate and get more air since it read richer. My best guess was it was the O2 sensor starting to go.

 

[Rokusek]

No idle issues that I’ve noticed.

Tuner has said that he thought it was likely plug related. I had mine gapped at .026 and went down to .024 to check. No difference. He also said it could be a leaky BOV, bad or dirty O2 sensor, dirty MAF sensor, filter, etc.

I have cleaned the MAF and the filter is brand new. I haven’t tested another MAF, but that’s something additional I could try. I don’t know if the O2 sensor has ever been replaced either. I haven’t done any boost leak testing, but the BOV flange is welded and I replaced the c-clip within the last 2 years.

As for the logs, I’m not the best at making much from them. I just noticed the AFRs seem to dip intermittently and figured that was caused the car to open the throttle plate and get more air since it read richer. My best guess was it was the O2 sensor starting to go.

O2 sensor is possible. It's the fuel trims and wastegate percentage that makes me question the o2 sensor... But no idle issues... What DP do you have?

 

[Brado]

O2 sensor is possible. It's the fuel trims and wastegate percentage that makes me question the o2 sensor... But no idle issues... What DP do you have?

I’ve got the eBay catless downpipe which I believe is “Manzo” brand.

For fuel, I’ve got injectors that were recently serviced, but even then I’ve felt this hesitation for a long time.

 

[Rokusek]

I’ve got the eBay catless downpipe which I believe is “Manzo” brand.

For fuel, I’ve got injectors that were recently serviced, but even then I’ve felt this hesitation for a long time.

Even before the DP? With the time your saying this has been going on... O2 would have failed already, same with purge valve.

Old vacuum leak that hasn't been discovered yet???

 

[Brado]

Even before the DP? With the time your saying this has been going on... O2 would have failed already, same with purge valve.

Old vacuum leak that hasn't been discovered yet???

I bought the car with the downpipe installed. I’ve never driven it on anything else aside from OEM motor mounts which I replaced with Damond. I rebuilt the car with the same parts if they were presumed good, so ifs possible there’s a vacuum leak somewhere that I never did find. Im not sure where to check first as the only soft vacuum lines I have are for boost. The others are hard lines, correct?

 

[Rokusek]

I bought the car with the downpipe installed. I’ve never driven it on anything else aside from OEM motor mounts which I replaced with Damond. I rebuilt the car with the same parts if they were presumed good, so ifs possible there’s a vacuum leak somewhere that I never did find. Im not sure where to check first as the only soft vacuum lines I have are for boost. The others are hard lines, correct?

You have the two lines under the manifold for the pcv system, which you've replaced, soft vacuum lines for boost and hard lines for fuel tank pressure (purge valve). Hardline from VC to Intake... Softlines on the vacuum box on top of intake manifold.

For shits and giggles... Do you have an option to swap the DP?

If the bung on the DP isn't in the right spot, too close into the pipe or to far out, too close to the turbo or too far away, that could cause problems. Unlikely, but a potential thing to look at.

Highly unlikely as those eBay pipes are (dare I say)... Solid for the most part. But something outside of the box to consider. Especially at this point.

 

[Brado]

You have the two lines under the manifold for the pcv system, which you've replaced, soft vacuum lines for boost and hard lines for fuel tank pressure (purge valve). Hardline from VC to Intake... Softlines on the vacuum box on top of intake manifold.

For shits and giggles... Do you have an option to swap the DP?

If the bung on the DP isn't in the right spot, too close into the pipe or to far out, too close to the turbo or too far away, that could cause problems. Unlikely, but a potential thing to look at.

Highly unlikely as those eBay pipes are (dare I say)... Solid for the most part. But something outside of the box to consider. Especially at this point.

I have also heard the eBay downpipes are solid. That said, getting it back on the car was a pain in the ass. Ill start with checking for vacuum leaks at the points you mentioned.

I can try and get a picture of the bungs as well. I wasn’t aware the placement was that important.

Some things to check! Thanks!

 

[Rokusek]

I have also heard the eBay downpipes are solid. That said, getting it back on the car was a pain in the ass. Ill start with checking for vacuum leaks at the points you mentioned.

I can try and get a picture of the bungs as well. I wasn’t aware the placement was that important.

Some things to check! Thanks!

Absolutely man. You absolutely have to think outside the box in these cases. When you think it's not possible to be related... Somehow it is.

Shit... Maybe even the PCV valve... Worth a look.

 

[Brado]

Alright updating this as I think I may have fixed my issue. Upon breaking a vacuum line to the turbo due to heat from the exhaust manifold, I decided to run new vacuum line and also replace the PCV hose from the valve cover to the intake. Upon doing these repairs, the car no longer has this issue and partial throttle boost holds consistent without any weird fluctuations.

If I had to guess, I would lean to say that it was the PCV hose that came with the car, and replacing it with new hose and a fresh clamp nice and tight probably sealed up a leak after the MAF that I wasn't aware of prior. In any case, check your hoses and clamps no matter how tight they might look because the drive-ability is 100% better now and I'm blown away by how smooth the throttle response is now!