Odd tip-in hesitation - any help would be appreciated! - Mazda3 Forums : The #1 Mazda 3 Forum
 
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post #1 of 4 (permalink) Old 12-16-2018, 11:42 PM Thread Starter
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Odd tip-in hesitation - any help would be appreciated!

First off, I'm not usually the type of person to ask to be spoon-fed on car forums, but I'm a bit stuck here, very short on time, and very short on money. I'm sorry if this is a basic issue and I'm simply overlooking the obvious. I've search high and low and I can't find anyone having exactly this issue.

Car is a 2007, 193k miles, 2.0L, manual, California emissions, only mod is Injen short ram and this was happening before I installed the intake.

The issue: intermittent hesitation at tip-in when the car is warm. I have no issues with idle at any temperature. The car runs great first thing in the morning and/or after sitting for a while. It also runs great when I'm giving it a high-rpm thrashing. Gas mileage seems normal. The car doesn't feel like it's down on power at all. No check engine light at any point.

Things already done with no difference:

- New plugs
- New upstream O2 (like I said, money's tight or else I would have done all 3)
- Cleaned MAF
- Replaced MAF
- Capped off purge valve
- Disabled IMRC (always open)

Could this be a faulty EGR valve? I'm just trying to think of things that only happen when it's warm. I'm pretty sure that things like the purge valve and EGR valve remain closed until the engine is at operating temperature.

Any help would be appreciated. I've already worked out so many bugs in this car and it's almost perfect. I'm just trying to get this thing 100% soon. My wife and I are expecting a daughter by this time next month and if it's not fixed by then, it may never be, haha.

'07 Mazda 3i
Previously driven by sensible wife, now being modded by gearhead husband. Uh oh...
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post #2 of 4 (permalink) Old 12-17-2018, 02:14 AM
mrb
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$10 part -

A bad PCV valve that doesn't close properly might allow the entrance of oxygen into the combustion chamber, which results in dilution of fuel and air, causing the buildup of pressure in the exhaust. This could cause the engine's performance to suffer, or it could even cause the engine to stall out.

if you haven't replaced it yet.
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post #3 of 4 (permalink) Old 12-21-2018, 01:04 AM
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Quote:
Originally Posted by jennyzoomzoom View Post

Could this be a faulty EGR valve?
Very possible. The symptom could be due to a intermittent EGR opening at tip in causing a dilution problem with the air/fuel ratio mixture. Have seen EGR's cause surging on various makes and models over the years. Seems like I have seen them cause this issue also, although I don't remember a specific case off hand. To verify, loosen the EGR from the block and insert a cut piece of a soda can (because it is thin) between the EGR and block making sure to cover the port thereby blocking all EGR flow and then tightening it back up. If it is the EGR, then the symptom disappears. This EGR opening is usually caused by a weak return spring allowing the EGR to open under strong intake vacuum even though it isn't being controlled to open by the ECU. Hope this makes sense and I hope this is the issue.

Congratulations on the coming baby girl!

Jesus Saves

Last edited by rickkari; 12-21-2018 at 01:14 AM.
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post #4 of 4 (permalink) Old 12-21-2018, 01:09 PM Thread Starter
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Location: MA
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Thanks so much for the help and the well wishes!

I've done some more investigating in the past few days with my scanner, trying to find ANY clues I could get. I may have found one! My LTFT has been around -15. When I watch my STFT during tip-in, it stays at 0.0 whenever it hesitates, then shoots up to a high positive number as soon as the power kicks back in, like it's trying hard to "correct the correction".

For the hell of it, I looked up diagnostic steps for a P0172 since it looks like I'm apparently not far from it (I believe -25 LTFT will give you that code). MAF, EGR, purge solenoid, and fuel pressure are all mentioned. Since the purge valve is easy, I did the same thing as before and capped off the vacuum port at the manifold. No significant changes in LTFT that I could see. Next is to start messing with the EGR I guess. I don't have any great way of tee-ing off the fuel line to check fuel pressure.

This car has done this to some degree as far back as I can remember (car has been in the family since 2010). My last car had no drive-by-wire, no VVT, no variable intake manifold, and no MAF, so I just assumed that cars with all of those things just didn't drive as well. Kind of the old "they don't make 'em like they used to" mentality. But I think something is actually wrong here. It's never thrown a code related to it though. More chasing I guess.

Great suggestion about the soda can. I was discouraged to see that there's a coolant line through it (and another annoyingly in front of it) preventing me from simply blocking it off entirely. Slipping some thin aluminum in there is a great idea!

'07 Mazda 3i
Previously driven by sensible wife, now being modded by gearhead husband. Uh oh...
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