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Author Topic: Hesitation, Cold Idle, & Mileage Issues  (Read 2936 times)
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m3nate
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Posts: 8


« Reply #15 on: August 29, 2016, 03:41:09 PM »

Hi everyone, 

Quick update from the weekend.  I discovered that the "shudder" i'm hearing on shut down is actually a baffle letting go in the CAT of the Flyin' Miata downpipe.  It's getting worse.  Definitely no vacuum leak.  Checked multiple ways with the test procedures outlined here & with the propane/carb cleaner methods. 

Got gas this morning - 17.9 MPG last tank.  The really bad idle & bucking issues are centralized to when the car is cold & clear up somewhat once it warms up.  Could the loose baffle in the CAT be the root cause of these and the mileage issues?  Thinking that if the exhaust is X% plugged, it may not throw a code, but might not perform well, especially when cold.
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SilverMiataRacer
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« Reply #16 on: August 29, 2016, 07:38:57 PM »

A clogged cat will produce poor performance and therefore poor gas mileage.  Cat failures are not normal and usually are caused by things like driving the car with a failed coil pack or aq poor tune running it excessively rich.
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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
m3nate
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Posts: 8


« Reply #17 on: October 01, 2016, 01:53:34 PM »

It's been a while since my last update as I encountered some issues changing out the mid pipe...broke a couple of exhaust studs and had to get some new ones put in at the bottom of the header.  I've tried a bunch of things and the problems are still persisting and are getting worse, primarily the hesitation.  The car is missing at idle and clearly up through the rev range as well, but I've got no CEL.  Here's what I've done since the last post.  Any additional guidance would be most appreciated.

1. Changed the mid pipe to get rid of the CAT baffle issue. - No change in performance
2. Changed plug wires - no difference
3. Changed plugs  - no difference
4. Changed TPS - no difference.
5. Changed both O2 sensors - I damaged one during the removal of the exhaust.  No change.

I also got an OBDII reader that does data, which has lead me to 2 things:

1. The TPS sweep readings are strange.  At 0 throttle the TPS reads 11% in the data, and at full throttle it reads 74% throttle.  > This was consistent with both the new and old TPS, both are OEM parts.   Can /should the throttle body be adjusted to fix this?   Could this cause the issue?

2.  The rear O2 sensor is reading 0.00 volts all of the time.  >  This is the Bank 1, Sensor 2 readout.  I never get voltage on it.  Have replaced the sensor and this is the same.  It is connected under the drivers seat, but I'm not getting anything.  Could that be causing it?

Other than that I'm stumped.  The cars performance is degrading over time but I have no CEL to track down.  I would think that a miss or a bad O2 reading would trigger a CEL but I'm not getting one. 

Thanks again in advance.

- Nate
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SilverMiataRacer
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« Reply #18 on: October 01, 2016, 02:11:30 PM »

As far as your O2 sensor. 

First things first.  The rear sensor has zero effect on running the car.  All it is there for is to keep track of the Cat to make sure it is working.  As for getting a zero voltage reading but no code.  That should not be happening.  If the voltage is zero the ECU should be generating a P0140 code.  So there is something wrong with your reader checking the codes.  But again this has nothing to do with any other problems you are having.

Second the TPS voltages.  I'm not sure of the exact voltages but they are never zero percent and never 100 percent so I don't think you have an issue there either.

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Larry

4 Miatas but who's counting!!   Cool

White Knight    1991 Crystal White   #99 CSP
Silver Bullet     1992 Silverstone     #17 SM2  FM I+ Turbo  (Gone but not forgotten)
Honey B          1992 Sunburst Yellow #99 SM2 J.R. M45
Whooosh         2004 Titanium MazdaSpeed MX5  #403 of 4000
Subie              2006 Steel Gray WRX STi Cobb Stage 2 (Gone but not forgotten)
No name yet    2008 Velocity Yellow Tintcoat Z06 Corvette
No Name yet    2014 Ashen Grey Metallic Camaro 2SS 1LE

“There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.”
– Ernest Hemingway
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