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Discussion Starter #122 (Edited)
The annoying GR stumbles have come back after driving a while on big injectors. Prior to that, I was on stock injectors and didn't have the stumble. But when I did a bigger pump, the stumble showed itself and I purchased the IAP fpr stumble fix. It disappeared after installing it and got more smooth after zeroing out the load comps. I read up on the latest findings from Cobb tuning and Injector Dynamics about intake resonance also contributing to the stumble. I decided to look into this and proceeded to go to the auto parts store and put together my own. It was unsuccessful. After following the instructions from Cobb and the Injector Dynamics video on resonance and the sound theory they had brought up, I decided to do go the complete opposite. The organ pipe theory sounded good, the shorter hose theory, also. But I got to thinking that rubber is used as a damper as its all over the car such as motor mounts, air box mount, transmission, etc and some cases the fuel line. Some folks found that adding a long 3ft fuel hose fixed their stumble. So the long hose on the fuel system dampened the resonance, it should do the same for the intake resonance that's causing the fpr to fluctuate, which causes the fpr to a lean fire condition=stumble. The hose is short already from the factory. To get an even pulse from the intake manifold, I kept the hose intended by Cobb tunings findings and cut a fpr vacuum hose to about 10-12 inches. Stumbles are gone.
 

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Discussion Starter #124
I drive to work this morning and ran in in all gears in the stumble area. When I did the Cobb reference relocation, I had the stumble much worse than the stock location vacuum source. So bad that I had a CEL for #3 cylinder misfire. I noticed strong fluctuations in my boost gauge in the stumble area. I went with a long 12" vacuum hose and kept the vacuum source at the bypass valve. Stumbles are very faint, but much more smoother than the short 2-4" hose (experimented from 2" to longer) and tolerable. I then added the Ixiz Concept ixizMADblk and keeping the fpr vacuum hose 12". I drove in the stumble area again and my boost gauge once again registers smooth build in boost and no fluctuations! Stumbles gone!
 

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Discussion Starter #126
I replaced my old scratched up lug nuts with black ones from Gorilla. I like how the wheels appear to be bigger with the 255 40 18 Bridgestone and the appearance of depth from the lug nuts.

 

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Discussion Starter #128
As the car ages come the vacuum leaks. There are probably more, I'll have to look at ever intake manifold vacuum port. At least the car runs better, for now.
 

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Discussion Starter #129
I added some clamps and zip ties to all the 6mm vacuum hoses and noticed the a/f correction dropped down to -10 and steadily adjusted itself to zero at idle. Feels powerful again and no smoking from the tailpipe. The evap solenoid #1 was the hardest to get to so they got zip tied. Everything else is clamped. I need a retune considering it was tuned with the vacuum leaks not known at the time. I guess Subarus are prone to vacuum leaks. I also went with the Prova AOS. It was an easy 5 min install and my intercooler is clean again. It didn't cost as much as the other AOS I had and it doesn't have all the crazy vent hoses going all over the place, it works as advertised.
 

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Discussion Starter #130 (Edited)
Fixing vacuum leaks is a very tedious process. I had a/f learning 1 as high as 20%. I proceeded to clamp down all the vacuum ports on the intake manifold and found another leak at the vacuum hose to the bypass valve. Right now, it's at 14%, plugging up the leak at the bypass valve dropped it down to around 8%. So many vacuum leaks!
 

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Discussion Starter #134
The NGK spark plugs didn't last long. I gapped them to .025" and they are a year old and 18k miles. The gap enlarged to almost .030"! It had been misfiring in the #3 cylinder and I decided to go with Denso iridium IKH22 and gap the to .023".
 

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Discussion Starter #135
#3 cylinder misfire is still there, but not as bad with the new plugs. I went ahead and replaced the #3 cylinder ignition coil. Test drive tomorrow while driving to work.
 

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Discussion Starter #136
Misfire is still there. I removed and clean off the crank position sensor and it smoothed it out a bit after ecu reset. I need to drive it more to see if it's relearning the stumble. I do have a new O2 sensor to install. Hopefully it fixes that and improve power, response, and fuel mileage.
 

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Discussion Starter #137
The new O2 sensor brought back some pep. I need to drive it more to see if it reverts to misfiring again. It has better throttle response and part throttle power. It looks promising. So far, it seems like the old O2 sensor was a little lazy as it did not set off a CEL for the O2 sensor.
 
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