Like the title states, my 2006 EVO IX has been tuned and running well for quite some time, but recently began to run almost a full point more lean than it was tuned at. I am trying to figure out what could cause such an issue. Keep in mind this all occurred while it was still warm, so I am ruling out the weather. Things to know about the car.
full bolt ons in my signature below including a labonte methanol kit. At first I thought maybe I was getting less methanol due to an equipment failure, but pending answer from dan at labonte regarding some flow figures, I think I have ruled that out as well. So my thoughts are, possible lazy primary 02 sensor, weak dying walbro, lazy injector.

PLugs look good, no CEL, car drives just fine, but I cant figure why it would run fine and then all of the sudden go lean. Also worth mentioning, I can not recall if it went lean over night or if it was a gradual change. Any thoughts? thanks guys

 

Is it possible that its because of the weather change, its getting cold in NJ at this time of the year?

 

Read what he said, but it could be your walboro dying. How many miles on it/ how long have you had it?

 

I read a similar thread recently, and the filter sock on the fuel pump was the issue. Something for you to check.

 

Hmm I will check The sock for sure. The walbro gas about 48k and 4 years on it. Whinnying like crazy. But that's expected.


As far as testing the meth I know it's spraying because the tank empties. I still ha r to confirm it's spraying
Enough.

 

When was the tune? if you have proper logging equipt and are knowledgeable enough to flash the rom you can pm me ill fix it for cheap if its just AFR related.

 

also if you can hear your walbro in a evo with the back seats in then its gotta be the pump. id check it asap. the evos run a relay for open and closed loop for the fuel pump, at idle the fuel pump receives less voltages so it should not be heard in an evo really. I have 2 walbro 255's in my car and cant hear them unless i go outside and put my head under my trunk area.

 

Oh no no. I can hear it whine/hum while I'm sitting in the car at idle. And outside the car also...after flogging it a bit it also whines louder

 

Definitely swap it out and see if it stops. glad you caught it early.

 

i tuned a mostly stock evo a while back. he came back to me a few weeks later with it running 1 point leaner than i tuned it for. replaced the fuel pump, all good!

 

Also using EvoScan you can test the injectors 1 at a time. When selecting the actuator for each one make sure it's changing the AFR the same amount, that should rule out the injectors.

 

Our cars dont use the primary o2 sensor for WOT runs. So that should be ruled out.

Are the injector seals ok? No tears or cracks and are not leaking?

Make sure the FPR boost/vacuum line did not pop off and or is not torn/damaged slightly that could cause it too leak pressure.

If you can borrow a friends Walboro to test it out or have a spare/buy new one...


I've had similar issue. I changed my Walboro pump with a brand new one and it didnt make any difference. After double checking everything, I just came to the conclusion I was running out of pump for my HTA green and E85 setup in colder weather. I then installed a boost-a-pump that bumps the electricity to the fuel pump and my a/f is back to the same as tuned.

 

I'll check by the fuel
Pressure reg and surrounding lines. They looked ok upon my last inspection. I know I'm not running out of pump. It's 93 with 100% meth. But it was tunes and fine in the past cold weather so I don't think I'm running out of pump. If anything my stock Injectors at getting close to max

 

My guess is cold weather or fuel pump.

 

Verify if your meth pump flow & psi is okay.
Over time the pump seals get weaker using 100% meth.



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