I have a 2005 Evo 8 with about 100,000 miles on it. Just recently the car started stuttering/missing with knock at WOT with a really rich AFR between 8-9.8. But the car still idles fine and cruises fine with a AFR around 14.7. As soon as it builds boost even from 3000 the AFR dips below 10 and stays there and starts knocking. I don't even have to go WOT or build boost, just give it about half throttle and the AFRs will go to the low 10s. The car was running just fine before this.

Changed plugs to brand new NGK BPR7ES gapped at 0.024. Didn't help.
Checked for boost leaks and didn't find or hear anything.
Disconnected battery trying to reset fuel trims. Didn't help.

Mods are:
Tephra mod V7
Perrin Intake
Catless Catback Exhaust
AEM 320 Fuel pump
AEM Tru Boost EBC
Innovate LC-1 Wideband

Could I have a sensor, coil pack, or something fuel related going out?

 

Boost leak test?

 

Yep, checked for boost leaks and pressured it up to about 18-20 psi. I didn't hear anything but the pressure slowly dropped over a few minutes.

 

What about at 25psi? If its tuned, it's makeing more than 18-20psi of boost.

 

Did find out what the issue was?

 

Didn't pressurize it to 25 yet, Ill give that a try tomorrow and report back. The car hasn't been properly tuned yet, so I have been keeping it around stock boost.

Still haven't found the problem, but I have been doing some reading about fuel pressure regulator issues. I wonder if my AEM 320 fuel pump has started out flowing the stock FPR in boost?

 

hmmmm, front o2 sensor going out?

 

Just seen this thread:

https://www.evolutionm.net/forums/ec...i-do-maps.html

I think this may be the same problems that I am having. I just checked lines from the FPR and no gas in them, so I dont think its the FRP but I dont have a fuel gauge or adapters to test it.

Also, I just noticed that my return line has started leaking and dripping at the small rubber hose under the car that connects the hard line from the car to the tank. I wonder if its leaking because of high pressure in the return line?

If my return line is clogged, how would I unclog it?

 

I would hook up a fuel pressure gauge, and go from there, that would help determine if you have a clogged return line. is there a CEL present?

 

It was definitely a clogged return. I pulled the hose off to see if I could blow through it and hear bubbles at the tank, but I couldn't. Hooked up my air compressor and tried blowing air through it at over 100 psi and couldn't.

Traced the clog back to the hard line that is bolted to the tank, so I bought 2 feet of fuel line and bypassed the hard line and that fixed the problem.

When the pump switched to high voltage, it must have been overrunning the injectors from the buildup in pressure. I need to get a fuel pressure gauge for future reference.

 

i love happy endings

 

Can someone post a picture of the return fuel line I'm having this same issue?