Ok, so my poor Evo is a mess right now and im going insane trying to figure out what the deal is. I've always had this strange lean 'hop' from 5500rpm until redline. Wideband shows 11.2-11.5 afrs and then right at 5500rpm it jumps to 12.1 until redline!? A month or so ago i dynoed at 340whp/325tq on a mustang dyno even w/ this strange afr w/ zero knock. So since i couldnt fix it (neither could my tuner) i just left it. Now that winter chill has come... im knocking like mad from 5500rpms and up. Im sure its got to do w/ the lean condition in that area. Now no matter how much fuel i throw at it using ECUFlash, it will not richen up?! Its weird... So im thinking its NOT the tune? I am leaning towards a hardware issue now. BUT i have NO check engine lights, ever. I changed the walbro fuel pump to a new one just in case, nada... i even got my injectors cleaned/balanced at RC engineering, nada... problem still there. I've had 2 top tuners give me flashes and still unable to resolve the lean hop at 5500rpm. (yes i made sure to use the evo fit pkg for the walbro pump and made sure it was snug) nada...

So... im at my wits end... Is/are there any other fuel related hard parts that could have failed w/out triggering a check engine light? what changes at 5500rpm that doesnt happen anywhere else? I know there is a factory rising rate solenoid linked to the stock regulator... does this solenoid activate at this rpm? can it fail causing this problem and perhaps not increasing my fuel pressure correctly? im grasping at any possible scenarios... but im sick of replacing all these parts dont do squat... if anyone has an educated guess or has run into this similar issue... pls chime in. Heck... i'll paypal the first guy w/ a cure (that works) 100bucks for your troubles!!

Thx guys!

-Tom

 

if its not richening up, u need bigger injectors....

 

stock turbo, 93 pump at 24psi... IDC dont go over 95-97% at the most. Injectors are fine. In fact better than stock since i just got them balanced/flowed at RC and the printout shows flowing a true 560cc now (stock they are grossly unbalanced). This also happens when i turn the boost down to 20psi. Now if i get crazy on the fuel increases it will slightly richen up, but it shouldnt need to that much fuel to richen up .5 afr point. Its not the tune i'm sure... as it was fine a long time ago... and nothing in the tune suggests it would cause this. Im convinced its a hardware part that im not aware of. Again, fuel pump and injectors have been changed... im almost about to put in a stock pump just to see what happens....

 

im thinking its one of these... or possible a combo... only things i havent replaced yet that have an effect on fuel delivery.

1) the MAF
2) fuel pressure regulator and/or the solenoid that alters pressure

so if anyone has any ideas worth tryin... im game... lol

 

dang... noone?... LOL... guess this is hopeless.

 

well.... so i put in some Lucas Oil Octane Booster (i heard its the only one that actually works) and woolah... my knock is totally gone. Interesting... So this rules out any false knock triggering my knock sensor i suppose. Ok, so its real knock for sure. BUT i've had previous dyno runs w/ this tune and zero knock (very safe tune) so im wondering what happened? If there was a boost leak, wouldnt it still register knock w/ the octane booster in? (im doing a leak test this wknd) My friends say its bad gas... but its been going on for 3 full tanks at 2 different Shell gas stations in my area.

 

Do they oxygenate gas (winter blend) in TX? They do it here in the north. Causes the same problems for me in terms of knock v. psi.

 

Cars act differently in real word conditions vs. being strapped to a dyno. Maybe this is part of the equation

 

so if its still running lean and the tuner added fuel and the afr's are not getting richer... its most likely a fuel pump.

 

well i ran a walbro 255. i just replaced it w/ a new one. Nothing changed. My injectors were cleaned/balanced by RC... nothing. Its still dipping lean right at 5500rpm no matter what we do to the fuel. Funny thing is if you go crazy and richen it up like mad, it will richen up, but the "dip" to lean is still there... it just kinda brings it all down a bit. But after a few runs, bam its back to 12.1 again. Its frustrating... The octane boost seems to just allow me to run the 12.1 afr above 5500rpm in the current state im in. I used to be able to run on 93 just fine... so im taking that 'oxygenated gas' into consideration. I have no idea if they do that in Texas... but my car is definately running like crap since winter came upon us... A bunch of Evos actually are popping and having tuning issues in Houston (not all, but i've counted about 4 in my area). We are all tuned by different people also... i dunno. Adding fuel or retarding timing just makes the car run like crap. And doesnt get rid of all the knock. The ONLY things thats been curing it is higher octane. I think i have 2 issues
1) something is failing and causing the lean spike at 5500rpm. (what else in the fuel sys can fail? any sensors? regulators? what about that solenoid w/ the vacuum line from intake mani?)

2) fuel... something is up w/ the fuel...

 

Do you have the install kit installed with the fuel pump? Are the O-ring and collar on the pump as well?

 

Hi John,

Yes i have the walbro w/ the evo install kit. I have the collar on it, but no O-Ring. I couldnt see how it would work. The pump just slid into the rubber inside the female inlet on the pump housing. It fit snug and tight. Barely put back the end plastic cap that held the pump secure. The only things i really used from the kit is the bottom rubber piece for the bottom of the pump. Can someone send me a pic of how its supposed to look like?

 

John, nevermind... i did an install how to search and read up. Looks like i maintained the stock rubber insert seal in the outlet like the how to advises. Im guessing, you are recommending me to pull out the stock rubber insert which would allow me to use that plastic cap w/ O-ring that came in the install kit. Could that be a reason why it leans out after 5500 rpm? if this fixes my problem... i swear i'll paypal you 100 bucks, lol... ive been battling this for a while!

 

w/ the cap on the end, the O-ring right behind it... that spacer thing isnt long enough to keep the O-ring from moving back/forth. What am i missing...

 

ok what im doing is playing w/ my spare walbro (before i yank the one in my car, because its a biotch w/ that ring etc). So i want to understand fully before ripping it out again.
I used the thicker isolator for the bottom of the pump to make it fit snug. And it does. Its using the new filter also from the kit. The ONLY thing i re-used was i left the stock rubber insert for the top inlet and i re-used that collar/spacer thing.

I didnt use the O-ring and end cap, because i couldnt figure out how to. so i just used the stock setup for that end. I assumed the cap goes over the end of the inlet, w the O ring right behind it. The collar after that... but the O ring slides back/forth. It doesnt seem right like that?