Why so lean

[Vlad Busta]

Hey there guys and gals I'm having problems tuning.  A little background on the car:

91 Eagle Talon Tsi
94 Chevron Octane all the time
No intake leaks up to 20 psi
255 ltr/hr hp fuel pump
Spooling up fpr set at psi without the vacuum hose connected
new 650 injectors from Kinetic (Thanks Ryan!)
2G Mas
knob afc
stock smic
3" intake tube
2.5" upper and lower ic piping
TMO stage 3 chip
HKS 264 regrinds

My afc settings are 26 for 900 RPM, 28 for 2400 RPM, 26 for 4000, 6 for 5200 RPM and 8 for 7000 rpm.

My question is why do I have to add so much fuel to get the trims right?  I've tried to swap out the TMO chip with the stocker and that didn't help.  The mas checks out OK, the baro and intake temp sensors are OK and it reads 37 hz to 45 hz at idle.  The fuel pressure at idle is solid.

I'm thinking that it's the O2 sensor that is screwed or maybe I need to take a look at my timing belt to make sure everything lines up properly.  Does anyone else have any ideas?  

I know it's rich because at idle I checked under the hood if there was a leak near my injectors and my eyes started to water.  Plugs are not fouled though, they are tan and clean.

I'm not worried about WOT runs, just gotta figure out why so much fuel is needed for the low trims to be around 100 to 110.

[John Novo]

I was running lean for a while too and couldn't figure it out either. Finally the CEL came on for the O2 sensor. I replaced it and everything is fine.

The bad one was an OEM O2 sensor which didn't last that long and I didn't use race gas either. I replaced it with a Plug-n-Play Bosch sensor.

[John Hartman]

Vlad, set at what PSI?

also if you are getting gas fumes at the injectors, you should fix that up.

fuel filter plugged?

fuel line under the car kinked/dented by rock?

are you using the stock B&M pressure guage fitting?  I found mine to have a really small passage in it, like half the size of the stocker and drilled it out.  Had to change my safc settings after I did that.

Also, try running it leaner anyways, when I run my car at 100 - 110% on the trims, it has poor throttle response and crappy mileage.  Try running it at 120 or 125% on low and med trims.

Check for broken/cracking lines on the pressure regulator/solenoid/boost guage lines etc.  If one of those is leaking you will have diffferent pressure than you might want, and fluctuations that are hard to tune with.


Best of luck, you know more about this stuff than I do, so I'm just throwing some ideas out for you to try.

[Vlad Busta]

Swapped out the O2 sensor and that wasn't it.  Forgot to mention that my 2G mas has both side honeycombs removed.  I fabbed up a blockoff plate for one side and now the AFC setting for idle is at +2 instead of +26.  I figure this is a good start and I'll see if I can start tuning it.  If I do run into MAs overrun then I'll remove the blockoff plate and look for my problems elsewhere.

John, I'm running 15 psi right now.  No gas fumes from the injectors, it was a crack in my downpipe letting exhaust fumes come up into my face  

I have the stocker banjo bolt drilled out and threaded for the B&M gauge so there's no restriction there.  The fuel filter was replaced last year so I don't think it's that.  Maybe a kinked line, I'll have to check.

I'll do some tuning with the blockoff plate and see how it goes.  I'm thinking not having the honey combs on both sides bypassed a bunch of air and in turn was causing the car to run really lean.

We'll see.

Thanks, Vlad.

[John Hartman]

o god yea.  When I first put in my 2g maf, I was trying to think ahead.   :roll:

I took out the lower and side honecombs, screwed out that screw flush with the bottom, and did some dremel work.  Just some smoothing basically but some anyway.

I had to put my safc at +45   :shock:   Just to get it to idle!!!

These things don't behave the same way as a 1g maf at all.

I just put the lower and side HC back in and it ran well at between +1 and +6, with my old injectors.

[Chris Andrews]

There is simply NO GOOD REASON for removing ANY honeycombs in the 2G MAS.

Now put on the dunce cap and go sit in the corner.

Stupid kids.........

[Vlad Busta]

It was stupid of me to buy the 2G Mas without looking at a picture of it.  Oh well, when I got it there were no honeycombs but buddy assured me it would run OK.  Yah right  :evil:

Got some honey comb from Lowell and put the main and lower ones back in but wasn't able to shape the sides well enough.  

Block off plate on one of the side passages seems to be helping now.  I've got my nobber settings to 2 -8 -12 -10 -8 for now.  Gotta get out there an tune it some more.

Thanks for all the suggestions guys, much appreciated!

Vlad.

[John Hartman]

hey as long as my dunce cap is made of aluminum foil