Running lean, what's the problem?
 

https://www.evolutionm.net/forums/sh...d.php?t=135775

that's the dyno graph with the a/f.

I have Turbo back exhaust without cat, (3'') that has 2 resonators built into it.

MBC, 21 psi daily.

stock everything else. stock ecu, never been flashed... except for the dealership flash to get rid of the p0300 misfire bs.

Now, I'm running that lean, what could be the problem?

injectors, fuel pump, spark plugs, ignition coils? what the hell is causing this?

I have 40,000 miles on stock plugs so far. Those iridium stock plugs are good for 60,000 miles. anyway...

I did get a dealership flash, but I was suspecting they didn't know what the hell they're doing, since they were refering to the manual.

anyhelp would be great.

that's the problem, man...you can't expect to run 21 psi and not run lean. You're cramming in more air than you have fuel. You need to have your ECU tweaked to allow more fuel to get into the cylinder - then you won't have that problem. Just ship your ECU out to Dynoflash and have them do the $200 mail-in tune for your mods. You won't regret it.

Plus you are running a 3 inch exhaust right? That will also cause a leaner condition.

yeah, especially with an untuned ECU. Basically, any mods you do to increase air flow into or out of the engine requires upgrading or tuning the ECU fuel map to compensate for those mods

Log it.
If the ECU is not pulling ignition timing, your not knocking. If your not knocking it's fine. What do your EGT's say?

EGT says nothing, since I don't have it.

but here is the thing, we turned the boost way down to 19 psi, and it's still in that same curve at that same place...

From what I've noticed, you tend to run richer when you put 3 inch exhaust in, correct?

what is your reasoning behind thinking that?

what is your reason behind asking me that?

because that's what I saw on baseline dyno from other evos. On the topic of exhaust making it run richer...

but I'm here to get some info. I can't seem to find any non-tuned dyno charts with an exhaust on this board.

Untuned with your mods running that much boost...bottomline, you need to be tuned.

I don't think that's that much boost from stock setting, where most of the time, it'll boost peak at 21 psi + before tapering down.

On a colder days, i use to peak at 23psi without the MBC.

Bottomline is I do need to be tuned. But that's the easy and painfully obvious answer that noone asked. :rolleyes:

I want to find out what's causing this effect.

i don't know... i always though freeing up the exhaust made your boost pressure rise slightly... making you run lean... but you have a boost controller so that changes the story alltogether anyway. so why would you expect the stock fuel curve to be normal if you're running more than normal boost pressure?

the spikes you talk about are normal... your susutained boost pressure is not. spikes don't really require matching a/f because they're momentary (unless you're getting a long spike with taper because your stock turbo is being pushed to the limits and runs out of breath, but that's a different kind of spike).

why are you all worried about it all of a sudden? you were driving fine before right? you should have checked all this stuff before you turned up the boost.

this isn't something that lowering boost cures. and I'm not worried.

I'm just curious. I ran fine all this time and I didn't get knocks and my engine didn't blow up .

and honestly, this isn't due to the turning the boost up, so don't say "you should have checked all this stuff before you turned up the boost".

I dynoed both with the boost at 23psi and at 19psi, the A/f wasn't even different from each other. Same curve same location. maybe 0.1 difference from lowering the boost down 4 psi.

I just want to figure out why this is happening.

I almost think that the MAF sensor might be dirty or have oil on them...

Swapping in a larger exhaust may cause the fuel mixture to go lean.

Why is this?

Because the larger exhaust allows for better scavenging and better VE at higher engine speeds. The ECU doesn't see much of a change because it is in open loop mode at WOT, and therefore will only adapt to whatever it sees in closed loop operation and apply those settings globally.

Nevertheless, the A/F graph does seem to reflect a rather large deviation from the factory curve. If the exhaust is solely responsible for this deviation, it's a rather stark indicator of what type of difference a large exhaust system makes in this application.

The mileage you stated for the iridium plugs are good for average driving under lower boost. I would reccomend changing your plugs for starters. Cleaning your MAF sensor won't hurty anything, plus its free. Check boost source, maybe you are hitting higher boost than your gauge is showing. Just some starting points.

Chris

that could be a good reason. "Check boost source, maybe you are hitting higher boost than your gauge is showing. Just some starting points."

looks like after 20 psi, autometer ultra lite boost gauge is off by a bit.

anyway, i will do that. I'm in the process of getting another TBE.

that and NGK bpr7es...