Going lean up top - SRT Forums

Bactine · 10-09-2009, 07:39 PM

Hey, I just installed an LC-1 with a DB guage, so for those familiar with the setup I know the afr readings are reliant on a proper ground but this is assuming they are accurate until my serial cable comes in and I can use the logworks to verify everything.

I'm running about 14.3 at idle sometimes hitting 13.9 but mostly low 14s. Driving around its mid 14s sometimes really low 15s. Now when I go WOT I hit 10s then 11s until about 4500rpms then it hit 13.2 and I backed off right away. This was with an 18psi spike off of pcm controlled boost. Stage 1, BFMIC, 3" exhaust, FM WGA and some other bolt-ons nothing crazy but bone stock fuel setup with about 75k miles. I lowered the boost to about 17 psi and the same thing where its rich during the midrange but up top it hits 12.9 -13.0

I'm hoping the afrs might be off because of a bad ground or something but I'm not going to mess with anything until I get a reading with the serial cable because that will tell me for sure what my afrs are then I can compare it to the gauge readings.

What I'm asking is, it doesn't seem normal to be going this lean with so little boost. Could it be a fuel pump or fuel filter causing something like this? I literally shit my pants when I went WOT the first time with a wideband and saw 13.0

ChadSRT · 10-10-2009, 01:06 AM

i did a return line and bottle neck fix and fixed the problem

Bactine · 10-10-2009, 07:30 PM

Cool, so it's not completely abnormal for some cars to run lean up top with a 17-18spike. That was my biggest concern. I've got a walbro and a pieced together return line going in next week, that should help me out. Thanks for the input.

ChadSRT · 10-10-2009, 07:34 PM

i was running lean around 5-5500 with a 255 pump and did the return line bottle neck fix and helped dramaticly

Bactine · 10-10-2009, 09:20 PM

That's good to know, thanks man. I fell under the impression that we have a decent amount of fuel to play around with stock the way everyone made it sound. But looking at my afr's stock boost levels are pretty much all I can get safely

Maybe it's this brisk new england air leaning me out

duster360 · 10-12-2009, 12:48 PM

Quote: Originally Posted by Bactine

I'm hoping the afrs might be off because of a bad ground or something but I'm not going to mess with anything until I get a reading with the serial cable because that will tell me for sure what my afrs are then I can compare it to the gauge readings.

What I'm asking is, it doesn't seem normal to be going this lean with so little boost. Could it be a fuel pump or fuel filter causing something like this? I literally shit my pants when I went WOT the first time with a wideband and saw 13.0

I was just going to suggest Logging the serial output.
I always record the log on the laptop instead of trying to eyeball a gauge when tuning. Its much easier that way and more accurate.

With a stock tune and 17-18psi you should be in the low 11.0x past 5000rpm.
I wouldn't freak out until you've varified the A/F. Be sure to properly calibrate the sensor too for good measure. I'd also disconnet the battery to reset LTFT just in case LTFT was pulling fuel at WOT.

If A/F is still in the 13.0,,you should check fuel pressure at WOT. It should be 58psi +/-5psi and stable. If it drops at all it could be the pump or a restiction. If the pressure is stable but lower than ~50psi the regulator might have issues(rare but possible)

Also, an exhaust leak ahead of the O2 can cause a false lean. If you have the wideband installed after a cat, that would cause a false lean reading too.

ps Bottleneck isn't an issue until about 350whp. Returnlines just dump fuel and imo probably just masked ChadSRT other issues.

Bactine · 10-12-2009, 01:50 PM

Thanks Duster, that's a lot of good info. I'm still waiting on the serial to usb to show up so I can log, I'm trying my best not to freak too much until I know exactly what my afr's are doing.

I know you are right about there being an underlying issue if I really am hitting 13s on only 17psi, the fuel pump has 75k on it do they fail around there?

porksword · 10-13-2009, 11:38 PM

Quote: Originally Posted by Bactine

I literally shit my pants

I guess the first thing to do would be clean your seat.

Bactine · 10-14-2009, 01:13 PM

Haha yeah I'll make sure that accident never makes it to CarFax