Running lean at idle; 550s at maximum Vf correction!

[Supraman]

Hey all. My car (mods in image below) is apparently running lean at idle...with the ECU performing maximum fuel dump (5V at Vf terminal). My LM-1 wideband showed readings from 15.5 to 16.5AFR, or thereabouts, at idle when the car is fully warmed up. I tried cranking up the base fuel pressure to something like 48PSI, and I suppose that helped, getting me to the 15.0 to 15.5 range--but still with Vf pegged at 5V. The 12V fuel modification has been implemented, and I'm running a Walboro. Honestly, I can't think of something that would cause this--one possibility is that the base fuel calculation is very incorrect, but I have no vacuum or boost leaks. My Lexus AFM screw is only halfway out, or so. At cruise, the car is very normal with its automatic fluctuation on either side of 14.7, though I have not measured Vf while the car is moving.

Any ideas? It's kindof a scary problem for me, given that the computer can't even correct the error! I have an E-Manage, currently zeroed out, but I want to fix this the right way before I get on with the tuning...thanks guys! :icon_bigg

Aforementioned modifications:

 

[turboa7mgte]

try unhooking your Emanage and see what happens

try recalibrating the LM-1

 

[Supraman]

I was recently diagnosing electrical issues, and took out the glovebox where the E-Manage was mounted. As such, I've been running without it--with, of course, the AFM wire jumpered.

I recalibrated the LM-1 after a night of sitting (to let the exhaust clear), followed by emptying an air compressor at 120PSI through the narrowband hole. Thus, it's been well calibrated in atmospheric air. Given the fact that the ECU also thinks the car is running lean (it's adding as much fuel as it is allowed), and the fact that the cruise readings are completely normal, I'm pretty sure it is truly running lean at idle. Yet, again, I have no idea :nono:

 

[isnms]

I have the same situation at operating temp and idle.
Computer sees it running lean and is adding max fuel, VF=5, sometimes 3.75. At cruise everything is normal, wideband=14.7, VF=2.5

My mods are not as far along as yours. check below.

 

[scottiedawg66]

are your injectors new? My wideband reads 14.9 - 15.5 at idle, and I had it tuned to 11.2:1 at WOT...lean idle only saves you gas money, it wouldnt hurt your engine at all.

~scott

 

[isnms]

My injectors are not new and at WOT I'm crazy rich 9.6

 

[scottiedawg66]

so why worry? As long as you arent rich at idle, cruize, and lean at WOT you are in great shape? Tune that sucker to low 11s under at WOT and you should be ready to roll.

~scott

 

[Supraman]

Well, the reason to worry is that we don't know what's causing this. The engine computer is MORE than 20% wrong with the base fuel calculation, because even with a 20% correction towards rich, it's still running lean. Not knowing what causes that is a little frightening.

Scottie, what is your Vf at idle? The AFR should also bounce below 14.7, so it's a good chance you're getting 5V too...

The injectors are decently new, and are from RC Engineering. They use the solenoid type or whatever, as compared to pintle.

 

[scottiedawg66]

I use RC 550s, and once i get warm at im around 14.7-15.2, cold i run pretty lean. I was not running at 5v to the fuel pump, and i never did that mod because i didnt wanna run rich at idle. I cant remember my VF readings from SAFCII, and my car is down now, but it was in the mid 20s, which would translate to 2.5 I believe. Have you checked your timing, do you have TPS (code 51, and 51) or any other codes? Temp sensor? Check you plugs. If some look real rich, and others look lean you might have a clogged fuel injector.

~scott

 

[atlpd3147]

Im having the same issues as described.
My wideband shows very lean conditions at idle. 17 or 16 ish at idle when the car is warm. But at intial start up I have very rich conditions.. The wideband shows 14 15ish at cruise but at wot the wideband shows very rich conditions.
Mods are afcII/vpc combo with a plx R-500 wideband sensor. Vpc has 550chip and I have 750cc injectors in the motor. I've had the car run correctly before even with such large injectors so I know it aint the fact that my injectors are soo large. Will neely ran 720cc in his mkiii with a safc/vpc with 550chip installed. He just leaned out the hi map on his safc to tune out wot pulls. At idle the ecu was able to keep a nice 14.7 ratio.
Did a compression check the other day. Got 190 in #6,5,2,3 and 180 in #1 and 182 in #4
Yes there's some carbon on the piston tops and the motor has only about 5k on it.

 

[Shawndude]

I would suspect a small leak at the intake manifold somewhere. A tiny leak makes a huge difference in the A/F calculation at idle, but is basically a non-issue at higher loads, since the leaked percentage to total air ratio is so small then. Since the intake manifold sees very hight vacuum at idle, I'd look there first. Spray some carb cleaner on all the hoses, throttle body and anywhere around there and see if the engine stumbles a bit. Don't forget the brake booster also, since that can leak as well. Is your PCV stock by the way?

 

[Idealsupra]

wait....im confused...your problem is your running lean at idle? AND? lol... 14-16 at idle is perfectly fine...you dont need fuel until you need to make hp .... as long as it doesnt say "lean" on the wb or anything like 18:1+ i wouldnt worry about it...

and of course as long as it gets richer as you get on the throttle and especially into boost.

 

[isnms]

I would suspect a small leak at the intake manifold somewhere...

That's a BINGO

That's what mine turned out to be, I followed up in another thread here somewhere.
Turns out I had a hole in the intake manifold gasket.

 

[atlpd3147]

Correction... Mine at idle after the car got warm was 17 18ish airfuel ratio readings. When cruising it would be aorund 13 14 a/f readings. And when WOT it would go pig rich. 9ish in airfuel..