Random Running lean under more than 1/4 throttle?
 

Hey everyone,
I am looking for some advice for the turbo Miata I have recently bought. I bought the car a few weeks back running solid, stayed at a constant safe 10.0 A/F under boost. I took it to a recent lapping day and the car has developed some lean issues. During the last heat of the day I noticed my A/F ratio was slowly climbing under boost, creeping into the 11's to mid 12's. I exited the track and went home avoiding boost the entire time. Now when I go into boost at anything more than 1/4 throttle the car shoots into the high 12's to low 13's on the A/F gauge. My question is what is causing this lean tendency all of a sudden. Here is the list of fuel/tuning items on the car.

Greddy Emanage plus autotune
305cc supra fuel injectors
BEGi AFPR
I thought I was told it has an aftermarket fuel pump....I can't find it on the parts list though. walboro 190???


The car will stay in solid 10's in boost all the way through the RPM range as long as you do not push the gas pedal in more than 1/4 throttle. Anything more than that and the A/F ratio shoots up. I have not touched any part of the emanage so I don't think my problem involves that.

The car has a new fuel filter, and I just OHM checked the injectors today and they were fine. I am not sure what is causing this lean issue. any suggestions? I was thinking it had something to do with the MAF/Vein meter going bad? Anyone? Thanks for the input.

10.0 is fairly rich i would say

af ratio should be in lower 11's under boost

Have you tried adjusting your adjustable fuel pressure regulator?

I know that 10's under boost is quite rich, but I would rather have it running rich than lean.

I have not adjusted the FPR since I have owned the car. Do you think its possible that it changed itself somehow? To be honest I'm not sure what I need to do to go about adjusting it, any advice as to what I should change it to and how? Thanks for the responses.

You're from my hometown (area). About time some turbo miatas showed up there. Of course I don't live there any more. Did you do a lapping day with FVSCC at Shawano? I autocrossed with them for a couple years.

Do you have a fuel pressure gauge hooked up? When I first turbo'd my miata (and I currently have a very similar setup) my stock fuel pump would only do 60psi at most after a couple weeks.

You're probably going to want to hook up your laptop, too and start doing some datalogging. Definitely watch your injector duty cycles.

If you're at a total loss, I know Extreme Performance in Neenah is familiar with the Emanage.

Can he even do that?

If he has the GReddy Support Tool, which can be found online or from members on here and a laptop he can.


It's limited datalogging at best, but it steered me in the right direction because I shouldn't have needed 90% DC on 330cc injectors @ 95psi of rail pressure to maintain 11.5:1 AFR at 6psi. My stock pump supplied 95psi with the return line clamped, but didn't hold it long while driving.

I was at an FVSCC event when it happend. I have been running with them for about three years now.

I will look into the AFPR. I find it odd that it just changed all of a sudden, thats why I figured it was something more mechanical broke rather than a tuning issue.


So what it comes down to (if this is a tuning issue) is that should I go have the car re-tuned on the EManage, Or should I invest into megasquirt and have it tuned(which would cost almost twice as much, but MS seems like a far better system).

Could it be possible that the autotune tried to adjust the emanage for the hour of constant track time and abuse and messed itself up?


Also the car does have a 190 fuel pump in it.

I guess the first two things to check would be fuel pressure (tee in a gauge on the return line from the fuel rail between the AFPR and the rail) and make sure the correct voltage from the wideband o2 sensor is getting to the Emanage. I don't recall exactly how the autotune works, but there is a description of of it in the EMB forum by olderguy (he makes them). The tables in the Emanage can only edited with the tuning tool. The autotune just changes one of the input variables, which corresponds to a cell in the fuel map. Oh, just thought of this, too. Check for an exhaust leak before the wideband o2 sensor. Since the emanage make adjustments based on that sensor reading, a leak could throw it off.

FWIW, I'm going to replace my emanage setup because I never could get it running the way I wanted (accel enrichment doesn't work) with a megasquirt. Just ordered a DIYPNP with all the goodies.

Usually aftermarket fuel pumps make noise, at the ones I have installed.

You will hear an audible humming sound on the fuel tank.

Thats way too rich, there is a point where adding fuel no longer helps prevent detonation, and you have long passed that point.