Okay, so I have a 1999 miata which I just finished turbocharging today. I have converted the fuel system to a return style system so that I could run my brand new vortech fmu. The problem is, as soon as it sees any boost it starts to lean out.

im using the stock ecu, injectors, and fuel pump.

please don't reply with something dumb... I've spent the past hour looking through threads on here but haven't found anything that has helped me.

 

Using a archaic setup like the Vortech FMU, it is going to be very difficult for anyone to diagnose this given there are no data logs. Your best (and only IMO) bet to fix this is to download the manual and see what screws it says to turn to adjust the correction curve.

You have provided no information whatsoever on the rest of your build either. Assuming you're actually building boost, it is incredibly likely you have already maxed out your OEM 260cc injectors.

I'm surprised you spend an hour researching on this forum, and concluded your post provided us enough information to try and help you in any way.

 

I just didn't want to make the first post super long. Let me know what you need to know and I'll tell you. Basically I have to shift at 3k or it will try to build boost and go lean. I don't see how injectors would be maxed out at not even 1psi. I haven't reached any amount of Boost yet...

 

What turbo are you running?
What AFR are you referring to as "lean"?
What manifold are you using?
What exhaust are you using?
What wideband are you using?
Where are you sourcing your boost signal?
Are you using an intercooler?
Where are you sourcing your wideband signal? Before or after cats?
Are you at WOT when this is happening?
Did your bandaid box provide a manual indicating what AFR it things you SHOULD be at?
If so, how does what your seeing compare?
Why did you choose archaic bandaids over a tested and proven megasquirt?
What is your date of birth?
What is your mother's madam name?
Who was your childhood best friend?
What street did you grow up on?

 

T28
15,16,17
Cast iron ebay manifold
open downpipe
innovate mix-l with a bosh sensor
to the ic piping after the intercooler before the tb
yes
no cats, only dogs here
i don't know how to answer that one. It's anytime I try to go into boost. Foot to the floor, halfway, doesn't matter.
no. I don't have the money for megasquirt right now. I know I should be seeing around a 12.5 though
its lean. No fuel, no boost.
like I stated earlier, I don't have the money.
09/23/1996
burns
cayden
vail dr
i can just give you my password if you want it haha

 

excuse all of the screw ups. I'm on my phone and its autocorrecting every other word.

 

Does something dumb. Excepts folks not to reply in kind...

Since you didn't have the moolah for a megasquirt, I hope you have the dough for a new engine.

 

the jokes on you. I already expected to hear a bunch of bs. Megasquirt isn't the only way to go. My setup will work fine for now. who said I'm not going to get a megasquirt 3 months or so from now? If you don't have any useful input please don't say anything at all.

 

Facts, bs. Potaytoe, potahto.

Somehow I've had lots of issues with being a bonehead and breaking things, but leaning out hasn't seemed to be an issue yet.

In your position, I'd try the largest injectors the stock ECU could handle, but you're right that you shouldn't have an issue with stock injectors at super low boost. How do you know the fmu is working?

 

I'm just trying to reach about 5psi for now so nothing crazy. And im not sure that it is. Im about to go check it. I disconnected the return line and I'm going to start it and blow into the vacuum hose to see if I can get it to slow down the fuel return (doubt it). At this point idk what else to do. I also just found out adjusting timing on an NB is not as easy as an NA. So I'm really looking into a diy megasquirt. I'll build it. I just don't have 7-800$ to blow on an ecu right now. Which one would you suggest for someone on a budget?

 

An already put together PNP used one, not trying to be judgemental but I'd really hate to have to buy another half finished MS project off the classifieds. I'm sure you have the soldering skills to do it or you wouldn't be thinking of the attempt, but the issue is documentation isn't great to darn near nonexistent and looking at your search skills here you'll get frustrated quickly.

 

Okay, so I'm back with some new info. If I pinch the return line, the fuel pressure doesn't rise. So it seems that a bad fmu should be out of the question. If the fuel is not returning to the tank, where the heck is it going?

 

philosoraptor.jpeg

 

Welcome back, @Schuyler! Seeing you post again is the redemption of this thread.

 

Any ideas?

 

Really? It should be pretty obvious to you that your fuel pump it's dieing.

 

what makes you think that? It's able to push 75 psi. Isn't that in the range of what it's supposed to be able to push? if it can get the correct amount of fuel to the rail which is 60 psi stock... it seems like the pump should be fine.

So what do YOU think is happening when I block the return line? Are you saying the pump is doing nothing?

 

It's very simple, if you are truly blocking the return line and the pressure isnt pegging sky high then your pump is doing everything it can to supply enough fuel to idle. Once you get the car moving and the injectors open up your fuel pressure is diving and you're leaning out.

 

Then why can I drive it out of boost perfectly fine? I've driven the car for 4 months n/a with no problems. I'm not saying you're wrong but I would like to know before I go buy a pump.

 

Because when you're not in boost the fuel needed is much less.

Honestly I wouldn't go buying parts based on my suggestion..... You've barely explained your setup and done hardly any real diagnostics. I'm playing keyboard Houdini beard off of what little you've given us to help you. I would continue to investigate why the fuel pressure doesn't go up when the return line is pinched, as you said that fuel doesn't disappear and if there isn't a puddle on the ground then someone is not right.