Leaning out
 

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.

There aren't any puddles, and I keep an eye on the afr gauge all the time. It never leans out with no boost pressure. Before I put the turbo on, it would richen up to about 12.8 at WOT. I've told you pretty much all I've done to the car. what else do you need to know?

Let's start with how you converted to a return style system, I assume you removed the in tank regulator? How exactly did you plumb the FMU? How are you monitoring fuel pressure? Any way to tape said fuel pressure guage to the windshield so you can watch FP as you make a pull?

I used this link https://www.miataturbo.net/diy-turbo...l-style-74629/ . Yes, the in tank regulator was removed. So here's how my fuel system is plumbed: fuel tank, fuel pump, fuel filter, rail, isr fuel rail adapter, afpr, fmu, back to the tank. The only way I can see the fuel pressure is on the afpr. And it's pointed towards the front of the car.

Since we're driving finishing nails with a rock...... Point a go pro at the guage and take a drive. Or start throwing parts at it.

Okay. I'll report back when I figure out what it's doing. Thanks

I just got done watching the video. The pressure is not dropping. It looks like it's going up a very small amount. I would say 10psi max.

So you've verified that things are working in the right direction.

Looking at this link Vortech Fuel Management Units | JEGS

You'll see there are different rising rate settings. Again with the lack of data you've provided I'm assuming that was 5 psi of boost and you saw 10 PSI rise so that would be 2 to 1 and that isn't one of the options. you need to keep cranking up the fuel pressure till you're not lean. If u come back and say you have it setup for 5 to 1 then your fuel pump isn't keeping up . This is assuming you understand that fuel pressure is less than the set point under vaccum, equal to set point at 100kpa and rises at the FMU rate in boost. What actual pressures are you seeing.

I have an 8:1 disk. I plan to cut a12:1 (2.72") disk tomorrow at work to see if that changes anything... and honestly i didn't watch the boost gauge. As soon as I saw the afr at 16 I stopped. It didn't feel like there was any boost at all though. I didn't rev past 4K

if I crank up the fuel pressure it will only get me to 75ish psi. I think it would still be running lean but I can go try it

with the video I took it was hard to tell... all I can tell is that it's at 60psi at idle and got to about 70psi when I tried to get on it.

I like cats.

At this point you're lean with 60 to 70 psi something is wrong and honestly there is no good way to trouble shoot it with a FMU. You're left to guessing and checking and doing rediculouse things to try to log data. This is why you got a bunch of snarky smart ass responses when you started this thread. It's expected that you take the advise of those with a high post count or their names in green. I also understand that simply accepting the "because I said so" reasoning behind the short answers is tough to swallow. I'm pissing off the old guard by spoon feeding you but it was obvious your weren't going to figure it out yourself.

Just so you're aware the correct way to deal with this is to wire in a pressure transducer into the fuel system and log it through your megasquirt. This is what I did, I discovered an issue with my fuel pump and corrected it in literally one log and a single click on Amazon for a new fuel pump.

At some point you have to ask yourself, what's my time worth?

well I don't want to bother anyone anymore. Thanks for the help.

Thanks David! I am in China this week, but work is slowing down some. I've been spending ~1 week a month at my house lately. Hopefully going to start putting some time in to the car here soon and begin posting once again in my own build thread. I'll post my to-do list once I'm back state-side. I have a track day scheduled in July, as well as a travel freeze for that month. So, I'm running out of excuses to not get working on the car.

I may be reaching out to you regarding some MS stuff in the coming weeks.

Sure. Remind me where you are located now. What track would you be running?