Learn me some miata fuel pressure

T

TStiles

New member
I've been chasing lean AFR's on my 95 Miata on a Megasquirt ECU

I don't have an adjustable FPR on the car right now

First steps were to change fuel filter , and clean injectors. Injector #1 "before test" showed that it was " dripping ". The other 3 were within the acceptable range. OK , that should solve the lean condition in #1

I added a pressure gauge and I'm getting 33 PSI at idle. When I give it a few RPM's ( maybe 3,000 ) it goes to 45'ish then drops back in the 33 range

It's sunday afternoon in my deed restricted neighborhood , so I can't really see what the FP or AFR is going to look like between 6000-7000 RPM.

Can somebody confirm that I'm on the right path , and/or add to my understanding of what I'm looking for :shrug:
 
Deed restrictions don't usually cover noise, but local ordinances/codes might. Check it out. TBS, our town has no noise time limits, but you can file a complaint about excessive noise at any time.
 
The megasquirt should be able to adjust the AFR? No?

I have a MS and was able to change the AFR substantially with no FPR. Am I hearing the question correctly?
BB
 
rhygin said:
The megasquirt should be able to adjust the AFR? No?

I have a MS and was able to change the AFR substantially with no FPR. Am I hearing the question correctly?
BB
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I hate to admit this , I get Louie Rivera to tune the MS and then I typically forget it unless I see something abnormal. Plan is to add an adj FPR so I can mechanically add some fuel if I'm at a race and it starts going lean.

I'm a terrible mechanic , so I do all the EZ stuff and then take it to Louie for the stuff I'm not as comfortable with ( and to check my work )

I'm trying to eliminate the basics before taking it down to Louie's
 
Eh, guilty. Jesse Prather does my mech work. I have the MS as well, should be able to adjust the AFR from your lap top, I think. :P
 
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So with the corrected injector, are you still getting a lean condition? All your adjustments should be able to be make with the MS assuming you have good stock pressure and consistent spark. You do not need an FPR...
 
Andy Bettencourt said:
So with the corrected injector, are you still getting a lean condition? All your adjustments should be able to be make with the MS assuming you have good stock pressure and consistent spark. You do not need an FPR...
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Thanks for the reply

I'm not sure if it's running lean up top ( too loud to run 7000 RPM in my neighborhood )

I think it should be OK , I've changed injectors ( which should have been the problem ) , fuel filter , plugs , wires. I was trying to insure the fuel pump was solid before moving on to other projects.

I'm a Mac user ( don't have a PC ) , I don't think the MS softwear runs on Mac. Another reason why Louie tunes my car , but he's on the other side of Houston.

I was thinking that having a FRP would be an EZ at the track adjustment if the issue presented it'self again. It's not a huge issue with the current motor , but if I build an STL motor is going to be a big deal if I hurt it.
 
TStiles said:
Thanks for the reply

I'm not sure if it's running lean up top ( too loud to run 7000 RPM in my neighborhood )

I think it should be OK , I've changed injectors ( which should have been the problem ) , fuel filter , plugs , wires. I was trying to insure the fuel pump was solid before moving on to other projects.

I'm a Mac user ( don't have a PC ) , I don't think the MS softwear runs on Mac. Another reason why Louie tunes my car , but he's on the other side of Houston.

I was thinking that having a FRP would be an EZ at the track adjustment if the issue presented it'self again. It's not a huge issue with the current motor , but if I build an STL motor is going to be a big deal if I hurt it.
Click to expand...

If you build a 100% STL motor, you will end up needing a MAJOR reconfigure of the fuel system and ECU anyway. You will need a minimum of 375cc injectors @45psi. You will also want to remove the MAF, it is easy but will require an added temp sensor and settings changes to the ECU. Lastly, with optimised cams and compression, the PNP Megasquirt is not going to be sufficent. It has way too little resolution on the spark/fuel tables and the timing provided by the factory cam sensor is not acccurate enough. You will really need to switch to MS2 preferably MS3 and use a crank trigger with a multi toothed wheel as well as a modified cam sensor to allow sequential spark and fuel. This will allow you to tune spark and fuel on each individual cylinder. You will need a 100% built BP4W to have a snowballs chance in hell against any decently prepped Honda.

Back to the original question, your fuel pressure at rest and accel look spot on for a '95, other than the snotty injector I dont see a problem with fuel supply.
 
TStiles said:
It's sunday afternoon in my deed restricted neighborhood , so I can't really see what the FP or AFR is going to look like between 6000-7000 RPM.
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Especially if you are concerned about a flow issue. You probably know this, but you need to know what FP is doing under load not just a free rev in your driveway.

If something changed check for issues before making adjustments. you can crank that AFPR all day long and still be lacking fuel and lean under a load, especially at RPM.
 
Thanks Guys ,

Looks like I'm not going to get a chance to test this before the Hallett Super Tour event , so I guess I'll test it on one of the DE's before our TMS event.

I'm really on the fence about doing an STL engine. I prefer to take a wait and see approach to see how the developed Hondas run before I dump $$$$ into an STL miata motor. Right now down here it's just ITA Miatas & SM's competing in STL , but it looks like a few builds are going to start soon.
 
x2 on Chris Rallo's post above. There are different settings for the injectors at rpm and manifold pressure levels. If you are reving it in your driveway or in a low gear, you are not seeing what it will do at speed. There is a big diffence between holding 6000 rpm in 2nd or third and a wfo pass down the back straight in 5th at 6000.

You either need the ability to tune, or the confidence in your tuner that you don't need to. It is really not hard, especially with the auto tune software that you can get for the ms systems. A cheap, used laptop can run this all day long. I have three I bought off ebay from Dell financial systems and the most I paid was $232 delivered with Vista or XP Pro.

Just my two cents.
Mike
 
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