28 replies to this topic

[SaulSpeedwell]

I didn't read all the posts in the middle, but check the injectors.  Undersized injectors may have been installed in an attempt to lean out the car in its past life.

[DrDomm]

I'm back, and thanks again for all these thoughts...

 

Domm, there are so many possibilities here and at the risk of sending you in more directions here are a couple thoughts.

 

You could have 1 injector that is messed up which is causing an aggregate lean reading.  Look at plugs as suggested for one that looks different.  Have you changed the airflow meter?

 

I once had a similar situation and the throttle positioning was the cause. 

 

This is the 3rd plug...the others were white.

 

[DrDomm]

Domm

Not sure what Danny is referring to.. But That a:f in the graph(especially red- green) looks like every 99-00 we have ever done here.

 

Here is what we typically see around 50-52 psi on 99-00 Sm above and below 180 degree water temps. Mine is a dynojet and Bret uses something different, the shape varies a little dyno to dyno and where sensor is located.

Jim

 

 

 

This is my dyno plot from the mobile dyno at the Runoffs.  I guess it isn't that far off...other than I'm needing such high fuel pressure.  Red was about 56 psi, and blue at 60 psi.

 

 

I do, but have had one that I changed anything and everything people could think of on here and it ended at 57psi, which is 6-7 lbs more than EVERY other 99/00 I have built. Ran great, made great power, but always needed more psi than all other cars in same conditions. It bugged the hell out of me and at least two or three full day attempts at rectifying this "problem", finally gave up as the "problem" was only a problem in my mind, it didnt act any differently on track and was no symptom of other pending pending.. Nonetheless it did bug the hell out of me

 

I'm starting to feel this way.  I'll try to tweak a few things, and then just accept it.

[DrDomm]

^^^^ Similar Miata   (SM) 

There is "normal"(which is a range)and sometimes a little outside the norm...kind of like dyno numbers across the country, you will drive yourself crazy trying to repeat/get what someone else has published when in reality your numbers are fine! 

Jim's AFR is what I see...not sure why you think 13.2 is too lean at 5500 rpm Domm?

 

Perhaps I misunderstood things, but Jim led me to believe that AFR at 5500rpm should be around 12.7.  Looking at his numbers, over 180 degrees, that doesn't seem to be the case.

 

When checking plugs, pay pictular attention to #4.

 

Hmmm...this is it.

 

[DrDomm]

I didn't read all the posts in the middle, but check the injectors.  Undersized injectors may have been installed in an attempt to lean out the car in its past life.

 

Injectors were rebuilt from Advanced.

[Bench Racer]

For my 2 cents the prefect plug color is a bit to dark. My ideal is a slight tan. Remember folks, different strokes for different folks. Without seeing your plugs with my eyeballs real time, your lean as you suggested. Next time on the dyno try a cooler plug, check numbers and plug color.

 

https://www.bing.com...ex=3&ajaxhist=0

[SaulSpeedwell]

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[DrDomm]

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[SaulSpeedwell]

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LOL, I don't know what I posted.  Apparently I didn't agree with myself after doing so? 

 

I can tell you this - one of my favorite things to do is "cheat" to make the car run perfect AFR on the dyno, so that I know what gains I am fighting for with legal tuning.  Easy to do on the 1.6 - just manipulate the wiper arm with your hand while watching the AFR during the pull. 

 

With the '99 it is a little tougher - but a potentiometer hooked up to the IAT sensor will do the trick.  Easy to test with an OBD2 ScanGauge hooked up, so that you can see what resistance will "pull up" the IAT from ambient to the end of the map (scale is -40 to 205 F?  IIRC?). 

 

Once you get some runs with theoretically perfect AFR, you know whether you are missing out, and how much.