Need tuning help, engine not meeting AFR goals- poor gas mileage
 

You guys will have to understand that I’m new at tuning with MS. I’ve read a ton of stickies and searched a number of threads but I still need some help with a few particulars. :noob:

I’ve got an issue that I’m trying to resolve in regards to gas mileage. Below is my AFR table.
https://www.miataturbo.net/attachmen...alafrtable-jpg
I’ve been trying to reach a 15.2 target cruising at 70mph in 5th gear (approx 3,800rpm). However, the best that I’ve been able to manage through my LC-1’s read out is 14.0. At 65mph I can almost achieve 15.0.

As a result, the best tank of gas I can get is 250 miles. I also know that I'm losing the mileage on the highway because 90% of the miles when I drive the car are highway miles. There has got to be a piece of the puzzle missing in order to achieve my target AFR.

Can someone help me out? Is there another table I need to change such as pulse width or ignition table? Is it a matter of increasing the AFR target in the table? I just don't want to change something and learn the hard way that I shouldn't have changed it. If I do have to change it, can you please explain the logic behind it?

The car is a ’91 naturally aspirated n/a and is stock aside from a K&N filter and MSPNP2. Timing is spot on.

I want my 30+ mpg back, 250 miles to a tank is a bummer!

Thanks for your help!

You want to first set up the AFR table to be what air/fuel ratio you want, then tune the VE table to hit your targets.

Thanks for pointing me in the right direction!

Manually change your ve map to lean out your afr to 15.2 during cruise. You shouldnt be worrying about the gas pedal to hit the afr you want. Simply if its too rich. Pull some fuel. Nothing hard to it. The MS will do what you want it to do so tell it what to do. What is "spot on timing"?

Sorry, southern speak. By 'spot on' I mean that the engine was correctly timed upon installation of the MS.

I'll decrease fuel from the table this evening after work. Is there a lower limit threshold that I shouldn't cross?

The point where you start going leaner than your AFR target...

This is one of those sections where you're going to have to go through a few iterations of trying some settings out, logging the results, and repeating until you get what you want. Your AFR table doesn't look like a bad start out of boost, so it might be time to try the VE Analyzer in Megalogviewer or VEAL in Tunerstudio, especially if your not used to setting up a VE table already. You run the car and it takes feedback from the wideband and to get your VE table to correspond to the AFR table. It's not an end-all replacement for adjusting the VE table by hand, but it can help get you close and help you understand what you need to do to get the results you want.

Have you run VE Analyzer Live in TunerStudio yet? It will adjust your VE table to match your target AFRs. If you don't implement something to manipulate the VE table to match your target AFRs, you can change all of your targets to 20.2 but it won't actually change your fueling. The VE table dictates fueling. The AFR table only acts when you are using other software to manipulate the VE table to match it.

If you haven't autotuned fuel with something like TunerStudio's VEAL yet, you haven't really tuned fuel yet.

This is a simplification, but a useful way to picture it.

I recently posted a good AFR table, good luck finding it.

... and I am using it with resounding success.

Thank you for the great explanation, I didn't know they went hand in hand. As mentioned, I'm new at this so thank you for the pardon.

I haven't used VEAL yet, mainly because there are commands to read that are too small to see while driving. Not a fan of distracted driving. :) I'll have a passenger available this evening so I'll take your advice and give it a shot to use for a baseline and apply the 'smoothing' techniques I was reading about in another thread. I'll post up my VE table for some more pointers afterwards, too.

This is an excellent site with some knowledgeable folk- thanks for all of the help so far!

If you haven't purchased the Tunerstudio software yet (just running the free version), you'll have to take a datalog in Tunerstudio then use MegaLogViewer to analyze the datalog and pull fuel. This also allows you to play with the numbers and get familiar with what's going on after you've stopped driving the car. This is what I do and I haven't blown the car up yet:

1. Open Tunerstudio -> Datalogging -> Start Datalog
2. Drive around 10-15 minutes
3. Datalogging -> Stop Datalog
4. Open the datalog you just created in MegaLogViewer
5. Select Open MSQ (find your current tune)
6. VEAnalyzer -> Run Analysis (the software will adjust the fuel map)
7. Review changes to make sure nothing was altered TOO significantly
8. Save MSQ
9. Open Tunerstudio -> File -> Load MSQ (this loads the new tune)
10. Repeat until the tune is how you want it.

I highly recommend spending the $40 to have the awesomeness of just turning it on, driving around on a weekend afternoon for a couple of hours in various conditions and types of roads, and having it be virtually perfect when you get done. It changes the VE table in real time while you drive and fine tunes it automatically. I really, REALLY like that feature.

And to frapjap, press the start button, start driving. When you get done driving you pull over and press stop. Then you save your revised tune. Done.

And this "correctly time upon installation of the ms" doesnt tell us shit.

"Why is this man in jail?" "Oh who knows he was born at 8lb"

No offense, but my statement allows for at least one potential issue to be ruled out considering that if the spark is not delivered at the proper time to the combustion chamber you can be left with horrendous fuel (and power)efficency. You will not get the same “push” each time the engine fires, and the pcm will command the engine to run faster to get the desired rpm causing the titled symptom.

Instead of having someone in the thread ask "are you sure timing is correct," I thought better to note that it was.

I may only have 10 posts on this website, but I am mechanically inclined and have a good understanding of automotive appliances. I am not familiar with how tuning with a standalone computer and a Megasquirt work, which is why I am here asking for advice.

Thank you both very much for the step by step and tips for how to use the program. I have paid for and installed the logging & tuning package but have yet to use it- mainly because I lacked the knowledge. I wasn't aware that I could do all of this alone and am very glad to know I don't need to bug any friends to sit in the passenger seat and walk me though the steps.

Much appreciation!

It might make is easier if I gave you the really simple version of how the ecu determines how much fuel to inject because that seemed like your stumbling block.

Take in sensor data
match up sensor data to a position on the ve map, any compensation maps, and the commanded afr map
take the VE value at that position and average it with the cells near by weighted by how close to the edge of the cell you are, also multiply/add the values from the compensation tables
do the idea gas law computations to determine how much air is flowing
take the commanded afr and combine with the VE value and the air flow value to determine the amount of fuel required
look up the size of the injectors based on the required fuel table
determine how long such an injector would need to fire to get the correct amount of fuel
inject fuel
repeat

Hopefully knowing whats going on and the fact that just changing the commanded afr table didnt do much. Also note that this isnt MS specific, the order might be different and some of those steps happen as basically the same time.

And by timing I assume you meant cam timing, because you can and will need to adjust spark timing in the MS.

Excellent explanation of the process involved, thanks a ton. I do like knowing what is happening along with the advice to "do 'X' and you'll have 'Y' result."

You timing assumption is correct. I've had coil pack vehicles before, but none that I've modded this extensively. In my other cars I'm working off a distributor so there is a learning curve here in order to gain some new knowledge.

Also, you're not all too far from me. I'm on the southcoast of MA.

0. Register Tunerstudio
1. Open Tunerstudio -> VE Live -> Start Autotuning
2. Drive around 10-15 minutes
3. click burn

car is tuned.

If you are new to EFI tuning, this is probably worth a read.

Since I don't yet have my MS, I can't speak to its depth, but it is very easy for a beginner to understand.

I'm referring to your entire ignition map bud. Motors run different timings at different rpm and different loads and megasquirt has an ignition map it runs off of for different rpms/loads. Ignition map that you tune on your own. I highly doubt the tunner did your entire ignition map on the dyno.