Also worth noting, in Tunerstudio my lag factors are set to 100% (no smoothing) for AFR, RPM, MAP, battery. Just about everything. So that smooth trace isn't smooth from the signal being smoothed in software. That's my actual AFR staying flat.

Best way to get rid of any signal variance is to get a digital input for your wideband. Easiest way to do this is with the MSLabs box.

@patsmx5, I can see what you're saying about me missing misfires, but I'm paying enough attention that I hope I'd notice that. I suppose it's possible that I'm not so I'll ask my tuner about that. I'd like to see what we can do with my current equipment before I start adding even more. If possible, I'd like to stabilize this configuration before it becomes even more complicated.

@aidandj, is the digital input box the only way to improve the signals from my O2 sensor? I found the page talking about that box that said voltage offset could be caused by bad power and ground. Perhaps it was incorrectly installed? Alternatively, if the signal to the ECU is off by .3, can I offset the AFR table by the same amount to account for that?

If you can't fix the issue in tuner studio with .3 afr difference then yeah your afr target table will have to adjusted for the misread.

I know there is an afr calibration table you can adjust to get them closer than .3.
It under tools in the top tool bar

Adding to the original question, Brandon is correct that on an old Link FM2 GT2560R we'd see 28-30 on the highway driving conservatively. With the same setup running a Hydra we'd see 30-32 mpg on average. With a Hydra FM2 built engine GT3071R we've had multiple customers report 33-35 MPG during highway cruising.

Thanks for the contribution, Jeremy. I know what you run for AFR targets on the Link, which is 14.7 at cruise. What are your targets with the Hydra? Are they the same?

I've got a bit of an update to share with the group so the timing is good.

Based on feedback from folks on this thread, I bought the Flow Force injectors from Nigel and brought the car back to the shop for further work over the last few weeks. Recall that this was to replace the RC 550s I had on there before.

I just heard that they're seeing about 30 mpg with the new injectors, new AFR targets at cruise of around 15.5, adding in a little bit of timing, and a little bit of tuning. They're running it on the dyno today to see what else they can get.

I'm hoping to get the car tomorrow or Thursday to see how everything turned out. I'll be happy to pass along some feedback and hopefully close this thread with a happy ending.

Thanks again to everybody's help on this. I couldn't have done it without you all.

I always target 14.7 below ~70 kPa in my FI maps.

Glad to hear you're making progress.

hey there Ace, this is Nate from Tork... decided to finally create a forum account haha. how has everything been since you picked up the car? had a chance to calculate what your averaging now? hope your finally getting to enjoy it!

Glad you joined the party, Nate. I think we've still got a bit of work to do. I drove 47 miles since leaving the shop last night and got 19.57mpg. That's over the 30 mile highway drive from your shop and 17 miles of city driving. There were probably 3-4 cold starts in there as well.

Needless to say, that's pretty different than the 31mpg you were seeing. I can't explain the difference right now so we'll need to talk it through. I'll call you at the shop on Monday or you can call my cell tomorrow if you feel like it.

Ya thats very different. Driving to and from work the last few days with it i averaged 30.5 and 29.5. Only time i saw even 20 was when i was brake boosting and doing boost pulls to adjust the fuel maps.

just out of curiosity and previous experience with doing this myself a few days ago, you didnt accidentally divide your mileage driven by the price of gas did you? cause i did the math at 45 miles divided by a guess of 2.40 a gallon and it equalled out to about the mpg you were seeing. just a possibility i thought id throw out there.

No, I calculated my mileage as the number of miles on the tripmeter divided by the number of gallons of fuel to fill the tank.

For the sake of completeness and thanking everybody for their help, I wanted to bring everybody up to speed on what we've done to improve fuel economy and where things stand now.

First, we installed the Flow Force injectors that had been recommended. Second, the valve timing was way off as had been suggested so the shop re-baselined that. Third, the fuel pressure at the rail was lower than we'd realized so that was updated in the Megasquirt tune. Fourth, we modified the cold start curves to be a little less aggressive and burn less fuel. Fifth, we leaned out the AFR targets in non-boosted areas of the VE table.

So we made all these changes and retuned. The result is about 30 mpg on the highway, about 20 in stop-and-go traffic, and 23 in general city driving. This is a massive improvement over the 15-17 I had before. I'm hoping for even more improvement in the city fuel mileage once the weather gets warmer. I figure the higher energy density of summer gas paired with less warmup enrichment time should reduce fuel consumption.

The new fuel injectors really smoothed out the idle so I'd say that was a worthwhile addition. We suspect that my old RC 550 injectors might have been gummed up. But while that's possible, I'd run a lot of fuel injector cleaner through them over the time they were running my supercharger so I find that hard to believe. Another possibility is that the Megasquirt had trouble running them for some reason. And I suppose a final issue would have been the lower-than-expected pressure at the fuel rail. In any case, we're running much better now.

After making all these changes I had some stalling issues on warm restart, especially when running the headlights, which imposed a substantial electrical load. I noticed it was running in open loop idle mode so I switched to closed loop mode. I also set up the idle VE table and set the mixture to ~14.6. Now the engine is idling much better, it's able to handle different electrical loads, and the AFRs are more steady.

I think I'm still seeing some lean conditions after warm restart. I found the thread at https://www.miataturbo.net/megasquir...estarts-79819/, which suggests modifying the ASE taper to extend the time that ASE runs. I'm going to make sure the current tune is stable and observe the ASE behavior for a while. I'll play with the settings in that other thread if it turns out there's a problem.

I want to thank everybody again for all the help. I really appreciate how we all contributed to solve this multi-faceted problem.

Super happy we were able to help get you where you wanted to be. It was def a learning curve for me and I learned a lot as I know you have as well. I'm working on some tune stuff for my Miata as well right now so once I get it dialed in I will share with you the settings I used for cold starts and warm starts etc.

anyone have any idea why i got negative cats for these posts? seems pretty lame to get a bad rep right off the bat for trying to help

anyone have any idea why i got negative cats for these posts? seems pretty lame to get a bad rep right off the bat for trying to help