Need tuning bad, gas mileage sucks real bad
 

Hey guys. I recently bought my car off a friend. It runs great but extra rich. It has a Megasquirt that has not been tuned 100% yet, 550cc primary and 1600cc secondary, street ported, full turbo back exhaust, and FMIC.


I filled the gas yesturday, drove to work and back, which is 50 miles. I am almost 50% empty according to my gauge. do those stock fuel gauge go off? I checked my wideband gauge, and I am around 14.0 A/F ratio on the freeways.

I konw rotaries get bad mileage, but 7-10 mpg on freeway!!??


What af ratio's are good for idle, full throttle, partial throttle? I almost want to check for holes in my gas tank. lol BTW, I dont drive hard because the car is not tuned yet, I rarely hit boost.

lol welcome to the world of the rotary. You may be able to dial it in a little better but dont expect drastic changes especially with those 1600's.

well, even though they are 1600cc injectors, they need to squirt the right amount for the proper A/F ratio, right? I see 2 other posts about bad gas mileage, But I jsut got 50 miles on half my tank!!!!! And that is freeway. Maybe hitting boost on 3 occasions less than 3 seconds each time

Ifyou arnt engaging those secondaries they shouldnt have any effect on a/r ratios. IIRC you need to be over 3800 rpms for the secondaries to come on, but thats with a stock ecu.

Since you are running a megasquirt you are probably batch firing the secondaries at all RPMS. MS allows you to run two seperate fuel curves. One for the primary, one for the secondaries. i would look into it.

Because of how MS works the 1600cc aren't NEARLY as adjustable as the 550cc's are. Your 550cc should be able to handle off boost fueling all by themselves. You can lean out the cruising a/r some more, but I would monitor EGTs or knock if I were doing that.

Long story short you have a LOT of research to do on MS and how it provides fuel and spark. I would talk to RotaryGod here on the boards. IIRC he runs two seperate maps for the primary and secondary injectors.

BC

Cool, the answer I have been looking for.
Im going to check the firing order, and when injectors go on. Im very familiar to cyl engines operation, and how EFI systems work.

So the secondaries are more for extra enrichment, and not as tunable? Darn, maybe I should switch the primaries and secondaries. Haha. I feel like such a newb

IIRC the MS is an 8x8 fuel map. So it will only handle 64 different fuel points. With the 550cc injectors each one of those fuel points is a smaller amount of gas so when you change it by 2% you are only marginally changing the actual amount of fuel being injected. Whereas with the 1600cc injectors that 2% change is roughing 3 x the amount of fuel as with the 550cc injectors. Even if it is 16x16 map the changes are still larger, though in the case of a 16x16 map can be more finely tuned.

I still suggest you go to the MS help boards, or the sub-forum here and learn about the seperate maps. It will let you fine tune the 1600cc injectors better instead of having one map for both. It will definitely allow you to fine tune off boost fueling much better since a 2% change will be a lot less with just teh 550cc injectors instead of both the 550cc and 1600cc injectors increasing by 2%.


BC

Cool. The guy I bought my car from had plans for a 400hp turbocharger. Personally I would b happy wiht around 300hp. Which injectors would you recomend?

thats out of my knowledge base. I would suggest searching 300hp in the serach function.

Im an NA guy. :)


BC

Most of the information here on the MS is not entirely accurate unless you're using the standard firmware.

If you're using the MS for ignition and fuel, he must be using ms1/extra, which has 12x12 tables, and support for staged injection.

If that's the case, the staging *can* work exactly like factory (it's configurable).

Ken

I have the megasquirt v3 setup. I'm going to research it more. Hopefully the other half of my gas tank survives today's commute

If you're getting 7-10mpg on the freeway cruising at 14:1 afr, there's something seriously wrong. Either massive fuel leak or you're towing a 20' camping trailer! As muy says, the rest of the info in this thread is very dated and does not represent the typical MS rotary install these days.

Good news, I guess the fuel level gauge goes down really fast for the first half. The 2nd half of the gauge is moving slower. My buddy claimed he got around 160 miles out of a full tank

Can someone please explain staging a bit more, I'm planning a similar setup, S5 intake with 2x550cc and 2x900cc siemens injectors

Tee Hee Hee , you said "siemen". JK . SOrry I dont have anything else to add.

I jsut wanted to update I am getting 12mpg untuned, aminly freeway and driving pretty conservatively

welcome to MS!

fwiw ... you should find good idle afrs will be around 12-13.5ish.

This could be argueable, but I aim for 11-12.5ish wot... and 15+ for light cruise.
(however I am consistently putting down 300+ a tank for avg socal traffic and a few beats here and there)

Nice. Thanks for the info. I started playing with a/f ratios today. I didnt touch any ignition stuff though

What a/f ratios should I look for for light-medium acceleration? Should I be looking for a steady A/R as rpm increases, or should it get richer? Thanks for the help. Im hoping to get better mileage than 12mpg mainly freeway

Just an update, I get 120miles on 8 gallons this time after some minor tuning!!! Usually I would get 100 miles for a solid 8-8.5 gallons!

care to write an update? I have many Q's and perfer to read before I post, but now I've come to the point in my build where ecu determines what I do next and need some answers. If anyone cares to address them, I have some questions that I believe are valid and have not been answered in the forums.

If it's rotary-specific and has not covered in the FAQ, then start a new thread with the questions clearly identified. I tried to address the most common ones in my build thread here:

https://www.rx7club.com/megasquirt-forum-153/v3-0-ms-build-pics-534544/