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Old 03-22-2016, 11:14 AM   #461
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IMHO - returnless is inconsistent and actually harder to accurately "predict" than it seems to most. You can predict some of the weirdness, but ultimately it's a pain in the butt and you're still left with mediocre control at best. And you also get the lovely fuel/injectors heating issue which rears its ugly head on hot restarts.

It's definitely worth it to conver to return style. Just my .02
Agreed- return style has several advantages, and is preferable if available. It's certainly easier to tune for.

That said, lots of OEMs are using returnless systems these days, and they've certainly gotten the engines running pretty well on them. You don't hear much about things like hot-restart problems or mixture instability on unmodified cars.
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Old 03-22-2016, 11:22 AM   #462
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True, but they're also not using megasquirt.

And even on the ultra-awesome modern OEM ecu's there is difficulty with hot restarts once you upgrade injectors: example - Subaru and ID1000's run into multiple mis-fires SPECIFICALLY on hot re-starts.

To the point that Cobb had to create specific tables/parameters to fix this very issue. They "solved" it by lowering fuel pump duty/voltage on hot re-start, otherwise no matter what you do you either get uber rich to the point of flooding, or lean, or mis-fires. So the "fix" is more of a bandaid. Returnless systems still suck and IMO are a cost cutting measure more than an evolution in technology.
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Old 03-22-2016, 11:33 AM   #463
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Good discussion thanks. I was just hoping for an easy all in one solution.
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Old 03-22-2016, 11:43 AM   #464
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Good discussion thanks. I was just hoping for an easy all in one solution.
Summit Racing® Stainless Steel Fuel and Brake Hard Line SUM-220256 - Free Shipping on Orders Over $99 at Summit Racing

I can't recall the exact diameter of a Miata fuel line off the top of my head, but that's basically the simple solution.

Combine it with either an NA or aftermarket return-style, MAP-referenced fuel pressure regulator, and you've got a complete fuel solution. If you use an aftermarket regulator, you can mount it on the firewall if clearance is an issue.
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Old 03-22-2016, 11:45 AM   #465
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yup, or just do the "cheater" method and use the oem tank vent line as a return and figure out a vent solution near the tank so you don't need to run a whole nother line
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Old 03-22-2016, 11:52 AM   #466
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5/16" fuel line. 1/4" evap line.
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Old 03-22-2016, 12:52 PM   #467
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i'm not interested in using the evap line. I have no problem spending the money and time to run a dedicated return line, especially considering I was considering buying the $950 FM kit...

Time to do research on exactly what parts I need to make this happen. Anyone have a favorite vacuum referenced pressure regulator?
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Old 03-22-2016, 01:08 PM   #468
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Fuel lab makes good stuff. Best return line IMO is to replace the evap line with another NB fuel line. It fits prefect.

If you want to run AN6 lines: You need a bunch of 5/16 quick disconnect to 6an. The aluminum screw in kind. Not the plastic snap in kind. You need a way to bypass the stock FPR. I recommend the Turbo smart 0402-1002. Then just assorted AN fittings.

If you want to run rubber line: you just need 5/16 quick disconnect to hose barb, and adapters from your FPR to hose barb.
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Old 03-22-2016, 01:29 PM   #469
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check out what G did (EO2K). that should be all you need to do it 100% proper
he outlined it all in his thread iirc
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Old 04-28-2016, 07:32 PM   #470
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School is winding down so I may get the spare motor disassembled and off to be chemically stripped. Any reason this is a bad idea?

I stopped at the machine shop a week and a half ago and we agreed that they would do all the machine work and I would handle the assembly (either myself or find another builder). This shop has about a 14 month wait if I was going to have them build it.
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Old 04-28-2016, 07:50 PM   #471
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yup, or just do the "cheater" method and use the oem tank vent line as a return and figure out a vent solution near the tank so you don't need to run a whole nother line
I was just about to ask if that was a possibility. Any explanation on why that's not a preferred method?
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Old 04-28-2016, 09:31 PM   #472
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I was just about to ask if that was a possibility. Any explanation on why that's not a preferred method?
The only complaint that I can recall hearing is that the vent line is not as big as the supply line. I still would like to retain the charcoal cannister and OEM evap system. Don't ask me to give a good reason why. lol.
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Old 04-28-2016, 09:58 PM   #473
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hahah fair enough
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Old 04-28-2016, 10:32 PM   #474
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The only complaint that I can recall hearing is that the vent line is not as big as the supply line. I still would like to retain the charcoal cannister and OEM evap system. Don't ask me to give a good reason why. lol.
MS will not control it in any manner. I.E., it will never purge.
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Old 04-29-2016, 01:42 AM   #475
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lol yep and it takes all of 5 minutes to yank that whole rats nest, intact, out of there, and significantly clean up the bay. And re-install will be another 5 minutes cause it just drops back in together.
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Old 04-29-2016, 12:24 PM   #476
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MS will not control it in any manner. I.E., it will never purge.
Not true (in all applications). My megasquirt 3x is setup to draw a vacuum through the charcoal cannister during certain conditions. Certainly this makes tuning a bit more complicated because I have to remember to turn it off when doing VEAL, but when cruising using EGO it adjusts fine.

When I get the MSpnpPro is installed I will see if I can duplicate the functionality if not I will have no choice.
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Old 04-29-2016, 01:01 PM   #477
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Not true (in all applications). My megasquirt 3x is setup to draw a vacuum through the charcoal cannister during certain conditions. Certainly this makes tuning a bit more complicated because I have to remember to turn it off when doing VEAL, but when cruising using EGO it adjusts fine.

When I get the MSpnpPro is installed I will see if I can duplicate the functionality if not I will have no choice.
Oh yeah, I do recall now someone setting an MS3X to do that. Was looking for information on when stock system purged. OK then.

The only reason I regret pulling and trashing my Evap and EGR stuff is that now that I want to use active barrometric compensation, I need the MAP (BOOST) sensor that I threw away.
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Old 04-29-2016, 01:26 PM   #478
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Was looking for information on when stock system purged.
The stock control system is PWM-based. It varies the duty cycle of the purge valve proportionally to engine load (MAF / VAF), after warmup is complete, and whenever:
1: The transmission is not in neutral,
2: The clutch pedal is not depressed,
3: The throttle is not at idle position,
4: The O2 sensor is known to be functioning properly, and
5: RPM is above some value which I can't find.

Also, don't forget the canister drain valve, on vehicles which are so equipped.
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Old 04-29-2016, 01:52 PM   #479
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Interesting. Mine is set to be simple on/off. I have the rpm window somewhere. I'll pull it when I have time.

maybe I'll pull the canister after all. I just prefer to leave everything as functional as possible so there is less to reverse come emissions time.

edit: just pulled my setup spreadsheet and I had it set to purge between 48 and 88kpa.
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Old 04-29-2016, 02:05 PM   #480
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edit: just pulled my setup spreadsheet and I had it set to purge between 48 and 88kpa.
Yeah, that's similar to how I did mine on the MS1.

I'm sure there's some minor technical justification for the use of PWM rather than on/off, but in the end, on/off seems to work fine.
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