Lex

What link??

Reverant

iTrader: (10)

Read the first post in this thread.

Jim

Lex

Posted in the forum ... my feeling is that it has to do with the IAT correction on hot restarts and the physical nature of the engine itself .... while the PW is so small (idle) fuel delivery that is interrupted by restarting the MS can enlean or richen the mixture.

Running without the IAT correction at idle and rich I eliminated the problem completely.

Keen to see if it can be eliminated otherwise.

grippgoat

iTrader: (1)

Hrm. Since I'm going full standalone with my MSEFI, I was curious what the solenoid on the FPR vacuum line was for. Here is the response I got from my local miata gearheads community:

"Factory ’95 manual indicates the solenoid valve raises fuel pressure to reduce the chance of vapor lock during hot restarts & hot idle, hot being coolant over 194f, intake air over 158f in the MAF."

It seems like that could point the need to enrich the fuel mixture on hot idle, at least on the older cars. I'm guessing 99+ doesn't have that solenoid since it's a returnless system.

-Mike

Reverant

iTrader: (10)

Then you are not experiencing this specific problem but something similar in symptoms. It has nothing to do with IAT correction - read my post above ["Repeat N times within S seconds (with the IAT and CLT not changing more than 3* F) and the results vary tremendously."].

Jim

Lex

I've had the exact problem. Resetting the MS by doing a "Burn" brought the car back to a very smooth idle or kept it in poor idle. It was quite random and unpredictable while trying to maintain a ~14.7 AFR idle.

I am just sharing what cured the problem for me .... running rich at idle and most importantly not allowing the IAT to pull fuel at idle as the sensor heat soaked. It runs smooth every time now.

This leads me to believe that at idle since the pulse width is small enough and depending on your injector wiring the injection event happens at different times in the engine cycle (ie pistons are at different positions with respect to each other in the 4 stroke cycle depending on which of the 4 triggers injection happens on) a physical characteristic of the injection process and exhaust gas scavenging coupled with an injector timing issue is causing the random idle issues.

I run 2 alternating squirts myself but I have heard that if you are able to run 4 alternating you will be in much better shape. The idle PW becomes too small at this point for me. 4 alternating would at least ensure that fuel is injected at the same time within the cycle to each cylinder.

FoundSoul

iTrader: (5)

Those of you experience this issue-- please email me your .msq file with the subject "Miata idle issue-- slight misfire"

I got together with James, Ken, Bruce and actually a crowd of people developed that helped some, this past weekend at the meet. I was able to reproduce the issue on my '91 and I think we've got it nailed... before I spill the beans though I want to see your .msq files to verify something.

Please only send me you .msq's if you feel you're having the exact issue described here.... send them to websales AT diyautotune DOT com

cjernigan

iTrader: (13)

I might be experiencing this issue, my idle just sucks all the time though

Lex

Please do post your hypothesis, I can't wait to try it out!

Reverant

iTrader: (10)

You have email!

Jim

Braineack

iTrader: (62)

I think mines also missed once at idle, and that was mainly due to the a/c as it would do that before the MS....

richyvrlimited

iTrader: (1)

from me too!

Lex

Dammit so what's this new theory??

cjernigan

iTrader: (13)

Chill the hell out man. They're probably not going to release any info until they have the time to analyze everyone's MSQs to make sure there is consistency amongst people that have this problem.

Lex

This is not some commercial product release, a bunch of people using a DIY controller got together and came up with a theory and mentioned it on an internet forum - there is nothing wrong with sharing their findings and saying they are untested.

Perhaps you should be taking things a little less seriously.

cjernigan

iTrader: (13)

Sorry if that came off serious. I want to know as much as you and i understand what you're saying. Hopefully we'll get to see what's up before they release the PnP. I need good idle now and can't seem to get it right :(

Lex

No worries, have you tried my suggestions? I have a great idle now, but it is in the 12's A/F wise. So it no longer depends on "how I start the car" or when I reset the ECU - the idle is always smooth but not emissions friendly.

I really do believe that the issue is with the idle control in that the feedback controller. The O2 sensor feedback controller at idle is not designed to respond like the OEM one does and oscillate the A/Fs as consistently causing the bad idle..

FoundSoul

iTrader: (5)

Wow... Patience guys . I just wanted to compare some of your .msq's to see if it lined up with our findings over the weekend. I had some more testing to do before I could share anything that would be universally helpful -- but I think I can do that now, hopefully.

I can tell you that Ken and James both feel pretty confident it's not a code issue. We had a scope out in the parking lot for a while, along with using the trigger monitor tool in MegaTunix to view the triggers watching for anything funky in the ignition triggering. They couldn't find anything out of the ordinary there. James drew out the wheel pattern and traced it out, and we did change the wheel decoder settings at one point to what he felt may be the better way to set it up, but it didn't change the 'slight misfire' issue for me. It continued.


They kept going back to something in the config/tune. We checked out dwell, played with it a bit, it didn't seem to be the issue for me. Though for someone else it could cause a similar issue. It was running around stoich at idle, mid 14's really. Richened it up a bit to high 13's, better but still missing some. Tried 16deg ign adv, also 12, and 10, no change. Found something that should have been set long ago differently-- I had originally grabbed someone's map off the forums for the base settings back probably 6 months ago-- it was set to 1 squirt, simultaneous. That often isn't best on most motors-- generally 2 squirts alternating is better. We set it to that, and immediately the issue went away on my car. Purred like a kitten.

Looking at the 2 .msq's I recieved (yep, that's it) in response to this thread-- one of them had a REQ_FUEL setting in the recommended range of 6-15ms, and the other didn't. This can make idling a challenge if you're outside of this range. Both users DID have 2 squirts, alternating. So immediately I knew more experimenting was going to be needed. James and Ken are pretty confident this isn't a code issue-- and pretty confident it is a tuning issue, but I know they do want to see it resolved for people. What we found in VA was that going to 2 squirts alternating fixed it for me. The only other change we made was the wheel decoder settings, which I'll be glad to share. That could be related too though in my case it didn't seem to make a difference. On paper it sortof made sense why it could play a role, and in an intermittent sort of fashion like had been reported, and if that's it the new settings should resolve it.

Going further on the theory that worked for me. Different setups are going to have slightly different needs. If you're running different injectors, with different opening times (real opening times, not what's been guesstimated into MT), as well as vastly different size meaning vastly different REQ_FUEL numbers you're just going to have to play with this a bit. The theory is that in a batch/bank fire setup like this, particularly with 1 squirt simultaneous, you pretty much are always running two cylinders potentially lean as the fuel is firing at the same time on all 4 cylinders, but only 2 are close enough to firing time (at idle speed) to get good even fuel atomization in the cylinders-- the other two cylinders, especially the last one in the cycle, is getting fuel that's had time to 'settle' a bit, isn't as well atomized, etc.

But the stock ECU idles just fine right? Why not the MS? Well... it will idle just fine. What we have here I believe is something in the config/tune. On a stock car it's easy to nail-- my car now idles like stock. Purrs like a kitten. Every time. AFRs are now in the low 13's at idle once warmed up.

I leaned it back out to 14.7:1 and it started missing again. Hmmm... that's strange. No other changes, still 2 squirts alternating. So what the heck is the stock ECU commanding at idle-- well that's easy to check. 10 minutes later the stock ECU is in the car, I fire it up, let it settle in fully warmed up, and it's idling at 13.2-13.3:1. Rev the crap out of it, let it settle.... right back to 13.2-13.4:1 range. Leave and come back 10 minutes later (letting it idle), still at 13.2-13.4:1. Purring like a kitten.

The stock computer commands low 13's at idle too. My MR2 on the stock computer liked low 13's. Talking to Justin who works here now but is an ex-Subaru tech he said Subarus on the stock ECU idle in the mid-13's. This is pretty common as I've seen it repeatedly on different makes of cars. Engines make just a bit more power there than at 14.7:1, it makes for a smoother idle, which also makes for better recovery in the event of a stumble for any reason, or increased load, etc. All of which overall contribute to the bottom line of a smoother idle....

My belief-- after spending a good bit of time on this and working with the coders and hardware designers themselves on it (I should have taken a picture, Ken, James, Bruce, DieselGeek, Peter Florance, Dave (megatunix), myself, and several others all standing around this car with a scope, two timing lights, and multiple laptops.) is this--- we just need to tune a bit different here. 2 squirts alternating (for some 4 may work better), I'll get you the new wheel decoder settings in case that does play a role though it didn't seem to for us, and richen your mixture to the 13.2-13.3:1 range at idle once the car is warm.

As for the wheel decoder settings-- pic below-- make sure to check your base timing after changing this just in case it moves!

Lex

So after all I was correct - a motor needs a richer mixture at idle to be smooth IF (and this is a big IF) the A/F ratios are kept constant.

Now, I know this because I've done a lot of experimenting and a rich idle will always be smooth, especially since there is so much more vacuum at idle causing exhaust gas scavenging. Here's another tip, wire your injectors in the way that they come up in the bores. In other words, put 1,4 and 2,3 on the same bank, not like the stock configuration which follows the firing order. If you can, run as many squirts alternating as possible without having too small of a PW as well.

Stock ECU does another trick. The engineers figured out that if you oscillate the PW and timing at a certain rate while always starting injection at the same point in the cycle, it will maintain a smooth idle. The MS can start at more than a single point in the cycle causing for these erratic sometimes it works sometimes it doesn't cases.

This was programmed by Mazda and this is why a stock ECU keeps a steady, stoich idle. In order to get this right on the MS, a lot of experimentation with the feedback sensor must be done or some way of oscillating the PW in open loop. Furthermore, you'd have to start injection at the same point in the cycle all the time - can't specify this in MS.

Easiest solution is to just stick to a richer idle. It will always be smooth. I wanted to see what you guys come up with, but when I brought this up, I did it with experience behind it and lots of thinking. I work as a controls engineer in the automotive field, so I do have an idea of what's going on

richyvrlimited

iTrader: (1)

Jerry, I assume the guy whp's Req_Fuel is out of scope is me :( I'm running RX7 550cc injectors that I had cleaned and flowtested. they actually flow 600cc. A little more than I was expecting :(

I guess that's half my problem then!