it exits closed loop becuase of the draw on the engine is momentarily large, so its probably intended to enrich a bit since there is no throttle input, this will keep it from harshly dropping in normal circumstances
There is a switch in the PS hose on 5.0 for the same purpose, but it kicks the idle speed up

 

I have one, I removed it when I installed the megasquirt ecu. Everything I read stated to remove it since the ecu should be able to control it!

 

theres no reason to remove it, but i believe the reason for it was due to 2 things
1) potential for electrical purgatory for the processor to control idle properly, which i could see the megasquirt being able to avoid that (as did later eec-iv)
2) Keeps the air rate proper and consistent despite the changes that will occur because of sludge/oil/dirt buildup in the throttle body
But as it pertains to getting your settings rightr, shouldnt overall tchange things.

 

Yes it will, your close with dialing it in.

engine is at full operating temperature?

 

Yes Sir, GA afternoon weather! I’ve been waiting to the hottest part of the day so the AC is working hard as well.

You’re saying to put it back on also?

 

im saying put it on because it shoudlnt hurt, but you would have to remesss with the stop screw and whatever megasquirt stuff. But

I think white is saying your pcm will control it just fine, so wasnt necessarily saying to put it on or take it off but that the pcm should be fine to control it.

 

Ok, so more reading and screwing around (maybe screwing up haha) on things that’s been mentioned. There’s not a lot of info on tuning f150s with megasquirt that I can find so I mostly read Mustang crap, it’s close enough it seems to keep me running every day. I read more on injector set up. It said high impedance should have a dwell time of .9-1.1. Mine (it was in basic tune provided) was set at 1. I changed to .9 to see and she hated that, with a passion. So next logical step is 1.1. That has actually smoothed my idle with ac off even more and now my oscillation is within 100 rpm. I’ve shut it off and turned back on, truck and ac, multiple times and no crazy oscillation. I know there’s more to go, but I’m getting there.

I ran autotune at idle since the afr dropped to 12.8. It’s back to 14.4 idle where I like it. Thank you EVERYONE that has given input! This has been a challenge for me since I am a Chevy carb guy! Never been a fan of people saying “you can’t do that or it won’t work right” I make those experiences lessons!

 

Another place to look/ask is at efidynotuning.com, there’s lots of write ups and tuning info, concepts are the same, I’ll try and find the iac ac write up, it does exist and will solve your problem. It’s a matter of knowing which parameter to adjust in the tune.

 

Yes, still a massive learning curve for me, but I enjoy it. I will look at that website, thanks!

 

In megasquirt dead time is applied as an over-simplification assumption that for the duration of dead time no fuel is injected. When it's set right a little gets through but not much.

So the way you dial in dead time is to play with squirts per cycle. When your dead time is close then changing from 1, 2, or 4 squirts per cycle will not create major changes to your AFR.

This is because if your dead time is too big, then you're getting too much un-accounted for fuel during the dead time. Doubling your squirts per cycle doubles the application of dead time, doubling that mass of un-accounted for fuel so a dead time that is too big goes richer and richer the more squirts per cycle you configure.

It's the opposite when your dead time is too small, since in that scenario you're still not getting meaningful fuel flow immediately after the dead time so the VE table ends up a little bigger than it should be to compensate. As you double squirts per cycle you double this leaning effect and go leaner and leaner the more squirts per cycle you configure.

I recommend doing the testing while holding an RPM of 2500 or so, injector behavior at small idle pulse widths idle is often too inconsistent.

 

Making sure I understand correctly, bring up rpm and set a dead time and change squirting. The dead time that produces the least braising between squirts is most accurate one? Can it be higher than 1.1? I have 19lb Bosch 4 holes.

I tinkered a little when I got home. With 4 squirts, I was able to reduce the whole VE table by 4 points to get my AFR back up. Currently at 1.1 dead time and 4 squirts. After changing the table, my oscillation with ac is down to about 60-65 rpm and now no initial surge!

 

Yes dead time can be higher than 1.1.

Start with squirts per cycle at 1. Hold at 2500 RPM and note your average AFR over some time period, 1-2 minutes should be fine, easier to do if you're logging.

Then change squirts per cycle to 4 and repeat noting the average AFR over the same time period.

If you went richer going from 1 to 4, then your dead time is too long. If you went leaner then your dead time is too short. If it pretty much stayed the same, you're good.

There's some more nuance here as well because injectors respond differently to different fuel pressures, and different voltages, so it helps if you also log voltage and make sure it's basically the same for both too but assuming other things aren't moving around too much then this works pretty well.

 

So.. it will only let me choose 2,4 and 8 squirts. Every other option gives an error due to 8 injectors. How did you get around that? Or is that the right numbers and 1234 is just examples?

I truly appreciate the detailed responses!! I got the .9-1.1 range of the diyautotune set up page. That’s who I bought mine from. It’s supposed to rain this weekend and we need it! Good excuse to sit in the truck for a spell haha!

 

Ah sorry I forgot, you can only choose 1 if you define simultaneous injection, if you have alternating then the minimum is 2. I'm assuming you aren't doing full sequential, is that true? You can do the same thing without starting at 1. The greater you increase the squirts from wherever you start the more exaggerated the results. You can get the same effect going from 2 to 4, but you'll get it even more exaggerated going from 2 to 8. I usually just do 1 to 4 but not because I've scientifically determined that's the best or anything, it's just my thumb in the wind.

 

It is not full sequential. More homework before I look into that! I don’t know that I use the truck to see full benefit in that. 99%of driving is stop and go inside a small town. It’s rare that I get the truck on a road and get above 45. I do landscaping and most clients are less than 3 miles away.

90% of my tuning has been: read some things, take a pic of my settings and then change to see what it does haha. Those pics have helped quite a few times…

I will tinker this weekend and report back with numbers, thanks again!