91chevz71

Hey guys, what's up-
Just wondering if anybody out there has attained a good idle with
this combination for the 350HO, 90 lb/hr inj's, stock psi, and a 50mm
TBI (small block). I've been chasing this for a while-
I think it might be the nature of the beast with the large inj's with low psi.


Thanks,
Mike

Fast355

iTrader: (2)

I don't think so. Big injectors as long as the spray cone looks good, should idle fine. I would go for an open loop idle though as the cam in the HO 350 is not the most ECM friendly around idle. I did this with the ZZ4 cam in my Van. Tuned the idle timing and air/fuel ratio for the highest vacuum in both park/neutral, drive, with and without the AC. I idle perfectly smooth now without surging or roughness.

91chevz71

nice. So you disabled closed loop and messed with the open loop AFR's.
I'll change that around. How did doing this help the closed loop idle?
How did you disable closed loop during idle?

Fast355

iTrader: (2)

Yes I have. I don't think you will be able to run that cam in closed loop very well. It has alot more overlap than a stock cam. That passes oxygen right past the oxygen sensor, which sends a lean command back to the ECM and confuses the heck out of it.

To enable open loop idle, go to the Switches section (middle column), option word 1, bit 2, OPIDL.

My engine likes the command air/fuel ratio and the wideband at about 13.5-13.7:1 at idle.

Fast355

iTrader: (2)

Here you go the two tables you need to look at.

I run open loop cruise as well, but that is personal preference.

91chevz71

Excellent.
quick question- If the BLM's are good, what would be the advantage of going into open loop during idle? I don't want to sound ignorant, just wondering what is different besides the computer not listening to the O2
My table (Open Loop AFRvsCTSvsVAC) looks almost identical to yours. This is what your're running with the ZZ4?
Yeah, I just wonder what the difference would be between 128/128 closed loop and 14.5 open. Good stuff.

Fast355

iTrader: (2)

It will idle slightly richer, which is commonly needed on a cammed engine. The stock engine barely likes to idle at 14.7:1, much less a cammed engine.

Also don't forget that in closed loop you have proportional gains to deal with as well.

91chevz71

O yeah. The prp switching for the rich/lean stuff. I am definitely going to mess with this. I EXTREMELY APPRECIATE your help/tips/advice/knowledge!!!
Hmmm...I like this open loop idle idea A LOT


Keep it coming....lol
Mike

alvanwie

Don't have a problem with mine running closed loop idle. The idle is great, but it did take a lot of time to get it there.

91chevz71

Which areas gave you the problems? How did you set up the bin for the injectors?

91chevz71

Ok. Switched to Open loop idle, and it helped considerably. The idle AFR is at 12.3 for right now. Something makes me think my injector terms are off in the bin, hearing everybody else's results are good with these inj's...
I doubt it needs to be THAT rich, that's what makes me think something else is off
Hey Fast, what's your sync pulse width at idle in open loop?

Mike

RBob

iTrader: (1)

A must do for TBI idling is to run betwen 5 and 10 IAC counts. This is with a warmed up engine that has been idling for a copule of minutes, no A/C, no heavy electrical loads.

Turn the throttle screw in to lower the IAC counts. Once the TPS% increases by 2% or so, the ECM will drop out of idle mode (it thinks that the driver is pushing on the go pedal). WIll need to do a shut down, wait 5 seconds, and restart before continuing.

Or, if it currently idles with a lot of counts, crank the throttle screw in with the engine off. Then start the engine, let it idle for a couple of minutes, then turn the screw out until about 5 IAC steps are used.

What this does is to have the majority of the air go past the blades. This pulls the fuel into the mix better then having the air bypass the blades via the IAC.

RBob.

91chevz71

Idles CONSIDERABLY better with open loop, IAC counts about 15. I'll open the blades a little more and see what happens. THanks Rbob

Mike

alvanwie

Attached are some of the changes I made to get a good idle with my setup. This is with th 8746 ecu and I started with the stock ANTT bin. Yes, I set the injector constant for the injectors and fuel pressure that I am running. The engine is set to idle at about 800 rpm and my SA table is set for 26 degrees in the idle region. My IAC steps at idle are generally around 30. Not all of this will be correct for your engine, but maybe it will give you some ideas to try. You will notice the changes to prevent it from going into async fueling at idle. About the only time it goes into async is during decel.

Al

91chevz71

Cool!!! I'll take a look and compare. Do you have any lope at idle at all, or is it like butta?
-Do you need some kind of software to take pictures of the tunerpro screen?

Thanks,
Mike

alvanwie

Once I had the idle work out correctly, it actually sounds pretty mild. You still know it has a cam but the idle is quite smooth.

To get a picture from the screen - hit the screen print key, then open up the "Paint" program, go to the 'edit' menu and select 'paste', then go to the 'file' menu and select 'save as', set the file type to 'jpg'.

Ronny

iTrader: (1)

my idle smoothened out considerabley going to synch only fueling. before the transition from synch to asynch fuel would cause an erratic idle. Open loop helped as well 14.3/1 on WB. PW at idle 1.10-1.30 msec. 0-3 steps IAC at idle.80 lbs inj's at 23 lbs FP.

91chevz71

Right now, Async fuel is disabled. Mine idled extremely erratic with both enabled, but now mine is like yours-
1.1-1.2 sync pw, 40-43 MAP, 10 counts IAC, 650-675 rpm.
What's your BPC with 20 psi and 80's?

Ronny

iTrader: (1)

BPC should be 82 or so but that allows some VE cells over 100(well over) so I changed my BPC to allow max values in mid 90's for VE. Not sure why that is?

91chevz71

My BPC is 95, after trying a bunch and doing the math over. I think I got it though, no VE cell is >100, idle is about 45 %.
If ran less FP, your BPC would increase, yes?
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I'm willing to bet I'd get better fuel atomization and a cleaner idle by running 15 psi. I'm gonna try that. (recalc BPC for more PSI)

Ronny

iTrader: (1)

large injector is a smaller BPC.

so reducing the FP =injector acts as a smaller injector and BPC increases.

91chevz71

Dude, I am all screwed up. Anyway, that makes- It also makes sense that my BPC is 95 with 90/s and my stock 8-13 psi who knows whatever it wants in between there regulator...lol
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makes sense..god...duh- my stock L05 w/ 65's had a BPC of 135. sometimes I forget the common knowledge i guess