How's it going everyone? I've been lurking here for a few weeks now and this morning I made the jump and signed up.

The car is a 1990 Chevrolet Cavalier Z24, running a slightly modded '02 3.4L, soon to be heavily modded (big cam, p&p heads, 3 angle valve job). I've also got an Ostrich 2.0, an Xtreme ALDL from moates, and an AEM UEGO WB. And lets not forget the 7730 ecm.

My current question is, I read a lot of people on here recommend, or are running open loop 100% of the time, so they have total control over fueling. What are some other benefits of running open loop all the time? Also I don't seem to see much related to open loop in TunerPro RT in my .bin/.xdf/.ads.

So what do you guys think...should I be looking into running open loop, or just continue on tuning the closed loop? I'd like to get a better grasp on tuning before I jump in head first when the cam and other parts get installed.

 

ALWAYS ALWAYS ALWAYS, tune in open loop.

Trying to tune in closed loop will cause you to chase your tail. As you make changes, the ECM will also make changes on it's own, causing you to make more changes than you need to and constantly changing the same cells back and forth trying to get everything right.

Tuning in open loop will show you that the changes you make are either in the right direction or not, without the ECM trying to compensate for a wrong setting.

I currently run my Datsun in open loop 100% of the time, I did have closed loop turned on for a while, but decided to get back to tuning it it and just leave it in open loop now, this way I can see how close the tune is at anytime with my laptop plugged in and just cruising down the road. It actually seems to run better in open loop, showing me that the tune was not as close as I thought it was too.

I also run my friends '67 Chev pick up with a 365 (smaller version of the 409) with large cam and custom MPFI intake in open loop 100% of the time, closed loop causes it to run rough at idle and usually stall when coming to a stop or going from nuetral into gear. Open loop cured those problems and he loves driving it now.

 

Hey Six good to see you around, This is troublesomez24racing from v6z24.com. So how would I go about stopping the ECM from going into closed loop? And what tables would be tuned for that? Would I still tune the regular VE tables?

I notice on cold start up, the WB will read 14.7ish almost right away...but within 10 seconds it starts to richen up A LOT, is this normal for a cold start? Or does this have to do with my tune?

 

There should be a "Temp to enable closed loop" constant that you would set to a high temp, I usually just max it out to 151*C to be easy. If you're temp hits that high you have more to worry about than going into closed loop. LOL The name might be slightly different, but you shoudl be able to find it. ctrl+f and type in "closed loop" should bring up a few closed loop paramaters.

Yes all the same tables are used in closed and open loop, all closed loop does is trim or add to the VE table to get the BLMs as close to 128 as possible, which would represent running at 14.7 AFR, or better yet Lambda of 1, really the O2 sensor is a lambda switch, we just set the AFR to 14.7 for gasoline, if you are running an ethanol mix the AFR for stoich will change (be richer) but Lambda remains the same, a value of 1.

Usually a cold started engine will start off richer than 14.7 and then taper off to 14.7 as it warms up. Are you sure it's not just the WB warming up at that point? I'm not familar with the AEM WB to know what it displays while warming up.

 

Thanks for the help Six. I've taken your advice and turned on Open Loop 100%. I found the exact table you mentioned in my xdf. I set the temperature to 151*c and the car stays in open loop...and runs much better I might add. But my afr stays way rich. I found a table, "Open Loop AFR vs Coolant Temp vs MAP" and one called "Open Loop Idle AFR vs Coolant Temp" The 2nd table, I added about .14 to each cell, and it brought my idle AFR back around the 13.5 area. Before this I was idling at 10.5ish.

My .xdf has a flag/switch labeled "Idle BPW as a function of airflow - uncheck to tune idle". Dave, Whitelightning says that most 3400 cars do not idle with that box CHECKED. Mine's the opposite, it'll start and immediatly die with it unchecked. I've decreased and added fuel to the idle ve table with no change what so ever in the issue. I can't even feather it down to an idle by giving it gas to keep it running.

 

[quote=Six_Shooter;4268081]There should be a "Temp to enable closed loop" constant that you would set to a high temp, I usually just max it out to 151*C to be easy. If you're temp hits that high you have more to worry about than going into closed loop. LOL The name might be slightly different, but you shoudl be able to find it. ctrl+f and type in "closed loop" should bring up a few closed loop paramaters. quote]

i was thinking about doing this myself but when i looked i could not find that constant i did find min. closed loop coolant temp. is it the same thing???

 

[quote=slickhick;4274132]
It is the same thing. AIM me and we can chat, I'll share what I've learned so far. V6Z24Racing.

Jay

 

thanks i thought it was the samething, just wanted to be sure ill hit you up later im trying to learn as much as i can

walter

 

If your running a large cam with overlap, full open loop will be compulsory as the O2 in the exhaust will cause the engine to go very rich at idle and at lower RPMs. At idle, my O2s indicate on teh order of 40-100 mV, which causes the fueling to go very rich if the closed loop is enabled. Same thing with the wideband. You need to take care when tuning the VE table at lower RPMs as the indicated AFR will not be the true AFR.