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Old 10-07-2009, 09:14 PM   #1
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Default Runs better in open loop?

I have a 1989 firebird with a LQ9 swap, with a cam, exhaust, and stall. The car seems to run well in open loop, without the O2 sensors. However as soon as it goes into closed loop, it seems like it isn't as easy to rev the motor, it also seems to bog on decel.

I did have 2 vacuum leaks (unplugged vacuum ports on the manifold), apparently the guy who installed the motor didn't plug those. There was also a large leak around the drivers side collector that i recently fixed.

Is it possible that my tune is now off and the car actually runs more efficient in open loop? Is there a way I could keep it in open loop to test the theory? I just don't understand why it feels so much more "snappy" in open loop, and turns into a slug in closed loop.

No codes are shown, Both O2 sensors are new, no more exhaust leaks, good gaskets, etc.
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Old 10-08-2009, 12:22 AM   #2
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One possibility is that your fueling is way off and once it goes into closed loop the computer is pulling or adding too much fuel. Get that thing tuned.
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Old 10-08-2009, 10:48 AM   #3
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This could be sensor temperature related if you're
running long tubes (esp. uncoated), leading to a
false trimming. So could the exhaust air leaks, but
this should "settle in" over time.

If it runs well in open loop, at least your base tune
is not-insane. That's the good news. Trick is to get
closed loop to go along.

Got scan?
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Old 10-08-2009, 02:07 PM   #4
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I wish i had scan/tune software. Best I can do is make educated guesses at the moment and make sure everything works ok (scary I know). It runs awesome at WOT, and will spin the tires from a 60mph roll, but acts like a dog in most other situations. Drives me crazy!
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Old 10-08-2009, 02:47 PM   #5
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speed density FTW screw 02's and screw a maff
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Old 10-08-2009, 09:40 PM   #6
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What is the cheapest option to get tuning myself? I really don't want this motor going down hill, if it pops, the car is getting sold off for parts, and it's my high school car. Should have kept the TPI honestly LOL

HPtuners and LS1edit seem to be about the same price, but are all programs really THAT expensive? It's either buy the program myself, or pay some one the same amount to tune it for me, but I don't get to keep the software....
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Old 10-08-2009, 09:40 PM   #7
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Well since it double posted, Is there anyway I could try to keep the car in open loop? Also I remember the tuner saying they couldn't get the KR down, I believe it was because of false knock. So max timing is only ever 20*, which seems very low, considering some seem to run mid 30-40s...

Could I unplug the Knock sensor and see what it does?
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Old 10-08-2009, 10:58 PM   #8
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You sound like the kind of person that would be able to learn to tune with HP tuners or EFI Live pretty quickly. I personaly use HP Tuners and therefore I sugest it over others because I know it.

If you bought HP or EFI you can correct all your issues, learn how to tune, and be able to tune the car for future mods. Either realy is a great investment if you plan to play with your car. Both are more then worth the asking price. Thats were you should go before you start unpluging things.
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Old 10-09-2009, 12:24 AM   #9
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Quote:
Originally Posted by Texas_WS6 View Post
You sound like the kind of person that would be able to learn to tune with HP tuners or EFI Live pretty quickly. I personaly use HP Tuners and therefore I sugest it over others because I know it.

If you bought HP or EFI you can correct all your issues, learn how to tune, and be able to tune the car for future mods. Either realy is a great investment if you plan to play with your car. Both are more then worth the asking price. Thats were you should go before you start unpluging things.
agreed......


you shouldn't unplug you knock sensors, no. I had a case of false KR on my car and I tuned the sensors. I would say buy the hptuners software also, it will take time to become a good tuner but its worth it.
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Old 10-09-2009, 06:07 PM   #10
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I might be wrong but i was thinking it stays in open loop until the o2 sensors reach operating temp. If that's the case it would stay in open loop if you unplug o2 sensors, but that wouldn't be the way too fix the problem.
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Old 10-09-2009, 11:48 PM   #11
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Quote:
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I might be wrong but i was thinking it stays in open loop until the o2 sensors reach operating temp. If that's the case it would stay in open loop if you unplug o2 sensors, but that wouldn't be the way too fix the problem.
correct, but that's a hack way of dealing with the problem
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Old 10-10-2009, 11:25 AM   #12
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false it does not go into closed loop that way, it goes by enginge temp closed loop enable setting in your parameters.
Quote:
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I might be wrong but i was thinking it stays in open loop until the o2 sensors reach operating temp. If that's the case it would stay in open loop if you unplug o2 sensors, but that wouldn't be the way too fix the problem.
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Old 10-10-2009, 11:44 AM   #13
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Thanks for the correction, like i said i might be wrong.
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Old 10-10-2009, 01:57 PM   #14
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Just to clarify I wasn't agreeing that closed loop is dependent on O2 temperature, I was agreeing that disconnecting them will force the system into open loop.

and yes, closed loop is based on coolant temperature.
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Old 10-10-2009, 02:54 PM   #15
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part of the reason the engine runs better in Open loop is because while the coolant temp is still lower and the pcm is operating in OL the PCM is targetting a richer AFR then it does in Closed loop. Once it goes to CL it will be targetting Stoich (14.68). Depending on the size of the cam that might be too lean to make the engine idle right. It will make the engine choppier due to it being so much leaner. I personal have been running my setup in Open Loop Speed Density 3 bar and I target and tune my Open loop tables with a wide band to 13:1 AFR. At that richer setting the car sounds almost stock, very little lope. Once I let it go to Closed loop and the WB are reporting 14.6 as comanded it idles very ruff and the drivability goes to $h!t as compaired to Open Loop.

What i am saying is there comes a point depending on setup that closed loop operation becomes a hassle.

Pros to Open loop operation at all times is you can run wilder cams and mods and the engine will operate as desired.
Con to Open Loop operation; fuel economy is sacrificed. But I am not a green guy and could care less about economy.

I think you can tune to be in open loop more at slow speed and to go into closed loop once you get up to cruise speeds. I personaly have yet to get to that point. Maybe someone here can shed som light on this.
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Old 10-10-2009, 03:21 PM   #16
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Quote:
Originally Posted by Texas_WS6 View Post
part of the reason the engine runs better in Open loop is because while the coolant temp is still lower and the pcm is operating in OL the PCM is targetting a richer AFR then it does in Closed loop. Once it goes to CL it will be targetting Stoich (14.68). Depending on the size of the cam that might be too lean to make the engine idle right. It will make the engine choppier due to it being so much leaner. I personal have been running my setup in Open Loop Speed Density 3 bar and I target and tune my Open loop tables with a wide band to 13:1 AFR. At that richer setting the car sounds almost stock, very little lope. Once I let it go to Closed loop and the WB are reporting 14.6 as comanded it idles very ruff and the drivability goes to $h!t as compaired to Open Loop.

What i am saying is there comes a point depending on setup that closed loop operation becomes a hassle.

Pros to Open loop operation at all times is you can run wilder cams and mods and the engine will operate as desired.
Con to Open Loop operation; fuel economy is sacrificed. But I am not a green guy and could care less about economy.

I think you can tune to be in open loop more at slow speed and to go into closed loop once you get up to cruise speeds. I personaly have yet to get to that point. Maybe someone here can shed som light on this.
It's true you can run, what I call, a "hybrid" tune where it idles in open loop but goes to closed loop above idle. Open loop doesn't cause less gas mileage, the fact that you are commanding 13.0:1 causes worse mileage. Its for a good reason though, drive-ability over mileage.
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Old 10-10-2009, 06:29 PM   #17
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I need to get some pointers from you and how to make the tune "hybrid". I prefer the way my car idles and drives around town under 40 mph in OL but I would like to have it go into CL when I get out on the hyway, were it runs just fine at the leaner 14.6 comanded AFR.

Any direction on doing this would be very helpful.
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Old 10-12-2009, 10:29 AM   #18
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Awesome info guys, I appreciate it!
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Old 10-12-2009, 12:52 PM   #19
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I think 'Texas' was on to something.

Granted my cam is not wild, but I chose to stay closed-loop. I did all the usual tuning of the VE Table and MAF. For what it is worth I simply changed the O2 Switch-points to 550mv instead of the usually lower stock values.

Took almost all the air out of the Throttle Cracker below 2200 Rpm's. Whether changing the Narrow-band O2's 'really' work.while I can not specifically prove it..at least my wideband reads what I command and the Trims keep highway AFR at ~14.7.

If you can get closed-loop to work..it is really not a bad thing. It may just get to challenging as you start getting into the more wild cam profiles and larger injectors.

Good luck.

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Old 10-12-2009, 12:52 PM
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