What makes a tune an open loop tune? How do you accomplish this?

 

There is a tuning process that forces 'Open Loop" to allow the tuner absolute control of settings during the tuning process.Under normal conditions when you enter WOT, BLM ready drops, and the PCM goes into 'open loop' (no more O2 feedback & correction). BUT the BLM cell reading just prior to entering WOT (usually BLM cell 15 for ODB1 ) is remembered and is used in the WOT fueling calculation. Therefore that last BLM reading will effect the WOT AFR. To eliminate that problem tuners will reset PCM (all BLM values go to 128 = no PCM correction) and turn off 'closed loop' that will prevent BLM updating and stop the PCM from looking at the BLM cell prior to entering WOT. This allows the WOT AFR to always reflect the tuners changes w/o the PCM trying to richen or lean the AFR based on that last BLM cell reading. Some pro-racers w/modified setups force open loop all the time and rely 100% on the AFR gauge, that process takes the O2's out of the picture holds all the BLM's at 128 and you calculate fueling based 100% on your tune and engine sensor feedback w/o PCM trying to correct the AFR to 14.7. However if something fails and you go lean you suffer the consequences. You can force open loop by changing the closed loop coolant constant to a temp higher than you will hit.

 

thanks Bob, You made things much more clear. I have been learning how to tune over the past year and have my car running pretty well with the exception of when the car is in open loop it feels like it has much more power and it never logs knock. When it goes in to closed loop it only logs knock at lower RPM's and it is occasional. I have even put 110 octane in her and it seems to make no difference.......any ideas

 

In MAF mode open loop the PCM uses the " Open Loop AFR Vs Coolant Temp Vs MAP" table which is a little richer than the closed loop 14.7 AFR setting. Plus the coolant temp may be lower ? This could be altering (clearing up your knock) or you may have a bit too much timing adding to the problem. Knock is usually caused by either/or a combination of lean AFR, advanced timing or high temperature in combustion chamber. Altering any of the 3 could cause/cure real knock problems. If you can isolate the knock to a specific RPM range or BLM cell you can richen the mix (increase MAF tables for effected AFGS range) or decrease timing in the main table for that RPM/MAP range. Also dropping coolant temp could help. I chased 4800-5200 RPM knock for 6 months trying all the above with no avail. I finally bit the bullet and put in an LT4 KM and the darn thing cleared up my knock, apparently I was chasing a false knock, that I could not pin down. What are you using for Data Logging, I know you converted to ODB1 from other posts, can you post or e-mail a log of the knock in closed loop ?

 

Bob, I am using freescan and I can do a datalog later today and I can E-mail you the log or post it, just let me know which method u would like. I do have a lt4 KM also installed in to the PCM.

My car has been to the track once and I ran a 13.01 @ 113 MPH and started out with no knock counts on freescan when watching engine data while in the staging lanes, when I was through with the run at the end of the track I had like 12,000 + knock counts. I tried to datalog that run but my laptop was locking up everytime I tried to start a datalog.

When I drive the car around the block and just do part throttle, that is when to knock happens from 1,000 rpm's to about 3,000 rpm's.

 

Is the data indicating actual knock retard in degrees, or are you just going by the increasing "knock count"?

 

Fred I guess its just knock count, I tried to start a datalog of the run at the track but laptop was causing freescan to lockup everytime I started to log. When I drive the car around town and log it, the log shows knock only in lower RPM's and its occasional.

 

Took a look at your .cvs file. Looks like a basic around town street run. From what could see you fueling looks good, Timing looks good, Voltage, Temp, Baro, MAP, AFR, MAF, etc readings all look good. Your TPS voltage is a little high .8 volts at TPS=0, but you may have it set that way for your cam and TB. As far as knock retard I see when you do get knock (knock count and retard 1-4 degrees) you are at a steady cruising speed EG: 25 MPH or 45 MPH, the throttle is decreased and as you tap the gas slightly and increase TPS a couple of % knock count bumps up and timing is retarded. This happened in a 0-3% TPS swing and I saw it in a 3-8% TPS swing. Also your RPM was always in the 2100-2500 range when this occurred. The LT trims look +/- 5%, nothing radically out at this time, the AFGS is stable w/o any jumps, timing is close the the stock setting (40-41*). So basically you are getting knock count incremented and 1-4% retard in cruising BLM cells 7, 11, and 18 when you tap the throttle a couple of percent under low to no load (0-10% TPS) driving conditions. This could be a vibration problem !!! It's also something you probably don't feel under normal driving conditions as your RPM only fluctuates 25 RPM, not like a 10* retard during WOT that you can feel the 100 RPM dip. I also see the PCM retarding spark when you are not incrementing the knock count. This is because the PCM remembers the operational conditions and BLM cell(s) that previously caused knock and it will retard timing automatically to prevent the condition. This prevention retard go's away eventually if the knock does not return. Your knock could be false caused by engine or exhaust vibration when just taping the gas a bit.."usually" pre-detonation does not occur at no to low engine load conditions. Would be nice to see a WOT run to see if your getting any retard when the engine is pulling...

 

Bob, I will do a WOT log sometime this weekend and will email it to you. I do think it is "false" knock too, when I log a WOT run I really do not see any knock retard. I could send u my bin file, if you wanted too see it.

 

This may sound confusing, and may have to be read a couple of times.. What you have to think about during a WOT run is 'Burst Knock' This is a condition when the TB opens fast and air rushes into the intake faster than the PCM/Injectors can react. This lean mix condition can cause knock. To prevent this the PCM retards timing when it thinks burst knock may occur "Burst Knock Vs Coolant temp" table AND a looks at constant entry that tells the PCM when to activate the table retard "Burst Enable% Diff AF Threshold" Under normal conditions if the % AF per/ ? time frame exceeds the constant the PCM will pull timing. (timing retard w/o knock bumping) Now the kicker.. many tuners Zero out the burst retard table to prevent automatic pulling of timing during fast acceleration, however with a set up that rapidly sucks a lot of air if TB suddenly opens wide this opens you up to a real knock caused by a lean mix condition.. Bottom line... If your burst knock retard is zeroed out then you may be open to real knock due to lean mix at the start of WOT conditions.. Just something to look at.

 

"In MAF mode open loop the PCM uses the " Open Loop AFR Vs Coolant Temp Vs MAP" table which is a little richer than the closed loop 14.7 AFR setting."

I also have an open loop tune with MAF. I've changed the values in this table to 14.7-15.0 at my corresponding idle MAP cell values at all coolant temps and this doesn't seem to have effectively leaned my idle. Are there any other tables in TunerPro5 that should be adjusted for open loop AFR tuning?

 

lightskindwonder, Sorry I can't answer why richening the table does not effect your AFR readings. Some things in these PCM's decisions depend on other variables that we don't know about. What is you AFR at idle ? If your problem is at idle only I would look at the "Individual Cyl Fuel Trim Multiplier" table IDLE settings. Decreasing the multipliers x% for all cylinders should lean you out x% at idle. The OFF IDLE settings are for low TPS operation controlled by a "Indv Cyl Fuel Trim Disable %' in the constants. Stock setting uses the off idle settings for TPS below 14.8%. Also another way to lean idle would be to tweak the MAF table at idle AFGS, but that's not a precise, the multiplier table is easier. How are you correlating your wideband readings to AFGS in order to run OPEN Loop MAF Mode ?

 

Bobdec, thanks for the information. I'm not sure I understand your question, but my tune has closed loop enabled at 151C. MAF still plugged in. My dyno session sheet showed a constant AFR of around 13 from 2k rpm through 6k rpm, but no readings were recorded before 2k (i.e. around idle). I do not have a wideband with me, so I have no way of recording AFR from home, but I'm just trying to adjust my idle so that I can breathe without cracking the window at idle . I don't have manifold leaks, and this rich condition clogged my brand new cat within months so I've since hollowed it out. The fact that the O2 sensors are still plugged into the harness shouldn't affect fueling since they're only enabled @ 151C, right? Any additional help is greatly appreciated.

 

With closed loop enabled at 151C you should be in open loop and the O2's are out of the PCM fueling picture. I assume the AFR readings on the dyno were at WOT so the 13 is OK. In Open Loop SD Mode the PCM uses RPM, MAP and the VE tables as the major factor to calculate the injector PW. There is no O2 feedback correction and the AFR depends on correct setting of the VE tables. In Open Loop MAF Mode the major controller to the PCM is the MAF air flow grams per second (AFGS). The PCM divides the weight of the air (among other sensor data) by 14.7 and fires the injectors to add fuel (14.7 grams of air requires 1.0 gram of fuel) Again there is no O2 feedback correction. Fueling is based on the injector settings and the MAF readings. To adjust AFR in that condition you need to know the AFGS readings during rich operation. So you need a data log AND a wideband synchronized together automatically on a trace or manually by viewing each log to identify what AFGS ranges to alter in the MAF tables. Since SD mode only looks at RPM not AFGS it's much easier to tune an SD open loop than a MAF open loop. As a sidebar why are you using an open loop tune, your mods do not seem that drastic to require open loop operation. Also what tuning software and logging software/scanner are you using ?

 

Speed density actually calculates AFG/S from RPM, VE, MAP and IAT. From that point forward, there is no difference in how the system proportions mass fuel flow to mass air flow. Mass air/target A/F ratio = mass fuel.