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Discussion Starter · #1 ·
having a bitch of a time getting my car to idle low enough. attached is a datalog- spark source is consistently at 2 until load raises and then it goes to the desired 9. what could be causing this. and also the ISC duty cycle and integrator are way off as well. it will surge but hold-however if I drive the car down the road aggressively for 10 to 15 minutes- it will lose it's ability to hold the idle and the car won't stay alive.
 

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· Yes...it can be done
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Touchy game, isn't it? =) There's a few things I did on mine to get it to work low, and come down soft with 15 degrees cam overlap @.050.

The first thing I notice in your datalog is the IAC duty cycle. Second is MAF counts. Third is bank2 front O2. Fourth is TPS. Fifth is coolant temp.

It appears the car is relying heavily on IAC duty cycle for idle control. I like 30% duty cycle when the car is up to temp. That indicates a good balance between air passing the throttle blade with a measured control through the IAC. If the IAC closes all the way, you'll still have a good amount of air passing through the throttle body to maintain engine idle. It also gives the IAC sufficient headroom to add air when it needs to...for example, when first starting the car with cold coolant temps.

MAF counts. Put on a stock MAF for now if you can. Yeah, I know it sounds weird. And yes, it may even be a pain in the ass to do it. But with the cams on the car, you need a known good transfer function and a MAF working in a nice resolution area. Your MAF counts are in a somewhat decent working range (140-150), but a stock MAF will put you a bit higher (180+). It will make life simpler while you calibrate other things like IAC/TPS/throttle blade relationship, injector delay, base fuel, idle spark gain, minimum idle spark clip, etc.

Bank 2 front O2. Put the car in open loop full time for now, as it appears to be in open loop in the log due to coolant temp. With a heavy overlap cam, don't sweat closed loop at idle. That O2 is blanking on you for now.

TPS. The TPS A/D counts are at 155-156. Everyone has there preference for what they like to see as a closed throttle point. The EEC will keep the lowest measured TPS in its keep alive memory, and establish that as closed throttle. The TPS reading, along with the high IAC duty cycle, indicate a choked throttle blade to me. Personally, I like 185-190 TPS counts as closed throttle, with IAC around 30% at operating temperature. My preference. Getting all that is a combination of TPS clocking and set throttle body set screw adjustment.

Coolant temp. 96-108 degrees coolant temp is typically a cold engine to the EEC. There are quite a few variables based upon coolant temp, including fueling, idle RPM adder, etc. Try to work with a warm engine.

Set idle high to start. 1000-1100 RPM. Get that down first. Go down in small increments, getting a feel for the throttle blade/TPS reading/IAC duty cycle. Remember that exhaust valve overlap will grab a little fuel out. You may need a little extra lambda in the base fuel at idle. Getting the throttle blade position right is critical. The right throttle blade position will be advantageous for cold/warm/hot start, dashpot, and maintaining idle.

It isn't rocket science, but it is an art. You'll get this eventually (note the MAF I am using for initial calibration):

Cobra Comp Cams Stage 2 106360 - YouTube
 

· Yes...it can be done
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Couple more notes...

The idle air integrator is telling you something. It's saying "more more more". The EEC wants the IAC to open even more in an attempt to maintain the idle setpoint. Definitely indicating a choked throttle blade. I bet if you were to remove the throttle body and hold it up to a light that you would see very little light emitting around the blade.

Also...analog 1. That looks like an air/fuel reading. You are averaging around 15.0:1. It's tough to gauge the accuracy of the AFR reading in a cammed car when at idle, but I wouldn't rule out going a point richer at idle. Remember...a car going a point lean will have a greater tendency to die than a car going a point rich.

Another good thing to grab in the log will be "idle mode flag". It will give you an indication of what process the EEC is using to control the RPM. I forget the cross reference of the flag number to identify what process the car is in, but I'm sure you will be able to find it and use it as an indicator of what mode the EEC is using for control.
 

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Discussion Starter · #5 · (Edited)
SO- I am in forced Open loop right now (so if my o2 is blanking does that mean it's bad?) and my tps sensor is set to 15.7% and yes I do still need to adjust the TB sensor screw. I had everything bout dead on at 1050rpm for a while but I want it lower in rpm so I am not sitting in traffic using gobs of fuel. Also- I cannot switch to a stock maf- this is a blowthrough F1a setup with a SCT BA5000 maf. so what you're saying is open the throttle position a little more, to reduce the IAC duty cycle (I can log and watch to see at what point in position the IAC is around 30% yes?) and I get confused on the idle air integrator-if it is a postitive value do I subtract from my idle neutral air values, or do I add to them? and lastly- I have it idling so lean right now because I am still trying to get it to stop surging at idle and when it does of course it shoots rich- so trying to get the air right before I tackle the fuel. thanks for your help.
 

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I'm not sure what the 0volts from the O2 means. Could be a number of things. It's not going to be a problem with the car in open loop though, so it's a low priority.

Yep, that's what I'm saying. When I do it, I have the car running with the laptop on the rollaround. As you open the throttle screw, you'll see a few things happening. One, the TPS A/D counts will increase. Two, the IAC duty cycle will begin to decrease. Three, the integrator will begin to decrease. When the integrator is a positive value, all that means is the EEC would like to add more air with the IAC. When it's negative, it would like to take away air. It is looking at the target RPM, the actual RPM, and generating a positive or negative value to blend air in or out (respectively) to better match the actual RPM to target. The neutral idle air values can be used for final fine adjustment (typically a bit higher for a cammed car), but the initial coarse adjustment is in the throttle blade. Don't forget that when adjusting up, you will have to reset the car's keep alive memory so the EEC can re-learn the closed throttle A/D count.

Don't rule out the 15.0:1 as a contributor to the surging. Example: When setting up the desired stoich point and injector slopes on my car after an E85 switch, I was continuously adjust the AFR at idle. When the car was rich, it would surge. When it was lean, it would surge. However...a point richer from 14.7 AFR will not cause idle surge. A point leaner will. With a cammed car, you want an idle that is a bit richer than stock.

Hey, kinda off topic...but how many sets of the keyless cam gears do you have for sale?
 

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Discussion Starter · #7 ·
thanks so much for the help- SCT technical service can suck it. I will try again tonight hopefully. as far as the cam gears go- you talking about the stock cam gears I have for sale? I think I have 1 complete set and a set of exhausts- I will have to check though. I am using the TFS crank gears and cloyes adjustable on my exhaust sides
 

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idle mode flag, make sure its correct

if the PCM isnt in idle mode it will never enter spark source 9 (idle spark control)

Easy way to set the TB blade is lock the IAC x-fer at about 30-40% then set the vehicle to run at that speed via the blade. Fueling has to be correct also otherwise it will skew your number. Then unlock the IAC in the tune and start working your ISC air tables.

Alot of the issues with idle spark control etc is due to the fact of a binding TB blade that otherwise was fine when cold. Car gets hot...blade swells, catches the inside of the TB and the TPS relative reading never zero's out. The pcm thinks the car is in part throttle mode and now runs on spark source 1 or 2.
 

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Discussion Starter · #9 ·
idle mode flag, make sure its correct

if the PCM isnt in idle mode it will never enter spark source 9 (idle spark control)

Easy way to set the TB blade is lock the IAC x-fer at about 30-40% then set the vehicle to run at that speed via the blade. Fueling has to be correct also otherwise it will skew your number. Then unlock the IAC in the tune and start working your ISC air tables.

Alot of the issues with idle spark control etc is due to the fact of a binding TB blade that otherwise was fine when cold. Car gets hot...blade swells, catches the inside of the TB and the TPS relative reading never zero's out. The pcm thinks the car is in part throttle mode and now runs on spark source 1 or 2.
where can I find the idle mode flag?
my SCT pro racer doesn't have a means of setting the ISC duty to 30%- believe me I have looked (I am using a LLX4 ECU
 

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Discussion Starter · #11 ·
when I get home I will checkfor sure- but I never saw where I could hard set ISC duty cycle. also- when I do reach 30% ISC duty cycle and around 0 for the integrator. what method do I use to low my idle rpm? my commanded is 850, when the ISC is around 30% I remember my rpm being in the 1050 range. so what do I change to lower it, the idle neutral air table?
 

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when I get home I will checkfor sure- but I never saw where I could hard set ISC duty cycle. also- when I do reach 30% ISC duty cycle and around 0 for the integrator. what method do I use to low my idle rpm? my commanded is 850, when the ISC is around 30% I remember my rpm being in the 1050 range. so what do I change to lower it, the idle neutral air table?
After you set the throttle blade to your "commanded in tune setting" you rewrite the tune with the x-fer function back to stock. You also have to ensure your fueling and spark isnt over influencing the idle. Otherwise you will be running in circles. If you are in open loop, make sure you are idling at or near stoich to have a fighting chance of making accurate isc air table corrections.

After you warm vehicle up....look at the integrator.....it will tell you what the pcm is trying to do to the iac in order to hit target idle. AGAIN look at spark source and make sure its running in mode 9....otherwise you will have elevated spark...hence an elevated idle due to the increase of torque overcoming the engine drag.

If its in spark source 9....let the integrator stabalize and these are the corrections you make to the isc air tables at the appropriate rpm levels.
 

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Discussion Starter · #14 ·
right now I have my lowest spark at idle set to 0*, idle gain at .75, and borderline spark at idle at 10* per eric brooks suggestion. with these settings, if I am not at 9 for spark source what should I change spark wise?
 

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Discussion Starter · #15 ·
it's funny- this is most help I've had with tuning the car- this is my first tuning experience and SCT give me the most vague answers when I ask very specific questions. thanks again everyone for your guidance here, the car ahs been giving me such a hassle lately I even dreamed of trading it yesterday for a while
 

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Discussion Starter · #18 ·
it poured rain all day yesterday and last night so I didn't get a chance to back my car out (can't crank it in the garage or I'll choke to death) so I will update this when I get a chance to make some changes this weekend. I did find the idle xfer function table Kevin- I am going to try and tackle this without setting all of the values to .30 first though. I also ordered Don lasotta's new book last night as soon as I got his email- so looking forward to that as well. thanks again all.
 

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it poured rain all day yesterday and last night so I didn't get a chance to back my car out (can't crank it in the garage or I'll choke to death) so I will update this when I get a chance to make some changes this weekend. I did find the idle xfer function table Kevin- I am going to try and tackle this without setting all of the values to .30 first though. I also ordered Don lasotta's new book last night as soon as I got his email- so looking forward to that as well. thanks again all.
why try to tackle it and not follow correct proceedure?

set the iac....and TB blade....this insures a correct foundation....
 

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Discussion Starter · #20 ·
ok-I just get so tired to loading tunes everytime I change anything.
I will set all values in the idle xfer fuction table to .30, set TB screw until intergrator reads zero- then reload stock values into idle xfer function table and clear KAM . is that right? and by hard setting the IAC I don't have to disconnect it and all that right? thanks again
 
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