Still having idle issues, experts inside!
01-09-2012, 11:11 PM
#1
Still having idle issues, experts inside! So I've been dealing with an idle surge for years now, but I finally have access to HPT so I'm slowly making changes. When I first start the car it will run decently, then randomly start surging. It will happen in both open and closed loop. This will happen if the car is hot or cold. It really doesn't matter the variables, the surge still is present.
The car has been tuned a few times in the past by pretty knowledgeable guys, but I still thinks there are some changes to be made. Mods are LS6 heads, 230/234 cam, FAST 90/90, full bolt-ons, 4600 stall.
Attached is my tune and a few logs. Please look these over and let me know if you see any glaring mistakes or changes that can be made. A few things I've noticed:
1. My tune seems to have more timing at idle than most like (according to searches on here). Is low 30s too much?
2. My stoich AFR was set to 15.5. Is this just a factor for multiplication, or does this value actually change my AFR?
3. My VE table looks solid, so I don't think this is a fueling issue. FP is a solid 58 psi at the rail at idle.
I'm deploying for 30 days on Wednesday, so I'm trying to get this done before I leave. Thanks!
Log 1-Cold start
Log 2-Idle after ~5 minutes of running
Log 3-Idle after ~7 minutes of running
The car has been tuned a few times in the past by pretty knowledgeable guys, but I still thinks there are some changes to be made. Mods are LS6 heads, 230/234 cam, FAST 90/90, full bolt-ons, 4600 stall.
Attached is my tune and a few logs. Please look these over and let me know if you see any glaring mistakes or changes that can be made. A few things I've noticed:
1. My tune seems to have more timing at idle than most like (according to searches on here). Is low 30s too much?
2. My stoich AFR was set to 15.5. Is this just a factor for multiplication, or does this value actually change my AFR?
3. My VE table looks solid, so I don't think this is a fueling issue. FP is a solid 58 psi at the rail at idle.
I'm deploying for 30 days on Wednesday, so I'm trying to get this done before I leave. Thanks!
Log 1-Cold start
Log 2-Idle after ~5 minutes of running
Log 3-Idle after ~7 minutes of running
01-10-2012, 08:33 AM
#2
I can't look at your stuff since I have EFI live and I am still a newb at this too but I am doing a lot of idle tuning lately.
My car behaved the way you describe when I tried to reduce the overspeed/underspeed timing tables too much. I expected this to reduce surge fighting the cam but it had quite the opposite effect. The car could never catch itself once a minor surge started. Just one of the many possibilities I guess.
I am also curious about your timing question, my car really wanted 26* to run steady and it still fluctuates a little up to 28-30*. It sounds high to me, but if that's what the car wants and there are no downsides to it, I'm fine with it too.
My car behaved the way you describe when I tried to reduce the overspeed/underspeed timing tables too much. I expected this to reduce surge fighting the cam but it had quite the opposite effect. The car could never catch itself once a minor surge started. Just one of the many possibilities I guess.
I am also curious about your timing question, my car really wanted 26* to run steady and it still fluctuates a little up to 28-30*. It sounds high to me, but if that's what the car wants and there are no downsides to it, I'm fine with it too.
01-11-2012, 10:32 PM
#3
01-12-2012, 09:01 AM
#4
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Idle is by far the toughest part of tuning.
First step is to determine exactly what is going on with your surging.
You must watch closely and test to see if the surge is created due to fueling, spark, or IAC hunting.
Keep in mind that IAC hunting is often present even when the real cause is fuel or spark.
I haven't seen it all, but in most cases the surge is caused by fueling changes, not spark.
Once your SA is up pretty high ( like 30* ) then a two or three degree change either way isn't really going to do anything, and would not cause your surge, so I wouldn't get too wrapped up in worrying about that.
You must keep in mind that long duration cams create reversion in the intake manifold, and this physically creates a fluctuating vacuum signal at idle. The vacuum in the intake ports has a direct effect on how much fuel is delivered from your fuel injectors. The pressure differential between the fuel rail and the intake port determines fuel flow given X-amount of pulse-width. The injector will deliver more fuel into a high vacuum than into a low vacuum. When your vacuum is surging, your fuel flow changes accordingly.
You can reduce the % change of fuel flow a few ways. Having a vacuum referenced adjustable fuel pressure regulator gives you some options to try.
Referencing the fuel pressure to intake vacuum "can" provide some relief to idle surge, but often the compensation can be too much, in which case it won't help the problem, or can actually make the surge worse.
The amount or % of compensation needs to be adjustable, and sometimes you have to get creative there. If your PCM wasn't already set up for vacuum referenced fuel delivery, then you will need to make significant changes to your fuel injector tables if you add the different regulator.
Also, raising the base fuel pressure can also reduce surge a big, because the % change in vacuum then becomes smaller in relation to the fuel pressure, - because the fuel pressure value is then larger. Again, your fuel injector tables have to be adjusted for any change in fuel pressure.
So, a combination of high fuel pressure and a small % of vacuum referenced compensation will reduce the fluctuation of fuel delivery at idle.
At that point you want to slow down the IAC correction factors. How you do this depends on how many particular IAC calibrations your tuning software makes available to you.
Physically reducing IAC compensation has taken on several forms over the years. Drilling the idle hole to increase the minimum air rate is one way. opening the throttle more is another. You may add restriction to your IAC passages to reduce total flow capacity. Some people have disconnected the IAC to disable it from moving once it is a desired position. I would consider these your back-up options if you are unable to make the proper calibration changes with your tuning software.
If your commanded fuel delivery is jumping around at this point, then you might want to take some bite out of your MAF and MAP sensitivity at idle. In the software you can flatten the values in the MAF and VE tables where your car idles. This doesn't necessarily mean completely flat, - but sometimes some smoothing of the transitions is enough.
Physically it is hard to take bite out of your MAF output without causing another problem, though sometimes moving it further away from the throttle plate can slow down its response and lessen sensitivity.
Similarly, mounting your MAP sensor further away using a good sized and relatively long vacuum hose can reduce the sensitivity of the MAP.
Again, these physical changes are backup options.
You should find some very good advice at the link posted above. Don't be surprised if it takes a good bit of time to remedy the surge using your tuning software. Consider the physical changes only after you've given up on the ability of your software to get the results
First step is to determine exactly what is going on with your surging.
You must watch closely and test to see if the surge is created due to fueling, spark, or IAC hunting.
Keep in mind that IAC hunting is often present even when the real cause is fuel or spark.
I haven't seen it all, but in most cases the surge is caused by fueling changes, not spark.
Once your SA is up pretty high ( like 30* ) then a two or three degree change either way isn't really going to do anything, and would not cause your surge, so I wouldn't get too wrapped up in worrying about that.
You must keep in mind that long duration cams create reversion in the intake manifold, and this physically creates a fluctuating vacuum signal at idle. The vacuum in the intake ports has a direct effect on how much fuel is delivered from your fuel injectors. The pressure differential between the fuel rail and the intake port determines fuel flow given X-amount of pulse-width. The injector will deliver more fuel into a high vacuum than into a low vacuum. When your vacuum is surging, your fuel flow changes accordingly.
You can reduce the % change of fuel flow a few ways. Having a vacuum referenced adjustable fuel pressure regulator gives you some options to try.
Referencing the fuel pressure to intake vacuum "can" provide some relief to idle surge, but often the compensation can be too much, in which case it won't help the problem, or can actually make the surge worse.
The amount or % of compensation needs to be adjustable, and sometimes you have to get creative there. If your PCM wasn't already set up for vacuum referenced fuel delivery, then you will need to make significant changes to your fuel injector tables if you add the different regulator.
Also, raising the base fuel pressure can also reduce surge a big, because the % change in vacuum then becomes smaller in relation to the fuel pressure, - because the fuel pressure value is then larger. Again, your fuel injector tables have to be adjusted for any change in fuel pressure.
So, a combination of high fuel pressure and a small % of vacuum referenced compensation will reduce the fluctuation of fuel delivery at idle.
At that point you want to slow down the IAC correction factors. How you do this depends on how many particular IAC calibrations your tuning software makes available to you.
Physically reducing IAC compensation has taken on several forms over the years. Drilling the idle hole to increase the minimum air rate is one way. opening the throttle more is another. You may add restriction to your IAC passages to reduce total flow capacity. Some people have disconnected the IAC to disable it from moving once it is a desired position. I would consider these your back-up options if you are unable to make the proper calibration changes with your tuning software.
If your commanded fuel delivery is jumping around at this point, then you might want to take some bite out of your MAF and MAP sensitivity at idle. In the software you can flatten the values in the MAF and VE tables where your car idles. This doesn't necessarily mean completely flat, - but sometimes some smoothing of the transitions is enough.
Physically it is hard to take bite out of your MAF output without causing another problem, though sometimes moving it further away from the throttle plate can slow down its response and lessen sensitivity.
Similarly, mounting your MAP sensor further away using a good sized and relatively long vacuum hose can reduce the sensitivity of the MAP.
Again, these physical changes are backup options.
You should find some very good advice at the link posted above. Don't be surprised if it takes a good bit of time to remedy the surge using your tuning software. Consider the physical changes only after you've given up on the ability of your software to get the results
