What kind of rwtq are we talking about here?

 

Ok are you just observing or are you really concerned about low rpm torque below 850 rpm?

 

Assumeing this is the real problem that is bugging you I have a couple of ideas that might fix your problem at least worth 15minutes of data logging to see if they are happening. The other thing i am assuming is your injectors are not stock. There is a table for pulsewidth correction vs pulsewidth. This is used to linerarize the injector output over it's dynamic range. One of the things I could envision happening is at very low pulse width this table is not correct so in essence adding a small amout of throttle and very small change in airflow the fuel flow is not increasing to what would be expected causing a flat spot. The injectors if not stock should be flowed dynamically in order to fill in the table correctly as none of the enrichments will be correct if this table is wrong. Another thing is the stoic A/F ratio with 10% ethanol I assume you have it set to 14.3 rather than 14.7 that is used with straight gasoline. Another thing is to see if the Mass air flow is changing with a slight increase in throttle it may no be if there is enough reversion. A MAFmeasures airflow and has no idea which direction the air is going so the same gram could come and go past the sensor and read two grams and adding throttle may not change the measured airflow at first until you reach an rpm that will cause a change. These previous issues should be able to detect with a wideband O2 sensor and a datalog. The only other thing I could envision would be the IAC closing at the same rate you are opening the throttle so initial throttle movement ends up with no increase in airflow. Personally I don't think the cam you have is a problem in anyway. The only last thought is if you have a non stock throttle body and the lever ratio is screwed up in some way that initial movement does not cause anything to happen at the throttle body side of things. I hope one of these helps and all pretty simple and non invasive for the most part.
Dave

 

Give it a little more manual trans IAC offset for rolling above the 1.8 mph PID velocty threshold, or raise the threshold to extend idle PID control to allow it to continue to control rpm while rolling slowly in gear. 10-12 mph should be sufficient to permit rpm controlled idling in 1st or 2nd gear.

Let the controller handle some of the finesse.

 

I have wanted a VooDoo for awhile....I think they are 112 cams. Rough idle is fine....but idle surge would bug me. I like to experiment, so I will prolly run the 110 XE256 just to see what happens. I also am adding a ported Eddy Hi Flo and my home siamesed runners. It is now warm enough around here to start tearing it down. I like these tuning discussions!

 

Jon @ FIC hooked me up with the specs sheet when I bought the injectors. I used manufacturer's data to repopulate the pulsewidth correction vs Voltage table. Rechecked it more than once. The new injectors aren't terribly different than the OEM with regard to voltage offset. I don't think that's it.

Still have mine set to 14.7. I assumed O2 sensor data would provide the necessary feedback for ethanol. IOW, since it "needs" more fuel with ethanol, I thought the MAF table adjustments I made (based INT values) would point my fueling in the correct direction. I will say (as mentioned earlier in this thread), I deliberated set the sub 1g value a hair on the lean side to maximize idling mpg.

I'm seeing what looks like good sensitivity. MAF data even changes with the start-up surging. IOW, it moves up/down with the idle see-saw.

Stock TB is in use and I've reset the IAC (weeks ago). Interesting thought though. I could double check that in my logs.

 

Are you talking about the "Enable IAC PID if MPG is GT" parm? Mine is set to the factory value of 6.88MPH.

What does this parmeter do? What is PID? I would have guessed this to be the threshold for "dashpot" operation -- holding idle up to prevent stall. IOW, if over 6.88mph, the IAC doesn't let idle back down to the preset.

After viewing my logs, it seems the initial surge follows the pattern of higher rpms as load decreases and visa-versa. I'm going to try lowering timing in the startup correction table for lower loads. I'm also going to zero a couple of the IAC parms. For example, does IAC deadband in N/D control how much oscillation room the motor has? If I zero it, will it become more stable or die easier? Last fall, I noticed adding to this value seemed to help provide more idle/off-idle power but it also raised idle rpms. IOW, it seemed to be an idle-added -- same result as changing "Idle vs Temp" table.

Oh yeah...I really don't have an issue rollling at 2-3mph expect lurching if I let the clutch all the way out. It could be better getting it rolling too.

 

Rick and Ron, I wouldn't have started this thread if it was just idle talk!

Get it? Idle talk?


Based on similar builds WITHOUT using the more advanced AFR 195 heads, I should be making at least 525FT/LBS at the crank. In actual driving conditions, I can always spin my 315 rears just by pressing the gas pedal in 1st or 2nd. I even (profusely) broke it loose in 3rd at 45mpg getting on the hwy the other day. (No clutch assist).

My tune is definitely getting better. If I could just find a friggin' sasa-frasin' job, I'd get it dyno'd.

 

This has actually been one of the most in depth discussions on the subtler parts of tuning I've seen in a while! I'd say it's a pretty damn good thread for just puttin' around!

 

Is this a 110LSA cam? Remember, 1.6 rockers increase the slope of the overlap. So does the use of shorter rods. Not sure you need to go too crazy with overlap under a TPI. They already give you a significant mid-range boost. OTOH, match the components....

 

Yes. However, the factory setting is 1.875 mph or (0x06 raw hex) in every bin that I've seen (not 6.88 mph).

Below this velocity, PID (Proportional-Integral-Differential) control may be enabled to control the idle rpm according to the desired idle rpm target value.

Above this velocity, PID control will be disabled. To smooth the transition, manual trans cars add a small fixed offset (typically 5-10 counts) to the IAC position, this offset is in addition to the normal value obtained from the warm park position table along with throttle following effects once you are out of PID control.

You may just need a little more IAC opening to help with the transition out of PID control as you attempt to drive off with very small throttle openings.

You have several options. You can increase this offset value, you can increase the warm park vs coolant temp table, you can increase the throttle following gain, or you can continue to stay in PID control to help maintain the target rpm at even higher velocities.

If you elect to extend the PID control, then you also have the option of increasing the various control gains to amplify the effect.

With enough gain, the PID controller should be sufficient to avoid stall all by itself with a closed throttle clutch engagement.

You will likely need to spend some time digging for the appropriate addresses of all of the relevant parameters.

You want the spark table to help promote stability around the target idle rpm. If rpm falls below the target, you want the torque to increase to counter the rpm drop, if the rpm rises, you want the torque to fall to counter the rise. Since the target rpm varies with coolant temperature, you need to find a compromise.

Take a little spark out above the target rpm and increase it a little below.

 

It wont surge at idle it has good manners, thats 100% tuning which is easy to do with a cam that size. Believe me the one I descibed sounds stock....but "huskier". You know somethings up but its not lopey or doesnt shake the car. Very mild, torque is strong though. We used a ported TPI system and box stock performer head, shortie headers with a catback. Pulls very strong, mimics a mild stroker.

 

By increasing the IAC steps by coolant?

To make sure I understand...I can:
1) Increase IAC steps by coolant
2) Increase Idle speed by temp
3) What parm is throttle following gain?
4) Increase from 1.88 to 6mph and higher?

Can you explain a bit more what PID does (how it works)?

Note: After a google, I think I understand standard PID operation (in many types of media). So, for a car, there is a monitoring process to figure out how to keep idle where the setting dictates. Since I'm never seeing the TPS value move while the COLD engine oscillates in rpm, I have to assume the IAC, fuel, and timing are the 3 elements that control idle speed.

After setting adjacent PRIMARY timing table and STARTUP timing table values to the same numbers, my oscillation changed. Its wasn't as fast but I also had raised 50-deg startup rpm to 1250. It slowly moved from 1100 to 1250 and back. It's "hunt" seemed to get wider and slower. I also raised cold AFR setting (IOW lessened the percentage of fuel being added).

 

There is a second table for injector linearization it is named
Low Pulse Width Injector Offset Vs. BPW It is different from the battery comp values. It is to correct the flow at low pulsewidths so the fuel that is delivered is what is commanded.

I think everyone seems to believe the simplest of systems are not smart enough to do a simple fueling calculation. If the mass air flow and other sensors are functioning correctly and the constants entered correctly the math is wildly simple. there are 3 places to enter injector flow rate and 2 correction tables for the injectors a lambda value table that has to have the correct value for the fuel used in this case E10. Unless you are using your Vette for a taxi cab why worry about idle mileage when you put more cam in the engine will self EGR leaning itself out and waste a bit of fuel at idle to make it run smoothly at light loads. Why not fill in the constants table correctly with the stock map and see what happens.

Here is a table or two that show the problems with using a static flow rate with no pulse width corrections and while not the injectors you are using does describe some issues to think about. The injectors dogo wildly non linear after 85% duty cycle but if sized correctly you will never go there so the low pulse with corrections really the only one to be concerned with. I think I would concentrate on making the car drive very well first and then worry about something like idle mileage or a slightly smelly idle. You might play with the stall saver spark advance to smooth the idle out as well it is much faster than the IAC.
Dave
http://siemensdeka.com/specsheets/FI114992.jpg

 

good stuff. what rpm does it peak at around?

 

According to my logs, 1.8ms is about the smallest my setup runs at idle. The tune is set for a [factory] min 1.6ms PW. My specsheet says 1.05ms is the MIN linear PW. I lowered the tune to 1.25ms just to be sure. But it sounds like there's no problem there.

I deliberately picked an injector on the smallish side to maximize atomization (24SVOs). More importantly, they were my only option for a polished setup. I'm staying just under 85% range for maximum PW during WOT pulls. I'm also happy with that.

Last fall, I tried setting "Stall Saver 3" 150rpms higher. Since there's also a disable parm, maybe I needed to raise it accordingly. I'll try that this week.

One last thought...My min rpm for ESC operation was set to 900rpms. With forged pistons, I might get the slightest of knocks during startup. Maybe the cold see-saw is the ESC and normal timing fighting to equalize....at least until it's run 60s and gets warmer. I'm also going to raise it to 1200rpms. (OTOH, logs don't seem to support this theory).

FWIW, Spark is varying less than 1-deg during my cold, wavering idle.

 

What is the Baro Update RPM Threshold What is it doing below this RPM and what is it doing above this RPM??????

 

Ok listen to what you just said both now and the original complaint of not picking the throttle up off a 650 rpm idle but runs fine if you set the idle at 950 rpm. Now you are saying the ESC is not enabled until 900 rpm. I fail to see the surprise here. With ESC disabled below 900 rpm you will get poor off idle performance and nothing to help stabilise the idle that is why the idle hunts and it will not take throttle as once you get it past 900 rpm the ignition timing comes in all at once. You should see the timing moving around with ESC enabled it is supposed to in order to maintain idle speed. Setting the minimum pulse with from 1.6 ms down to 1.25 is meaningless if the minimum to see is 1.8. I would not worry about knock counts at idle from running forged pistons the new style stuff runs much tighter than something from the 70's or should be clearanced tighter but that is between you and your engine builder. There is no way at idle you can have actual knock as there is not even close to enough cylinder pressure.
dave

 

Greg,
Driveablity is always a subjective defination but I would assume you could make it drive near stock but it may not be able to idle at 650 RPM and sound stock. The jumpyness and cold starting issues of the car are probably a tuning issue. It could be the cam but I am not convinced. (Maybe you are expecting too smooth of an idle?) The reason I say this is the hot cam which was designed (BY GM) for the 1996 LT4 has specifications of 218/228 on a 112 LCA with .525 lift and 1.6 rockers, and it was to be installed in a 350 with a 6-speed.

If GM designed that cam for a stock car and considered it smooth enough for the average consumer then your cam should also fall into that catagory.

 

I disagree. As pointed out, my spark is wavering less than 1-deg. This is when it's above 900 (actually 800 is my hot idle speed). I also review my logs for the 1200rpm starts I used late last week. I only got one knock count RIGHT at start-up. Even though my KS seems a hair sensitive, I'm really not getting knocks with my timing. (I get about six in a 15-minute drive). FYI: I'm using 4032 pistons. Higher silicone, tighter fit.

Mostly, I'm throwing ever POSSIBLE thought out there I can think of. I'll probably end up back at my original conclusion about the definition of driveable. But, I'm certainly hoping to be proved wrong.

1.25 may be meaningless -- unless I try lowering my idle speed again. The logical assumption is my PW will go down with any reduction in idle speed. (What would have happened if I hit the minimum PW with prior tunes? Keep in mind the injectors should have been fine. It just would have been bumping off an ECM parm).

My guess is it was ignored. I've seen a couple of other parms ignored by the ECM. For example, maximum total timing had been exceeding in my earlier efforts.

So, without knocks, the ESC being enabled -- or not -- could not have made any difference. Also, having the ESC enabled for rpms lower than say...1200 might help guard against accidental lugging at higher loads. (Notice how low the factory sets low rpm/high LV8 spark advance.)