accessory torque with under drive pulley/ low speed stall

[redmaroz]

I have been having issues with the car wanting to stall at parking lot speeds, mainly when turning. i thought i had it corrected but i guess i was wrong. I have ran the idle config, adjusted raf as needed along with spark. I have throttle cracker disabled because no matter what i did it didint help. And it actually behaves better with disablled. I have my idle set at 800 rpm which i think is totally doable with my set up. Ive attached a copy of my tune, and a log from earlier today. Ive also leaned out the 400 rpm column of my ve table. I had came across a couple threads stating that with an underdrive pulley that sometimes the accessory torque table needs adjusted. Im just not sure which way it needs to go, and didnt want to mess with it not knowing. Any insight or help is appreciated. as the car runs great besides this. and for clarification its a 6 speed car and its only happening when in neutral rolling through a corner. Its an 01 os with the 1 bar sd upgrade.

[Fast4.7]

I have been having issues with the car wanting to stall at parking lot speeds, mainly when turning. i thought i had it corrected but i guess i was wrong. I have ran the idle config, adjusted raf as needed along with spark. I have throttle cracker disabled because no matter what i did it didint help. And it actually behaves better with disablled. I have my idle set at 800 rpm which i think is totally doable with my set up. Ive attached a copy of my tune, and a log from earlier today. Ive also leaned out the 400 rpm column of my ve table. I had came across a couple threads stating that with an underdrive pulley that sometimes the accessory torque table needs adjusted. Im just not sure which way it needs to go, and didnt want to mess with it not knowing. Any insight or help is appreciated. as the car runs great besides this. and for clarification its a 6 speed car and its only happening when in neutral rolling through a corner. Its an 01 os with the 1 bar sd upgrade.

My 5.7 Express van running the 2002 0411 PCM was overshooting the idle and then over-reacting and trying to stall with a 25% underdrive pulley especially when the a/c compressor cycled. I reduced the accessory and a/c torque by multiplying the tables by 0.75. Everything went back to normal after doing that.

[Fast4.7]

If you know the percentage underdrive, put a decimal point in front of the percentage. Subtract that number from 1.00. Use the number you get and multiply the whole table value by that number. 30% underdrive would be 0.70 multiplier for example. It should work out pretty accurate to the torque reduction the crank is actually seeing.

[Fast4.7]

One other thing that tends to help. If the engine likes say 30? of timing at idle. Reduce your idle spark to 22?. This will force the IAC to open slighly more to keep the idle speed up. In the idle underspeed table add 8? of timing by 150 rpm underspeed. The PCM and engine both respond quicker to timing changes than IAC changes when controlling the idle speed. The reason I pull a little idle timing is if you already have the timing set for a near optimim value you cannot increase the timing and get more idle torque.

[redmaroz]

Thanks for the help! I'll give it a try!

[redmaroz]

when you say add 8* on the underspeed table, are you meaning across the table or just at the 150 area?

[Fast4.7]

when you say add 8* on the underspeed table, are you meaning across the table or just at the 150 area?

It was just an example. I would start around 16-20* in the idle table in the 400-1,200 rpm range at the gm/cylinder volume you idle at. Probably in the 0.18-.030 range. Then make the RPM underspeed table from 150 rpm and above 8*. Below that smooth the underpseed down to 0* at 50 rpm underspeed. With a big cam you want about a 100 rpm range around the desired idle speed with nearly no timing changes to help stabilize the idle as the rpm will jump around some. However once the idle starts to drop you want a good increase to keep it from falling too quickly. I would also set your overspeed table to about -4* at 150 rpm. In my experience you want the idle overspeed table about 50% of the underspeed table. This will help keep the engine from surging at idle.

The easiest way to tell where the engine likes to idle timing wise is with the Vehicle Scanner and the VCM control. You can manually take control of the timing. At idle set the timing to 16* in the manual (Absolute Timing) control and then turn it on. You want to increase the timing 1* at a time giving about 5-10 seconds for the PCM/Engine to stabilize between changes until either the MAP KPa reaches the lowest value or the engine starts to idle noticeably rougher. Once you see the KPa start to rise again or experience the rougher running back off 2* and consider that the maximum idle timing you should run. From that value retard your timing in the idle table 6-8* and run the overspeed 6-8* at 150 rpm and above. I have tuned some BIG cams with lots of overlap that idle very well using this method.

[redmaroz]

Just got back from a drive after making the changes. Car did really well except for it did try to stumble on me just a little while turning into the garage. Then it dawned on me that my ps pulley is also smaller than the normal ls fbody one, so would it make since to reduce the accessory torque table by another 3 to 5%? Again thanks for your help as this is the best the car has behaved at low speed since it was stock.