Underdrive Pulley and Fuel tuning

[The Devils Own Chariot]

I have always been getting weird lean spots that come and go around 3% TPS and 30% TPS. Even at idle AFR always seems to be changing. Even after you change the F29x table its good for a bit and then AFR changes again. This condition never happens under WOT.

I can get the truck to idle well if its super rich. like 12.5 to 13.5
I have played with timing,IAC, and RPM using code59

I have some gut feelings:
There is an underdrive pulley on the truck but my battery voltage never drops bellow 13V. Could I have an amperage issue with the underdrive pulley and not a voltage issue?

I test fuel pressure at idle and its solid at 42psi. never fluctuates.Turning the truck off and the fuel pump off I get 0 pressure drop after 30min. I left the fuel pressure gauge on the fuel rail over night and around 8 hours later the pressure is 0.

What is normal here and what is not?

Im also wondering if my 60# injectors are bad.

What can we make of this?

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

Im also interested in the stock pulley if anyone has one. I will even trade if they want. I'm running the stock clutch fan and it would be nice to get more rpms out of that for cooling.

 

[Sportmachines]

Re: Underdrive Pulley and Fuel tuning

I have to think about the info for a bit before I offer any suggestions, but as for borrowing a stock pulley, we have a pile of them, so just let me know where to send it and you can test that out at least.

 

[MadMike]

Re: Underdrive Pulley and Fuel tuning

Isn't there a voltage correction factor? Would that help for underdriven alternator users?

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

Isn't there a voltage correction factor? Would that help for underdriven alternator users?

I see a table for battery voltage correction. I just dont see any change in voltage to make a correction.

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

I have to think about the info for a bit before I offer any suggestions, but as for borrowing a stock pulley, we have a pile of them, so just let me know where to send it and you can test that out at least.

I would like a pulley. Would it be okay to keep it? What do you need for it? I can Pm you my address

 

[Sportmachines]

Re: Underdrive Pulley and Fuel tuning

Even if you dont' see a voltage change, that tables voltage increments are broad, I always smooth the curve out so just incase theres a random drop, it doesnt effect the tune.

How lean does it go? At the 3% i would suspect tip in, but at 30% idk.

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

Even if you dont' see a voltage change, that tables voltage increments are broad, I always smooth the curve out so just incase theres a random drop, it doesnt effect the tune.

How lean does it go? At the 3% i would suspect tip in, but at 30% idk.

16/ 17 afr when at 5 or 8% TPS just cruising sometimes. Air intake temps seemed to effect that but I did mess with the air intake correction and it seems to be better.

 

[skwayb]

Re: Underdrive Pulley and Fuel tuning

You are in open loop correct?

I would make sure the values in this table

Fuel Injector Offset -vs- Battery Voltage (F92)

From 11.2v to 14.4v are the same. What ever value is in 14.4 put it in 12.8 and 11.2. That will help smooth out the idle.

For Tip in, you may need to play with the AE settings, both the MAP change and the TPS%Change factors

AE - Delta MAP Contrib -vs- Delta MAP (F21)
AE - Delta Throttle Contrib -vs- Delta TPS% (F22)

Also in the F29x table in the IDLE area, put all the values to be the same number. That way your VE isn't changing and making you INJECTOR PULSE WIDTH Change. Look at the INJECTOR BASE PULSE WIDTH in the aldl. If that is fluctuating then your AFR will fluctuate. You want this to be steady at idle. The F92 table should help this.

 

[5678TA]

Re: Underdrive Pulley and Fuel tuning

i have a stock pulley you can have... its not pretty but cover shipping and you can have it.

 

[Sportmachines]

Re: Underdrive Pulley and Fuel tuning

You are in open loop correct?

I would make sure the values in this table

Fuel Injector Offset -vs- Battery Voltage (F92)

From 11.2v to 14.4v are the same. What ever value is in 14.4 put it in 12.8 and 11.2. That will help smooth out the idle.

For Tip in, you may need to play with the AE settings, both the MAP change and the TPS%Change factors

AE - Delta MAP Contrib -vs- Delta MAP (F21)
AE - Delta Throttle Contrib -vs- Delta TPS% (F22)

Also in the F29x table in the IDLE area, put all the values to be the same number. That way your VE isn't changing and making you INJECTOR PULSE WIDTH Change. Look at the INJECTOR BASE PULSE WIDTH in the aldl. If that is fluctuating then your AFR will fluctuate. You want this to be steady at idle. The F92 table should help this.

All excellent points Paul. Made me think of one additional thing. On a customer truck, with 60# injectors, at low tps, and cruise like that, it was going lean and acting wierd, it was because the base inj PW min setting in code 59 was too high, and it was not allowing us to adjust it by changing values in F29x. So make sure you're not bumping into the min setting, or lower it.

 

[skwayb]

Re: Underdrive Pulley and Fuel tuning

All excellent points Paul. Made me think of one additional thing. On a customer truck, with 60# injectors, at low tps, and cruise like that, it was going lean and acting wierd, it was because the base inj PW min setting in code 59 was too high, and it was not allowing us to adjust it by changing values in F29x. So make sure you're not bumping into the min setting, or lower it.

What value did you use in thw F28 tabel to correct this? And what was your Injector Base Pulse Width in the ALDL when you ran into this problem on 60's before you changed your F28 table.

 

[Sportmachines]

Re: Underdrive Pulley and Fuel tuning

I will have to go back and check what it was and what we changed it to.

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

Anyone have anything to contribute to the fuel pressure comment I made. Is that normal?

 

[cloneman315]

Re: Underdrive Pulley and Fuel tuning

These trucks like a rich idle to idle smooth,did you try the voltage mod?I run a under drive with full msd,power inverter boost a pump dual fans etc on a pc680 battery

 

[SY2455]

Re: Underdrive Pulley and Fuel tuning

Im also interested in the stock pulley if anyone has one. I will even trade if they want. I'm running the stock clutch fan and it would be nice to get more rpms out of that for cooling.

If you want to improve cooling using the stock fan clutch, Install the fan from a 2001 GMC Safari GM part # 15976889 :tup:.

 

[cloneman315]

Re: Underdrive Pulley and Fuel tuning

Yes dropping off after that long is fine,fuel pressure that is

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

Great info guys. This tuning thing gets more and more deep every time I do it. I have been studying it for about 6 months and its a real chore.

I think I have a deal worked out with sportmachines on the stock pulley. Im running the stock clutch fan because I like it. The stock pulley should give me a lot more RPMs out of it.

 

[The Devils Own Chariot]

Re: Underdrive Pulley and Fuel tuning

You are in open loop correct?

.

I am in open loop. good info thanks!

 

[MadMike]

Re: Underdrive Pulley and Fuel tuning

The base pulse width is set by reducing it until u notice a idle go 'off' or run rough w/e. Then step it up a bit to keep of the bottom where the injector isn't opening off that pulse width. FYI I think all off your pulse widths are then added to that number so if you fattening it up to much it will carry across the rest of the fueling equation.