Tuning my 16G car - 3000GT/Stealth International Message Center

ZephTheChef · 04-05-2008, 06:26 PM

Summary of relevant mods: twin 16Gs, blow through setup, 680cc injectors, fuel pressure at 43psi with vacuum unhooked, tuning with SAFC and LC-1.

Just fired up the car for the first time the other day and I've been playing with the idle and free rev fuel...if I rev the engine up to say 3000-4000rpm everything is fine, but the wideband goes off the chart lean as soon as I get off the throttle, the car sputters and tries to die. Obviously something is going on, but I have no clue where to look. What are some things that would cause me to run so lean when the throttle closes? I'm mildly suspicious of the Krank Vents are having something to do with it. I do have a small leak somewhere into the crankcase, I can hear it for a few seconds after I shut the car off (goes away if I pull the dipstick). I think I'm going to block them off and see if that changes anything.

Trevor · 04-05-2008, 07:33 PM

Although I haven't driven my car for 5 months (ugh) I'm sure it's supposed to shut off the injectors on decel. Your problem lies with the idle recovery. On the back side of the throttle body is a little plunger type device that holds the throttle slightly open for a second or two after you close it. Check the function of it. Your throttle body should not go straight to full closed when you release the throttle.

Also if your fuel trims are screwed it'll cause this.

Say your idle is set too lean and 3-4k is set too rich. Idle is fine when it's sitting for a while because the computer has adjusted the short term fuel trims to add fuel (say +14%). You go up to 3-4k and it's a little too fat. As you hold it there the computer pulls the fuel back so that the O2's start sweeping again (say -14%). Release the throttle and the computer tries to recover but it can't...suddenly it's running 28% short on fuel and it can't adjust fast enough. Boom...motor dies.

Even out the fuel trims. Get both close to zero and that will help too.

ZephTheChef · 04-05-2008, 07:54 PM

Yeah, I've been doing some more reading on what's supposed to happen off throttle and I guess reading way lean is normal. Good call on getting the fuel trims closer, I know I'm definitely running considerably richer at 4k than at idle.

04-05-2008, 06:26 PM	#1 (permalink)
ZephTheChef Forum Member Join Date: Nov 2004 Location: Wichita, KS Drives: Red 1991 VR-4 (#3) Trader Rating: (2)	Tuning my 16G car Summary of relevant mods: twin 16Gs, blow through setup, 680cc injectors, fuel pressure at 43psi with vacuum unhooked, tuning with SAFC and LC-1. Just fired up the car for the first time the other day and I've been playing with the idle and free rev fuel...if I rev the engine up to say 3000-4000rpm everything is fine, but the wideband goes off the chart lean as soon as I get off the throttle, the car sputters and tries to die. Obviously something is going on, but I have no clue where to look. What are some things that would cause me to run so lean when the throttle closes? I'm mildly suspicious of the Krank Vents are having something to do with it. I do have a small leak somewhere into the crankcase, I can hear it for a few seconds after I shut the car off (goes away if I pull the dipstick). I think I'm going to block them off and see if that changes anything. __________________ "why its a tubloidial butt noid!" - Ray Pampena, 2006

04-05-2008, 07:33 PM	#2 (permalink)
Trevor Z15A Tweaker Join Date: Sep 1999 Location: Tucson, AZ. Trader Rating: (13)	Re: Tuning my 16G car Although I haven't driven my car for 5 months (ugh) I'm sure it's supposed to shut off the injectors on decel. Your problem lies with the idle recovery. On the back side of the throttle body is a little plunger type device that holds the throttle slightly open for a second or two after you close it. Check the function of it. Your throttle body should not go straight to full closed when you release the throttle. Also if your fuel trims are screwed it'll cause this. Say your idle is set too lean and 3-4k is set too rich. Idle is fine when it's sitting for a while because the computer has adjusted the short term fuel trims to add fuel (say +14%). You go up to 3-4k and it's a little too fat. As you hold it there the computer pulls the fuel back so that the O2's start sweeping again (say -14%). Release the throttle and the computer tries to recover but it can't...suddenly it's running 28% short on fuel and it can't adjust fast enough. Boom...motor dies. Even out the fuel trims. Get both close to zero and that will help too. __________________ 96 Dodge Stealth R/T TT w/58k 10.396 @ 138.94 (C16+Meth) 10.898 @ 130.00 (91+Meth) 05 Mercedes Benz C230 6-Speed Sedan 06 Dodge Magnum SRT-8

04-05-2008, 07:54 PM	#3 (permalink)
ZephTheChef Forum Member Join Date: Nov 2004 Location: Wichita, KS Drives: Red 1991 VR-4 (#3) Trader Rating: (2)	Re: Tuning my 16G car Yeah, I've been doing some more reading on what's supposed to happen off throttle and I guess reading way lean is normal. Good call on getting the fuel trims closer, I know I'm definitely running considerably richer at 4k than at idle.

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