Engine stumbles, badly

Raptor13x · 06-20-2009, 10:51 AM

I just finished my 20v BT swap, and the engine is stumbling badly, especially at 2k-4k rpm. It's lessened somewhat if the throttle is kept near closed. I threw some 94 octane gas in the car to offset the 87 that was in there, so it's probably something more than that. What do you think? Timing?

Raptor13x · 06-20-2009, 11:18 AM

I just played around with it- advancing the timing helped considerably, but it's still not perfect. Why, though, would the timing setting it had been on be incorrect? Is there a timing advance I should be aware of that may not be hooked up/operating correctly?

Raptor13x · 06-20-2009, 11:33 AM

One thing I noticed... there's what looks like a place for a vacuum tube there... what is that part?

Raptor13x · 06-22-2009, 11:45 AM

Also, I'm getting a simply horrible resonance in the exhaust from around 3500-5500rpm, i.e. any time I'm on the highway. I'm trying to figure out how to quiet that down without spending a ton of money or adding much weight.

mr220v · 06-22-2009, 01:13 PM

That vacuum valve is for AC idle up. When the AC is on, this valve opens up and creates a vacuum leak causing the motor to idle up. You're probably not going to bother with AC.

Typical causes for the stumbling are TPS and o2.

06-20-2009, 10:51 AM	#1 (permalink)
Raptor13x Legendary Join Date: Apr 2006 Location: Farmington Hills, MI Posts: 3,987 Thanks: 7 Thanked 40 Times in 34 Posts My Google Map iTrader Rating: (5/100% )	Engine stumbles, badly I just finished my 20v BT swap, and the engine is stumbling badly, especially at 2k-4k rpm. It's lessened somewhat if the throttle is kept near closed. I threw some 94 octane gas in the car to offset the 87 that was in there, so it's probably something more than that. What do you think? Timing?

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06-20-2009, 11:18 AM	#2 (permalink)
Raptor13x Legendary Join Date: Apr 2006 Location: Farmington Hills, MI Posts: 3,987 Thanks: 7 Thanked 40 Times in 34 Posts My Google Map iTrader Rating: (5/100% )	I just played around with it- advancing the timing helped considerably, but it's still not perfect. Why, though, would the timing setting it had been on be incorrect? Is there a timing advance I should be aware of that may not be hooked up/operating correctly?

06-20-2009, 11:33 AM	#3 (permalink)
Raptor13x Legendary Join Date: Apr 2006 Location: Farmington Hills, MI Posts: 3,987 Thanks: 7 Thanked 40 Times in 34 Posts My Google Map iTrader Rating: (5/100% )	One thing I noticed... there's what looks like a place for a vacuum tube there... what is that part?

06-22-2009, 11:45 AM	#4 (permalink)
Raptor13x Legendary Join Date: Apr 2006 Location: Farmington Hills, MI Posts: 3,987 Thanks: 7 Thanked 40 Times in 34 Posts My Google Map iTrader Rating: (5/100% )	Also, I'm getting a simply horrible resonance in the exhaust from around 3500-5500rpm, i.e. any time I'm on the highway. I'm trying to figure out how to quiet that down without spending a ton of money or adding much weight.

06-22-2009, 01:13 PM	#5 (permalink)
mr220v Beams Owners Group Join Date: Mar 2006 Posts: 1,775 Thanks: 13 Thanked 139 Times in 117 Posts iTrader Rating: (8/100% )	That vacuum valve is for AC idle up. When the AC is on, this valve opens up and creates a vacuum leak causing the motor to idle up. You're probably not going to bother with AC. Typical causes for the stumbling are TPS and o2.