Low RPMs bucking - Page 6 - ZR-1 Net Registry Forums

XfireZ51 · 05-17-2016

The sootiness of the plugs is a result of the lean condition the ECM is "seeing" so it's adding more fuel where it really doesn't need it. The O2 sensor must be broadcasting a lean condition which could be a result of a vacuum leak/exhaust leak bringing fresh air past the O2 and therefore it's reporting a "false" lean.

MuRCieLaGo · 05-17-2016

Quote:

Originally Posted by XfireZ51

The sootiness of the plugs is a result of the lean condition the ECM is "seeing" so it's adding more fuel where it really doesn't need it. The O2 sensor must be broadcasting a lean condition which could be a result of a vacuum leak/exhaust leak bringing fresh air past the O2 and therefore it's reporting a "false" lean.

I know I got a vacuum leak. Tiny one, vacuum pump turns on one time every 3 seconds.

Exhaust leak is also VERY possible... Nobody mentionned it before but it makes sense.

Updated todo list:
3. Tested the resistance on the fuel injectors (car hot).

Primaries

#1: 17.8 ohms
#2: 17.8 ohms
#3: 17.9 ohms
#4: 17.9 ohms
#5: 17.7 ohms
#6: 17.6 ohms
#7: 17.5 ohms
#8: 17.5 ohms

Secondaries

#1: 17.8 ohms
#2: 17.8 ohms
#3: 17.8 ohms
#4: 17.8 ohms
#5: 17.5 ohms
#6: 17.5 ohms
#7: 17.4 ohms
#8: 17.3 ohms

To do:
4. Dynamic test fuel pressure.
5. Check for exhaust leaks.

MuRCieLaGo · 05-18-2016

Checked for exhaust leaks tonight, I got a tiny one on each side, about 6 inches after each o2 sensor.

Gonna get it fixed on next tuesday morning, but I don't think it'll fix something here.

RussMcB · 05-18-2016

I agree. I've noticed a couple leaks in my exhaust and they haven't affected how it runs (AFAIK).

XfireZ51 · 05-19-2016

If the exhaust leak is behind the O2, what happens is that fresh air gets drawn in during times of high vacuum such as decel and idle. At cruise, vacuum
Is not so high and you won't see an issue.

MuRCieLaGo · 05-19-2016

Quote:

Originally Posted by XfireZ51

If the exhaust leak is behind the O2, what happens is that fresh air gets drawn in during times of high vacuum such as decel and idle. At cruise, vacuum
Is not so high and you won't see an issue.

You're a bit right there. Gonna get it fixed as soon as possible anyway, you're giving me some hope now.

G8nightman · 05-19-2016

Quote:

Originally Posted by MuRCieLaGo

Checked for exhaust leaks tonight, I got a tiny one on each side, about 6 inches after each o2 sensor.

Gonna get it fixed on next tuesday morning, but I don't think it'll fix something here.

How did you test for the leak?

XfireZ51 · 05-19-2016

Just to illustrate how a small leak can make a difference, I had been data logging and tuning my 84 Xfire. At low MAP and decel, I needed to constantly add fuel.
One day, I was looking behind the car and noticed one of the mufflers hanging a bit low. The joint at the muffler/exhaust pipe was loose. This was enough to skew results. And I had a catalytic converter that was between the muffler and Y-pipe between where the muffler joint was and the O2 sensor. It was pulling fresh air from the back to the front. So there really is no such thing as a "small exhaust leak" when it comes to emissions ECM controlled vehicles running closed loop.

MuRCieLaGo · 05-19-2016

Quote:

Originally Posted by G8nightman

How did you test for the leak?

Put my hand near the flanges/clamps and I felt some air.

Quote:

Originally Posted by XfireZ51

Just to illustrate how a small leak can make a difference, I had been data logging and tuning my 84 Xfire. At low MAP and decel, I needed to constantly add fuel.
One day, I was looking behind the car and noticed one of the mufflers hanging a bit low. The joint at the muffler/exhaust pipe was loose. This was enough to skew results. And I had a catalytic converter that was between the muffler and Y-pipe between where the muffler joint was and the O2 sensor. It was pulling fresh air from the back to the front. So there really is no such thing as a "small exhaust leak" when it comes to emissions ECM controlled vehicles running closed loop.

I really need to do some researches regarding that closed loop thingy. I'm not sure I understand how it works.

Thanks a lot for your help.

G8nightman · 05-19-2016

I will be testing for leaks on my system was thinking of using a smoke machine..

05-17-2016	#51
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: Low RPMs bucking The sootiness of the plugs is a result of the lean condition the ECM is "seeing" so it's adding more fuel where it really doesn't need it. The O2 sensor must be broadcasting a lean condition which could be a result of a vacuum leak/exhaust leak bringing fresh air past the O2 and therefore it's reporting a "false" lean. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

05-18-2016	#53
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: Low RPMs bucking Checked for exhaust leaks tonight, I got a tiny one on each side, about 6 inches after each o2 sensor. Gonna get it fixed on next tuesday morning, but I don't think it'll fix something here.

05-18-2016	#54
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,160	Re: Low RPMs bucking I agree. I've noticed a couple leaks in my exhaust and they haven't affected how it runs (AFAIK).

05-19-2016	#55
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: Low RPMs bucking If the exhaust leak is behind the O2, what happens is that fresh air gets drawn in during times of high vacuum such as decel and idle. At cruise, vacuum Is not so high and you won't see an issue. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

05-19-2016	#58
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: Low RPMs bucking Just to illustrate how a small leak can make a difference, I had been data logging and tuning my 84 Xfire. At low MAP and decel, I needed to constantly add fuel. One day, I was looking behind the car and noticed one of the mufflers hanging a bit low. The joint at the muffler/exhaust pipe was loose. This was enough to skew results. And I had a catalytic converter that was between the muffler and Y-pipe between where the muffler joint was and the O2 sensor. It was pulling fresh air from the back to the front. So there really is no such thing as a "small exhaust leak" when it comes to emissions ECM controlled vehicles running closed loop. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

05-19-2016	#60
G8nightman Join Date: Dec 2007 Location: NYC Posts: 1,189	Re: Low RPMs bucking I will be testing for leaks on my system was thinking of using a smoke machine.. __________________ 90 Chevy ZR1 LPE #2315 'SOLD' 90 Chevy ZR1 LPE #2774 'SOLD' 91 Chevy ZR1 Callaway aerobody 91 Chevy ZR1 #1512 91 Chevy ZR1 #951 95 Chevy ZR1 #338 'SOLD' 91 BMW 850i 94 BMW 850csi 95 BMW 850csi 94 Lotus Esprit S4 07 Benz CLS550 06 BMW M5 "SOLD"