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Old 05-17-2016   #51
XfireZ51
 
Join Date: May 2007
Location: Chicagoland, IL
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Default 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.
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Old 05-17-2016   #52
MuRCieLaGo
 
Join Date: Aug 2014
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Default Re: Low RPMs bucking

Quote:
Originally Posted by XfireZ51 View Post
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.
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Old 05-18-2016   #53
MuRCieLaGo
 
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Default 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.
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Old 05-18-2016   #54
RussMcB
 
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Default Re: Low RPMs bucking

I agree. I've noticed a couple leaks in my exhaust and they haven't affected how it runs (AFAIK).
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Old 05-19-2016   #55
XfireZ51
 
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Default 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.
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Old 05-19-2016   #56
MuRCieLaGo
 
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Default Re: Low RPMs bucking

Quote:
Originally Posted by XfireZ51 View Post
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.
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Old 05-19-2016   #57
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Default Re: Low RPMs bucking

Quote:
Originally Posted by MuRCieLaGo View Post
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?
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Old 05-19-2016   #58
XfireZ51
 
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Default 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.
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Old 05-19-2016   #59
MuRCieLaGo
 
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Default Re: Low RPMs bucking

Quote:
Originally Posted by G8nightman View Post
How did you test for the leak?
Put my hand near the flanges/clamps and I felt some air.

Quote:
Originally Posted by XfireZ51 View Post
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.
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Old 05-19-2016   #60
G8nightman
 
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Default Re: Low RPMs bucking

I will be testing for leaks on my system was thinking of using a smoke machine..
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95 Chevy ZR1 #338 'SOLD'
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