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milling machine
User
Nov 19, 2012, 9:52 AM
Post #1 of 8
(7018 views)
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I have a question concerning a rich or lean code for a stuck opened egr valve I have read in some service manuals that this condition
might cause a rich code and then again I have read in some service manuals just the opposite that this condition could throw out a
lean code-it would seem as though to much egr exhaust gas would replace the oxygen there-by causing a rich condition but as just
said I have read just the opposite also--there is nothing wrong with my vehicle I just wanted some clarification concerning this subject
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 19, 2012, 10:03 AM
Post #2 of 8
(6997 views)
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You'll do tons better if you state what this vehicle is and post the code numbers!
T
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Hammer Time
Ultimate Carjunky
/ Moderator
Nov 19, 2012, 10:05 AM
Post #3 of 8
(6992 views)
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A stuck open or leaking EGR valve creates a vacuum leak which would cause a lean condition.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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milling machine
User
Nov 19, 2012, 10:23 AM
Post #4 of 8
(6981 views)
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Thanks for the answer
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Discretesignals
Ultimate Carjunky
/ Moderator
Nov 19, 2012, 11:18 AM
Post #5 of 8
(6967 views)
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That depends. If it is on a speed density fuel system (MAP), it will cause a rich condition because the lower manifold vacuum will cause the engine controller to add more fuel.
On a MAF fuel system it will cause a lean condition because the load calculation is based on the amount of air flowing through the sensor. The amount of air flowing through the sensor will be less, so the PCM will be faked into adding less fuel causing the engine to be lean.
Either way a stuck open EGR will cause a rough idle and higher than normal manifold pressure.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 19, 2012, 11:22 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Nov 19, 2012, 11:24 AM
Post #6 of 8
(6961 views)
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I don't believe a leaking EGR valve will reduce the vacuum sufficiently to cause a rich code.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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milling machine
User
Nov 19, 2012, 11:51 AM
Post #7 of 8
(6953 views)
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What Discretesignals says makes sense -- I read the rich condition from a factory service manual that was for a chevy beretta with
a 2. 8 engine that uses a map sensor and the lean condition for an Ford explorer that uses a maf sensor
It turned out to be a good question though I learned something today
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DanD
Veteran
/ Moderator
Nov 20, 2012, 8:03 AM
Post #8 of 8
(6908 views)
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A rich or lean code is set by the PCM while monitoring O2 signal and we have to remember that an O2 can only read oxygen levels and nothing else. That being said, it also depends on how bad an EGR is leaking as to whether the O2 reports a lean or rich condition
An EGR that has a small leak (one that would only cause a small shutter at idle for example) could cause the O2 to show rich; because of the inert exhaust gas is displacing the oxygen entering the combustion chamber.
An EGR leak that is sufficient to cause a slight misfire would show lean O2 readings because the EGR is recirculating un-burnt oxygen from the misfire (that the EGR caused) along with exhaust gases.
Then of course the PCM will start playing with fuel trim; in an attempt to get the O2 toggling again; which in turn can and will mask the EGR leak; again depending on the size of leak.
Dan.
Canadian "EH"
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