EGR Flow Sensing
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Mountain Pass
Joined: Dec 2009
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EGR Flow Sensing
Hi Guys,
I'm confused. I have seen several threads/posts talking about a code for insufficient air flow through the EGR system. How does the computer recognize this? On my 03 I just had it all apart and I did not find any sensor in that path. I did block off my EGR cooler with no resulting CEL. I have the valve still installed and connected. Would mine have stored the EGR air flow code anyway and do I need to do anything about it?
thanks
Steve
I'm confused. I have seen several threads/posts talking about a code for insufficient air flow through the EGR system. How does the computer recognize this? On my 03 I just had it all apart and I did not find any sensor in that path. I did block off my EGR cooler with no resulting CEL. I have the valve still installed and connected. Would mine have stored the EGR air flow code anyway and do I need to do anything about it?
thanks
Steve
Senior User
Joined: Mar 2007
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From: Qld Australia
The ECU can calculate gas flow through the EGR. During a period of steady cruising speed it will close the EGR valve, takes note of the air flow going into the engine via the MAF, the opens the EGR valve again, it is looking for a decrease in flow through the MAF because some gas should be coming through the EGR. If it doesn't sense an appropriate drop in air flow it assumes the EGR it clogged (or otherwise tampered with) and will run the engine with fuel injected a little retarded (effectively richer) in an attempt to reduce NOx exhaust emissions. That's the EPA for ya!
The result of this is that fuel economy may suffer a little. But you would need to keep good fuel consumption/mileage records to confirm if that's the case for your truck. Some people have noticed a difference, some haven't. It might depend on which strategy is loaded into your ECU's memory.
Hope I got that all right. I'm sure someone will correct me if I'm wrong..........
The result of this is that fuel economy may suffer a little. But you would need to keep good fuel consumption/mileage records to confirm if that's the case for your truck. Some people have noticed a difference, some haven't. It might depend on which strategy is loaded into your ECU's memory.
Hope I got that all right. I'm sure someone will correct me if I'm wrong..........
Post Fiend
Joined: Jul 2005
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The ECU can calculate gas flow through the EGR. During a period of steady cruising speed it will close the EGR valve, takes note of the air flow going into the engine via the MAF, the opens the EGR valve again, it is looking for a decrease in flow through the MAF because some gas should be coming through the EGR. If it doesn't sense an appropriate drop in air flow it assumes the EGR it clogged (or otherwise tampered with) and will run the engine with fuel injected a little retarded (effectively richer) in an attempt to reduce NOx exhaust emissions. That's the EPA for ya!
The result of this is that fuel economy may suffer a little. But you would need to keep good fuel consumption/mileage records to confirm if that's the case for your truck. Some people have noticed a difference, some haven't. It might depend on which strategy is loaded into your ECU's memory.
Hope I got that all right. I'm sure someone will correct me if I'm wrong..........
The result of this is that fuel economy may suffer a little. But you would need to keep good fuel consumption/mileage records to confirm if that's the case for your truck. Some people have noticed a difference, some haven't. It might depend on which strategy is loaded into your ECU's memory.
Hope I got that all right. I'm sure someone will correct me if I'm wrong..........
I am using the factory flash - and the drop in fuel economy is sizable.
Somewhere in the 10% range.
That is why clearing the CEL for EGR failure is so important - unless there is a way to turn off the monitoring of EGR function.
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From: Lakewood, Ca.
Originally Posted by satwood
I have seen several threads/posts talking about a code for insufficient air flow through the EGR system. How does the computer recognize this?
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Mountain Pass
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Well, it's hard to say if I have any reduction in mileage because I did not drive the truck long enough before I made the change. But, thanks for explaining the sensing process for me. I did not realize it was that sophisticated. Mine is a non-CA early 2003 and it did not throw the CEL either when I had the EGR unplugged or now with the cooler blockoff. I don't have a code reader so I don't know if it is storing anything internally. What is the preferred device to read those codes and can they be permanently cleared without a tuner or is that my next investment?
Thanks
Steve
Thanks
Steve
Post Fiend
Joined: Jul 2005
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There are two IAT (intake air temperature) sensors. IAT1 is integral to MAF, and IAT 2 is mounted in the intake manifold. The PCM recognizes EGR flow by the temperature differential between these two sensors....if IAT2 reads a lower than expected temp, the PCM figures there's not enough EGR flow.
Interesting. On some of the coldest days this past winter (-20F or lower) I had an MAF error.
Wonder what that might be?
Using temp differentials to computer flow... interesting... I would like to see the algorithmic.
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Post Fiend
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From: N. Fort Worth, tx
There are two IAT (intake air temperature) sensors. IAT1 is integral to MAF, and IAT 2 is mounted in the intake manifold. The PCM recognizes EGR flow by the temperature differential between these two sensors....if IAT2 reads a lower than expected temp, the PCM figures there's not enough EGR flow.
this is correct but missing some more info.
we also look at ebp and expect to see a change in back pressure when the valve moves.
also we look at its reaction with the vgt, and how its driving the map pressure.
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From: waynesville, mo.
Using this knowledge, you can see why we have a smile on our face when someone posts "Just block it off, then put the cooler back on, they'll never see a difference.".
Post Fiend
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I just had the P0299 with the P0405 code together, and right after it coded, the turbo started to fart.
This is with engine thoroughly warm, with me flooring it to clean it up.
Funny, because as soon as I erased the codes, the turbo fart and other problems ceased.
So the VGT solenoid somehow, have something to do with this/
In the past, I had the P0405 several times after the EGR was cleaned, and once when the engine will not accelerate past 10mph that I put down to carbon stuck on intake or exhaust or EGR valve jamming it open.
I cleared that problem by pulling over, reving it, and it cleared (and codes were cleared later).
This is with engine thoroughly warm, with me flooring it to clean it up.
Funny, because as soon as I erased the codes, the turbo fart and other problems ceased.
So the VGT solenoid somehow, have something to do with this/
In the past, I had the P0405 several times after the EGR was cleaned, and once when the engine will not accelerate past 10mph that I put down to carbon stuck on intake or exhaust or EGR valve jamming it open.
I cleared that problem by pulling over, reving it, and it cleared (and codes were cleared later).
Cargo Master
Joined: Jan 2009
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From: Lubbock
from what i have read there are at least 3 different intake manifolds. 03-04 and alot depends on the build date dont have sensors to detect egr flow. this is partially why the computer dosent throw a code. now im not a tech but i try really hard to pay attention..
Cargo Master
Joined: Jan 2009
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From: Lubbock
other issues are the veins not functioning properly. a year or so ago they were calling it limp programming. people were seeing it when they unplugged the egr valve as well as blocking the egr or deleting it. the solution is thru tuning although im not positive some of the ficm tuning is effected or was thought to be effected. its been a day or two since it was discussed heavily
Mountain Pass
Joined: May 2010
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I just had the P0299 with the P0405 code together, and right after it coded, the turbo started to fart.
This is with engine thoroughly warm, with me flooring it to clean it up.
Funny, because as soon as I erased the codes, the turbo fart and other problems ceased.
So the VGT solenoid somehow, have something to do with this/
In the past, I had the P0405 several times after the EGR was cleaned, and once when the engine will not accelerate past 10mph that I put down to carbon stuck on intake or exhaust or EGR valve jamming it open.
I cleared that problem by pulling over, reving it, and it cleared (and codes were cleared later).
This is with engine thoroughly warm, with me flooring it to clean it up.
Funny, because as soon as I erased the codes, the turbo fart and other problems ceased.
So the VGT solenoid somehow, have something to do with this/
In the past, I had the P0405 several times after the EGR was cleaned, and once when the engine will not accelerate past 10mph that I put down to carbon stuck on intake or exhaust or EGR valve jamming it open.
I cleared that problem by pulling over, reving it, and it cleared (and codes were cleared later).
um....... turbo fart?????????????????????????
Senior User
Joined: Oct 2008
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I have a home made sneaky pipe, a plug in the EGR valve hole, (egr valve plugged in but mounted to the firewall) and have removed the butterfly valve below the elbow. I am running a sct tune at stock HP that was suppose to fix the egr issues. great power, runs fine, no lights or codes, but only 17.5 MPGs on the highway. Understand i have been stranded 3 times due to EGR so I am not going back, after all this, it has never let me down again (about 40k miles like this) but I do wonder if I am still running a some kind of limp fuel table. Oh, and someone let the kitty out, and the CCV is to atmosphere.
One other thing. I unplugged the EGR and notice a drop in top intake or turbo pressure. performed all the above mods and no more loss of pressure, SCT did something.
One other thing. I unplugged the EGR and notice a drop in top intake or turbo pressure. performed all the above mods and no more loss of pressure, SCT did something.
Last edited by yz400f; May 13, 2010 at 11:22 PM. Reason: Thought of something else..........