Does anyone know what exactly the ECU does when it detects an EGR problem? People say it makes the car runs bad, but why? Does the ECU dial out timing? Change the mixture? In the Helm's, it says when the car runs poorly, stalls, or idles rough, it's a good clue that it's the EGR system. But why?

What I can't figure out is, if the EGR's not working it means it's *not* putting exhaust gasses back into the engine. How can the absence of exhaust gas make the car run *worse?*

 

the ECU does not chekc the EGR for flow, just to make sure its there. i think once it doesnt read it, it will throw a CEL and put the car in "limp home" mode. the EGR just adds the burnt gasses to richen up the mixture. technically with no EGR to make it rich, the O2 sensor should read the leaner condition and make the appropriate changes

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo Sam &raquo;</TD></TR><TR><TD CLASS="quote">the ECU does not chekc the EGR for flow, just to make sure its there. i think once it doesnt read it, it will throw a CEL and put the car in "limp home" mode. the EGR just adds the burnt gasses to richen up the mixture. technically with no EGR to make it rich, the O2 sensor should read the leaner condition and make the appropriate changes</TD></TR></TABLE>

I know how it works... it commands a position, then reads back the position to see if it got there. If not it sets error code 12. What happens next is what I don't understand. I thought there was no "limp home mode," so what's it actually doing? (BTW, in my case this is a 95 H22A1, OBD1.) Like you said, if it's broken, there's no exhaust gasses to lean out the mixture, so does it go rich? Does the O2 sensor then fix the problem? Or, without exhaust gasses, does that mean there's then more oxygen so it goes lean.... Aaaaaa, brain hurt... Anyways, that's why I'm asking. I'm hoping we can figure this out once and for all... or at least me anyway...

 

when you add exhuast gas, it causes it to go rich, therefore decreasing the amount of fuel needed.... its an economy thing

 

Well from my horrible experience that is still going on with my EGR...It does NOT set the car in to limp mode. From what i gather from every one of my honda mechanic friends the only thing that sets off CEL 12 is improper flow (vacum) or bad/improper wiring.

As far as your other questions about CEL 12 making things rich...I would assume so..but im not sure. But I know damn sure im running really rich, but that probably has to do with the other crap in the motor on top of the EGR.

I wish I could help more.

 

if you've got a 3rd gen, then your car is OBD0, and the EGR won't cause a CEL

 

Right... except I have a 95 4G H22A1... stock P13 ECU

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo Sam &raquo;</TD></TR><TR><TD CLASS="quote">if you've got a 3rd gen, then your car is OBD0, and the EGR won't cause a CEL</TD></TR></TABLE>


JDM H22 (p13) hence my user name.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 3gLudeH22A &raquo;</TD></TR><TR><TD CLASS="quote">


JDM H22 (p13) hence my user name. </TD></TR></TABLE>
lol, didnt know if you had a swap in it yet or not

 

Yea its in..but runs like shiot...EGR problem and no dyno time is killing me...

But back on topic....KB only thing I can say is go back and look at your vacuum and wiring. Or first you can buy my an EGR valve that I have on my spare intake manifold.

EDIT: Also improperly working EGR systems raise intake temps...And as we all know class.....Hot intake air temps= less power.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 3gLudeH22A &raquo;</TD></TR><TR><TD CLASS="quote">...only thing I can say is go back and look at your vacuum and wiring. </TD></TR></TABLE>

I don't have an EGR system connected, and at the moment it's not throwing a code (though I know it will.) The engine idles perfectly smooth. What I want to know is, what does the ECU do *after* it discovers there's a problem... Sure, it sets the code, but anything else? No one seems to know for sure. If the ECU does nothing other then setting the code, then it's odd how the engine runs worse *without* exhaust gasses being fed into it... Just curious...

 

much like with a bad o2 sensor. i believe when the egr is malfunctioning. the ecu senses it. trips the cel and pulls timing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDMlude92 &raquo;</TD></TR><TR><TD CLASS="quote">much like with a bad o2 sensor. i believe when the egr is malfunctioning. the ecu senses it. trips the cel and pulls timing.</TD></TR></TABLE>

Do you know this for sure, that it pulls timing? The ECU in question is a 95 OBD1 P13.

 

allmost everytime you throw a cel. it will pull timing. because the cel is only there for emissions purposes. so if it runs too lean. it will either correct itself by the o2 sensor. or pull timing to correct and it'll throw the cel.

i'm not 100% sure that the egr problems goes with this category. but the easies way to check it out is if you drive it and it bogs or hesitates until past 5500rpm. if it were too bog or feel sluggish below 3k and between 4800-5600. your ecu is pulling timing.

btw if you need an egr pm me i think i might have an extra one.

 

I got all the parts, thanks to skrewdlude here. I'm just debating whether to hook it all up or not, hence the EGR question. No one seems to know for sure about the timing issue. Some of the guys here are trying to get me out to the next timetrial event at Streets of Willow... bastards, all of you. I'm thinking about it...

 

might as well put it on there for reassurance. it doesn't rob any power at full throttle so why even take it off?

 

just plug the thing in, done actualyl run it, or use a block off plate, like i said, it only checks to make sure its there and the peaice itself works, not to check for flow

 

Yeah that seems to be the best thing to do, putting it all back. I just wanted to know what the ECU did... guess we'll never know...

FWIW, I received the engine with no EGR stuff on it... so "technically" I didn't remove it. Finding the parts and adding them on is more work and more weight, and I just wanted to know the consequences of leaving it off. "Runs bad" seems to be the only conclusion, and one worthy of installing the stuff...

 

The EGR system is designed to reduce oxides of nitrogen emissions by recirculating exhaust gas through the EGR valve and the inakte manifold into the combustion chambers. It is composed of the EGR valve, EGR vacuum contorl valve, EGr control solenoid valve, ECU and various sensors.

The ECU memory contains ideal EGR valve lifts for varying operating conditions. The EGR valve lift sensor detects the amount of EGR valve lift and sends the info to the ECU. The ECU then compares it with the ideal EGR valve lift which is determined by signals sent from other sensors. If there is any difference between the two, the ECU varies current to the EGr control solenoid valve to further regulate vacuum applied to the EGR valve.(1994 Honda Prelude Helms).

If you want a picture of it all hook up let me know, Ill take one.

 

I understand and agree with all the above, but the BIG MISSING PIECE is what else the ECU does once it decides it's not working, other then setting the error code.

I guess I've beating this to death... The conclusion is that no one knows for sure what the ECU does if it decides the EGR circuit is bad, but we more-or-less agree the engine runs poorly once the error is set, and that all the EGR parts should be left in. Blanked off perhaps, but left connected.

Thanks for everyone's help.

 

does the CEL come on, or does it flash w/o the EGR?

If it flashs, that means the ECU is now dumping fuel into the engine to make sure there is no chance for a lean situation, along with limiting the RPMs to like 3200 or so, retards timing, etc.

If it's not flashing, I'm not sure...

 

In my case? I haven't driven it without the system so I can't say. I'm only passing on the anecdotal stories from others, that removing it makes the car run bad. That... and Helms saying if the car runs bad the EGR circuit is probably why.

 

I unplugged mine... i think i got a light nearly right away. I tried to trick the ECU using some resistors to make it think the sensor on the EGR was still there.. didn't work quite right lol

 

Yeah I don't think it's that easy because there are two inputs, the commanded position, and the amount of vacuum. Some combination of the two creates the expected position. There's no easy way to measure vacuum... oooo, yes there is... MAP.... hummmm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo Sam &raquo;</TD></TR><TR><TD CLASS="quote">when you add exhuast gas, it causes it to go rich, therefore decreasing the amount of fuel needed.... its an economy thing</TD></TR></TABLE>.
An egr system does not make the engine rich,what it does it makes your car purposely loose power when combustion temperatures get really high,When they do,your engine will emit more Nox emmisions.The exhaust gas is just recycled to your combustion chamber to take up space really,it wont burn again because it is basically an inert gas.So your engine will lose power, the cylinder temps will cool down,and once normal emmisions are met,the ecu will close the egr system.Ideally you engine tries to keep the a/f ratio of 14.7 to 1,but as temperatures get higher,Oxides of nitrogen form,they are very harmfull to the outside air,so its there for emmision reasons also.It also saves your engine from detonating too.so yes,timing is pulled when the egr system is not working properly.