O2 Simulators are great, they even pass emmisions as far as the OBD2 ECM is concerned and they allow for removal of your cats.

What I need now is an EGR simulator so I can remove my EGR valve.

I dont beleive programming the egr out will pass OBD2 emmisions since the ECM would no longer test the EGR. What I need is a simulator. Any ideas?

 

I've never heard of/seen an EGR simulator, I don't think they make them.

 

You could take it out and block the hole,leaving the valve hooked up.No ses,all is well.

 

No, I'm not aware of anybody making one either. On OBD2 there is something that provides feedback to the ECM on its performance though. So I am told if you just block it off it will set off the SES. I dont know enough about the EGR system to trick it or simulate it.
If anybody knows more about the ECM's monitoring of the EGR on OBD2 please explain.

 

The electrical side of things is easy, just stick an appropriate resistor in place of the EGR solenoid. The tough part is the diagnostic test. When the PCM commands the EGR system on it looks for a drop in manifold pressure (by monitoring the MAP sensor). If this drop isn't seen than the PCM assumes that no EGR gasses are being introduced into the plenum and that the system is failing.

The best thing to do is leave the system on the car or if you just, absolutely, must have !EGR, have the PCM reprogrammed. Why do you have !EGR?

 

So thats the feedback, a drop in MAP pressure.

The !EGR benefit is negligable at best from what I have read but I have had problems with mine since the header install. I think it was P400, I know it was "EGR flow malfuntion". The way OBD2 testing is done basically relies on the ECM to rat you out. No actual emissions testing is done. The only thing they do besides read the ECM is turn the car over just to make sure the SES light is operating and not tampered with.

So (if) I simulate it I could pass but if I program it out I will fail.

The only mechanical benefit I know of !EGR is no exhaust gasses heating the intake manifold. This is also what causes the valve to stick or clog IMO.

If I let it pull fresh, filtered air instead of spent exhaust gasses would it know the difference?

 

First of all, I use OBDI so I'm not entirely clear with OBDII specifics, take this with a grain of salt.

It is my understanding that by disabling the EGR test it will remain as "not-performed" in the PCM which is NOT the same as a "failed" test (otherwise you'd get an SES light anyway ) I have heard several times that the new OBDII testing will allow up to two unperformed, non-critical, tests and still pass you. I believe EGR function test is one of those "non-critical" types. This may vary from state to state and I may be way off base but I know there are people here that can correct me when wrong

The reason you're getting a code after the headers is probably because there isn't enough backpressure to push the exhaust gasses into the plenum, not enough MAP change, and the test fails so you will more than likely need the PCM reprogrammed anyways. If you have an A4 you might want to try an EGR valve for an M6 car, I *think* the M6 valve uses a lighter spring... might want to double check on that one though.

You could vent fresh air into the plenum but you will have to make sure that it is filtered and metered (after the MAF) air. To do this you would still have all the EGR system in place and would not benefit it all, you might as well use the EGR as intended. The EGR system is only used during cruise and does not hurt WOT performance. "Gunk" on the valves is from bad gas that leaves deposits, the PCV system, and also reversion that happens anyway, I don't think the EGR contributes much. If you use good clean gas this shouldn't be a problem.

The only time I can see using !EGR is if you have constant problems with stuck EGR valves which hurt emmisions, performance, and the wallet.

 

I recently swapped the ORP's for the cats and set the fan temps all the way up for inspection and that fixed it. Initially it took a few weeks after the header install to set the code. I have removed the cats now and the code has not returned, yet. That being considered I am more suspect of the condition of the valve. I think the vacuum leak created by the EGR would affect the MAP no matter if it was pulling exhaust gas or normal atmosphere, although the exhaust would have more pressure.
If something like that mod worked it would yeild the same benefit as !EGR, no hot gasses in the intake.
At first thought it would need to be metered HOWEVER, the EGR is a back door and not metered. Yes the exhaust was originally metered but the MAF is a real time measurement.
What do ya think?

 

The EGR gasses do not need to be metered because there isn't any oxygen in it. If you are pulling in fresh air it would need to be metered because the added O2 will result in a temporary lean condition when the EGR is engaged and a temporary rich condition when it is disengaged. The PCM will be chasing its tail trying to meter the fuel correctly.

When the EGR system is working properly it is not used under WOT so those hot gasses are of no concern. Under cruise it reduces combustion chamber temps and also slightly raises the dynamic CR. It eliminates NOx emissions and also improves gas milage a bit.

 

quicksilver97ta:

I have the exact same problem you do. Whenever I'm running offroad pipes I get the P0400 code (EGR Flow Malfunction), but when I have the cats in the code never shows up. You're right that it's because of the lack of backpressure and I have yet to find a cure for this problem, hence the reason I'm running with cats. I'd really like to find a fix for this besides having it programmed out, but I have yet to find anything.

 

Yeah, it would need to be metered since it is fresh air. Your right. And no doubt the EGR has the benefits mentioned but theres got to be away to run with my orp and not throw a code. I'm just trying to think one up. Any suggestions?

 

I guess I could program it out for use with an orp and then program it back in for cats and inspection. Just didnt see the need for spending $$ on LT1 edit till I needed to tune for heads/cam.

 

I made my own "EGR simulator" using a vacuum switch and some resistors. Basically, instead of the vacuum line going to the EGR valve, it goes to a vacuum switch. When the PCM commands the EGR valve to open, the vacuum closes this switch. I have some resistors connected from the 5 volt reference from the MAP sensor to the vacuum switch and then to the signal wire. When the vacuum switch closes, it increases the voltage signal to the computer and the computer "thinks" the EGR valve opened. I have been running this for over 3 years on my 96 (OBD II) and have NEVER had a PO400 code. I don't even have the tube from the passengers side header to the back of the intake on my car. I made everything just plug in, I did not cut any wires so that returning to stock would take about 1 minute. Probably less than $20 in parts.

 

That sound like the exact set up I am looking for. 3 years is a long time ago but it would help if I knew:

1. An application I can ask for to get that kind of switch.
2. The ohm's the resistor(s) rated at.
3. The color and location of the MAP wire where you spliced in.

So I guess the MAP voltage signal received by the ECM goes up as the MAP itself goes down. I wasnt sure if these cars actually had a MAP sensor or if MAP was just calculated from other engine data. Where is the MAP sensor?

That is a great mod if I can reproduce what you did. Any detailed info would be much appreciated.

 

I would be interested in this information as well.