Permanently removing EGR valve and associated air passages

[myhui]

Has anyone thought of permanently welding shut the exhaust recirculation port on the intake manifold? With engine warm, there is no need for EGR in order to pass smog test, and there is no requirement that smog test be run with a cold engine. The weld needs to be done properly so that intake air flow is not disturbed.

 

[Briank]

Unplugging the EGR valve will cause a CEL/MIL

 

[myhui]

That's fine, I was looking past that problem. I was thinking of the physical benefits of that mod.

 

[stevenlee]

Has anyone thought of permanently welding shut the exhaust recirculation port on the intake manifold? With engine warm, there is no need for EGR in order to pass smog test, and there is no requirement that smog test be run with a cold engine. The weld needs to be done properly so that intake air flow is not disturbed.

Do you mean like this?

I removed my EGR passages after I ported and polished my intake manifold. It was impossible to get the sanding debris out of the passages so I machined them away and welded them shut.
To weld the small holes drilled into each intake runner, I machined a round aluminum plug with a head and welded the head to the outside of the runner. I then sanded the end of the plug that was sticking into the runner with a rotary drum for a perfectly smooth runner.

Removing the ERG valve made space available for a new self-draining Oil/Air separator tank I designed and built.



SOS has an EGR delete kit that I used and it's an easy way to seal off the port left by removing that heavy EGR valve.

 

[Daedalus]

With engine warm, there is no need for EGR in order to pass smog test, and there is no requirement that smog test be run with a cold engine.

Why do you say that? The EGR is needed to reduce combustion temps to reduce NOx, which is the most challenging part of the CA smog test to pass. It is never activated when the engine is cold since the ECU must be in closed loop. It even improves gas mileage when operating. There is no benefit to removing it from a stock NSX. Not even sure there's a benefit to removing it from a FI NSX.

 

[myhui]

I see. Thanks for correcting me.

The reason I want it removed is that I am worried a malfunctioning EGR can cause improper AF ratio when idling with warm engine and ECU operating in closed loop.

Here is an interesting peek into what the next 20 years hold for putting fuel into our cars. Page 88 onwards is very interesting.

http://www.arb.ca.gov/fuels/lcfs/workgroups/advisorypanel/20111025WorkingDraftReportv.1.pdf

 

[Briank]

I see. Thanks for correcting me.

The reason I want it removed is that I am worried a malfunctioning EGR can cause improper AF ratio when idling with warm engine and ECU operating in closed loop.

http://www.arb.ca.gov/fuels/lcfs/workgroups/advisorypanel/20111025WorkingDraftReportv.1.pdf

If it malfunctions the ecu will through a code, so you don't need to worry about it doing that.

 

[Eddy]

Unless there is a valid reason, EGR should not impact most of your driving. In fact, at idle and at WOT, the EGR valve is not even open. It's only in operation mostly during cruising under medium load.

See this EGR valve lift map from a 91 MT NSX. The cursor is highlighting the idle position. There is no lift. EGR valve only comes into play between 1500-5000 RPM part throttle on this particular map.

I see. Thanks for correcting me.

The reason I want it removed is that I am worried a malfunctioning EGR can cause improper AF ratio when idling with warm engine and ECU operating in closed loop.

Here is an interesting peek into what the next 20 years hold for putting fuel into our cars. Page 88 onwards is very interesting.

http://www.arb.ca.gov/fuels/lcfs/workgroups/advisorypanel/20111025WorkingDraftReportv.1.pdf

 

[myhui]

Thank you very much for sharing your data.

If EGR is malfunctioning and ECU does not know it, then the mixture will be wrong, and that will be detrimental to both idle smoothness and power at WOT.

 

[greenberet]

So from the information we have, if the EGR system is working properly it will reduce combustion temperatures, fuel consumption, and emissions but will not impact maximum horsepower because it turns off at full throttle.

It could reduce maximum horsepower and idle smoothness if

• the Exhaust Gas Recirculation solenoid valve is stuck open or otherwise doesn’t open and close as it’s supposed to.

For you not to get a check engine light (CEL) if that happens

• the EGR position sensor would have to falsely keep reporting the proper valve lift measurements to the PGM-FI engine computer at all engine speeds and throttle positions
• potentially the oxygen sensors would have to erroneously keep reporting the proper oxygen measurements to the PGM-FI (if the EGR isn’t operating correctly that will impact the amount of unburned oxygen in the exhaust at different engine speeds and loads)

So theoretically the EGR could reduce horsepower and idle smoothness without you knowing about it. But you probably have a better chance of being struck by lightning. On the other hand, unless you’ve replaced your PGM-FI with a stand-alone engine management system, the chances of you getting a CEL if you remove the EGR are probably as high as the chances of the Pope being Catholic.

 

[myhui]

How does EGR valve send positional info back to ECU? How does stock ECU treat that info? Without source code of ECU, we don't know.

 

[greenberet]

We don’t know the format of the data the EGR valve lift sensor sends to the ECU. But we do know that it does send positional information to the ECU.

On page 11-24 of the 1991 Service Manual is a description of the PGM-FI engine management system. Among the inputs listed is the EGR Valve Lift Sensor. Among the outputs is the EGR Control Solenoid Valve.

On page 11-128 of the 1991 Service Manual is a description of the Exhaust Gas Recirculation System. To quote:

[The EGR system] “is composed of the EGR valve, CVC valve, EGR control solenoid valve, PGM-FI ECU and various sensors.

The ECU contains memories for ideal EGR valve lifts for varying operating conditions. The EGR valve lift sensor detects the amount of EGR valve lift and sends the information to the ECU. The ECU then compares it with the ideal EGR valve lift which is determined by signals sent from the other sensors. If there is any difference between the two, the ECU cuts current to the EGR control solenoid valve to reduce vacuum applied to the EGR valve.”

 

[myhui]

Several things can still go wrong:

1) the feedback loop may operate perfectly between EGR valve actuator and EGR valve position sensor, but the exhaust gas being let through is not at all correct for the position reported by the sensor. Hence feedback loop seems perfect to ECU, but the mixture is wrong. This wrong mixture can be detected by O2 sensor, but how much error does ECU allow? Does ECU even detect this anormaly? The O2 sensor is not at all accurate over short time duration. Reading the documentation is one thing. Checking the operation of the ECU against the documentation is something else.

2) the EGR valve position sensor's signal is not treated as a high accuracy input by the ECU, so a large amount of error is tolerated since control loop does not know the true position of the EGR valve based on the sensor's reading.

 

[greenberet]

In case #1, if the pressure in the EGR line is higher or lower than expected, the EGR valve will still only be open at part throttle and then only between 1500 and 5000 rpm so neither idle nor maximum horsepower will be affected. However, you may get more or less exhaust gases passing through the EGR when the valve is open. Best case, the ECU recognizes that and adjusts the EGR valve lift to get the right amount of gases flowing through (like the PGM-FI adjusts the fuel injector pulse width to compensate for variations in fuel pressure due to a tired fuel pump or a stopped up fuel filter) so maybe that’s not a problem. If the ECU doesn’t automatically adjust the EGR valve lift, at least it will adjust the amount of fuel injected to get combustion back to lambda 1. So worst case, NOx emissions at part throttle between 1500 and 5000 rpm may be higher than necessary. Personally, that worst case scenario doesn’t make me lose sleep.

In case #2, if the ECU tolerates a large amount of error in the EGR valve lift measurement – yes, that would be bad. Then the valve may actually be open at idle and at full throttle, giving you an unstable idle and costing you horsepower. Looking at the overall quality of engineering in the NSX, I doubt Honda would be so sloppy (then why would they have bothered with a feedback loop at all?) but theoretically I guess anything is possible.

To answer your original question – yes, I did think about permanently removing the EGR valve after reading DAL Motorsports’ notes (see here: http://ojas.net/nsx/mirror/dal). However, after doing a search on NSX Prime and finding lots of threads on the matter (for example here: http://nsxprime.com/forum/showthread.php?t=103187 or here: http://nsxprime.com/forum/showthread.php?t=71768), I decided to leave it alone because the EGR doesn’t recirculate exhaust gases into the engine at full throttle so it’s not going to cost you any horsepower and if I remove it I’ll constantly get a check engine light.

Anyway, those are just my thoughts regarding an EGR delete.

 

[goldNSX]

We don’t know the format of the data the EGR valve lift sensor sends to the ECU. But we do know that it does send positional information to the ECU.

There is a potentiometer built into the EGR unit which tells the ECU it's position. In other Hondas the poti goes bad and will throw a CEL or result in sluggish behaviour at part throttle.

 

[myhui]

The EGR valve does not intend to recirculate exhaust gas into the intake at improper times. But it can, since it's a mechanical device. So it's important to frame this discussion as: what can go wrong without the ECU seeing it?

This came about because my other car, a 2001 Prelude base model, had everything check out fine but still had a loping idle. Compression, leak down, spark, fuel injectors (cleaned at RC Eng), IAC valve all checked out fine. But it still idled like a Harley, with no CEL, unless a cylinder missed, then you get a CEL. All spark plugs have the perfect color.

Swapped in a new EGR and it runs fine.

I am very much interested in these feedback systems, so I want to (in a bench-racing sort of way, since I lack both time and money now) build an NSX engine that has extensive instrumentation. The custom-built ECU (or get it from McLaren Electronics) will present each measurement via multiple sensors. They all have to correlate depending on the physics. Only then will I be satisfied that the data I see reflects reality.

Assuming use of ITBs instead of intake manifold, intake vacuum can be measured via high bandwidth instrumentation mounted at a tiny port downstream of ITB's butterfly valves, one per cylinder. Do the same at the upper lip of each throttle body trumpet. ADCs will have to run at 10KHz sampling rate and both the shape of curve and area under the curve is relevant.

Intake fuel vaporization is harder to measure in a running engine. Any takers?

Last is intake air composition. You can't do spectrometry analysis in real time. But we want data nevertheless. Any takers?

 

[sicarius82]

Why would you remove the EGR valve ESPECIALLY since you live in California. A faulty EGR is indicated by removing the vacuum line to it and applying another tube with a suction apparatus. When under a vacuum, the engine will choke and turn off.

California Emissions requires the EGR to be installed. You will fail on high NOx every time with a faulty/missing EGR. I understand that there are ways around smog, but it requires additional fees. Is that really necessary?

Not trying to rain on your parade. If you have a PO box in Humbolt County or have plates out of state, removal of the EGR valve won't affect you. Other wise, I suggest keeping it from a CA emissions stand point.

 

[myhui]

You assume EGR valve is mechanically sound when you apply that vacuum test. What if it leaks in either air or exhaust while still giving correct electrical feedback to ECU?

 

[Briank]

If it leaks exhaust you will have have idle issues. It only controls exhaust going to the intake not air.

 

[myhui]

It can also be the cause of a vacuum leak, and that will affect idle.

 

[myhui]

By vacuum leak, I mean a faulty EGR valve lets some air into the intake manifold. Remember that the EGR is in the part of the manifold that is at partial vacuum when throttle is not wide open. But then the MAP sensor should notice that, and so should the ECU. But the ECU may decide not to report that condition.