EGR Mystery

[mattferguson14]

So, like others here I have an intermittent EGR code. The CEL comes on and goes off about once a week (it is on all the time, but goes off about once a week). The code I get is P-1404 (if I remember correctly) which is EGR open, meaning the valve is sticking open for some reason. I have cleaned the EGR out and still no luck. But here is the "mystery", I can FEEL my truck start running BETTER right before the check engine light goes off. My acceleration gets a little better and I can just feel the performance boost. I can literally tell that the light is about to go off before it does because of this performance boost. And vice-versa as well, after a day or so of the light going out, I can feel the performance start to suffer a bit (less pedal response, a tad bit of hesitation) and I know the CEL will be coming on shortly and it always does. As far as I know, the EGR should not affect the engine's performance, even if you completely disconnect it. So what is this "boost" I am experiencing (or performance LOSS if you want to be a pessimist about it )? Could the code be coming from a different problem? Any advice or input is greatly appreciated.

Thanks!

[KILNA]

If I understand how this works correctly... The engine is designed such that exhaust gas which the EGR system re-introduces will cool the temperature inside your cylinders as combustion happens (this is to create less NOx). The EGR valve regulates the amount of exhaust re-introduced into the engine. Sounds like your EGR valve is stuck open (introducing the max amount of cooling exhaust gas) most of the time, with occasional intermittent times where it works (and the code goes away). Since you have too much exhaust gas most of the time, it will run poorly and probably have poor mileage since you'll have more unburned fuel. Once it warms up/jiggles enough/you get lucky enough for it to get un-stuck, the engine would run more smoothly since the temps in the cylinders are what they're tuned to.

[bartmanS4]

if and EGR is stuck open it will effect performance.

[KILNA]

In other words, if your EGR was stuck closed you might expect higher performance (and temperatures, and any other problems associated with running hot)... but yours is probably stuck open, meaning you get the opposite effect.

[mattferguson14]

Hmmm.. the second post on my old thread is conflicting.. http://www.vehicross.info/forums/sho...&highlight=egr Maybe I'm reading it wrong but I was told the EGR does not effect engine performance. Maybe I got some faulty advice. I'll get a new one on EBAY and see what happens.

[KILNA]

It looks like a few of the folks in your previous thread were slightly confusing, muddling the two problems of blocking/clogging/keeping closed the EGR valve and the opposite issue of the EGR being clear and stuck open. The 2nd post was correct, however he seems to have missed that yours failed open, not closed... most EGR failures are the valve being closed or a blocked EGR tube. Generally, when folks are talking about "disabling", "deleting" or "removing" the EGR valve, they're talking about blocking it off. This is the same as the valve being in the always closed position, or the tube being clogged. What you have, according to the CEL code, is a valve which is always open. This would effect performance, it's always venting more exhaust than desired back into the engine (making it cooler than the engine is tuned for and throwing off the fuel/air mix).

[mattferguson14]

It looks like a few of the folks in your previous thread were slightly confusing, muddling the two problems of blocking/clogging/keeping closed the EGR valve and the opposite issue of the EGR being clear and stuck open. The 2nd post was correct, however. Generally, when folks are talking about "disabling", "deleting" or "removing" the EGR valve, they're talking about blocking it off. This is the same as the valve being in the always closed position. What you have, according to the CEL code, is a valve which is always open. This would effect performance, it's always venting more exhaust than desired back into the engine.

Do you think it may be beneficial then to disconnect my EGR until I get a new one? that way it should stay closed right? When I had the EGR off the truck, the valve seemed to open and close fine. I cleaned a bit of carbon out of it. But I'm assuming that it gets stuck open when the engine is running because it has an internal electrical problem. If I disconnect, in theory it should stay closed, which would not necessarily effect my engine performance??

[KILNA]

Do you think it may be beneficial then to disconnect my EGR until I get a new one? that way it should stay closed right? When I had the EGR off the truck, the valve seemed to open and close fine. I cleaned a bit of carbon out of it. But I'm assuming that it gets stuck open when the engine is running because it has an internal electrical problem. If I disconnect, in theory it should stay closed, which would not necessarily effect my engine performance??

I *think* the default position is closed, so if that is the case, I'd expect that any rough engine behavior would go away. It'd be more similar to what it's like when you don't have your code being thrown. Obviously, it'll throw other codes now instead. Generally speaking, the ill effects of the closed position are less than the open position though, I'd probably do what you're planning until I got the replacement.

[mattferguson14]

I went ahead and disconnected it and viola! She's running a lot smoother. Of course I have another code now but I can live with that. As far as what you said about poor mileage, mine has been horrible, somewhere around 10-11 MPG. We'll see how she does with it disconnected. I just filled up and I have a feeling I'll get a lot more than 220 miles out of this tank. I posted another thread about my exhaust smelling like fuel, like the engine was running really rich. I was going to replace the fuel pressure regulator, but I think I found my culprit! Two birds with one stone! thanks KILNA!

[KILNA]

So in summary the three states the EGR system can be in:

1. Normal operation... a small amount of exhaust is routed back into the system, as controlled by the computer, based on criteria to keep the temperature, pressure, fuel and oxygen at a sweet spot. Fuel economy is at an optimum, while not effecting performance.

2. Exhaust gasses blocked... the normal amount of exhaust cannot be routed back to the engine for one reason or another... blocked EGR tubes, EGR valve failed in closed position, or someone intentionally blocked the EGR. The fuel, instead of burning smoothly over the entire stroke of the piston, will burn quicker at the beginning because of the extra oxygen. Early burn also means that, because fuel is injected over the course of the stroke, not all of the fuel will get burned (the later fuel is wasted). It means less efficient transfer of energy from the explosion in the piston in mechanical terms. The engine runs hotter because more of the energy is transferred thermally as opposed to mechanically. Performance is generally not effected much, but fuel economy is.

3. Too much exhaust gasses... if the valve is stuck in open position. This can produce misfires and partial burns. The engine will be cooler (there's less oxygen), you'll have bad fuel economy because there's not enough oxygen in the cylinder to mix with the fuel for the explosion. The explosions happen later in the stroke, which leads to bad transfer into mechanical energy. Sometimes they don't happen fully or at all, and the engine will sputter and misfire. As a result, both performance and fuel economy are poor.

Most people with EGR problems have state #2... but you sound like you have #3 with it occasionally going back to #1. If you switch to state #2, know that it has it's own trade-offs. I'd just fix or replace the valve as soon as it were feasible.

[mattferguson14]

So in summary the three states the EGR system can be in:

1. Normal operation... a small amount of exhaust is routed back into the system, as controlled by the computer, based on criteria to keep the temperature, pressure, fuel and oxygen at a sweet spot. Fuel economy is at an optimum, while not effecting performance.

2. Exhaust gasses blocked... the normal amount of exhaust cannot be routed back to the engine for one reason or another... blocked EGR tubes, EGR valve failed in closed position, or someone intentionally blocked the EGR. The fuel, instead of burning smoothly over the entire stroke of the piston, will burn quicker at the beginning because of the extra oxygen. Early burn also means that, because fuel is injected over the course of the stroke, not all of the fuel will get burned (the later fuel is wasted). It means less efficient transfer of energy from the explosion in the piston in mechanical terms. The engine runs hotter because more of the energy is transferred thermally as opposed to mechanically. Performance is generally not effected much, but fuel economy is.

3. Too much exhaust gasses... if the valve is stuck in open position. This can produce misfires and partial burns. The engine will be cooler (there's less oxygen), you'll have bad fuel economy because there's not enough oxygen in the cylinder to mix with the fuel for the explosion. The explosions happen later in the stroke, which leads to bad transfer into mechanical energy. Sometimes they don't happen fully or at all, and the engine will sputter and misfire. As a result, both performance and fuel economy are poor.

Most people with EGR problems have state #2... but you sound like you have #3 with it occasionally going back to #1. If you switch to state #2, know that it has it's own trade-offs. I'd just fix or replace the valve as soon as it were feasible.

That is a nice synopsis. Someone should post this as a sticky thread in the repairs section under EGR troubleshooting.

[Leon R]

You shouldn't just "disconnect" your EGR valve, if you want to disable it. You need to block the flow between the exhaust and intake. This can be done with a plate or with a simple gasket that lacks holes for exhaust gas to travel. The simplest way to make such gasket is to cut one from Coke can! This will surely cause a permanent CE light.

I do not know what you are "feeling", it typically take 10% of power to feel the difference without using instrumentation, and I can't imagine EGR making THAT much difference.

[KILNA]

Maybe I'll whack it up as a new thread, and post the associated codes, and quote sources as well. I was super confused by all of this when I first started trying to figure out my EGR issues, and it took a lot of reading before I thought I understood what was going on. There's tons of conjecture being passed around as facts, not just here, but on loads of other auto-related message boards. There's people who want to tell you to just block it off permanently, but all you're doing in that case (other than breaking the law) is decreasing your fuel efficiency and causing unnecessary pinging/knocking because your ignition is happening too soon in the stroke. The EGR system isn't there because hippies want to make your engine less powerful, it's there because the oxygen mix in the piston is an important factor for proper function of the engine.

http://www.newton.dep.anl.gov/askasc...9/eng99611.htm

[Leon R]

The EGR system isn't there because hippies want to make your engine less powerful, it's there because the oxygen mix in the piston is an important factor for proper function of the engine.

Actually... It is a terrible system, this is one of those things the sounded OK on paper so "hippies" passes the laws to require it, but it has crabby unintended consequences. Some cars do OK with it, but others require frequent maintenance and cleaning!

I have seen many older cars that suffered from al the carbon deposits on: throttle bodies, intake valves and even injectors!

The only reason some cars need it, is because their ECUs are tuned to run with EGR.

[mattferguson14]

Bad system or not, it is equipped on our VXes and we have to deal with it. I personally want my truck running at peak performance wherever possible, so I went ahead and bought a new EGR. Should be here by Friday. I'll slap it on and see what happens.