EGR valves

[Lomac]

I'm not a mechanic by any means but I know a little about cars and I was wondering - What exactly are the symptoms of a bad EGR valve and how difficult are they to replace in general? I've heard horror stories by my friend as was just wondering if they really are that bad.

[quaddriver]

Originally Posted by Lomac

I'm not a mechanic by any means but I know a little about cars and I was wondering - What exactly are the symptoms of a bad EGR valve and how difficult are they to replace in general? I've heard horror stories by my friend as was just wondering if they really are that bad.

you dont say what you have, but egrs are fairly easy to get to and replace...as for symptoms,

well one that is not working, you might 'ping' a lot more as combustion temps are high, one that is working too much, you will idle roughly, lose top end power, and shudder and shake a lot.

typically however the ECM detects such malfeasance and turns that funny little light on.

[KC Ron Carter]

EGR is Exhaust Gas Recirculation.

If it sticks closed, no one knows or cares.

If it sticks open the idle AFM, Air Fuel Mixture is lean and the idle will be rough.

The purpose is to add exhaust gasses to the combustion chamber, above idle, that are not combustable so the engine will run slightly cooler and produce less NOX.

POS, no explanation availble here.

Later,

[-Josh-]

Actually the EGR is important, in a few more ways than that:
And you dont really want the back pressure from a closed EGR valve

1. Helps control detonation
2. It allows for greater ignition timing advance

[Fedexjetmx]

Sorry but gotta lol.
Z28Josh you need to learn a little more about it before you talk about it. The sole purpose of the egr system is for emissions. Has nothing to do with detonation, and nothing to do with allowing more timing advance.

[-Josh-]

lol..... Yes it is for emissions. And considering that in my Fuel and Emissions diagnosis class that i'm taking that's one of the things they talked about, i'm sure i know what i'm talking about. I also read it, if you dont believe me i can take the passage right out of the book if you want.

[KC Ron Carter]

I am ASE certifide and I stand by my statement.

Stuck closed no one knows.

Stuck open it makes the air fuel ratio lean.

Most modern manufactures use a 3 bed catalyst to lower nitrous oxides to acceptable levels without an EGR valve.

I realize that your youth makes taking my word for this an issue.

So here is the government site to explain it.

http://www.eia.doe.gov/oiaf/1605/gg97rpt/chap4.html

Later,

[quaddriver]

Originally Posted by KC Ron Carter

I am ASE certifide and I stand by my statement.

Stuck closed no one knows.

Stuck open it makes the air fuel ratio lean.

Most modern manufactures use a 3 bed catalyst to lower nitrous oxides to acceptable levels without an EGR valve.

I realize that your youth makes taking my word for this an issue.

So here is the government site to explain it.

http://www.eia.doe.gov/oiaf/1605/gg97rpt/chap4.html

Later,

'Cept you misread the govt paper. There are EXTREMELY few SI vehicles sold in the USA without an EGR. For the formation of NOx there is a 'sweet spot' of temperatures which an SI motor hits rather well. The newer generation of catalyst systems WITH proper air injection, lower the overall temp of the cat, where the unburned N in the air passed along would react with the injected air. This has absolutely nothing to do with the separate EGR system.

Stuck closed, a problem is detectable. If you do not outright hear 'spark knock' or see spot temp increases on a decent coolant temp gauge, on an OBD1 vehicle the KS counts per minute will exceed allowable and set a code, on some OBD1 vehicles insufficient EGR flow will set a code, on most all OBD1 vehciles the O2S will signal Rich with no crosscounts, and on all OBD2 vehicles the 'pre-catalyst' O2S output will cause a code to be set as well as the other mentioned conditions.

Stuck open and the following will exist: the vehicle will not idle. The narrow operating range of the idle control system cannot account for a stuck open EGR valve. You can verify this by simply applying vacuum to the valve at idle(if applicable). OBD2 will catch it immediately. some OBD1 vehicles will signal excessive EGR flow. The vehicle will buck, and perhaps stall in coast down mode if stuck open for the same reasons. The vehicle will not develop full power as the current EGR programmes stop flow at 75% or greater throttle. Aside from various codes, each of these are detectable by the driver.

Surely your ASE Cert courses covered this. The online study guides for ASE cert sure do

As for an earlier post of his you shot down, the proper use of EGR most certainly does allow timing variations. I have personally seen 45*+ advance when a functioning EGR, KS and EST system work properly. This flies in the face of conventional wisdom that says 36-38 is the max as has been rule of thumb for decades. Im sure other people with active scan tools have seen similar.

[calgary_redneck]

Originally Posted by Fedexjetmx

Sorry but gotta lol.
Z28Josh you need to learn a little more about it before you talk about it. The sole purpose of the egr system is for emissions. Has nothing to do with detonation, and nothing to do with allowing more timing advance.

Its kinda ironic that someone this ignorant would tell someone else they need to learn more beofer they talk.

Very oftain removal of misfuntioning of the egr valve will result in detonation in light throttle.

[JWMAX]

Help! I may have a possible EGR problem. My motor pings about every 3-5 seconds when it is at operating temperature and the knock sensor is going off and retarding the timing when I accelerate and very noticeable above 3000 rpm's and a little below that. The motor also pings for a while after the motor is turned off (until it cools down a bit). I don't know if this has anything to do with it either but when my car idles it sounds like George Jetson's hovercraft and is not very steady. When the motor is warm and I rev it up I can feel the valve moving up, or if I take off the vacuum hose I can feel it sucking when I rev up the motor. The car runs perfect before it warms up and has plenty of power all the way to the redline. Another part of the EGR system has a knob on it that looks like I can adjust it but I'm not sure what that's all about. It also has some plugs in it and stuff.

Just a little FYI: The car is a '92 Nissan Maxima SE w/ 130,000 miles. Replaced w/in last 3 months: spark plugs, air filter, fuel filter, knock sensor and harness, also cleaned out the fuel injection system and flushed the oil system with a cleaner called BG from a local shop. The car burns no oil and runs great other than the hesitation. I use 93 octane gas from various places with no improvement. The car has coil packs instead of wires and they dont seem to have any cracks in them. The timing is electronic and I haven't messed with it.