Re: Pontiac EGR Valve

Posted by Chris Vangel on September 06, 2004 at 15:41:09 from (68.75.154.138):

In Reply to: Re: Pontiac EGR Valve posted by Allan in NE on September 06, 2004 at 08:03:30:

That is not correct. The Exhaust Gas Recirculation Valve (EGR) introduces engine exhaust into the intake air stream to control emission of Oxides of Nitrogen (NOX). NOX is created when cylinder temperatures get too high. Exhaust is inert because it has already been burnt, because of this when exhaust enters the cylinder it lowers combustion chamber temperatures and thus prevents NOX from forming.

The pinging you might hear is pre-ignition. It is something else that happens when combustion chamber temps get too high. The fuel actually ignites early due to extreme heat of the metal in the cylinder instead of the spark. The pinging results because the piston is trying to compress the already burning fuel charge. As the piston pushes up on the ignited fuel charge, the spark arrives and ignites the other end of the cylinder, when the two explosions meet each other in the middle of the cylinder, pressure in the cylinder goes through the roof and the ping results. If you allow this to happen long enough, it will break/melt the top ring land of the piston or blow a hole through the piston top.

The easist way to prevent this it to correct the EGR valve operation. The valve is only supposed to open when the engine is off idle. If the valve opens at idle, the engine will run rough and/or stall. The valve opens as you accelerate and stays open during cruise. When you let off the throttle the valve closes completely. If the valve is alway open when the vacuum line is attached, the vacuum line is either hooked up to the wrong vacuum source or a control solenoid is stuck/broken allowing vacuum to hold the valve open. In short, if the throttle is closed, the valve has to be closed.

The only other ways to stop pinging without the EGR Valve working is the higher octane fuel, which may not be successful and will definately cost more money. The other way to stop it is to back the timing off, this drops engine power and again, results in higher fuel costs.

In short, it's easier and cheaper to fix it the right way. Sorry if this got to long, I've been a mechanic for 15 years and been to alot of schooling from GM and Chrysler. There are alot of misconceptions about why EGR systems exist. I hope it helps clear things up a bit.

Chris.

Follow Ups:

• Re: Pontiac EGR Valve TheRealRon 03:45:02 09/07/04 (1)
  • Re: Pontiac EGR Valve Chris Vangel 20:49:10 09/07/04 (0)
• Re: Pontiac EGR Valve Allan in NE 17:31:54 09/06/04 (0)

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