Pontiac EGR Valve

What that EGR system does is to make the engine eat a portion of it's own sewage during deceleration from hi way speeds.

This is when the unburnt gases in the cylinder are at their highest, so the thinking behind the system is to "reburn" a portion of the exhaust yet again to get the hydrocarbon count down.

It 'taint a gonna hurt the engine any to leave the EGR plugged off. Just don't know how legal it is tho.

Allan

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.

Absolutely EGR flow occurs during acceleration. Oftentimes, A fully warmed up engine will open the valve when you rev the engine in park.

Early systems were simply opened using Ported vacuum, which is available any time the throttle is off idle. The further you open the throttle, the more ported vacuum you have up to about 15"-18". This is if your vehicle is has a carb.

Later systems used a solenoid that simply switched manifold vacuum off and on to the valve.

A popular valve from GM used three solenoids which opened three different valves in one assembly to provide more controlled delivery of EGR gases.

The latest uses a motor that dials the valve open and closed at small increments for exact control. This one is called a Linear EGR Valve.

Manufacturers may wait for the engine to warm up first because the opening of the EGR valve on a cold engine can cause a flat spot in acceration on a cold engine. Timing is adjusted (advanced) by the ECM to supplement performance. The Knock sensor watches to ensure timing is not overly advanced.

No doubt things have changed a bunch since I attended those schools. But, I only went to the GM training schools in Omaha, Denver and the big one over in Minneapolis.

I guess I was rattlin' on about the old carbureted outfits, mostly.

I do know that Chrysler runs 'em almost all the time except idle; you can hear it when you pull the air cleaner off of some of those rigs.

Darn! I hate gettin' old! :>)

Thanks,

Allan