EGR valve and its operation

[trevbeadle]

Over the winter I tried to do an EGR delete. I did nothing more initially other than remove the vacuum EGR valve and replace it with a blanking plate and plug the associated vacuum line. Would the engine start?...Would it b&GG%$£*! Eventually I got it to go but it was rough as a badgers brush and wouldn't increase rpm. My question really is this. If this EGR valve is stuck in the open position, and the carb (Quadrajet) setup has been made while the valve is jammed open, would it give these symptoms? I'm thinking the air fuel ratio will be different because the blanking plate is completely restricting/reducing the amount of air entering the cylinders (whereas before it was always open), thus giving a different mixture.

 

[teamzr1]

Should not be any issue how engine runs with EGR removed, capped off, and carb vacuum port plugged off so no leak
You sure the plug you used on carb is sealing good ?

The EGR system works by returning a small portion of exhaust gas to the engine's combustion chambers through the intake manifold, lowering combustion temperatures and therefore reducing the amount of NOx emitted.

The EGR valve is the main component of the EGR system, and it's normally closed.
It connects the exhaust manifold to the intake manifold and is controlled by vacuum from the carb
The function of the EGR valve is to control the flow of exhaust gas being recirculated depending on the engine load.

 

[johng]

I'd be inclined to refit the EGR and test it as per this info from one of the US forums. That way you should be able to figure out what is causing the problem.

EGR can be checked in a couple of ways. The large EGR valves on our cars have access to the diaphram on the bottom of the large section of the valve. First at idle, reach under it and push the diaphram up. the car should bog, idle rough, or perhaps die. If it does this the passages are clear. If not the passages are clogged.

Now with still reaching under and feeling the diaphram, rev the warmed up engine. The valve should lift up. If it passed both of these test, all is functioning and okay. If it bogged when you pushed up, but does not when you rev the engine, pull the vacuum line and check for vacuum when the engine is revved up. If there is vacuum, but the valve did not respond, the valve is bad. If there is no vacuum you have a control problem.

Control comes from a ported vacuum on the carb. This should not have vacuum at idle but will with part throttle. Full throttle makes the vacuum drop to nothing. Don't try to go full throttle. That could damage the engine with no load. If vacuum responds properly, follow the line to a Thermo Vacumm Valve on the intake manifold. This prevents vacuum from reaching the EGR when the engine is cold. When warmed up, the valve opens and allows EGR.