I've just served my Camaro Z28 -96 because of an annoying SES-light. I found out that the EVAP and EGR systems didn't work as they should.

Regarding EVAP I don't have much info, what does this do exactly and what implications follows from a non-functional EVAP-system?

EGR is as I understand a system that lets exhaust gases back into the engine along with fresh air from the air intake? Doesn't this drastircally lower the compression? Performance wise I should be better off not fixing the EGR right?

After cleaning some contact surfaces the SES-light came off. But when the EGR-system is being tested it still doesn't do as it should, meaning it doesn't send exhaust gases back into the engine.

 

I can't speak for the EVAP, but as far as the EGR, it shouldn't affect performance too much either way. I had to replace the EGR valve on my '95. If anything, I believe it runs better now. It seems smoother on deceleration. It definitely should not affect your engine's compression.

Is it the EGR valve itself that is not functioning? There's also the EGR solenoid and a few vacuum lines that could be bad. If it's the valve, don't pay anyone to do it. I replaced mine in about 15 minutes. The dealer wanted $75 labor. The valve itself should run you less than $100.

 

Thanks for the input, I guess I'm pretty safe then.

However, doesn't the EGR send back exhaust gases into the engine again? If so I really can't see how this doesn't lower the compression. First the temperature gets higher which in itself expands the air and thus lower compression and also reduces the amount of oxygen which also should lower compression. But maybe I'm all wrong in how the EGR works?

BTW, can anyone give info in how the EVAP-system works?

 

I found this article which may suggest my EVAP problem since my car is a -96. And during a breif period of time during winter storage the garage owners told be they could smell gas. This lasted about a month with them unable to localize the source of the smell.

http://www.aircarecolorado.com/repair/acnews/jan02.htm

 

No it doesn't "lower compression"..... static compression ratio is determined from the bore, stroke, deck height, gasket thickness, combusion chamber cc's, piston reliefs, etc. The fact that the EGR valve it putting some recycled exhaust into the intake manifold doesn't change static or dynamic compression ratio. And it doesn't heat combustion up, it actually cools it down. It will lower pressure in the combustion chamber for the reasons you noted.

First, EGR is only used under limited engine operating conditions. Doesn't operate at idle, doesn't operate at WOT, doesn't operate over 3,500RPM. Its only activated when the engine is operated under conditions that produce high combustion chamber temps, which would cause formation of NOx. A typical operating condition is lugging the engine at cruise in too high a gear. The exhaust gas is admitted to displace oxygen, which means less O2, less fuel being burned = less heat in the combustion chamber. In addition to reducing NOx emissions, the lower combustion chamber temps reduce the chance of detonation (knock). And to some extent, its a mini "displacement on demand" system.

There is no performance gain by eliminating the EGR system. There are codes for both the electrical circuit to the EGR vacuum solenoid, and for low EGR flow into the intake manifold. You need to determine which code you are getting to know how to fix it.

The EVAP system uses a charcoal canister in the drivers side rear fender to collect vented fuel vapor from the fuel tank. Periodically, the PCM opens the EVAP solenoid on the passenger side of the intake manifold, and allows engine vacuum (connection on the throttle body) to pull air through the charcoal canister, to remove the fuel vapor and put it in the intake manifold to be burned as fuel. It probably helps fuel economy a little bit, and without the sytem, you need to have a way to vent the fuel tank. And you might notice a heavy fuel smell near the drivers back fender.

There are several codes for the EVAP... the electrical circuit to the solenoid, and a flow detector that will indicate "flow during non purge" or "no flow during purge". Again, you can only figure out how to fix the problem by havnig the exact code.

Both solenoids are supplied by the same fuse.... maybe its blown.

 

Thanks!

You're right of course, I was probably thinking the EGR was somethjing it's not. If I remember correctly the EVAP code was "flow during non purge".

 

The could be the EVAP solenoid stuck open, and pulling a vacuum on the purge system when its not supposed to. It might also be a problem with the two hoses on the solenoid on the wrong connections.

Photo courtesy of Shoebox:

http://shbox.com/1/evap_sol.jpg