EGR (is it safe to..?)

My check engine light is on and I know it is because of a faulty EGR valve. Is it okay to continue to drive for a few weeks before replacement. The shop ordered the part but the wrong one was sent. They say it is okay to drive till the right part arrives.

Once upon a time I e-mailed the cartalk web lackeys that there must be a requirement, when posting an initial discussion in ‘repair and maintenance’, to enter in the VEHICLE INFORMATON. ( make, model, year, eng., trans, vin.)
Either a red warning sentence or a required blank field ( prefered ) along with the discussion name and discussion body.

I guess this change hasn’t happened yet.

It’s safe to drive…you’ll just be polluting more.

Was the determination made that it had a defective EGR valve based solely on the check engine code; or, were diagnostics performed? If it’s an attempted repair based only on code, or only on symptom, a new EGR valve may not fix it.
Analogy, “Dr., my head hurts.” Dr., “Don’t worry. We’ll remove it!”.

The EGR system performs two functions. It prevents excessive production of oxides of nitrogen (NOx) and it prevents pinging. Both are byproducts of excessive cylinder temperatures.

It should be fine to drive it for a few weeks, but don’t romp on the gas pedal. And you may want to fill the tank with premium until you get the new valve put in. Both are precautionary measures, but hey, why not.

LIsten for knocking and pinging.

The fact that EGR systems reduce pinging is only a by-product of the EGR’s intended functionality, which is to reduce nitrous oxide.

Nitrogen and oxygen combine at high temperatures to form nitrous oxides. The EGR mixes in a small amount of ‘already burned’ exhaust gases with the intake air. That “dilution” of the incoming charge prevents the peak temperatures from occurring during combustion - and thus reduces some of the nitrous oxide from forming.

However, peak pressure (which equates to more push on the piston) also occurs with peak temperatures. Many would disable their EGR valves to preserve that peak pressure (and hence peak push on the piston). OBDII is good at detecting EGR valves which are disconnected.

As others have noted, reducing peak pressure also reduces the opportunity for pinging. Since this is a by-product of the EGR, I have no clue if the EGR’s ability to reduce the likelihood of pinging is done only when that reduction is needed. I suspect the engine knock sensor, which does detect and reduce pinging, does a far more accurate job of it.

Sort of. In the early 1970s, in response to the Clean Air Act, manufacturers made a few changes. One was that they raised the operating temperatures of the engines for more complete combustion. This created a few side effects. One was increasing NOx output, which they were trying to bring down at the same time via the addition of the cat converters, another was pinging, and another was dieseling (irrelevant to our conversation and solved with idle stop solenoids).

The EGR system was created to simply control internal cylinder temps. That controlled two of the three side effects of increased cylinder temps.

I should add that the peak pressure produces pinging because pressure generates heat. The excess heat produces the tendency for a secondard wavefront to occur, which crashes into the spark-induced wavefront.

As you said, the heat is what causes the oxygen and nitrogen to bond. But the heat is also what causes the pinging. The EGR system helps with both problems.

The cat converter only seperates the NOx molecules that come in contact with the surfaces of its honeycomb, only the molecules that contact the platinum-palladium. It isn’t 100%. Thus, the less generated the fewer will exit the tailpipe.

I guess my summary point would be that both both pinging and NOx are by-products of cylinder temperatures increased for more complete combustion, perhaps coupled with leaner metering (also for fewer unburned HCs) which also raises combustion temperatures, and that the EGR system helps control the temperatures themselves from which both pinging and NOx derive. Since pinging and NOx are both byproducts of the same cause, one is not the by-product of the other.

I know, we’re quibbling details.