All,
Finally did some testing on the EGR delay valve that is a part of the emissions recall Ford did in the 90s.
Quick background:
The delay valve is a black and green plastic disc, inline with the vacuum line supplying vacuum signal from the EGR control solenoid to the EGR valve. After installing the valve, the engine management computer (PCM, ECA, whatever) will display "code 34" during the KOER (key-on, engine-running) test. During a phase in the KOER test the computer sends signal to the EGR control solenoid to open the EGR valve. When the computer doesn't detect an appropriate change in the exhaust gas mixture, by way of the O2 sensor, it triggers "code 34."
It has been hypothesized that the EGR system complete fails to work with the delay valve in place. It has also been stated, by Rick Byrnes no less, that the 2.3 turbo motor can pass emissions tests without the EGR system in place. (However, passing the visual test is a different matter.)
Because the EGR system may not be working for the delay valve in place, and because the EGR valve itself, the vacuum lines and the EGR control solenoid are sources of potential vacuum leaks; some may view it as desirable to remove the system completely. Some racers (including myself), along with other folks, have taken it upon themselves to eliminate the system for the sake of a simplified exhaust, intake, plumbing and wiring system.
Today I set about laying to rest all theories about EGR operation with the delay valve in place.
Testing information:
I tested the EGR function with and without the delay valve. I tested the delay valve itself. I tested at a variety of vacuum levels, using my Mity-vac hand-operated vacuum pump and the vacuum gauge that comes with the pump. All tests were performed on my 87.5 XR4Ti, with the emissions recall. The proper EGR function, without the delay valve in place, was confirmed prior to starting the tests.
I tested the car (with the delay valve in place) for:
- time delay until the first opening of the EGR valve
- time delay until full opening of the EGR valve
- time to close EGR valve
I tested at two vacuum levels; 15 in hg (inches of mercury) (resembling a light highway cruise or coast down) and 25 in hg (highest vacuum easily/quickly applied by hand pump). All vacuum levels were manually maintained as the system leaked down.
Test Results:
Time delay until the first opening of the EGR valve:
15 in hg: 8 to 10 seconds
25 in hg: 8 to 9 seconds
Time delay until full opening of the EGR valve:
15 in hg: more than 90 seconds
25 in hg: approximately 90 seconds
I believe the valve never opens fully at 15 in hg. The valve does fully open at 25 in hg. "Fully open" is a very vague term, since the valve is moving so slowly. I tried to develop optical methods for sensing when the valve was fully open. I was mostly successful, so treat these data accordingly.
Time to close EGR valve:
The EGR takes approximately 1 second to close with the delay valve in place, regardless of the amount of vacuum applied. This is with the vacuum pump and a 6 foot section of vacuum line in place, as well. There are several factors that will determine real time-to-close, but I don't have the ability (or desire) to duplicate this. This data point seems to matter very little to the overall operation of the EGR system.
Leakdown of the delay valve:
I disconnected the delay valve entirely from the EGR system, leaving it hooked up to the vacuum pump, but the EGR side open to the atmosphere. I tested its leakdown while applying 25 in hg to it. It took 20 seconds to leak down from 25 in hg to 20 in hg.
Each test above was performed a minimum of three times. Some tests were performed on the order of 10 times to ensure my testing methods were providing accurate results.
Conclusions:
It appears as though the EGR system still functions during time periods where the EGR control solenoid is providing a vacuum signal to the EGR valve for extended periods of time.
During the KOER test, with the delay valve deleted from the system, the EGR valve opens quite rapidly. My estimate is that the EGR valve transitions from fully closed to fully open in less than two seconds. Since I have never actually seen the EGR system in operation during normal vehicle operation, I can't confirm that it behaves in the same manner during normal operation.
My testing isn't complete yet. My next test will be to connect a vacuum gauge to the vacuum signal output of the EGR control solenoid to determine if the EGR vacuum output is substantial enough to operate the EGR valve.
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The above data was originally posted to the following thread:
http://forum.merkurclub.com/forum/viewtopic.php?t=6355
