I have a 1991 Z-28 with mods, it has a TPI. The SES light always comes on but it usually take a while to come on. Sometimes it comes on fairly quick but other times it comes on after like half an hour, other times not at all. The car runs fine, but I checked the codes and a 12, 32 showed up. What would a bad EGR do, how much are they and where can I get one? thanx guys.

 

Not sure if this helps but I just pulled my heads yesterday to send them out to get rebuilt, and I found that both EGR ports were plugged solid with carbon.. they're smaller than the other ports on the head too. So even if you get a brand new EGR valve... the heads could still be clogged and ruin the whole purpose of it anyway. But the clogged ports weren't giving me any codes (although the little relay for the EGR was clicking like crazy...)

 

PT,

What kinds of "mods" have you done? The EGR system is sensitive to intake vacuum and exhaust backpressure. There are several things that can cause a DTC 32.

The reason you have the code is because the EGR is not being detected open when the ECM commands it to open. The EGR valve is operated by intake vacuum, and the source for this is on the underside of the throttle body. There is a solenoid valve that routes vacuum to the EGR valve, and this solenoid is operated by the ECM. The EGR valve itself has an internal pilot valve that controls the operation of the valve based on exhuast backpressure. The EGR also has a diagnostic temperature sensor in its base. This sensor reports temperature back to the ECM, and this is how the ECM determines whether or not the valve has been opened. Of course, the exhaust passages in the intake and EGR valve isteslf must be clean and unobstructed.

One of these hints should help.

 

Well i've got SLP headers, no cat, edelbrock base, trick flow heads, ZZ4 block with mild cam 209 duration and .474 lift. Runners and plenum are stock. I really can't tell how hot it gets, the temp usually stays little less than half way between 100 and 240 or 220 not sure without looking at it. I have stock chip with hypertech chip adapter.

 

PT,

Your exhaust modifications may have effectively reduced the exhaust backpressure as you intended, but the EGR valve probably doesn't like it one bit. You likely have a negative backpressure EGR valve, and the valve pilot will not operate with high scavenging of the headers and free-flowing exhaust system, since the negative pressure in the exhaust opens the pilot valve and prevents the EGR from opening. You may have to consider changing to a ported type EGR and adapting the diagnostic temperature sensor.

 

Your conclusion sounds right on, because the guy who I bought the car from said it comes on cause low backpressure in the exhaust. Now if I change to that other EGR what else do I have to change and will that effect the computer or anything else. Thanks for the info.

 

Do you have to remove the heads to clean out the ports mentioned earlier? Can I clean the whole system out with just the plenum and EGR removed?

I've got the same EGR code problem, it's usually only after I've driven at least 10 miles over 50 mph though. I was pondering just blocking the EGR and leaving it in to pass visual inspection, and also editing my PROM so the SES light doesn't come on, but I heard that the EGR cools combustion and prevents detonation. I'll end up just cleaning it out.

BTW, I have stock exhaust manifolds and stock dual cats with a Flowmaster cat-back, hopefully backpressure isn't the problem.

 

Synapsis,

You should be able to do a pretty effective job of clearing out the ports by simply removing the plenum and EGR valve. Remember NOT to use any solvents on the EGR valve itself. The pilot valve diaphragm in the valve is made of a rubber compound that stays flexible in high heat conditions, but because of the heat resistant material it cannot resist solvents. Use a stiff brush, scraper, and shop vacuum on the valve pintle and base.

You can use almost anything you want on the passages in the intake base, as long as you dry it out before replacing the EGR valve. A small scraper, wire brush, and vacuum work well there, too. If you are getting an EGR fault, you also need to check the EGR vacuum solenoid, vacuum source and lines, and the diagnostice temperature sensor on the base of the EGR valve.

Don't forget the anti-seize compound on the bolts when you reinstall the valve, plenum bolts, etc.

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PaveTim,

You could adapt a port-type EGR valve and reprogram your PROM to apply EGR only when at cruise.

Another option would be to restrict the pilot opening for the pressure sensing valve in the pintle of the EGR. I've never tried this, and it would unfortunately force you to modify the valve, reassemble the system, and try it again. You could have a lot of development time invested and never get really good results. I'm sure you're not the only one who has encountered this phenomenon, and I'm guessing there is a more positive solution other than just abandoning the EGR valve.