Long story short... I have a 350 TPI (mods in signature) running with a Delco 214-5538 EGR (5.0 TPI)

I am running higher than desired nox levels (as seen by my smog, barely passed nox). I'll get a soft egr CEL on freeway cruise.

Fueling appears right, as my BLMs are ranging +/- 4 of 128 at all times. I have verified the solenoid working, and vacuum being applied to the EGR valve at cruise (so for all intents and purposes, the EGR system is functioning at some level). No intake/vacuum leaks are present.

I am wondering..

1) What are the differences between the 5.0 and 5.7 EGR valves ? I couldn't find concrete info. Does the 5.7 valve flow more? I know both are Negative pressure types - though maybe the current Delco replacement is a positive type due to supplier change? It wasn't labeled either way.

2) Is there a source for a proper 5.7 EGR? Everything I can find is either Positive pressure (which, with my free-flowing exhaust, won't work well) or simply won't fit (one is too tall.) - or maybe you have a known working used one?

3) Running accel shorty plugs, they are heat range 6 (the cross reference for the r45ts which is technically heat range 5). They offer a heat range 4, but that cross references to r43ts (for 305s) - going to a cooler plug could help or is that just looking to foul the plugs at idle?

4) Too much timing in the tune? I don't really think it's the case, not exactly getting a ton of knocks.

Any feedback or ideas are welcome. I know the EGR system as far as functionality wise well and it's operating. The car runs fine, but it would be nice to get it dialed in. I will hate swapping the EGR valve it it comes to that, though.. it'll suck to remove the SR!

I’m not sure the differences between egrs. I think at cruising speeds when the egr is commanded on the ecm checks the temp sensor to see if it’s closed caused by the heat traveling through the egr passage. If it’s a open circuit I think that’s when a code 32 throws.

Yea, that's generally how it works. Means my intake temp is hot enough to flip the switch, so my combustion chamber temps are too high. The temp switch is new and tested.

I have a very similar issue, but being SD, I don't have an EGR temp sensor to deal with.

Also I'll note my intake manifold is brand new, so it's not clogged passages.

When I did my TPI swap several years ago, I had to research everything. I do not remember seeing a specific egr valve for 305 and 350 engines. I think both motors use the same egr valve. The only difference is a positive pressure or negative pressure as you mentioned in your post. Interesting idea about the free-flowing exhaust causing less backpressure therefore less exhaust gas is getting into the intake. I never thought of that. The fact that you are getting an egr error code means that the egr is not functioning as the ecm expects it to.

The only thing I can think of is to change your timing back to stock values before having the smog test done. That will not have any effect on the egr error code, but running stock timing may reduce your combustion temps thereby reducing nox. Good luck.

Yea I can't find any actual differences, other than the part numbers are entirely different and do not cross-reference. It's not like I have any good way to flow test EGR valves either LOL

As I understand it, the EGR valve is just a solenoid that allows exhaust to be sucked back into the intake manifold. When it is commanded to open, exhaust pressure AND intake vacuum pull exhaust through. A temperature sensor sees the hot exhaust flowing past the valve and tells the ECM that the EGR is working. If you are not getting a code 32 then the EGR system is functioning normally according to the ECM. Maybe its your cam? You passed you said but just barely on the NOx?

I've got that cam ready to go in as well.

Don't really believe it's the cam per-se. It's not really an aggressive cam in the grand scheme of things. The crane 2032 passes smog without a tune supposedly.

I just looked up EGR for someone and there were 3 different part numbers for 3 different transmissions (2 manual and 1 auto) on a 305 tpi. I have no idea why they would be like that at all.

EGR Valves are calibrated based on the needs of a specific engine/trans combination. If I were the OP I would first install the correct EGR Valve. Also, advancing Ign. timing tends to increase NOX. This can happen without being advanced to the point of "Pinging", (Spark Knock, Detonation, whatever you want to call it).

I'd love to run the correct EGR valve. Too bad I can't find any. (see #2 in my post) =/

rockauto list 2 for an 89 Firebird 350


STANDARD MOTOR PRODUCTS EGV393 {Click Info Button for Alternate/OEM Part Numbers} Info


WVE/AIRTEX/WELLS4F1113 {Click Info Button for Alternate/OEM Part Numbers} Includes Gasket

I have checked the readily available parts (that includes the obvious rock auto parts.)

One is too tall (plastic vacuum protrudes off the top so much it hits the top plenum) and the other is a positive pressure (aka incorrect) valve. That's part of the reason I made this post.

I am sorry to hear that! I have contemplated an L98 350 Long Block swap, on my 89 IROC Vert. Has the 305 TPI engine, now.

That makes sense to me. A manual trans car would have a lower vacuum signal when sitting at idle with the clutch out or the trans in neutral than an auto trans. I have read that the rpm idle spec for a manual trans car is lower than with an auto trans. Therefore I think the egr valve for a manual trans would be calibrated to flow more exhaust gas than a comparable auto trans egr valve.