Took the 91 GTA 5.7 in again today for smog and it failed, nox hovered around 2000ppm, supposed to be 700ish.. so its a gross polluter, no biggy. So I am leaning towards EGR. or even the egr vacuum solenoid. With the engine running, I manually pushed up on the diaphragm under the TPI plenum and it caused a great stumble at idle but cleared up of coarse until I let go again and it would stumble for a moment. I have a vacuum gauge I hooked up to the egr vacuum line and I pumped it but I could not get vacuum to hold. Is this normal on a running engine? It would hold vacuum fine when the engine is not running, and the diaphragm would open and hold open while the engine was off and I had the vacuum applied. Both cats are one day old. I have a complete ignition tune up which consists of cap, rotor, module, coil, wires and plugs. I have a bosch o2 in the car now, I think I am going to swap that for a ac delco however. I am also thinking of swapping coolant temp sensors just in case. Should I do Intake air temp as well? The other two categories of the smog test passed just fine! Some insight please?

I would like to add I scanned troublecodes and I have a 23/32/42

23 is manifold air temp sensor showed -22degrees after the engine had been running five minutes..

I think I will replace that guy.

32 is EGR open command did not change MAP sensor signal. Normal EGR flow should cause slight decrease in manifold vacuum which would change MAP sensor signal.

So maybe I am correct in my quest after the egr vacuum solenoid not functioning?

my girl, who drives this car has mentioned on the highway the CEL has lit a few times but then would go off.. it did not pop on for the test.

nox is from too high of a combustion chamber temp. for the test, make sure your base timing is at spec or slightly less. maybe run some gm top end cleaner thru the car and that will help clean out the combustion chamber and piston tops too. it may help lower your static c.r. a bit . you need to address the egr code. that, most likely is the problem.

Will the egr vacuum solenoid not engage at all if the air temp sensor is broke, and always showing cold?

I fixed a broken plastic line from the throttle body running to the egr vacuum solenoid, I might have broke it when removing the plenum, I dont know, but its fixed. at the solenoid, I get vacuum coming into it, but between the solenoid and egr, I am not getting any vacuum at all, idle and when I rev, or hold the rpm I still get no vacuum signal. meaning the solenoid is not letting the vacuum pull through.
I tested the egr vacuum switch off the vehicle by applying 12volts, and I can hear the solenoid physically click, and I can blow/suck through the line when its clicked, and I cannot when its not on. So I assume its functioning properly. I believe its just th ecm not telling it when to turn on/off?

I hAve a better idea how about we take my prominator and install it with those codes deleted and than we will retard timing so it will richen up the mixture and take away the nox

retarding the timing will not richen up the mixture. richening the mixture will increase the CO and probably some HC.

no offense but how about I try to fix it first and make sure its all in working order, after that, then I will take your advice.

i just checked your sig. you are running a megasquirt engine management system. does that even have the capability to control a pulse width modulated egr system? is this the vehicle that we are talking about passing smog?

No sorry, my sig is my iroc, the smogger in question is a 91 trans am, bone stock.

umm yes thats the point, co and nox have a direct effect on eachother, the higher the nox the lower the co the lower the nox the higher the co. so richening up the mixture in the poper manner ie retard the timing will cool the combustion chamber lowering nox as nox is created after tempatures reach 2800 degrees so flame on what the end result should be is more oxygen which will keep combustion temperatures down meaning no formation of nox.


traviz if u want to fix it borrow my solenoid and egr valve not like my car will need it anytime soon. if u want an exact diagnosis i can bring a vacuum gauge and we can work on her but the egr systems in these cars is ****ed it always throws that code on extended highway driving.

also very common for the temperature sensor to brake easiest fix.the cermaic breaks apart leaving a bad connection

well i guess it is another ad hominem attacker above. i reckon he called me an idiot. i dunno. back to the problem at hand here-traviz-do you have your readout-what is the co and prolly more importantly-what was the leftover 02 reading. post your results and lets check it out. i lived in southern cali for about 20 years and if i recall a gross polluter gets you to a referee station?

co was .01 at both 15mph and 25mph. and the other reading at both 15mph and 25mph was around 300 out of a max of 700ppm.and like I said in the original post, my nox was 2000/700!

i still have to fix mine. my nox was a bit over. like a few hundred.
my base timing was plus 3 degrees. my light is in storage now, so prob have to buy a cheapo if i need to set it back, but first i'm goin to try to address that 32 ses code also. i bought a new egr, as i wasnt sure if it is bad or solenoid or what, but with 20yrs old, and 130k miles, i figure wouldnt hurt to change it. also i have a little off idle accel knocking, so some things say that could be egr probs also. i did run thru a bunch of techroline additive. i know its really good stuff. but need to address the mechanical stuff now too.

like i was stressing to traviz get a new temerature sensor as well its only like 14bucks also i have found that gm is the only way to go on egr valves. went through 2 damn kragens ones although that was when it was niehoff now we carry borg warner with a lifetime warranty

ido have a new sensor and it is a gm egr.

I am pretty positive that if the intake temp sensor is bad the comp won't allow the EGR to open because I doesn't know the temp of the intake air, if the intake temps are to high it won't open the EGR valve to prevent detonation. Changing that sensor might have fixed the problem. When you fix trouble codes you always start at the lowest numbered one because they can cause the higher number ones. That is what I learned in vehicle mechanics school in the air force anyway

cool thanks for the reassurance. I am here to fix the problem and not bandage it, I did get a new sensor but I know that isnt the only problem because code 32 did set as well which is a egr code, and the ecu wouldnt set a 32 code if it never told the egr to open in the first place. car should be smogged in the next day or so. I will post new results.

Yes it would. It expects the egr to open, when it does not see it opening (a slight drop in manifold vacuum on a SD car) it will throw a code.

well, what you both said is true, but what he said isn't exactly what you replied.
It must "tell the egr" to at least try to open, before what you said will happen. so yes, even if it doesn't open it will throw a code. that's what happened in mine too, bad diaphragm, so no opening, but a code.

Insight The EGR Diagnostic does not determine whether the EGR valve, or Soleniod are faulty only that 1 of 4 conditions below was not met.

You need to test the EGR Temperature Diagnostic Switch first.

Code 32 means that the EGR diagnostic switch was closed during start-up or that the switch was not detected closed under the following conditions:

1. Coolant temperature greater than 80 degrees C (176 degrees F).
2. EGR duty cycle commanded by the ECM is greater than 48%.
3. TSP less than wide open throttle (WOT) but not at idle.
4. Codes 21, 22, 33, 34 not present.
5. All conditions above must be met for about 4 minutes.
   If the switch is detected closed during start-up, or if the switch is detected open when the above conditions are met, the "Service Engine Soon" light will remain "ON" unless the switch changes state.

Garcia that is awesome info!