Hi guys (and gal mechanics, if any), I have been lurking and reading and doing some searches. I can't find a solution yet. Some background: Been chasing the problem for sometime now; more than one mechanic has had their turn.

I replaced the EGR with a generic pos manifold pressure type as the car calls for (4.5). I have cleaned the TB and all the EGR passaages more than once. I have cleaned and reconnected most of the wiring loom connections and grounds. Replaced alt due to low voltage output. Cleaned injectors, checked plugs for mileage and gap. Checked for any vacuum leaks. Actually, the car runs fabulous. Idle speed controller is set right, the RPMs are constant in and out of gear and on and off on the AC. No missing or stumbling (except on quick RH turns with a low tank).

No sailing or high idle while coasting to a stop. That's about all I can think of, yet I failed smog at the low speed due to high NOX. At 26 MPH, I have a passing PPM but not at 15 MPH on the dyno (I'm in LA, CA). Oh and no codes, not even in the history.

The only things I can think to do at this point is try to find the factory EGR valve. I tossed the OEM one, so I don't have the actual PN. Or change out the plug wires on which I haven't done an Ohm test.

What would you do? TIA

Well, my dad helped invent the EGR valve :-)

As you probably know high NOX is caused in part by high cylinder temp. The EGR valve's job is to "posion" the mixture and reduce the temp.

I would check the entire EGR vacuum system and make sure that the diapharm is closing and opening with changes vacuum.

Also many cars suffer from a carbon buildup on the top of the pistons, this causes an effective increase in compression ratio that can also cause problems.

After you have checked everything, run two tanks of tier 1 gas (chevron/shell) and then retest with premium tier 1 gas.

jeff

OK, thanks Jeff. Anyone have the actual part no. for this car's EGR valve? Me thinks that the "generic" one I bought is calibrated slightly different for the vacuum it is receiving.

Oh, I'm not getting any pinging, so I guess the carbon build up isn't too bad. The car gets some freeway everyday, not just a grocery getter. But, if I don't hurry up and get the smog cert, the state is gonna require that I either sell it out of state or crush it. I've got a month or so left.

Did you replace the EGR solenoid as well as the valve?

Did you replace the EGR solenoid as well as the valve?No and I've been looking at the factory manual as well as Haynes (which is better in some respects) for the test method and parameters for the solenoid before just yanking it. Any info on that?

Hmm, well I just yanked mine lol...but if you have the factory manual, you could look up the diagnostic mode which displays whether the solenoid is engaged or not, and drive it with a vacuum gauge taped to the hood and hooked up to the solenoid hose...

I have done all that. If you disconnect any of the hoses, the EGR doesn't modulate correctly. You either go 100% open or 100 closed. Closed is fine for warm up, but it won't pass smog that way.

No, I can't be guessing anymore on this. I either have to find someone or some instruction on how to dial this in precisely. I have one mechanic who tells me there is a difference in PN's even between the 2 doors and the 4 door models as they weigh differently and therefore have a slightly different pull on the engine.

I don't know if I'm buying that altogether, but I'll say this, it has to be right or it doesn't work for the smog test. My biggest mistake was tossing the OEM EGR valve. If anyone can even give me the actual PN off a '90 Sedan De Ville, I will be able to purchase an OEM valve. I haven't talked to the Cadillac Dealer parts counter, but I suppose as a last resort I could.

But that's not why we are here, is it? ;)

BTW, I just quit posting on a major Porsche BBS at 10,000 posts. So, I know the drill on these BBS's. A little help from a tech would be much appreciated. I read the whole thread on EGR's here plus about 20 other threads before I asked for help. As I said, I know the drill. TIA

I didn't mean disconnect the vacuum hose, I meant hook a vacuum gauge up...like with a T in between the hose and the valve or something. Diagnostics will show you if the EGR is kicking on and off with slight pedal (I forget exactly which override, but I can look it up if you need it)... But anyway, should be in your FSM. In addition to that, you can see if the vacuum is consistent and not suspiciously low or anything.

As for the OEM valve, just go to www.gmpartsdirect.com . There is a catalog there where you can look up the P/N and order it if you're sure that's the issue.

Out of curiosity, how's your catalytic converter?

Don't crush it. I'll take if off your hands.

What kind of numbers are you getting for NOX? If you're just over the threshold, you might try a cooler thermostat or remove it for the test. CAUTION: A cooler running engine will lower NOX but raise the other numbers. It's a balancing game.

Do you have an aftermarket muffler installed? If so, the lack of backpressure could be preventing your EGR from opening correctly. I know because with my Flowmaster mufflers, there is not enough backpressure to open the EGR.

I also live in S. California and had quite a time to get mine to pass. My NOX was over 2000 ppm. What I did to pass was hook up the EGR valve directly to vacuum and retarded the timing as much as possible. The engine ran horrible and had barely enough power to turn the dyno but hey, it passed. Afterwards, I set everything back to normal.

If you give up, let me know so I can pick up the car.