Ok, Guys. I need some brain power here. I have an '89 5.0L TPI. Stock intake, custom dual header to tip exhaust WITH cats and AIR inj.
It's been sitting about 2+ yrs, now trying to get it to pass smog so I can drive it. Just before I parked it, I put roller rockers on.
My initial test, after fluid changes and a fuel added inj cleaner showed decent HC levels at 15 and 25 mph tesrs. Almost no CO at both speeds... BUT for NOx, over 2x the limit 15 mph, and half again the limit at 25mph.
So I: ran Seafoam thru the brake booster hose
replaced EGR valve n vacuum tubing
replaced O2 sensor
Drove it as much as I could around the block and such without legal tags... Then tested again...
2nd test showed better across the board, BUT still 100 PPM over NOx limit at 15mph (passed about avg PPm at 25mph)
WHAT ELSE CAN I DO????

I do think I noticed my thermostat is sticking and not opening/flowing correctly... so I'll replacing that. I am also going to double check the Throttle Position Sensor tuning.
Anything else I didn't think of? The cats are probably 10 yrs old. but there is 2 of them, so I'm putting off replacing them if I can. Would the cat even affect the NOx?

 

we need to know where your at and all the numbers from the sheet.

 

High NOx means you are getting a very good, efficient burn in your chambers. The spark is happening early, the combustion temperature is high, and your burn speed is fast. This is all good for great running.

It is the EGR system that detunes the combustion at part throttle to slow the burn, reduce combustion temperature, and reduce NOx.
You need to reproduce this effect during your test.

Normally if your EGR system was working well, you wouldn't be testing high for NOx. The EGR source starts at the center exhaust ports in your heads.
The higher the exhaust back-pressure, the more exhaust flows up the EGR passages. From the heads the exhaust passes through the intake gasket. Your gasket doesn't block off or restrict the exhaust crossover does it?
Something to check.

Next you should ensure that the EGR valve is working right and none of the entry & exit passages are restricted or clogged with Carbon. In a TPI the EGR travels up one of the small runner tubes and goes through a passage under the plenum to the two exit holes right behind the throttle body. The passages tend to clog.
Something else to check.

Adding a stiffer dedicated vacuum source & feed hose can sometimes improve the activation of your EGR valve. An older or flimsy vacuum line can collapse, and if the line is shared wtih another accessory the vacuum strength can get diluted.
Something else to check.

Once you've done all you can to get good exhaust flow through the EGR system, you can reduce your burn efficiency by starting the spark later - reducing your spark advance a few degrees. This is an easy way to reduce combustion temperature and NOx production.

Lastly, some fuel additives will slow your burn rate and effectively reduce NOx. This should be a last resort because this also has the effect of increasing CO. You have to balance your priorities. If they don't care about CO, or you have lots of wiggle room there, then no problem.
Adding in another 10% or so of Ethanol might be enough to get your NOx down to pass.

 

Here are my latest numbers. AFTER new EGR and vacuum line...


if you can't see, the 15mph NOx is 662(measured) with 541 (allowed). I'm in Cali, and sea level if that matters to ya... thanx

 

ps. I just finished re-aligning the TPS. it was set at 0.32, now it's at 0.51- also, noticed that 305sbc stated that EGR vacum could be an issue. Maybe I'll replace the EGR solenoid just to be safe. Does anyone think new cats are worth it?

 

normally if there is a problem with the EGR system, NOx is a lot higher, well over 1000.
so im pretty sure the EGR system is working, although it could have low EGR flow as mentioned by 305.
excessive combustion chamber deposits will rise combustion chamber temps which will raise NOx. a decarb treatment with Sea Foam probably won't hurt.

the cats could very well be a little weak, the only way to know for sure would be what the pre-cat numbers are and that would take a machine to test it.
from the numbers, it looks like it may be just a little lean. but again to know for sure you would have to get pre-cat numbers.
adjusting the TPS may have richened it up a touch.

from what i understand, Kali has tighter standards on replacement cats than the most of the rest of the country does, which isn't too bad of a thing.
here in Texas, there isn't much if any standards, so not all cats work as good as they should. some do little to nothing for HC or CO, others do HC and CO fine but don't do much for NOx.

being where you are, the ignition timing must be close to specs, IIRC + or - 2 degrees.
so you can check the timing and if its dead on or a little high, you can pull a little timing which as 305 also mentioned will help some. just don't go to what ever the limit is.
also as mentioned, a little more ethanol in the gas may help.

air the back tires up to the maximum pressure printed on the side wall of the tires. this can help reduce rolling resistance which can reduce the load on the motor during the test.

the sad thing, other than NOx, its running cleaner than what was required when it was new. even the NOx at 662 is actually a little bit lower than what was originally required.

 

When you say "a little more ethanol in the gas". How do you mean? E85? or an additive? I'm guessing 10% of the total fuel in tank?

 

around an extra 5-10%. if your using E10, then go to E20 tops.
E85 would be way too much, so much so that your car may be hard to start and won't perform very good.

i don't know if its available where your at, but here you can get some fuel additive called "guaranteed to pass". i don't know what it does, because you add such a small amount, i don't see it really affecting the gasoline.
my guess is it has something in it that helps old cats work a little better for a little while. on cars with pretty new cats and cars without cats it did very little to nothing.

 

^ +1
Usually you can get a gallon can of Ethanol from a hardware store.
You could also add a little E85, but not too much.
You're already probably at E10 with your pump gas.
By adding another 10% I did mean bringing your tank up to E20, - 20% total Ethanol.
Personally I don't like Ethanol, and I would try cleaning up the EGR passages and dropping the timing a little bit first.

 

Copy all of that. I had to order a EGR solenoid online. So I'm stuck waiting for that... BUt will be doing the Seafoam cleaning, might take apart EGR and see if I can clean passageway a little better with carb cleaner and a shop-vac. Got the Ethanol. Going over on Monday to discuss the Cat-situation with our local hot-rod-muffler-expert.
The prob I have using the Smog-Pass additive is you need to drive a full take of gas before going testing, and car registration is out of date so I can't drive it daily until it's smogged and has new reg tags... lol. Hopefully, I'll be ready to go by Thursday. I'll let you all know how these changes affect it... Thanx again for the wisdom!!!

 

Does anyone think a MSD ignition box would help reduce NOx? a hotter spark=better combustion, right? But as I understand, NOx is the result of an efficient burn in the chamber...Egr actually de-tunes the combustion to reduce NOx, correct?

 

I'm just curious.

Dig out your test sheet from two years ago and compare the measured numbers. Also, see if this year's max allowed numbers are lower.

 

High NOx is created at high temperature and high pressure. The EGR valve serves to lower the combustion temp.

Overly advance timing can lead to high NOx, so as already mentioned, make sure that is set correctly.

An EGR valve can't do its job even if it's working correctly if the exhaust passages are clogged, a very common problem. It's also common to not be able to get to the clog just by removing the valve. A simple test is to have the car idling, put a vacuum source directly on the EGR valve - if the engine dies, the valve is working and the passages are clear. Of course, yours is ECM-commanded via the vacuum solenoid, so the next step would be to check out that part of the system. If it doesn't die, make sure the valve opened. If it did, then you'll probably have to pull the intake and clean out the passages.

 

That's correct. An MSD can reduce HC and CO, especially if your stock ignition system was already having problems, or your tune is way off.
When the tune is right on the factory ignition is adequate when working properly.

 

Just retard the timing a lot more or unplug the tan black wire used to set timing and you'll pass if your cat is good but make sure you rig the check engine light because it will be on unless your cool with the smog guy he won't care

 

old thread, but no, he would not pass.
in California timing is checked & if its off by very much, i believe 2 degrees or more, its an automatic failure.