RandyJ75

My car (1990 L98) recently failed it's emission test for high NOx. The is basically stock w/ 24lb injectors, true dual exhaust w/ cats, and a custom chip to delete the EGR, which has been removed. The car has a recent tune up, w/ new plugs, wires, cap, fuel filter. It had it's intake removed and resealed using FelPro gaskets last April. Other then that, the car runs great, w/ no problems at all. Mileage is about 102K.

The strange thing to me is that it was well within the limits of the other two categories.
This what the test said;
hydrocarbons 1.4000gpm -0.4612 pass
carbon monoxide 30.0000gpm -5.1493 pass
oxides of nitrogen 2.5000gpm -2.8883 fail

Anyone have any ideas as to why it failed?

Thanks, Randy

farscape1a

the high NOx may be because of the EGR delete... is that at all possible?

RandyJ75

Many people here have deleted the EGR and still pass emissions.

farscape1a

okay...i was just curious...

jtc44

NOX hi caused by hi comb. temp. due to inop. egr or hot eng. lean cond. check comp. for cods. and eng temp, Good luck!!

CorvetteMike2024

Heres a good book to help you diagnos smog issues

RandyJ75

Thanks Mike, but I have it. Just looking for some other ideas.

GKK

High NOX levels are directly related to the EGR delete as mentioned earlier.

The EGR valve lowers the combustion temperatures which, when removed is why the NOX levels were higher than allowed.

Each State has different emmision standards which is why some who have removed the egr have still passed.

kab3

Randy,

Gotta believe it's the EGR delete, is this the first test without it? Did you discuss this with the chip guy to find out what changes he made to compensate for the EGR delete (i.e. richer mixtures, etc.)? Was the test done at idle or on a dyno?

Maybe trying to get the engine to run cooler (lower temp thermostat) would get you through the test, worth a try. Gotta keep as many of these charcoal ones going as we can.

I've got a pretty much stock setup (cat back exhaust only) and my NOx was good last test (about 13% of the allowable at 15 mph & 9% at 25 mph). I believe the EGR passes more at the higher speed.

Kab3

RandyJ75

The reason the EGR was deleted is because it set a code after the new exhaust system was installed. Everything was fine w/ it before the change, it seems that speed density cars need a certain amount of back pressure for the EGR to work correctly, so I really had no choice. That is the reason the car has a custom chip, to delete the EGR.

Benny42

Sorry, i mis-read. Hope you get it in line. Where is your base timing set?

jeffp1167

to run the egr without chip mod's just run its vacumn line straight to it from the throtthle body with a restrictor the valve only needs to open a bit to drop those numbers.

TJM

Deleting the EGR is the MOST likely reason for the "Fail". Right out of the book, problem #3 of 3

This is the purpose of the silly thing.

This does not sound at all like a chip issue. If it set a code it was likely the Temp Indicator The little gizmo that goes into the EGR tube, right as it enter the intake.

Without EGR, on a basically stock motor, you could be getting a good bit more knock, and may run hotter, & FAIL Emissions!!!


TJM

jeffp1167

speed density does not have that heat sensing gizzmo

steven mack

It's the egr plain and simple.

bjankuski

The problem is the lack of EGR, you may be able to pass the test by retarding your timing, lowering the water temperature to reduce combustion temperature, or running a higher octane fuel that may burn cooler at low loads. If that does not work you may be forced to put the EGR back on to pass the test.

I just did a little research and a failed catalytic convertor is also listed as a possible reason for high NoX readings, you may want to check into this a little more.

SunCr

Might be/Should be - but the 3 way Cat along with EGR scrubs up about 60 to 70% of NOX emissions and if the knock sensor chimes in, it retards timing and fattens it up. That shortens the life of the CAT. Looking at the HC and CO numbers, it doesn't look bad, so hopefully reconnecting EGR makes it pass OR if these are idle numbers and not cruise, it is the CAT (and it's possibly lean) because EGR isn't doing anything at idle. Otherwise, without a scan, you don't know what it's doing and scanning it under all possible conditions isn't an easy task, but you might just run one to narrow it down.

rlane5

Sometime pulling a little timing out will help emmission,
Randy

steven mack

I have passed emissions after failing by retarding timing and adding two cans of Dry Gas additive to the gas tank. Just be careful not to retard timing to much or the other numbers could go up.

Benny42

Try a few gallons of E85 in the tank when you test. Too
often WILL kill your Multec injectors, but you you should
slide thru the test. benny