93zder

Should my 1993 ODB1 system emit a code if there is something wrong with my emissions parts such as EGR or catalytic converter?

thanks

RamAir95TA

EGR yes, cat no. Only OBDII cars utilize post-cat O2s to determine whether or not the cat is functioning.

shoebox

The only EGR function monitored on a 1993 is the electrical circuit/control.

93zder

So the EGR valve could not be working properly and there would no codes to indicate this?

mrmint69

I bought block off plates on ebay for cheap and removed it. Then tuned it out when i got a mail order tune.

Injuneer

I believe that DTC 32 - EGR Circulation is applicable to the 93 model year. Chiltons shows it for 93, and Rob/Shoebox's LT1 code list does not show it as "N/A" in the 93 column on the right. That DTC cycles the EGR system and looks for an expected change in manifold absolute pressure (MAP). Code sets if the change is not detected. Problem is the OBD-I diagnostic does not appear to very very sensitive, and many people have completely deleted the EGR system without tripping the code. Maybe only 5% of the time it will set the code.

shoebox

Yeah, in a hurry I did not look closely at code 32. My bad. The sensitivity thing is still a concern.

93zder

If i tune it out can the car still pass emissions testing?

Also, our emissions testing here includes a physical look to see that things are still there in place so removing and blocking them off would not be a good idea.

shoebox

Why are you worried about it? It seems you have no real trouble (at least that you have indicated).

93zder

I failed emissions testing - and got it down to the CO being a little over on a re-test. So i still have something not quite right.

I was wondering if the EGR could be the or part of the problem.

I'm thinking it could be the Magnaflow cat not working 100%

pgerst

Bad EGR usually shows as high NOx. High CO is rich. As you have no codes for any bad sensors, my first guess is excess fuel from the injectors, and I would check first for leaking injector(s).

93zder

I had them tested a couple years ago and they were fine - but that could have changed i guess.

Could it be the cat converter?

Injuneer

Leaking injectors would show up as high HC.

What were the test results vs. limits for HC, CO and NOx?

93zder

They are:

limit Reading

HC. 52 21
CO. .29. .37
NO. 385. 298


The C0 is what's causing me to fail.

pgerst

This is a good summary:

Rich mixture

My personal experience was I was just barely passing on CO; I replaced injectors (on suggestion of smog guy) and reduced it to 1/3 prior levels. My understanding is high HC is more often bad ignition as it represents unburned fuel; high CO is more often bad injectors as it represents partial combustion of the fuel.