Hey guys. New member here. I have a 1989 Corvette, and I just failed my California Smog Test due to a lean condition. Everything was fine except for the NOX numbers. They were a little too high and he told me it was a lean condition. Also the car has somewhat of a hard start when cold. Once it has been running and warmed up, it fires right up and it always runs and drives well so I did not expect it to fail. I am here asking about how I can go about diagnosing this. Any advice or common occurences or tips to diagnose are greatly appreciated. Thanks guys. Let me know if you need any more information. Stock L98 as far as I know. There are no codes or service engine light.

 

I had my 1988 Coupe do the very same thing. It drove great, but sent the NOX out of bounds on the emissions test.
It sounds like the EGR valve has gone bad as that is frequently what causes the NOX issues. I am sure there are other ways to trigger High NOX. When my EGR failed, it failed open so it was a major vacuum leak.

I would start by checking all the wires and vacuum lines (hard and soft) that connect to the EGR valve. The operation of the EGR can be simulated with adding vacuum pump to the hose. It is not too tough to replace it, just hard to get to on some cars. Don't forget to check the little tube that has the sensor on it. Both of those can be replaced if needed, the sensor make good sense just to fix the whole thing at once.

This is a classic "While you are in there why don't you...." my little EGR job became a two week project

My EGR Solenoid (mounted on thermostat bolts) broke as well as the whole system on my car was full of carbon. I ended up replacing EGR, all 8 injectors, Rebuilding the Fuel Pressure Regulator, and removing half of my intake system because of the work involved.
Good Luck on your car!

 

Sounds good! Thanks for the advice. Do you think an EGR valve would go bad and still not throw a code? I know OBD2 cars will throw a code if it's bad, maybe because this is 1989 OBD1 it wouldn't. Would you happen to know?

 

read about lots of 89s cranking a bit cold mine did the same

Had a random lean condition it was the maf didnt set a code;would run great then once in awhile when you were "in it" would feel like it hit a 50mph headwind. A/F readout on dyno was a giveaway

one thing at a time.

 

Sorry, I couldn't resist.

My poor Corvette is 29 years old, yet it runs and it even has a tiny little computer in it! These poor old corvettes of the OBD1 days had very little information with which to work. They are a simple system compared to the modern stuff. They operate well within their limitations.

The biggest problem I have had with my C4 has been electrically related. My car sat after the EGR fiasco and developed many dirty, corroded connections. My radio worked intermittently and other electrical gremlins haunted me until I started at the battery and cleaned and coated every connection I could find.
Now my car has little to no voltage drop in my systems and most things work.


Like yourself, my car seemed like it was running well and I could not tell from the "seat of the Pants" that I had a major engine system fail which caused my car to pollute more than it should.

In my experience I have never noticed or received any warning from the car indicating a problem. You are right about the newer OBD2 cars being able to determine if you have a problem.

The car does have a sensor that measures heat (I think) at the top of the EGR pipe. Before my EGR Failure I did notice that the EGR pipe got so hot it melted the protective insulation off.

You mentioned that you car was hard to start when it was cold, right? There are sensors that activate the cold start injector which is like having a 9th injector. The Cold Start Injectors fail but test the sensors first and be sure your engine is not seeing something faulty. If the sensor fails and makes the computer think the coolant is warmer than it is, the cold start injector will not assist your cold engine. Be sure to check to see if it is producing the right resistance for the current temperature where you are. Before you go too far check the voltage between Alternator Positive (+) and Battery Negative (-), now go from Battery (+) Positive to Engine Block negative/ground (-). You should have the very same number at both places. We are just checking your grounds. Grounds are very important to this car as it is an early Fuel Injected cars and depends on reading from multiple sensors which are typically between 5 volts Reference voltage and ground.

Check the wires that go to the Cold Start Injector and be sure they are clean. I applied power (correct polarity being observed) to the Cold Start Injector and heard and felt it click. Just don't go applying power if there is any gasoline around. I tested mine away from the car with a "Power Probe", very useful tool for Corvette owners.

At some point you might want to check your fuel pressure as well. This could be contributing to your problems. Fuel pressure problems happen on older cars, very important to starting easily. If the system is not holding pressure this would cause hard starting this time of year.

By the way, I wish you a Hearty Welcome to the Corvette Forum!!

 

Thanks man! I appreciate all the advice. I am used to working on Camaros so I'm still new to, and learning about how the Corvettes are built. I'm going to replace the EGR valve and see if that helps at all. I'll definitely go through and clean all the connections as it is an old car and I'm sure would benefit from it.

 

Is this the factory EGR valve? I just replaced it on my car and this is what was on it.