Hi There. New to the site.

I have a 94 Z28 M6. Longblock is stock, 248K miles. Only have a K&N FIPK and an SLP 2OTL exhaust.

I'm the original owner of the car. Last year my son and I brought it back to life as a project. I went through everything on the car.

Parts that have been replaced: Entire cooling system, evap system including cannister and purge, Racetronix pump, new FPR, fuel filter, (FP is good), pulled tank and cleaned it, 24lb Bosch injectors, coil, coil module, opti, wires, plugs, MAP, IAT, TPS, O2s, EGR valve and solenoid, vacuum tested everything. New air pump check valves,

Cat is a Random Tech and it is at least 23 years old, but the car passes everything but NOx.
I ran two tanks full of Redline SI1, always use good gas and ran an aerosol bottle of water through the intake to clean the top end. The car runs absolutely amazing. When I first finished the project, it passed smog no problem. A year later, all is good except now the NOx is running about 750 for the 15 mph test and passes at 25 mph.

I don't want to spring for a cat if it isn't going to help NOx. I took a 9495 log file from warm up to a drive around the hood with a few WOT pulls. My IAC numbers look high at idle and my LTFT numbers seem high at idle as well. I reset both during the log and then went for a drive.

Anyone able to take a look and offer advice?

Thanks!

Dave

 

Why did you delete your two/duplicate earlier posts on this topic? I typed a response and tried to post it, but you had deleted both posts. Just wasted my time trying to help.

“New to the site”? You joined in November 2000, and posted to threads in 2003.

ADMINISTRATOR

 

EditApologies. I posted to the wrong forum (or at least thought I had.) and tried to repost here. I haven't used forums much and not very adept with the interface yet. Really sorry and appreciate that you responded. I also posted to a forum called LTX and copy/ pasted my post from there and forgot to delete that first line. Since I haven't posted here in 20 years, I might as well be new to the site anyway.

Greatly appreciate that you responded and very sorry for wasting your time. If you don't feel like responding again, I totally understand.

Dave

 

Engine file. But looks like it was a shorter capture. May need to do another log?

 

Please read post #2 in my “LT1 PCM Scanning Guide”:

https://www.camaroz28.com/forums/com...-guide-886891/

 

Thanks, Fred. I'll pull a good log this morning. I totally get your position about helping when folks didn't have the decency to follow up where you have tried to help.

If anyone else has the ability to read the files, and offer advice, I'd be grateful. I'm highly motivated to get this done as the car is going to be a gift to my son this Summer as he finishes his ME degree, He and I worked to get this thing together during COVID and has been a great project!

Dave

 

Log file attached using proper capture technique suggested by @Injuneer. Thanks for any insight that can be provided!

Dave

 

There was data from yesterday's log in the file. I deleted that so this file is just the clean capture from cold start this morning.
Thanks!

Dave

 

Forget post 2, your scan guide in post 1 is great info! Thanks for sharing that.

 

High NOx, with acceptable CO and unburned HC levels is usually the result of running lean, or the engine running hot. Also could be contamination of the specific precious metal in the catalytic converter that breaks down the NOx into nitrogen and oxygen.

Running lean could be a vacuum leak, air bypassing the MAF sensor, or a faulty injector. You indicate you replaced the injectors with 24 #/HR Bosch injectors. Did you buy them from a reliable source? eBay and Amazon are loaded with Chinese counterfeit copies of the Bosch injectors. They tend to call them “Bosch style”. A $95 set of Chinese rip-offs can be a major problem.

 

Injuneer, Thank you. I bought a matched set of Bosch 3 24 lb injectors from Fuel Injector Connection. $245 out the door. I pulled the intake manifold to reseal it during our work and completely cleaned it and replaced any rotted/brittle vacuum lines. Replaced rubber PVC pipe and vacuum lines have been checked with a nice mighty vac with the guage on it. I used 9495 to put the EGR into 100% duty cycle and checked vacuum at the line where it plugs into the EGR. Vacuum goes on/off as expected and engine stumbles when I do so I know there is enough vacuum to activate the EGR valve. I checked the seal of the intake elbows before and after the MAF. The MAF is original but clean. I think that the MAF and Cat are the only original accessories that would be associated with emmissions and tried to use GM parts where I could. I cleaned the metal EGR tube from the exhaust manifold to the intake as well.

I can't detect any kind of exhaust leak but have noticed a high pitched noise at WOT that makes me wonder if there is some kind of obstruction in the cat. At about 5000-5500 RPM the motor lets you know it is ready for the next gear.

 

 

OP

data scan file reading is beyond my pay grade. Ideally Injuneer can assist in commenting on your log.

Relative to CA smog I can note that at any point your car had an exhaust or vacuum leak pre 02 than the PCM would command more fuel thus creating a rich condition. Prolonged operation under those conditions will load up and kill a CAT.

The smallest of leaks can be very hard to find but necessary to do so. Cracked hard metal line fittings associated with the check valves on exhaust manifolds for example.

If your CAT has been compromised than replacing them is necessary.....at 238k mi they have considerably out lived their designed lifespan. Unfortunately, CA compliant CATS are not cheap but fortunately are available.

You may have other issues going on based on your log files but with that milage I suspect your CATS are quite used

 

Thanks much for your insight Chimera96. Definitely possible there was some kind of leak. I passed smog no probnlem about a year ago and have only put about 500-600 miles on the car since, I have driven it hard and possible the cat partially failed since then. Before bringing the car back online, it sat for about 18 years. My son and I went through the whole car. I do have a smoker to look for leaks so probably a good idea to do that. Otherwise it runs really good.

I want to check all the cheap things before dropping $600+ on a CARB certified cat. Flippin' CA.....

 

If you have an IR temp gun measure temp before and after CAT. If significantly higher going in CAT, it is restricted.