1992 Fails Smog All Measurements

[SMaeller]

I recently took a motor from a 1990 SHO that passed smog in May 2009 and put it in my 1992 SHO (which passed smog less than 1000 miles ago, before I spun a bearing). Along with the motor I used the year old O2 sensors that were in the '90 and my relatively new (less than 1000 miles) cats from my 1992. The car runs great except it fails smog across the board (CA emissions test). Initially it failed as a gross polluter across the board and I found a temp sensor that I had not connected (on the heater hose tube). After re-connecting the temp sensor it's no longer a gross polluter, but just barely and still on every measurement. You can stand behind the car and smell that it is running very rich. Note: oil, filter, plugs and wires are all new and the K&N air filter is clean.

So I took it to a well recommended local mechanic and he checked every connection, looked for codes, checked fuel pressure and nothing is wrong except it runs very rich. I'm stumped and more importantly, the mechanic is stumped too.

Has anyone ever seen this in a Gen 1 or 2 SHO? What would cause it to run rich and yet give no codes or any other indication of failure?

 

[needaQuaife]

do a search, theres a sensor you can unplug to pass smogs. I just installed new cats from Magna Flow and passed easy, with original O2 sensors.

 

[SMaeller]

Thanks, I have considered that and would do it if the car wasn't running so rich. I may do it yet, just to get it drivable for now, but I'd like to find out what the problem is.

 

[needaQuaife]

it may be running rich due to bad O2 sensor(s)...

 

[SHOmethewayhome]

check your spark plugs, and plug wires. does the car feel like its got a misfire?

your O2 sensors might be kaput as well.

 

[SMaeller]

check your spark plugs, and plug wires. does the car feel like its got a misfire?

your O2 sensors might be kaput as well.

All plugs and wires are good, no misfires. It's every bit as fast as I remember it being, just running very rich.

 

[fdogg96]

Hi,

This is off topic. I see you are in Calif., you should check out SHOCal. www.officialshocal.com See you on the boards!

 

[rocket455]

post up your results and i can help you

 

[SMaeller]

post up your results and i can help you

Here they are. I think the smog shop kept the 1st (and worst) test results, but I have the 2nd and 3rd tests. Thanks!

 

[sperold]

Pretty sure it is the O2 sensors. Make sure the grounds are well connected otherwise the heaters don't work. Use the 92 O2 sensors, your computer and them have gotten along for years. If you buy new....get the Motorcraft from Rockauto, that is the only one that gets me a pass.
The O2 sensors can be out of range by 25% before they give a code.
Don't let the high numbers get you down. They are all crazy high until everything is correct, then they all read near zero.
Try a new thermostat if it is running cold.
Just an interest note - The rpm looks high. Ours are done at 1800 rpm.
If it gives you more grief, pull the spout connector and try the test that way.

 

[Eric VerValin]

I'm wondering if its warmed up all the way. I had to pass smog when I lived in Dayton, and if it was cold it wouldn't pass... I lived right around the corner from the place, so that little drive wasn't enough.

 

[SMaeller]

Thanks to everyone who gave me suggestions. I really appreciate the help. So I finally have a good idea what the problem is - Catalytic Converters.

Yeah, I did change them less than 10,000 miles ago, but I didn't know how bad misfires are for them. Prior to parking the car for the past 3 years due to a rod knock I had a bad ignition module that would kick in and out, sometimes in places where I had to drive a long distance to get home. It took forever to find out that it was the ignition module. When the module wasn't working right the car felt like it was running on 3 cylinders and probably was - dumping lots of fuel out the exhaust. This is likely what trashed my cats, but I'm not taking any chances and I'm replacing the O2 sensors as well.

Anyway, I took the car to a smog repair shop and they had everything passing except HC and it was reading 144 when the cats were very hot. A CO2 test was done and it came in low (10.25), which the mechanic says indicates the cats are not doing their job.

I've ordered new cats and O2 sensors and I'll have them by the end of the week. I'll post again after I retest next week.

Thanks Again!

 

[Batasllc]

Where did you order the new cats and O2 sensors from?