The only change I have made since the last test is replacing the cats. The NO has gone from 124 @ 25mph to 751. I know nothing about this stuff but I assume it means there is too much air in the mixture. Given that this change from one extreme to another happened after replacing cats is there anything obvious to the experts? I had previously rebuilt the brain and replaced the 02 sensor.

 

Well, the little I know is telling me that problem is because your new cats don't have much catalyst in them. I mean, my car almost fails due to high HC, but it does pass NOx easily. That problem is more likely due to leanness somehow. Your problem seems quite different, and I don't know if high NOx with good HC can be a feature of leanness.

 

Thanks Safulop, at least you have a great avatar.

 

Huh..I have a second set of cats you can try..AFAIK, they're both good sets.

 

I assume with the dramatic improvement in HCs the cat is good.

 

Last I had those cats, THEY were good too.

I'll pack em in the car Monday, for whenever we can get together soon.

At Sears Pt this weekend.

 

If you can't hook up with Jeff, I have a set of cats you can borrow as well Charlie.

Also, was the car nice and hot? Several years ago another local guy came over to my place to swap out the cats. I suggested we go for a smog test first. He failed, and the smog guy suggested we take it out for a spirited run for 30 minutes. Did just that, then pulled in for another test. Passed.

Rich

 

Thanks guys, but because of the great HC numbers I find it hard to believe the cats are any longer the issue.

 

Something not clear.

In 2014, you had crazy high CO and excessive HC. Way, way, too much fuel causing a misfire.

12% CO is engine washing down, fuel getting into the oil kind of richness.

Was that problem repaired or just "masked" by new cats?

I ask, because your 2014 issue wasn't the cats, at all, but rather raw fuel dripping out the tailpipe.

If that problem wasn't repaired, your "new cats" have had a life of shear hell...even though the mileage traveled is very small.

My guess is that while they still may be "cleaning up" the excessive fuel, they are doing that at the cost of high NOX.

 

It was 90 degrees and I did a 30 mile high speed run before the test.

 

Well you know, if you're going to offer up a dumb idea, at least do it with a pretty face!

 

The LH had gone south so I had that rebuilt and a new 02 sensor installed.

 

Interesting.

I suspect that a really good factory cat will solve your current problem....the aftermarket cats are, quite simply, used car lot "sell this damn car, we don't care what happens next year" repair pieces.

Your .20 CO is actually a bit richer than I see these cars. They are usually .00 or .01, which drives the NOX up, from being too lean. This is tough to judge, with aftermarket cats, however.

In the shop, I'd put a volt meter on the O2 sensor output wire, while leaving it hooked up and monitor the voltage. Once warm, should move fairly quickly (every few seconds) between .2 to .8 volts. If it is stuck or slow at either end, that needs to be addressed, first.

The next thing I'd do is a "smoke test"....although the slightly high CO points away from an intake leak. An intake leak combined with a bad MAF is very common....especially with your mileage.

Speaking of the MAF, how old is it....and if it was rebuilt, who rebuilt it? I've had nothing but trouble with US rebuilt MAFs. I only trust ones from John Speake....he seems to be able to get the calibrations consistent....however he manages to accomplish that.

 

Edit....

Actually, the very first thing we do, in the shop, is pull the vacuum supply elbows off of the fuel dampers and regulators to see if they are leaking raw fuel into the vacuum system.

 

HOT cats are a 2 minute 'beat the **** outta it' before the test.