jdeuel

Hello, all.

My '87 Carrera failed CA dyno-smog yesterday with 15mph NOX at 1552 vs. 807 allowable, and 25mph NOX at 1381 vs. 746 allowable. CO failed, although not as spectacularly at 1.12 vs .76 and .85 vs .65, respectively. HC failed at 15mph with 143ppm vs 121ppm allowable. In fact, the only part that passed was HC at 25mph, with 80ppm vs 96ppm allowable!

Car is bone stock with 161k mi. It runs well with no visible smoke except at start-up. We tried getting it hot, no real change. The smog check guy said at idle, it would have passed 2 years ago, but the 'new' dyno test isn't happening.

Any suggestions? Octane boost was an idea I had thrown out, don't know if that'll help. Any other tips/tricks before I have a mechanic start replacing components?

Thanks in advance.

84_Carrera

High NOx usually indicates you're running lean. Check for vacuum leaks, possibly replace your O2 sensor.

art

my 944 failed last year for this,and it was just a poor (not broken) connection to the 02 sensor.

jdeuel

Thanks-my internet research seems to be pointing toward O2 sensors...I'll check it when I get home tonight.

SC-targa

I'm betting a failed converter because is failed NOX, which is usually caused by running lean, but it also failed CO and HC, which indicate a rich running. You don't have an aftermarket chip, do you?

Jerry Kroeger

jdeuel

Jerry,

No chip or anything aftermarket, for that matter. I wondered about the cat, but have never 'smelled the smell' or anything. What kind of life would one expect out of a cat? I've had the car 6 years and haven't replaced it or the O2 sensor. I've driven around 60k in that time, most of them hard, and most in the first 3 years I had it. Is there a way to check the cat?

Thanks-Jeff

ron mcatee

I think the life of an O2 sensor is somewhere in the 60,000 - 70,000mile range. Of course, some go further and some prematurely. I think you need to replace the O2 sensor, but have the mixture adjusted to ensure it's in the proper range.

jdeuel

Well, just ordered a new O2 sensor tonight-seems like the likely (and lowest-dollar) culprit. I'll pop that in and retest. The replacement almost looks too easy...any caveats? Thanks!

ron mcatee

I usually pull the left rear wheel so I have plenty of room to work. It takes a 22mm open end wrench (or line wrench that is slightly open on one end) to loosen it or a good adjustable metric (crescent wrench) if it's all you have. I just rotate the wires carefully while removing it and re-installing the new one. I would put some antisieze on the threads, but be careful not to get any anti-sieze on the end ot the sensor. I use a small silver brush with black hairs (cost 35-50 cents at an auto supply). By doing this, I've never had a problem if I had to remove the O2 sensor for some reason. I have done it several times due to removal of CAT's and putting on euro pre-mufflers. Hope you fix the problem. You are right, due the simple things first.

jdeuel

Okay-
Replaced the O2 sensor today ($102 online for a Bosch wOEM plug) Thanks for the tips Spider...took all of 10 minutes-most of it getting the grommet back in! Talked to the local tech about checking the mixturre. He recommended driving it hard for the weekend to clean the junk out of the cat that would have ended up in there from the bad O2 sensor. (Does that make sense?) Just for s&g, I went back by the smog place-at idle, it ran much cleaner, but on the dyno, it was still out of whack. Plan: Punish it for the weekend, burn out the cat, have mixture checked, back on the dyno-smogger. Any holes in my reasoning? Thanks!

DGaunt

I suggest an oil change if it's been a while and perhaps a set of plugs would be a cheap investment.

I wonder,do you suppose you have non-CA gas in the car since the EPA has suspended local formulation rules in the wake of Katrina?

jdeuel

Dave,

Plugs are pretty fresh (<2500 miles), but an oil change never hurts. When it failed, it was with pre-Katrina fuel, and going back yesterday, I had topped up with premium. Maybe it's me, but the car seemed to idle smoother and run stronger @ all speeds last night, so I'm guessing the O2 sensor was bad. I'm thinking about yanking the cat just to shake it around and look inside before I order one...

scottb

I've heard, but have no personal experience, that disconnecting one fuel injector helps in this situation. You might do a search on the Pelican board for more information.

I hope this is helpful.

Lorenfb

Check here ( www.systemsc.com/problems.htm ) for additional insights into emission
failures. Disconnecting an injector will not help a NOx failure, nor will a spark plug change.

redtdi96

what was the color of the OX sensor that you removed? black = rich, I think then the vacuum line may be the issue since you replaced the OXS. You can take your new one if black and take a propane torch and burn off the carbon.

TO check for a hiddden vacuum leak there are two ways

1) forget this one you may blow yourself up

2) Spray a nice highly atomized water spray around the rear of the engine where there may be vacuum lines. If you detect a change in engine RPM this will be due to the water vapor. You may need a schematic / map where the lines are.
On my 80 SC I had a hard line actually worn away and only say this after I dropped the engine. I'll try to find this picture.