RED SHARK 1990

Hello does anyone here can help chimed in on helping me with this problem?smog test failed-reading 15mph-1373rpm in 3third gear reads c02-meas-13.3-meas-2.0,HC(ppm) MAX-108,gp-116,CO%-max-0.71,GP-2.21,meas-0.02,NO(PPM),MAX-767,GP-1957,MEAS=2063=GROSS POLLUTER.Now at 25mph in third gear 1407 rpm-%co2-meas-13.04,%O2-meas-1.9,HC(PPM)-MAX-83-GP-233-MEAS-94,CO(%)-MAX0.58,GP-2.08-MEAS-0.02,NO(ppm)-MAX-706,-GP-1757,MEAS-2000=GROSS POLLUTER.hE RAN ALL IN THIRD GEAR AND I ASKED WHY NOT IN DRIVE?STATED THATS HOW ITS DONE..Car has x-pipe hi-cats--o2 sensor,airpump connected to x-pipe,new o2 in 2years,new caps,rotors-plugs are plat and iridium bosch fusion,rebuilt MAF,dAVE lOMAS SYSTEM.should i changed to bosch copper plus plug?new o2??????have 1 week to get it done....HELP...APRIL 22 DUE...

Randy V

I can't read that, sir.

Try again.

SeanR

You want the RPM's up on a smog test, don't let them do it in drive and going by speed. Did you make sure the cats were real hot before you took it in?

RED SHARK 1990

Hello SEAN does it make a difference if you have the air tube tap to the same position of the stock x-pipe to daves x-pipe?and anyharm to the cats?I drove only about 6-7 miles to the smog center and the weather here in SAN DIEGO was a little cool at 10 am,and it sat for about 30 minutes before the test.What gear should he be driving the car at 3 or fourth for the automatic.?I bought the rebuilt Maf from roger could the MAF makes it run rich?any input from other members are greatly appreciated....PLEASE CHIME IN....

AO

Man it's hard to read your posts...

For sure you should be running copper plugs. Bosch WR7DC. Make sure you drive the car at least 30 mins before testing to ensure car it at full operating temperature. 6-10 miles and it will still be cold.

We don't have emission tests here in Michigan, so I really can't adress your specific readings and what may be causing them. I am a GROSS POLUTER and I love it.

dr bob

Your numbers with high HC, low CO and high NOx all indicate a lean mixture, or they would if the readings were taken before the cats. No matter, you still want to go after the lean mixture issue to cure it. Look first for air leaks, vaccum hoses and the like. You should also be well into the range for the oxygen sensor to be working, so I'll pop the question about when you last changed that. You state that you have a rebuilt MAF so we can probably rule that out. Right now I'd be looking closely for air leaks into the intake, and at getting a new oxy sensor unless it was very recently replaced. Could be a loose clamp from when you replaced the MAF, a dislodged or leaking vacuum hose. Or the oxy sensor tired or not connected. Or one partially plugged injection nozzle, usually identifiable by reading the plugs.

blitz928

+1 on what Andrew said.

jcorenman

Red, I think this is what you meant:

If I am reading this correctly, your CO is very low, hydrocarbons are marginal, and NO is way high. The high NO indicates that you are running lean, which implicates the O2 sensor.
But HC being marginally high at the same time points a finger at the cat's, I think.

My understanding is that the hi-flow cat's don't have the long lifetime of the factory cats, that's part of the tradeoff for less restriction.
How old are the cat's? How many miles?

How many tries do you get in Calif these days?

SeanR

+2 on what Dr. Bob and Andrew say. Can't add anymore to that. I'd not worry about the MAF.

jcorenman

+1 on that. MAF's get leaner as they age, a newly-rebuilt one (properly done) would be a bit rich, open-loop. But the LH should be running closed-loop for the test so that should all be a non-issue. It would be nice to know if all the sensors are working.

jorj7

When I had readings like that, I had to install another set of cats, one that I knew was good. My
high flow cat couldn't pass smog, even the first year I had them. They get worse with age, so yours
are probably not up to snuff.

dprantl

Hmm, my high-flow cats passed emmissions just fine for the second year in a row now. I hope they stay that way...

Dan
'91 928GT S/C 475hp/460lb.ft

RED SHARK 1990

The HC(PPM)for 15mph-MAX=108,GP=283,MEAS=116.OK DR.BOB the intake refresh job kit from ROG a year ago and everything were replaced.Oxygen sensor bosch 2 years ago,cats are 100cc from DAVE LOMAS just last august.I had just changed the throttle cable roller and examined everything .Seems ok....

dr bob

Luan, there's an air leak someplace, or you have a wimpy injector or two, or the oxy sensor is going away.

For these tests, the LH is in closed-loop mode, meaning that the oxygen sensor drives the injectors to keep the CO level correct. The controller will correct for low CO within a limited range. John Speake can probably tell us the limits of correction. Anyway, with the lean mixture indicated by the low CO reading, you get a slight lean misfire in conjunction with higher combustion temps. The misfire allows unburned fuel to go out the exhaust, and the test picks that up as high hydrocarbons. The higher combustion temp from the too-lean burn causes NOx to go way up.

The challenge here is that we are speculating on what's happening before the cats, based on what is getting through the cats. It really is just speculating, unfortunately. There really was a reason to put those test pipes into the engine bay, so that pre-cat exhaust could be routed to an analyzer.

You might be able to fool the test with increased fuel pressure, but that's a crapshoot since you can't do any adjusting while the test is running. This is a band-aid thing; what you really want to do is cure the problem, and that's likely an air leak and/or tired oxy sensor in my amateur hobbyist judgement.

RED SHARK 1990

Hello DR.BOB i am planning to get to ROBS place around 9am to help out ,and if time permit i hope a group thinking would help track a leak?i have a new o2 ordered incase already....See you tomorrow..