biggles

I actually passed my test in Houston last year with a test pipe on a 1987 951 with 98k. Prior to the test, I drove the car real hard to get it very hot. Therefore, I would advise to do some driving with high rpm before getting the car tested.
biggles

FlyYellow

does houston have a rolling test (my undestanding is putting a load on a car can really increase emissions).

H2Opumpr

I routinely go through this every other year here in california.

I have been on the test only program since owning the car(5 years). This year I passed NOx by 2 points. I just redid the motor and it runs excellent.
I have also been a gross polluter a number of times try 2500 ppm NOx! Replaced a cat with a newer one and blew through the test 2 years ago but had trouble this year.

According to 2 smog techs I've talked to, they claim that the test only program tends to pin down certain engine groups, and they stay that way for the eternity of the smog program. Not sure I believe that or every 951 in Cali would be on the test only program.

Have you guys heard of the mobile smog machines. They are in the bigger cities like L.A, Sac, and San Diego. They create a checkpoint and and test you at random! This is the very reason I run a gutted cat, and not a test pipe. Guaranteed fine if you are caught running without a cat. In my case I may not pass the sniffer with a gutted cat, but they dont know its gutted. I've heard the fine to be upwards of $5000.00

Just something to think about for you guys in Cali running around with testpipes.

roadrunner

Bill:

I thought the 951 had a three-way cat...

biggles

Boris,
Yes to your question. Only young cars, not sure of the exact year are exempted from the rolling test.
Biggles

ken louie

Great topic poeple!! Quick question. I would like to upgrade to larger injectiors (65lbs), if I get the proper chip (Guru's) will I still be able to pass the rolling smog check. Any modified 951 in south Cal want to share their experiences.

TIA

ken

951sickness

Okay, I still fail to see how running at 0.46% and 0.28% CO with stock chips is running lean. I'm open to learning new things but so far I am not convinced I have a lean condition....high combustion temps yes...but lean? And not to beat a dead horse, but if it was running lean wouldn't HC's be really high?

B951S

A little OT, but if you had a wideband, does the CO values translate directly to a AFR? Also, how much load do they put the car under in the 2nd gear rolling test? Is this comparible to driving on a flat road at 25mph or what?
Cheers

Flight_951

In your first thread about this topic I suggested checking the afm voltage at idle. I also suggested doublechecking that your recently replaced vac lines were tight and leak-free. These are common reasons for otherwise decent-running 951s to have high or slightly high NOx. To my knowledge you've done neither and have started this new thread.

If you feel that the used cat has solved all your problems, leave it at that.

Bill

951sickness,

Hydro carbons (HC) in the tailpipe are just unburned fuel. The presence of high levels of HC (unburned fuel) can occur for several reasons.

Too much fuel (rich condition) - not enough air for proper combustion. Incorrect A/F mixture, failed O2, clogged air filter, high fuel pressure, leaking injectors, etc.

A weak spark (proper A/F to rich condition) - Plugs not firing mixture. Bad wires, plugs, cap, rotor, too much fuel to ignite mix, etc.

A lean miss fire (This is not just a lean mix, but a very lean mix) - Not enough fuel for proper combustion. Mix is so lean that it will not ignite, leaving raw fuel to exit tailpipe.

Keep in mind there are varying levels to the last senario.

At the "just lean" side of combustion, you will get all the HC being used in the process and have air to spare. When that extra air coupled with high combustion temps (a lean mix burns faster and hotter) combines with the by products of the HC combustion (Nitrogen, H2O) you get high Nox with little or no HC.

At the "very lean" side of combustion, the HC will not ignite at all, due to way to much air, and you end up with raw HC, low combustion temps and little or no Nox.


So by the description of the process, you can see that the just rich (raised HC) to very rich mix (high HC) or the very lean mix (some Nox, high HC) will all have low combustion temps that will not threaten your head gasket, valves, rings, or pistons. Its the just lean (high Nox, low HC) to almost very lean (lower Nox, raised HC) condition that will kill your motor. Nox is the critical indicator, not HC.


Flight 951 brings up a great point.

A cat will clean up the bad byproducts of bad combustion (ie passed smog test), but the improper combustion process still remains. That is why our cars have a pre-cat test port (little pipe on passenger side of motor with grey cap) that is used for mixture diagnostics.

It is really not that painful. All you need to do is take the car to someone who can sniff your mixture, pre-cat, to see how it is doing. Simple. Did the four smog techs check your car, pre-cat?

I for one, do not need to have a doctor's knowledge to know that when he says "come in and get it checked" THAT I NEED TO GO IN AND GET IT CHECKED.

We are just trying to help a fellow rennlister stay on the road.

Or as Flight 951 says, you can choose to ignore the signs of a heart attack and eventually die.

951sickness

Vacuum lines and the AFM voltage were checked and fell within the spec limits.

Bill thanks for the clarification on the "slightly lean" condition and how HC numbers don't always have to be high in a lean condition. The final grey area, at least for me, is that CO readings from the test. 0.48% doesn't seem to be lean, at least in relationship to the cutpoints of the test (0.74%). Does this mean that the CO should be right at if not very close to the cutpoint? Thanks.

Bill

See revised post above

You are concerning yourself wayyyyy to much with the smog test results. That test is post cat. If the cat is having a tough time cleaning up things, something definately need attention.

To find out how your A/F ratio TRULY is, the reading MUST be pre-cat.

lart951

by H2Opumpr,I have been driving in So. Cal for 23 years and I haven't seen one yet.

That's good to know because I run my car with a test pipe.

951sickness

Bill, first of all I do appreciate your and everyone's help. I believe that my efforts to understand which readings are bad vs. in spec shows that I want to make sure all is well even after passing a government mandated test. Would you happen to have the specs for the 951 emissions before the cat? Your right in that the guys did sample before the cat (they don't have a probe that fits in the small tube). At least if I have the spec values then I can start hunting down a shop with a gas analyzer that can sample the gas pre-cat. Thanks.

Bill

You are welcome. Keep it on the road.