Hi Guys,

I guess there is no direct problem associated with what my test results are so I am going to have to start looiking around.
Does a Porsche shop have the diagnostic equipment available to locate the culprit or is it just a matter of checking things out one part at a time?
I may be better off taking it in at least to try and isolate any bad components in the system if its possible.

I really appreciate everyones input and would invite anyone else to jump in.

Cheers
Bernie

I agree with what Mike S said. The cats are there just to polish up the exhaust. A well running 928 should pass without cats. (I know, mine did..although no NoX testing in WA state)...

Just a random thought....Can't the 85 and 86 32 valvers retard the timing via that little plug on the brain? The octane loop that has been discussed in the past. Don't know what effect it would have on the emissions, but may be worth a shot..

HTH...

Later,
Tom
midlman@seanet.com 87S4sale...89GT

[quote]Originally posted by Bernie:
<strong>Hi Guys,

I guess there is no direct problem associated with what my test results are so I am going to have to start looiking around.
Does a Porsche shop have the diagnostic equipment available to locate the culprit or is it just a matter of checking things out one part at a time?
I may be better off taking it in at least to try and isolate any bad components in the system if its possible.

I really appreciate everyones input and would invite anyone else to jump in.

Cheers
Bernie</strong><hr></blockquote>

For whatever its worth, I had mine tested and it didn't pass (CA car)...I will say mine is bone stock so exhaust system mods aren't a factor. The car was cold at the time of the original test. My mechanics shop is right next door to the smog test shop and had been there overnight. He suggested taking it for a spin around the block to get it warmed up....I did and it passed on our second try. I'm assuming your car was running at usual temp before you had it tested?

[quote]Originally posted by dshulik:
<strong>For whatever its worth, I had mine tested and it didn't pass (CA car)...I will say mine is bone stock so exhaust system mods aren't a factor. The car was cold at the time of the original test. My mechanics shop is right next door to the smog test shop and had been there overnight. He suggested taking it for a spin around the block to get it warmed up....I did and it passed on our second try. I'm assuming your car was running at usual temp before you had it tested?</strong><hr></blockquote>

I'm interested in what kept your car from passing on the first go. Our thread subject here is high NOx reading, and a cold engine should help rather than hinder the NOx. What cold engines have problems with is lean misfire as the fuel charge condenses on the ports, intake valves and cylinder walls. The common solution is a rich mixture while cold, figuring that the increase in CO and cold driveability will more than offset the savings in HC pouring into the tailpipe.

The one thing that a good run just ahead of test will do is get the catalyst up to temperature. Car manufacturers recommend that you drive off immediately after starting the engine so that you put enough load on to get the cat up to temp quickly. Bernie mentioned that he had a half hour lag between drive-up and test, all due to the visual/mechanical portion of the test. Since the car has already endured those indignities, perhaps it's possible to roll right up to the test with a
catalyst that's up to temp already.

Bernie,

I've heard that painting the cam covers black may increase NOx.

seriously, it may help to fatten up the mixture a little. I cant remember if you can do that on our cars.

Also, you may have some carbon deposits in the combustion chamber (I know I do) that may be messing things up. Look down one of the spark plug holes with a bright light and see.

on another note, I'm changing the timing belt if you want to take a peek. I wasn't going to but one thing led to another. Oh well, now it will be another month probably before I get to drive it again...

NOx is formed when combustion temps are over 2500 deg, so a leaner mixture (closer to stocheometric) creates more Nox due to the higher combustion temps. In other words, a rich mix does not create NOx.

The 928 has a three-way cat, and thus (for most years) does not have EGR (Exhaust Gas Recirculation), which is commonly used to dilute the mixture and reduce combustion temps.

The reduction of NOx in the cat is dependent upon the presence of CO. If you have a lean mix, your raw output (before the cat) of CO will be low.

On the 928, reduction of NOx seems to be almost entirely the province of the three-way cat, so that is my first guess.

You can try to reduce the amount of NOx produced by lowering the combustion temps. The only ways that I can think of for this are:
Use very high octane unleaded fuel (do NOT use leaded fuel!),
Richen the mixture using the adjustment screw under the plug on the side of the MAF,
Connect both octane loops on the ECUs.

Otherwise, I suspect that you will need a new cat - make certain that you get a three-way.

Wally,

Can you expound on exactly what a three-way cat is? I'm guessing these universal cheapies I have seen are not three-way's, but I've not seen any reference the "three way" on the cat sites I've searched, and really don't know what to look for.

TIA,
Greg

My understanding is that the cat is not getting hot enough to burn off the nox. When my nox was too high I found the vaccuum line to the air pump valve had disconnected at the throttle body. I reconnected it and passed.

So, I'd look to see if the vaccuum is good first. Second that the air pump is working, too.

My two cents in Georgia.

Greg,


I have some pictures to post but my web site and e-mail are down. I need to change my host, they suck.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

A three-way catalytic is one that reduces tailpipe emission of oxides of nitrogen as well as hydrocarbons and carbon monoxide.

A dual-bed cat, such as is used in the later 928s, uses rhodium in the first bed to reduce NOx, and platinum and/or palladium and injected excess air in the second bed to reduce HC and CO. A monolithic substrate, with a surface area greater than a USA football field in each bed, is used to hold the precious metal elements, along with the ceria that greatly improves oxygen storage and injection.

Reduction of NOx needs a richer-than-stochiometric mixture, with some included CO, to work effectively, while reduction of HC and CO needs a leaner-than-stochiometric mixture. This is why air is injected between the beds - the first bed gets the rich mixture with CO from the engine, while the second bed sees a leaner mixture to reduce HC and CO. The oscillation of the mixture around stochiometric (14.6:1), combined with the air injection, gives the reach/lean mixture needed.

This means:
A rich mixture gives low NOx (lower combustion temps, plus lots of CO).
A lean mixture gives high NOx (higher temps and less CO)
The air pump has basically no effect on NOx from the tailpipe - it only affects CO and HC reduction.
A bad plug or plug wire will greatly increase HC and CO into the cat, with little effect on NOx.
High engine temps will slightly increase NOx.
Higer octane fuel will burn slightly cooler, slightly reducing NOx.

It became very obvious in the early '80s that an effective cat replacement system was vital to lower emissions. The EPA stepped up and established such a system. As a result, any after-market cat sold in the USA has to be pretty good, and must meet its advertised performance. If you get the actual advertised specs, the cat must meet those specs.

It is my understanding that virtually all cats are now three-way, and may or may not be dual bed with injected air. This includes (I think) aftermarket cats.

Later cars (not 928s) now have new-technology sensors behind the cats (inaddition to the normal sensors before the cats) to more accurately control the engine parameters, allowing more power and/or efficiency along with lower emissions.

So, while I'm up hanging out in Vegas for the weekend, I find all my sharkster buddies are busy trying to solve my problem with NOX.
Sorry lads, I didn't have any computer access over the weekend. Hence, my lack of response to the much appreciated posts.
Seems that the gurus are steering me towards the cat? Others claim that the car should have passed even without one? My curiousity lies in the smog test I had 2 years ago. Car came through it with flying colors.
So now that we have some things to check, how do I check them? If I am to test the cat, what do I do? I hope I don't have to buy a new one for the sole purpose of checking it? I will dive into the vacuum lines and such just to be sure I haven't missed anything there but the car is idling and running very smooth right now. I can't imagine that I have a vacuum leak of any magnitude.
So here's the question(s):
How do I check the cat
Could the O2 sensor be playing a role here?
I am going to need some test procedures to verify that the cat is indeed the culprit -

BTW- 2am on highway 126 last night.
How many times and different ways does one have to kick a ricers *** before he gets the joke?
Round 1 - 4 lane highway - ricer drives slow until I am just about to go around. Hammers it (ha!!) and tries to keep up. Nope
Round 2 - Side by side and I jam it. Ricer dissappears into distance.
Round 3 - Let ricer jam it first and give him 2 car lengths before jamming it (see round 2)
Round 4 - Stoplight stage - well you know the rest.

At some point, you gotta figure that there is nothing to gain by this. I think he was dreaming about that scene in the "Fast And The Furious". You know the one - ricer vs. Ferrari on the PCH.
Ground effects and a coffee can exhaust does not produce an extra 200bhp. I think he knows that now.
The last round would have been - throttle - throttle - throttle until I see his pistons and rods flying through his bonnet but my exit came up before this could be realized. Oh well.
Woke me up for the 150 twisties anyway. Would have loved to play cat and mouse with him on that. hehehehe

Thanx Lads

Thanks Wally.

Bernie, I sent something to your email.

Greg

Bernie-

For a while now, I've had a problem with a high-throttle miss on my '85 S2. I've tried many things, to no avail. In frustration one day, I took it to a good shop in Orlando (Zotz Garage), and asked them to diagnose the problem.

They have a device that is mounted in a suitcase; it hooks up to multiple points of the engine and can test the various sensors. It might be worth calling around to various shops in your area and ask if they have the ability to do the same thing. This would serve to eliminate the obvious.

In my case, I discovered that there is an extra computer box mounted in my car, one that I've suspected existed for some time, and that also exists on most copiers and aircraft: the Necessity Computer. This device senses when you are in the direst need of your car and arranges for it to break down at that moment. It also has another function- to make your car run perfectly during testing so that your attempts at diagnosis are frustrated. As mine were...

Good luck!

Normy
'85 S2 5 Speed