stealth

86.5

Well, new cats were an excuse for a crossover pipe, but they didn't get my sticker. I've read all the other threads at this point on this subject (half of which are NOx failures, half CO or HC, which are both low on both my tests). Since the first failure, I also put on a new O2 sensor (there was no O2 sensor on the thing the first time, to my surprise) and replaced the intake rubber pieces (which were a source of significant vacuum leak) and fixed some charcoal-canister-related vacuum leaks.

The NOx reading actually got worse (3.06 gpm vs. 3.04 average, need 3.00 to pass).

Although there is surely a vacuum leak somewhere to plug (idle 800), I also want to get rid of the Autothority chipset until I pass to reduce the timing advance. Will the '85 fuel mappings (LH rev. 03) vs '86 "more aggressive" (LH rev 04) make me any more likely to get by? I can get either and I only failed by 2%, so a little change in mixture could make a difference.

I'm going to replace the plugs, as well (WR7DC).

The thing's running pretty well, a slight bog off the line but that's not entirely atypical with the early 32V/2.20 (someone with a supercharger will probably suggest that it's quite correctable).

a4sfed928

NOx is is produced when the combustion temperatures are high, which is usually an indication of a lean mixture. With your slight bog I would think this is the case. I think you are on the right track with th air leak.
Good Luck.

stealth

Guess I need to figure out the right mounting point for the ARM-1 meter I have lying around. I should've had the shop splice that in when they spliced the universal O2 onto the 928 harness...

worf928

Shane? What are the HC and CO numbers?

stealth

Hi, Dave,

First test: CO gpm .03 HC gpm .38
Today: CO gpm .20 HC gpm .23 (better combustion than before, no?)
Limits: 30.00/2.00

CO was adjusted when X/cats/O2 installed Wednesday.

The only significant difference between the graphs of 1st & 2nd tests is the O2 reduction from 4% to .5%.

worf928

Yup Shane looks better - slightly. No obvious signs of anything bizarre in combustion land.

I recall Louie Ott describing how, during development of his x-pipe he had problems getting the cats up to proper temperature because they were too far back from the manifold; IIRC he tried putting cats in-place of the resonators. But, they were so far back that the exhaust cooled enough to prevent them from 'lighting up.'

Do you have an idea of the motor temperature? Unless your cats are not, for some reason, getting hot enough to scrub the NOx - that's their job - lean and hot combustion would be the next thing to chase I suppose.

michaelathome

OK, been here done this.

As others have posted what you are describing is typical of running lean or HOT cumbustion. You SHOULD be able to pass with straight pipes though so you need to look for something other that cat's to do the scrubbing for a dirty engine.

- Fouled plugs
- Vacume leaks
- Dirty injectors
- Sure you have the right O2 sensor?

Try running an injector cleaner through the engine. You are SO close to passing. Lower octane fuel might help?? Just a guess.

Good luck and let us know,

Michael

Get the engine hot!! I ran mine in 2nd and 3rd gear(auto) for 30 or so miles and then ran the test.

stealth

I had it warmed up to normal temp, drove a couple of miles on 93/128 beforehand, though it sat about 20 minutes before my turn, so coolant was probably 130-140. These cats are a little back from where factory would be; the stock exhaust had 4-5" of pipe to slide into them.

It's possible the plugs that are in there are hotter than Bosch 7, haven't looked, going to replace.

Having an O2 sensor vs. no O2 sensor should've made a difference if it was mixture-related, so I think it has to be heat- or timing-related (or, both old and new cats are not right).

michaelathome

Shane,

On my '88 an O2 sensor made a HUGE difference. In my case the engine was in the default "wide open throttle" map IIRC with the O2 sensor unplugged. I am not sure if you car's mapping is the same. My car ran REALLY bad w/out the sensor. I wouldn't be focusing on that though unless yours is MIA as your #'s are way closer to normal than mine were.

People swear by Bosch coppers in these cars. Again I am pulling this out of my *** but IIRC W7/W8's are the way to go.

Michael


Michael

stealth

Oh, the O2 sensor DID make a huge difference (the X helped some, too, but I did get a test with X and no O2 thanks to the shop leaving it unplugged from setting CO...grrrr), the car's quite peppy now...I could not believe that a near-miss last time did not pass this time the way it is running now vs how it was running 7 days after I registered it.

I also read more praise for sticking with WR7DC's than trying anything else (although apparently I need fancier plugs for my GTS engine...Dave? lol), so I'm definitely going that route.