weez58

What shop did you use? I'm gonna need to test my '86 soon.

PEvans

I think the shop I used is shown on the report I posted. There were also some recommendations in the "951S with slight MODs, where to SMOG in Bay Area?" thread.

weez58

Got it, Thanks.

Dan Martinic

Due to recent emissions failure, I may have to replace my catalytic converter.


I wish to keep the same exhaust behaviour; stock sound (or lack of) and performance is fine for me.


The original is like a system in itself: I understand that the CAT is actually a large main converter with a buit-in resonator and a small converter on the wastegate dumping pipe?


That you in fact are replacing 3 items?


At this time, I cannot afford OEM OR direct-fit aftermarket (800+) replacements


I found a local used original for 200. Then there is the 'cut and weld' option with universal cheap converters. See pics.


Questions:


1. Is there really a resonator built into the stock CAT?
2. Can you somehow evaulate a used original for blockage or condition out-of-car?
3. How much does the small second converter on the wastegate pipe affect idle emissions? That's what I'm failing on






Thank you

fortysixandtwo

1. I have not heard of it being a resonator before. The replacement converter has a different internal shape/construction, so there is a possibility of the exhaust note changing. I've also never heard anyone who has installed universal replacement mention a change. Probably nothing to worry about.

2. Measurable? Yes. Practical to measure? No.

3. The smaller converter is for exhaust being bled off by the waste gate. The waste gate is closed at idle, so the condition of this smaller converter would have no impact on your idle measurements.

Dan Martinic

The owner of a well-respected custom local exhaust shop said that's what it is (he even pointed to the front 1/3 when he said "resonator", and funny thing is mine is very discoloured in that part where the rest is normal, making that front portion look as if it was different.

My understanding is that the rear 2/3 is the converter and the front part a resonator. I know the PET shows non-catalytic models having a resonator where our main converter is... so it kinda makes sense

Anyway, I'm thinking that used one is probably not going to be too far off of mine, so if I fail one more time (I'm going to try some tricks I keep hearing about like acetone in the gas tank), guess I might go for a 'cut & weld' --without a resonator I suppose

Up here in Ontario Canada the test is only HC & CO, 2500rpm & idle.

I'm passing 2500rpm pretty easy:
HC 59 (limit 200)
CO .59 (limit 1)

But idle is a different story:
HC 170
CO 1.74
(same limits)

Above is *after* a new O2 sensor. Engine pulls 16.5" vacuum at idle and runs very well after some recent maintenance work (new AOS seals, cleaned injectors, new ICV, vacuum hoses, spark plugs, more..)

I've never touched the CO setting on the AFM; I pulled out the CO tube anyway, and have been told never to open that and mess with it!

Tom M'Guinn

Sounds like you might be just running rich at idle. If you don't have to worry about NOx, then you should be able to get it to pass without a new cat. (HC, CO and NOx are like a three-seat seesaw, where reducing any two tends to drive up the third, absent a good cat to reduce them all -- so you're lucky you can just focus on HC and CO.)

I'd want to get to the root cause, but to pass the test, you might try setting the FQS to 6 (less fuel, less timing); reset the base idle per the FSM; change the oil in case its contaminated with unburned gas; replace cap/rotor/plugs/wires; and add a little E85 to the mix.

I don't know about a resonator, but it does "seem" to me like the factory cat quiets the car more than aftermarket replacements, though maybe that's just the psychological impact of wrestling such a heavy pipe into place compared to the feather light (and cheap) aftermarket units.

Dan Martinic

I'm not sure I'd call it "lucky", but given what I've been reading about California tests, this does seem a lot lighter!

The tech doesn't open the hood or even look underneath; he just sticks the probe into the tailpipe, sits in the car, and alternates revving it to 2500rpm and idle.

I have about 1 month to go until I can get pulled over without a sticker... so... I will continue hunting for the root cause (next up: check coolant sensor) but if I don't find one, you bet I will try all the tricks--including your suggestions.

Thanks!

PS.. what do you know about putting acetone in the gas? A *lot* of people have been telling me this! No Rennlisters though.. so.. it's suspect ha ha

PEvans

^^ What Tom said. If CO is expressed as a percent I have never had CO that high (over 1.00%), with good cats and bad cats, going back to the mid 1990s.

For what it is worth the cat on my car now is a used OEM cat that has passed the NOx test on a dyno here twice. So the chance that yours has some life left is not zero.

Laust Pedersen

Here in CA during the static test (no NOx data) the smog tech sets the engine to 2500 rpm (with an adjustable stick to the pedal), then let the computer sample for maybe 30 sec, after which it asks to go to idle, which the tech then sets (removing the stick) and let the computer sample for another maybe 30 seconds.
I don't know how the data are processed (average, worst case peak, data pruning or ?).

BUT, it is important that there is no "fiddling" with the accelerator pedal during the sampling, as it will actuate dynamic parameters such as acceleration enrichment, etc.

Laust

Tom M'Guinn

Two More Years! Two More Years! Happy to say I passed again with great numbers, posted below. Since I'm paranoid, I did a full tune-up first (cap, rotor, wires, BPR6ES at .28", wires, O2 sensor, oil, bone stock engine management, reset idle). Since I'm overly paranoid, I also bought yet another DEC cat as listed above and can report they have revised it again, making it an even better fit. Instead of a long tube running from the wastegate and dumping behind the cat, they now have a very short elbow that dumps the wastegate exhaust in front of the cat. With the prior version, exhaust from the wastegate never went through a cat, so this must help from an emissions standpoint (though not necessarily on the smog test) but also makes the pipe lighter and fit like a glove. Probably more back pressure at WOT though.

I got a particularly picky smog tech this time, who was convinced the DEC cat was not CARB certified (exactly why I'm so paranoid I guess). It had the correct EO # of 193-117 on the side. However, it also had a mfg. product ID on it of 332304 stamped on it. For OBDII cars, the product ID needs to match the car as listed on the state's website. 332304 does not appear on the state's database for the 944 turbo, so the tech wanted to fail me. DEC came to the rescue, however, and pointed me to the state's "ET BLAST # 27984 " which makes clear that for pre-OBDII cars like the 944 turbo, the product ID does not need to match and all that is required is for a valid OE # to appear on the cat (in this case 193-117). If you use this cat and are as paranoid as I am, it might be worth bringing a copy of that notice with you to the smog place (link below). I don't know if the tech was truly unaware of the rule or if he was up to something, but either way wanted to alert the masses so you can be better prepared than I was.

Here is the notice:
https://www.bar.ca.gov/PubWebQuery/E...ssageKey=27984



Very good numbers, but would have been even better had the cat not sat for an hour while we sorted out the catalytic converter "issue" (or lack thereof).


p.s., if anyone local is interested in my 2016 dec cat, I'd be willing to part with it. Chances are it would work just fine and/or could be modified to slip in a new cat when needed. I welded a wideband port in it, but can provide a plug if needed.

V2Rocket

fantastic numbers Tom.

again...whoda thought if you make it look and run like STOCK...it'll pass no problem

Dan Martinic

Dan Martinic

PEvans

Well, I got two 2-year cycles out of the used OEM cat I have been running, but no more. It looks like the DEC cats are still available on Amazon. Is that the preferred source?