jeffcoslacker wrote in news: snipped-for-privacy@no-mx.nodomain.com:
ok then, explain how they ever did it. They have had O2 sensors since before FI and were using air pumps then too, and not just to blow into the cat as some now do. (not an answer just a question) I am going to recheck some newer ones to see about the air pump and head air injection thing to be sure. KB
The Russian cars of the 80s had cats?
Early O2 sensor systems used air pumped into the forward portion of the cat, that and the O2 sensor resided upstream of that point, so it was monitoring pre-air injection gases. As soon as pre and post cat sensor setups and full closed loop became the rule, air injection had to be abandoned...not neccessary with the fine control of mixture that dual sensors and faster processing offered...
some real early ones had an O2 sensor right up next to the engine in the manifold, with air injected slightly downstream, those manifolds has a big "plenum" shape to them...the sensor still monitored mixture ahead of the incoming air...
Carbed engines with O2 sensors were very crude feedback systems, made to try to maintain an "overall" quality of mixture, rather than moment by moment control...
That would render the NOx bed inoperative.
Mid 90s GM OBD2 systems used an electric air pump that pumped into the exhaust manifolds. An example would be a 1996 Pontiac Grand Prix with a 3400 engine. Worked on a late 90s Audi a while back that had a secondary electric air pump also.
The original GM feedback system introduced in 1980 was called CCCC (Computer Controlled Catalytic Convertor) it controlled whether the air pump switched upstream to the manifolds, downstream to the cat or dumped to atmosphere. The CCCC moniker was changed in
1981 to CCC Computer Command Control, it was a bit more refined, a bit more powerful but still controlled whether the air pump switched upstream, downstream or atmospheric. On cold start open loop, it's no special trick to pump air into an exhaust manifold, on warm engine closed loop, it's no special trick to pump air downstream to an oxidizing bed of a catalytic convertor or to atmosphere, or in the case of an electric air pump, simply shut it off.
A 1996 Pontiac would still be OBD I...
These I never had to have any real reason to understand, was not doing emissions control work when they were still rolling in numbers, so thanks for that, it was interesting.
hey, tell me more about this system, please. Apperas I have a huge hole in my knowlege (apologies to any I led to believe they were wrong)...never run across trouble with it, but I did a little looking and it seems it's a quite common issue on some S Model GM trucks...
Wasn't OBDII government-mandated for all cars beginning in 1996?
Right you are...started in late 1995, all 1996 were OBDII, trucks all by 1997, which is what I was thinking of...
Musta smoked too much crack today:rofl:
Ever heard of "upstream sensor" and "downstream sensor?"
Well, yeah, by definition, a two way cat wouldn't be reducing NOx. Bulldozers don't float either. Define "early." You claim having a smog license since 1991.
It most certainly would not. Hell there were 'pull ahead' 94s and 95s that were OBD2.
Glad to help.
You misread everything I post, and then throw it back at me without comprehension as if you are making a point, when you are saying exactly what I just said....What did you think I meant by multiple sensors?
Yup, although there were some exemptions.
I know there were some that didn't fully incoporarte all the OBDII equipment but could be scanned as OBDII, they were called OBD 1.5 or something like that, never ran across one *with a reason for me to note that aspect of it anyway)
I meant real early. Back in the dark ages. Smog pumps. 2 way cats. Big block motors that couldn't pass a 1.5L Toyota Tercel with a rolling start...when did diagnostic connectors and check engine lights start showing up on everything, about 1981? That's the age I'm talking.
In 198O and later, there certainly was a preponderance of three way NOx reducing cats. That was the whole point of having the PCM control where the air pump introduced the O2 (either upstream into the exhaust manifold or downstream into the second bed of the cat). On cold start with a rich mixture, there isn't much NOx production but there is excess CO and HC, so the air pump pumped O2 into the exhaust manifolds to aid oxidization of CO and HC before it could overload the cat. On warm running with the PCM in closed loop, the air pump was switched to downstream where it pumped O2 to the rear oxidizing bed for final clean up of CO and HC, the NOx reducing bed was forward located in the cat ahead of the air pump inlet because O2 hinders the reduction of NOx. At some point into closed loop, the air pump -might- have been switched to dump to atmosphere if the NOx bed was reducing sufficiently to supply the rear oxidizing bed with the O2 it needed to work properly. Nowdays, with really efficient NOx reduction, there is enough O2 split off of the NOx molecules to feed the rear oxidizing bed the O2 supply that it needs, thus making air pumps somewhat less necessary but not totally extinct.
My bad- I missed the "before sensing" clause. Indeed the whole point of multiple O2 sensors is to have at least one of them always able to sense the raw O2 content of the exhaust coming out of the engine before its either corrupted by the reduction catalyst or by air injection. The downstream sensor measures how well everything works as a system, and enables OBD-II level diagnostics. IOW, the upstream sensor controls the fuel trim, the downstream sensor tells if the emission controls are working. But the whole point is that, even today, air injection is still used to make the oxidation catalyst perform better. LESS air is used, and the big belt-driven air pump is indeed almost (if not) extinct. But air injection lives on.
But getting back to the ORIGINAL post- I still say that a glowing exhaust is most likely the result of a misfiring cylinder (or several) since that is the process that dumps ready-to-burn air/fuel mix into the exhaust stream.
It could be...I just figured that most people would notice something strange and the post would be like "My car has been running like crap and now..." or "I've been getting terrible gas mileage, and now my manifold is glowing..."...but perhaps I assume too much...
Anyways, you got me on that secondary injection...wasn't part of my understanding of the system, and I apologize for doubting you.
silicon212 wrote in news: snipped-for-privacy@no-mx.nodomain.com:
In Canada they did after a certain point.
Until they fell off, anyway. Like everything else on the Lada.
--scott
So very likely the exhaust system or at least the converter(s) are already damaged. Excessive fuel from cyl miss-fire; most likely multiple miss-fire is the likely cause. Rising combustion temps will increase exhaust temp. Excessive exhaust temp that hinders combustion will in most cases lower combustion temp.
My 86 Jeep CJ7 didn't come with a cat, the 87's did though.
Maybe that's the cut off year?
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.