4.3L V6 emissions (second try)

It seems like my question deteriorated into a bunch of personal attacks and advice that the engine was trashed. I rather doubt the engine went from running well to having a nasty case of blow by during the last ten
percent of it's use. The engine has been maintained with regular oil and filter changes with mobile one. So, I'd like to ask again in hopes
of getting some more helpful answers. This time I have the data to post.
The car has 226,000 miles or so.
At around 19x,000 miles the car got a new catalytic converter becuase the old one plugged up and the car's performance dropped dramatically and suddenly. We had this around 160,000 miles on an '86 thunderbird so
this seems par for things. BTW, the Thunderbird went 245,000 miles before it was driven to be donated away, and was running strong. Mobile
One is good stuff...
At 205,000 miles in fall 1998 the data was:
HC 0.26 state limit 2.00 CO 2.2 state limit 30 NOx .5 state limit 3.0
At around 220,000 miles in fall 2000 the car failed. I had a new O2 sensor installed, new plugs, pcv valve, air filter and retested. The car passed but it is clear from the readings that something was deteriorating.
HC .7332 state limit 1.80 CO 19.38 state limit 19.38 NOx 1.16 state limit 2.8
At 226,000 miles it failed emissions under a different test last month:
15 MPH
HC 105 state limit 108 CO .062 state limit .61 NOx 1389 state limit 823 *fail
25MHP
HC 137 state limit 105 *fail CO .12 state limit .64 NOx 1457 state limit 750 *fail
I've read that high NOx is caused by catalyst failure or EGR circuit failure. I also read that the 4.3L engine (comments I read are about the GMC Jimmy, so probably most versions) has issues with the EGR valve and possiblly the EGR passage in the intake plugging up. So, I'm thinking the EGR system is the most likely suspect.
On the GMC Jimmy, I read that there is a new engine computer prom that opens the EGR wide open periodically to keep it clear. Is there such a prom available on the '86 model year for chevy/pontiac or was this specific to the Jimmy later on?
Does anyone agree that the EGR circuit is the issue, or should I be looking elsewhere? The check engine lamp used to come on after an hour of freeway driving before the new O2 sensor was replaced. It used to ping slightly under light load and high speed, also suggesting an EGR problem or a carbon build up in the cylinders.
I'd like to hear opinons and experiences concerning the use of Sea Foam cleaner or Mopar combustion chamber cleaner for cleaning out the carbon
deposits.
I'd like to know if the EGR passages in the intake can be properly cleaned without removing and replacing the manifold.
I'd be very interested in peoples advice who have experience specific to
this engine. Generalities such as flush the oil with kerosene don't help much. I've already got a Dodge 225 /six that burns a quart per 500
miles after I used that commercial "engine flush" product years ago. It's bad stuff.
Thanks all, and lets not attach the trolls. ;-)
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I can't help with specifics, but from basics -- EGR is utilized to lower combustion chamber temperature in order to control the production of oxides of nitrogen (NOx). Given that the NOx reading seems SO high, and your earlier research on the weakness with the 4.3, I think you are correct in pursuing that as the most likely culprit.
I'm told that EGR failure will also lead to troubles with mixture control that may be more than can be dealt with by the O2 feedback, so it might also explain the elevated HC readings. If that has been the case, it is also possible that your catalyst has been 'muddied' making it less effective too. Unfortunately, I don't think you can completely rule out something like a broken piston ring, though I would think you'd have other symptoms in that case.
Wish I could help more, hopefully you'll get specific assistance this time, it IS out there.
Sorry your request got ploughed under by the trolls, I know how that feels.

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I suggest retarding the timing, popping in some Platinum plugs, and replacing the oil with SAE50, or if you're not into that, some diesel 15W40. Also put in a new air filter. Generally, with all engines there are 3 main components to worry about: spark, fuel, and air. Make sure that the car is getting all three without any restrictions and you'll pass an emissions test, as long at your cat is functioning alright.
The reason for the heavier oil is that if your rings are beginning to wear down, it'll stop further wear by providing a "curtain" that prevents metal to metal contact despite the increase in play. It also won't seep into the combustion chamber quite so easily.

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I have a 4.3L truck. I had many problems with this engine (abused by previous owner), some of the problems I found were: PVC port was plugged, as well as gunk in the TPS area. Remove the throttle body, & remove the TPS. You will now have access to clean out all ports. I use laquer thinner to clean all parts, then use compressed air for blow-out.
Good-luck.

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