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
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
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:
HC 105 state limit 108
CO .062 state limit .61
NOx 1389 state limit 823 *fail
HC 137 state limit 105 *fail
CO .12 state limit .64
NOx 1457 state limit 750 *
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
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. ;-)