Need Help Please! PC0420 Caused by Head Gasket Failure

[Clem8fan]

Here's the deal, 2000 STS, I was going to take it to Lindsay but due to logistics I decided to take it to Moore (closer to my work). I had a PC0420 LCE code and figured it was catiyltic converter or something similar, I just spoke to the service adviser and am awaiting the official estimate, but she indicated it was due to head gaskets leaking and fouling the converter. I've read up on the head gasket issue but I haven't seen a corolation to the PC0420 code before. Any advice???

[derone]

Not sure about the correlation between leaking head gaskets and the low efficiency cat error 420. Mine got the 420 error shortly after I bought it with 68k on the clock. Grandma most have been driving it...I did a WOT during the test drive and fogged about 1/8mile of highway. After that, no smoke but a 420 error, a couple of hundred miles later. I figured the factory cat was plugged or fouled as a result of that little test. I've got ~30k miles on the Magnaflow aftermarket CA OBD2 cat(46006) with no issues or codes.

[Ranger]

Any other symptoms? Using coolant or overheating? If not, go see Bill (ewill3rd) at Lindsay for a second opinion.

[Clem8fan]

No excessive oil loss, radiator was recently replaced but not due to overheating, small leak at the upper hose inlet. I guess it could have gotten hot but the temp gauge never passed one mark beyond 12:00. It drives good, no smoke, this just blows my mind! I've messaged ewill3rd for his opinion and will probably be taking it to him early next week. The dealer told me, in their words, to "scrap the car and start over". Never been told that at a dealer or any shop before, I didn't really know what to say.

[Ranger]

Originally Posted by Clem8fan

No excessive oil loss, radiator was recently replaced but not due to overheating, small leak at the upper hose inlet. I guess it could have gotten hot but the temp gauge never passed one mark beyond 12:00. It drives good, no smoke, this just blows my mind! I've messaged ewill3rd for his opinion and will probably be taking it to him early next week. The dealer told me, in their words, to "scrap the car and start over". Never been told that at a dealer or any shop before, I didn't really know what to say.

And I'll bet they just happened to have a perfect replacement for you. I smell a rat. Please be sure to follow up and let us know what Bill finds.

[submariner409]

Clem8fan, Aside from our private conversations, have you taken the car out on the Beltway or Rt.66 and run it ? I mean drive it like you stole it. Read the WOT procedure up in Cadillac Technical Archive in the black bar ^^^. Get a 20 oz. jug of Chevron TECHRON and dump it in and fill the tank with Shell or Texaco 93. Go out on the road and do a few rolling starts: with the stick in 2 and put your foot through the firewall - let the engine go to redline in 1 where it will shift to 2. Just before 2 redline flip your foot off the gas and let the engine pull the car down to 20 or 30. Slow a bit more and do it again.

My guess is that there will be a fearsome amount of black crap out the tailpipe the first time, less and less after 3 or 4. (You won't break anything - the engine and transmission will not let you hurt therm; miss the slowdown at 2 redline and the transmission will shift happily to 3.) Watch the temp gauge. I doubt you will see it more than 1/8" past the 12:00 line. After all this you might find that the P0420 goes to History, and you had/have no SES light, do you ?

[Clem8fan]

Sub,

I haven't done the WOT procedure, however I have used the Techron for usual and daily driving (one jug about 1500 miles ago). I've definitely gotten it way up to speed and driven it hard but not in the actual manner described in the procedure. One thing I did learn is that the HC reading of 150 was in the coolant resivoir at idle, I was told that they stuck the sniffer in the tank and took a reading so maybe I am looking at heads. I dropped it off at Lindsay this morning and talked with Bill (ewill3rd) for a while about it. He is going to give it a look over and see what he thinks. I've also talked to Jake (97EldoCoupe) about his services and am awaiting a response about turnaround time, etc. I'm finding that I'm pretty hell bent on fixing this car, I can't see getting rid of it, at least not yet. If I have to take it or ship it to him in Canada than so be it, the rough pricing he has mentioned is far less than anything I've been quoted yet. I'll keep you posted and update the thread once I know more. Thanks for your help and all who have responded as well.

Jeremy (Clem8fan)

[the recluse]

Sub, when I replaced my plenum, I cleaned the intake manifold, the intake runners, the throttle body, and valves with carb/TB cleaner. Blew white smoke for 4 minutes straight. 3 days later came up with the P420 code.

Do you think the WOT procedure will help with this issue? The car has 94k on it. Any thoughts?

[Ranger]

Blew white smoke for 4 minutes straight. 3 days later came up with the P420 code.

How much of that stuff did you use? You probably killed the CAT.

[the recluse]

Originally Posted by Ranger

How much of that stuff did you use? You probably killed the CAT.

About a can. I cleaned EVERYTHING.

[submariner409]

Most CF Northstar owners and GM caution about trying to clean (all the passages in) the intake manifold because of the distinct possibility of leaving significant amounts of the cleaning agent pooled in the manifold. Yes, the manifold is a true mess on a high mileage car due to PCV vapor, but that's a fact of life in any PCV equipped engine, BUT more pronounced in a Northstar due to the location of the manifold vacuum fitting. The oily mess harms nothing. Ranger is correct: You may well have smoked the cat from foreign solvent intrusion, which is one reason I never like dumping undiluted (with gasoline) snake oils into the intake tract. You're probably very lucky that, when cleaning the ports and valves, you didn't get enough solvent into the cylinders to take out one or more sets of piston rings.

Why does the throttlebody get so filthy when it's not in the PCV vapor stream ?? Because the fresh air feed to the front cam cover comes off the throttlebody ahead of the butterfly. Normally, fresh filtered air flows into the front cam cover, down to the crankcase and chaincase, then up into the rear cam cover and out the PCV valve which is piped to the vacuum in the intake manifold. The engine burns all the nasties which the flowing air picks up. BUT under high load conditions manifold vacuum drops and blowby increases, so the airflow in the fresh air intake line reverses and you get vapor being sucked into the throttlebody area = oily buildup.

[the recluse]

What do you think of this stuff?

http://www.seafoamsales.com/motor-treatment/index.html

I didn't use this on the car this time, but it looks interesting...

[Ranger]

More unnecessary snake oil. Just clean the TB once a year and forget the manifold.

[submariner409]

Take a good flashlight and look long and hard down in the oil fill hole: you're looking into the chaincase. Nice and clean, isn't it ?

If your 2002 Northstar, running detergent oils and gasolines, is so filthy inside either the crankcase or combustion chambers that it takes flushing or burning solvents to clean it, then you have far, far greater problems than the common hype of "sludge".

Regular maintenance, including oil/filter changes and cleaning of intake ducting and filters, is all you need for an engine to live a long, happy life.

I'm on record in CF as being opposed to magic potions and quack gimmicks, and do not intend to change my position. I've built and blown up too many engines, wrecked too many cars, and drained enough oil that I have a fairly pragmatic outlook on aftermarket potions. I have spent a bloody fortune on snake oil: Hope springs eternal. But, it still doesn't work.

[the recluse]

I like you SUB, you say it like it is...