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2002 STS stock
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18 Posts
Discussion Starter #1
Hi, folks. My very first thread here, and it sounds like a recipe for disaster!

The '02 STS has been throwing a consistent P0300, sometimes a P0307, and the monitors have not been able to complete so that I can get it smogged (Calif).

Did a compression test today, to help isolate a pretty steady miss on 7, and found 130-160 on all cylinders except 7, which was 65 at best. I have not yet done anything to try to isolate further.

Coolant is staying steady, no bubbling or exhaust gases smelled.

Unknown oil consumption rate.

I want to squirt some oil into the cylinder to check for ring leakage, but don't have an oil can, or even a straw, yet.

I was thinking of pulling the cam cover, to have a look at the followers and valve springs, but I don't know if it would be worth the effort. I am not familiar with the N* valve train at all, so any input would be greatly appreciated.
 

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2002 STS stock
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18 Posts
Discussion Starter #2
Update: Did a quick top engine clean (so they claim) with Seafoam (about 8 oz.), but let it soak for ~9 hours between shutting it off and then restarting and driving it. Didn't get much smoke at all, just wisps for a minute. There hasn't been any change in its operation: still idles rough, throws the 0307 code, but runs like a champ at higher RPMs (can't detect the miss above about 2000). So, assuming the cleaning was kinda effective, I had been hoping for maybe some varnish or a chunk of carbon that was interfering with valve seating. I quite probably will repeat the cleaning, but without the very long soak time.

In the meantime, I want to add the remaining Seafoam to the crankcase, and run it for a few hundred miles, hoping that will free up any sticking rings or lifters that might be on #7. And I just changed the oil, and I'll have to do it again after this, so that's probably the best oil change interval the car's had in a while (the oil I drained out was pretty black).

Before I got a cheap scantool setup that would work, the Info Center thing would only tell me P0300 was current, and wasn't cylinder-specific. So I have been following along with a post by ParkerT98 (Impossible misfire to solve), and have put into that thread the actions I've done to get to this stage. Please review the last couple of pages of that post, if you have an interest.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Study this - written by a CF member who was a GM/Cadillac Northstar Systems powertrain engineer. The part titled "Occasional full throttle operation is good ..."


............regardless, I don't like the 65 psi compression in #7.
 

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2002 STS stock
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Discussion Starter #4
Lots of good info in those threads you directed me to. I'd already known about it, and have read a number of them, but didn't read the WOT one in depth...until now. That shouldn't be a problem for a couple of ex-cabbies!! I've had the heads off a number of Ford 4.6s (CVPIs), and can say that those cast iron blocks still had a good cross-hatching even after 200,000 or 300,000 blocks. Most of those failing engines were due to severely warped/cracked heads, which sometimes took out the main and rod bearings due to water intrusion. And the timing setup, which more than a few times have jumped time and bent numerous valves in those interference engines. The blocks and MLS head gaskets were bulletproof...never had one fail on me.

So, having said that, the plan is to try to free up any possibly sticking rings and/or valves. Failing that, I'll take a month to drop the engine, disassemble/check the heads, stud the block, and probably pull the pistons to have a look-see. Might as well, while I'm that deep into aluminum...:). I'm impressed by the current power of the engine, being used to CV Police Interceptors (they don't call them Whales for nothing!!). The N* has them beat by 75hp...
 
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