Piston Slap: The Quandary of The "Orient Panther"

Frank in Boston writes:

Sajeev,

I am the original owner and caretaker of a beloved 1995 Acura Integra LS. The car has only 68K pampered miles with all maintenance done based on “time-out” rather than mileage. It lives on a steady diet of E-10 Mobil regular dispensed in and around greater Boston. It is my ‘Orient Panther’ and ran like the proverbial Swiss watch until…

My problem began when an old glass-pack ANSA muffler imploded from years of internal rusting. The glass collapsed while driving and the subsequent back-pressure forced oil into two spark plug tubes through the gaskets, and shorted them out. The unburnt fuel from the 2 dead cylinders passed through to the exhaust where it cooked the cat in short order.

We towed the car to a local muffler place where everything from the stock header flange back was replaced. When we got the car back, it got new plugs, plug wires, fuel and air filter, PCV valve, valve adjustment, oil and filter. There were no unexpected findings with the “tune-up”, except the engine oil that was inside the #1 and #2 spark plug hole. Back to running like a watch after the work, except the odor from the exhaust was that of partially burnt acetone.

We drove it for about 10 days after the exhaust repair when I noticed a rattle from underneath. Close inspection revealed that the new cat’s core had broken loose inside the can-it was fried. At this point we had a “test pipe” installed in place of the cat, and I set about replacing the single O2 sensor.

Of course, the god-awful smell is worse (even after complete warm up), without the cat eating some of those unburnt hydrocarbons. I should say that the oil and coolant were and are clear, with no evidence of mixing. It starts with one turn, smoothly idles and revs all the way to the redline without missing or skipping. I think I can rule out a head gasket issue, or burnt valves. No unusual sounds, white or blue smoke under any conditions. No oil or coolant disappearing. Gas mileage is slightly down, but still in the mid to upper 20’s. I have not gone so far as to test Lambda, but I’ve never had a CEL and yes the light works. When stopped, if the right breeze pushes the exhaust towards the front of the car, it gets sucked in through the vents, and my eyes water from the smell.

So, am I missing something? Do I live with the burnt oxygenated E-10 winter-blend smell? Do I replace the cat morally, practically? If it is running rich, how do you adjust the fuel delivery on an OBD car? Thank you for any advice you have.

Sajeev answers:

That’s an excellent analysis. Honestly (and completely off topic) if we had more vocal politicians with your grasp of the situation and your ability to analyze a problem from multiple perspectives, we be a happier, healthier nation.

Odds are winter fuel isn’t a problem; it’s a necessary evil and nothing more. I looked into why catalytic converters fail and perhaps you drove over a snow bank, causing thermal shock to the honeycomb inside? Which is kinda fun: one of my college roommates used snow banks as parking “stops” around Metro Detroit one winter. Gave us all the giggles except the one time Audi 4000 Quattro in question couldn’t dig itself out. Then we stopped that stupid little game. But I digress…

I’d Seafoam this “Orient Panther.” Why? The rusty muffler forced oil into places it’s not supposed to go, so perhaps you have even more misplaced oil. Seafoam (fed via PCV) line will clean out any carbon/oil/crud in the PCV and intake system. Your neighbors will not appreciate the smoke signals so be careful where you do the dirty deed. On the plus side, if you see no smoke, you have no carbon!

Let’s say there’s no smoke, and the problem remains. Since the motor is running like a top and you changed the Lambda (Oxygen Sensor to most folks) I’d suggest a close look at your EGR/PCV systems and every vacuum line under the hood. Sometimes a bad PCV valve and associated rubber lines can cause a lean condition, but maybe the opposite is also true. And at this age, replacing (cracked, brittle or gooey) vacuum lines is never a bad idea.

I must admit, I’m drawing at straws with this diagnosis, it’s a tough one. But fear not, no matter how badly I screwed this up, we have the B&B to fix it!

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.