Interesting (textbook I guess) effects of a bad O2 sensor

Hi All,

I thought I would post the output of my OTC Monitor 4000E with the Pathfinder 97 cartridge, along with some comments, since it's such a textbook case of a bad O2 sensor. This is from my 1995 Chrysler Town & Country minivan with 3.8L engine. The '95 T&C is a pre-OBD-II vehicle, so I have to use a scantool that is designed for it. The scantool cartridge I have is the last cartridge year that OTC made that will work in the Monitor 4000E The 95 T&C has 2 vehicle diagnostic ports, one in the engine bay and one under the dash, the one in the engine bay talks to the engine computer, the one under the dash talks to the transmission computer. I have the adapters for both ports.

As part of the registration renewal here you have to go through emissions inspection. I first ran my van though 12/31/08 and it failed with an idle reading of:

HC 519ppm CO 9.2721% CO2 was at 8.5%

There was no check engine light visible.

I then waited for a weekend that wasn't snowing or raining and replaced the spark plugs and spark plug wires - the old plugs had worn to a gap that was almost double the factory spec and the plug wires were the original wires - and when you take the time to do plugs in that vehicle, (the back ones are not easy to get to, I put the car up on jackstands and used a creeper to get at the plugs from the bottom) you might as well do the wires. I replaced the plugs with Autolite Platinum that I bought from Walmart (yes, believe it or not they carried them)

I then took the van back through emissions on 1/24 and it failed with an idle reading of:

HC 477ppm CO 10.1685% CO2 7.9%

Ok, so now the easy/cheap/quick fixes were done it was time to break out the scantool and do some real diagnostics.

I warmed up the van and first pulled for any stored code and came up with code 51 which is a fuel/air mixture out of range problem. I then ran a printout of parameters from the scantool and got this( it looks best in a non-proportional font):

CHRYSLER 1995 3.3/3.8L SFI ----- REVIEW CODES ----- >> ENGINE CODES > ENGINE CODES

Reply to
Ted Mittelstaedt
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Not that ignition repairs weren't needed, but with CO at 9%, you're looking at a rich condition. As you found out, ignition repairs won't fix that. *Generally*, high CO indicates a mixture problem. High HC would indicate ignition problems. You have both high HC and CO. Here, the excess fuel that's not being burned is causing the high HC.

The low CO2 number indicates poor combustion, and the cat not working. The cat not working would be expected with a mixture that rich. To be efficient at oxidation process, a cat needs a near stoichiometric mixture (14.7:1). Your numbers are nowhere near that.

My experience has been that a cat converter is more likely to survive a rich condition than a lean or misfire condition.

Reply to
bllsht

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