So I've had this car for a few years now. The car was totally gone through during the first six months, complete tune up, PCV system, timing belt, fluids, hoses, etc. It has had codes for the O2 sensors on and off the entire time despite changing both of them several times with the recommended OEM versions. There have been periods of time where the CEL is not illuminated but it is mostly on. Changing the front O2 got the car through emissions one time, on the next test, I had to replace the CAT for it to pass. At one point, I noticed there was like a small dongle plug between the O2 sensor and the harness that was about 4 or 5 inches long, almost like an extension but that didn't make sense. I removed this and it seemed to run without the light for awhile then it came back on. I also tried to check pretty carefully for vacuum leaks several times and haven't come up with anything. I've kinda been lackadaisical about tracking down the cause of this issue but am determined to get it sorted out as the gas mileage is pretty terrible.



With the CEL on, the current trouble code is P0130 - O2 Circuit Bank 1 - Sensor 1 Circuit Malfunction with the following freeze frame data:


Calc Load - 31.0%
ECT - 183
STFT - 0.0
LTFT - -1.6
RPM - 2000
Speed - 55
Fuel sys 1 - OL
Fuel sys 2 - NA


Anyone have any ideas what might be amiss here? Thanks.

 

 

Wow, interesting. Do you have any pics of it? What's an average acceptable compression reading on these motors with over 120k?

 

 

 

turbos should test to around 150-160 PSI, NAs to 170-180. you should do both a dry and wet compression test on a warm engine. How do the plugs look?

 

Lol, that's a few miles for sure.

 

When I changed them awhile back they were unremarkable but I will check them again to see the current condition. Wet compression check...a few squirts of oil in each cylinder?

 

 

If you had a burned exhaust valve you would get a misfire code or some noticeable miss during idle.

 

 

I finally got around to this tonight. Here is a pic of the plugs:



Plugs 1-5

I also did the compression check:
Cyl 1 -185
Cyl 2 -180
Cyl 3 -182
Cyl 4 -182
Cyl 5 -175

Thoughts?

 

 

I went back and reread your original post and noted you reported a P0130 code - that is a fuel trim code that normally points to the front O2 sensor. That would definitely account for the loss of power and mileage but your plug #3 looks fouled - I'd consider doing the plugs/wires/cap/rotor as a tune up but wouldn't be surprised if you also need a new O2 sensor.

 

I think that middle plug got oil on the tip from some drip-down when I removed it. There was oil in that valley area and some in the plug holes when I took the cover off which re-appears there after I clean it up every so often. Changing PCV system didn't fix this problem.



Also, the front O2 has been changed at least twice (once in conjunction with the rear) with the recommended Bosch sensors but it doesn't fix the issue.

 

O2 sensor codes can also be set due to intake air leaks. did you try cleaning the MAF and IAC and inspecting boots/vacuum lines? As to the plugs - the tip shouldn't get wet from a leak on the top side (and you should check for a clogged PCV - the ports in the block should also be rodded out when done or you can still have a clog). Take a look at the date codes on the wires. if they are over 5 years do a "stage 0" tune to baseline the ignition. I'd also suggest a can of Techron in the tank to see if that can clean up the injectors a bit or run the next two tankfuls on 93 octane (unless you already run premium gas which has extra detergents).

 

I will try cleaning the MAF and IAC and re-inspect the vacuum lines. I believe the plug tip get wet by the oil dripping down the spark plug when I unscrewed it. I had to wipe the threads of all of them off after removing because there was varying amounts of oil in each spark plug hole that dripped down on the plugs as I was taking them out. It is probably getting close to 5 years/30k miles since I replaced everything (stage 0) when I got the car. The PCV system was also changed at this time though it did not stop the smoke out of the dipstick or the oil in that cover valley on top of the engine. Maybe there is an issue with the vacuum system/T.

 

 

do a glove test to see if you have positive crankcase pressure. If the shop that did the PCV system refresh didn't rod out the ports, you may still have a clogged PCV (which can push oil under the valve cover)