New car acting up already

turp23 · Jan 28, 2012

I just bought a 2ooo GT. I test drove it and put it through the paces, including let it idle for 20+ minutes. When I went back the next day to get it, it started to miss about a mile from home. I washed it, and cranked it up to find it was misfiring at idle. You can hear it in the exhaust. I let it sit for a day, and it still misses at idle and acceleration. Its throwing codes PO156 and PO161. It does have an off road h-pipe, with one of the O2 sensors completely missing. The harness is hanging under the car. Can a missing O2 sensor cause the engine to backfire like that? How do I fix it?

trombonedemon · Jan 28, 2012

The o2 (oxygen) sensors measure oxygen content in the exhaust. The PCM (powertrain control module) then uses this information to regulate fuel injector pulse. The o2 sensors are very important for the proper operation of the engine. Innacurate or faulty o2 sensors can cause the PCM to add or take away fuel based on the faulty o2 sensor voltage which can cause a host of problems.
A P0156 code refers to the Bank 2,2 o2 sensor or the downstream (post-cat) o2 sensor on Bank 2. It is a four wire sensor. The PCM supplies a ground circuit and a reference voltage circuit of about 0.5 volts. Also for the o2 sensor heater element there is a battery voltage supply wire and another ground circuit for that. The o2 sensor heater allows the o2 sensor to warm up faster, thus achieving closed loop in less time than it would normally take for the exhaust to warm the sensor up to operating temperature. The O2 sensor varies the supplied reference voltage based on oxygen content in the exhaust. It is

capable

of varying from about 0.1 to 0.9 volts, 0.1 V indicating lean exhaust and 0.9 V indicating rich exhaust. This P0156 code indicates that the Bank 2, 2 o2 sensor is stuck low for too long or isn\'t active at all.

Symptoms

Often post-cat o2 sensor problems present few symptoms since they are inputs to the PCM to monitor catalytic converter

quality

and don\'t directly control fuel. sometimes no symptoms are noticeable. However the following may be possible on some

vehicles

:

MIL (Malfunction Indicator Lamp) illumination
Decrease in
MPG
Increase in tailpipe emissions

Causes

Potential causes of an P0156 code include:

Bad O2 sensor
Signal shorted to voltage
Wiring problems due to contact with exhaust components
Holes in exhaust near o2 sensor

Possible Solutions

If you have access to a scan tool, check the signal voltage for the Bank 2,2 oxygen sensor with the engine at normal operating temperature. Is it stuck low currently? If so, increase RPM for a few seconds and see if it affects the reading. If it begins working with increased RPM, check for holes in the exhaust near the o2 sensor that may cause a false lean. If the exhaust pipe is intact, the sensor is sluggish, replace it.
If the Bank 2,2 o2 sensor voltage reading remains low with increased RPM, unplug it and then observe the reading. It should have increased to about 0.5 volts or thereabouts. If it did, check for water intrusion or other connector problems. If none are found, replace the shorted o2 sensor. If the voltage reading is still stuck low after unplugging the sensor, then suspect a wiring problem. Using a voltmeter, with the o2 sensor unplugged, check for voltage on the signal circuit at the o2 sensor connector(PCM side). It can vary with model, but should be about 0.5 volts and not above 1 volt. If the voltage reading is too high, repair short to voltage on signal circuit. If the signal voltage checks out, suspect the PCM.

trombonedemon · Jan 28, 2012

It basically means the PCM detected either an excessive current draw, or an open or short in the circuit powering the oxygen sensor's heater circuit. This is in reference to the Heated Oxygen Sensor (2) located rear of catalytic converter (Bank 2).
Symptoms

There will likely be no obvious symptoms other than MIL illumination.
Causes

A code P0161 may mean that one or more of the following has happened:

HO2S heater power circuit open
HO2S heater ground circuit open
HO2S signal tracking (due to oil or moisture in the connector)
HO2S is damaged or has failed PCM has failed

Possible Solutions

Replace HO2 Sensor
Repair open or short in power circuit
Repair open or short in ground circuit
Repair damaged connector due to tracking

turp23 · Jan 29, 2012

There is actually no O2 sensor for me to check. Just the connector. I dont think the off road H has a bung for the O2 sensor. But in a nutshell, it wouldnt make the car misfire?

turp23 · Jan 29, 2012

Correction- There are four sensors, no open bungs. The sensor to the rear, is fairly new, just not plugged in. It cannot reach the harness.

turp23 · Jan 29, 2012

Replaced the sensor with a new one with longer wire. Cleared codes, now I am getting P0300 amd a P1504. Now what?

vertigasen · Jan 29, 2012

P0300 is a random misfire and P1504 is the IAC. Check/replace/clean the IAC and go from there. Check all your vacuum lines make sure everything is routed correctly. I saw this same thing where a guy had all his connections wrong under the hood. It missed, sounded like crap, was shaking........2 minutes of rerouting the hoses worked miracles.

turp23 · Jan 31, 2012

I got it fixed. It finally threw a cyl 8 misfire so I replaced the plug and coil. I also replaced the rest of the plugs, and cleaned the springs on the coils. They had an funky slime on them. Im worried I aint done yet.

Bob Hughes · Feb 1, 2012

That funky slime is most likely di-electric grease....it aids in the electrical connection (prevents little arks from plug to coil). It should be on there

turp23 · Feb 1, 2012

Told you I wasnt done. I did clean all the springs on the coils, but I also put new grease on them. But it is missing again. But it rained, and the hood scoop leaks. PO drilled vent holes under the scoop, and I think the engine is getting wet. Can rain and washing create this much headache?

turp23 · Feb 1, 2012

Correction- There are holes under my hood scoop. It pours tons of water on my engine when I open the hood.

turp23 · Feb 1, 2012

Well, I figured it all out. It is either an aftermarket hood, or a hood from a different model stang. The holes in the hood are for the scoop to be functional. All of the holes in the honeycomb were also drilled out. Im going to need a drink.

2vNotch · Feb 1, 2012

trombonedemon said:
It basically means the PCM detected either an excessive current draw, or an open or short in the circuit powering the oxygen sensor's heater circuit. This is in reference to the Heated Oxygen Sensor (2) located rear of catalytic converter (Bank 2).
Symptoms

There will likely be no obvious symptoms other than MIL illumination.
Causes

A code P0161 may mean that one or more of the following has happened:

HO2S heater power circuit open

HO2S heater ground circuit open

HO2S signal tracking (due to oil or moisture in the connector)

HO2S is damaged or has failed PCM has failed

Possible Solutions

Replace HO2 Sensor

Repair open or short in power circuit

Repair open or short in ground circuit

Repair damaged connector due to tracking

Sooooo....i have a 2v in my 88 coupe and neither o2 sensors are hooked up....it must be runnin open loop all the time, correct? And is this affecting me performance wise....or...??

trombonedemon · Feb 1, 2012

2vNotch said:
Sooooo....i have a 2v in my 88 coupe and neither o2 sensors are hooked up....it must be runnin open loop all the time, correct? And is this affecting me performance wise....or...??

Not neccesarily, but you would be missing critical info from the 02 sensors, so its using info from temp and MAF sensor, but if you are running really rich or really lean, could be a toss up cause your ECU wouldn't know that it is running either way.

So if your gas mileage goes down and or your idle is low, you might have your answer.

P.s. I'm not big fan to turning off safety equipment on drag cars or street cars, is your car a dragging car. Might be worth getting some Cats and turning on your 02's so you can better diagnose your car.

Q: What is the difference between 'Open Loop' and 'Closed Loop'?
A: When the engine is first started, and rpm is above 400 rpm, the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen (O2) sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal.
The system will stay in 'Open Loop' until the following conditions are met:
1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.
The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.o

trombonedemon · Feb 1, 2012

turp23 said:
Well, I figured it all out. It is either an aftermarket hood, or a hood from a different model stang. The holes in the hood are for the scoop to be functional. All of the holes in the honeycomb were also drilled out. Im going to need a drink.

You might have your answers, aqua can cook the electrical components.

turp23 · Feb 2, 2012

Whats the most effective method of drying off the engine and plug tubes? Air compressor? I also bought the replacement boot set.

2vNotch · Feb 2, 2012

Air compressor will work, otherwise let er sit in the sun with the hood up! Open the distributor cap and dry that out with a rag also.....

New car acting up already

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