Long term adaptive high?

[jcaspar1]

I recently failed CA smog. Passed at the 15mph test but failed at 25 with high HC and CO, very low NO. I foolishly thought it was the cats and replaced them (Random Tech ceramics) with no change in emissions. Car runs well with no codes. Ran a scan on it today. O2 sensors cycle from .2 to .95 with reving engine, pulse on fuel injectors about 5ms each side. The one thing that seems odd is that the long term adaptive on the left bank is 10.5% and the right 0.8%. We smoked the intake and found no leaks. I retorked the intake manifold recently and we sprayed it today with no change in idle. Spark plugs look good on the left bank and are about 5k miles old.
Any suggestions what to try next? Was thinking of replacing the O2 sensors just to see. Seems it is running rich.

Thanks
Jeff

97 GTS, Random Tech Cats, Corsa exhaust, smooth tubes.

 

[speedracervr4]

When was the last time they were replaced? It's good (pretty cheap) preventative mantinance to change them every three years or so.

 

[Stonep185]

When replacing the o2 sensors do you replace all of them? Upstream and downstream?

 

[slysnake]

Any suggestions what to try next?

Move to a non-communist state.

 

[speedracervr4]

When replacing the o2 sensors do you replace all of them? Upstream and downstream?

I change the upstreams since they provide inputs (fuel trims) to the PCM. The down streams monitor the condition of the cat and provide no other function.

 

[Allan]

HC, Hydro-Carbons, is un-burned fuel. Caused by any condition that creates incomplete combustion. (over fueling, mechanical issue, ignition problem, lean misfire, rich misfire, anything that doesn't let the engine burn all of the fuel). CO, Carbon Monoxide, is the 'rich indicator' in 4 or 5 gas analysis. O2, Oxygen would be the 'lean indicator'. CO2, Carbon Dioxide, is the 'efficiency' indicator. NOX, Oxides of Nitrogen, is an 'emission control' / EGR function / combustion temp indicator. (NOX forms if the combustion temp exeeds 2500 degrees Far.)...............So, if you have high HC and CO, low O2 and CO2, and the engine 'seems to run OK' , you are over fueling for some reason under that particular run condition. If things are good at idle, it is not a leaking/dripping injector, or high fuel pressure. Probably a fuel control issue with the spread in the LFT's that you posted. Oxygen sensors may cure it if no other obvious problems are found. No codes yet due to "in range failure" (PCM doesn't see O2 activity problem and the readings are believeable') Keep driving it and it will probably set a lean code. (pcm is trying to compensate for a false lean condition-driving the system rich) I would need to drive the vehicle with a scan tool monitoring O2 activity and fuel trims to confirm before replacing parts to be sure......cuz it may be something else.........hope this info helps.....open to discuss further, Allan -ASE Master Tech, L-1 certified.

 

[Jack B]

If the exhaust flange on the engine side of the upstream O2's had a leak, the O2 sensor would read lean and the PCM would offset that with more fuel, therefore. a greater LTFT. A lazy O2 could also create be the culprit. Like you, I would have thought CAT.

Ltft is dependent on the balance between the closed loop fuel table and the oem engine efficiency. You could have an imbalance at a given rpm and load, but, if you do not drive in that range, the LTFT would be low. On the other hand if you drive in the range where you have the imbalance your LTFT would go up.

 

[Allan]

If the exhaust flange on the engine side of the upstream O2's had a leak, the O2 sensor would read lean and the PCM would offset that with more fuel, therefore. a greater LTFT. A lazy O2 could also create be the culprit. Like you, I would have thought CAT.

Ltft is dependent on the balance between the closed loop fuel table and the oem engine efficiency. You could have an imbalance at a given rpm and load, but, if you do not drive in that range, the LTFT would be low. On the other hand if you drive in the range where you have the imbalance your LTFT would go up.

An exhaust flange leak (that allows atmosphere/air to enter the exhaust stream under certain conditions)-(low pressure in the manifold) Would be seen on the gas analyzer/emission tester as a high O2 reading. Original post does not state high O2 with the other jacked-up readings. -----not an exhaust leak.

 

[Allan]

If the exhaust flange on the engine side of the upstream O2's had a leak, the O2 sensor would read lean and the PCM would offset that with more fuel, therefore. a greater LTFT. A lazy O2 could also create be the culprit. Like you, I would have thought CAT.

Ltft is dependent on the balance between the closed loop fuel table and the oem engine efficiency. You could have an imbalance at a given rpm and load, but, if you do not drive in that range, the LTFT would be low. On the other hand if you drive in the range where you have the imbalance your LTFT would go up.

Also, a lazy O2 will set a code for such condition. The O2 problem,(if that's what it is), is a lean biased sensor (falsely reporting a lean condition -driving the system rich on one bank) An in-range failure so far that does not set a code. Eventually it will once it gets outside the PCM's window of tolerance. Need to monitor the O2's with a data graphing scan tool to confirm. -Allan

 

[Dom426h]

Allen, Thanks for the very informative posts. I agree about checking the O2 sensors with a scan tool. We have a Actron 9185 at work and it is so simple to just look at an O2 sensors live graph and tell if it is good/bad/or going bad. I think the cheaper (sub $200)9580 model has the same capability. Also there are now Bluetooth obd thingys that can plug into the port on your car and communicate with your laptop or phone. All you need is the App.

 

[EllowViper]

As strange as this sounds, check the ground strap where it connects to the a/c compressor. This is the ground for the 02 sensor circuit. You might be experiencing impedance issues since these 4-wire 02 sensors utilize the ground circuit to establish/vary the sensor voltage. That's why you can't use the narrow band output on the Innovate WB sensor (sadly enough) since the Viper doesn't use a straight 0-1v methodology, but voltage is influenced by some trickery in the ground circuit.

 

[Mike Adams]

What where the numbers specifically CO's

 

[jcaspar1]

Thanks! I appreciate all the input. I took it to a mechanic friend who works on European cars. His scanner showed voltages of about .2 for both O2s at idle with brief boost to .85-.9 with reving the engine. I will see if his scanner can do a graph (Snapon scanner)
Emissions were:
15 mph 38HC .08CO 1 NO
25 mph 44HC .58CO 0 NO (Max for HC 35 Max for CO .46)

O2 sensors are original, car has about 38k miles

 

[MoparBoyy]

Move to a non-communist state.

more nanny state.. but ya. this.

 

[Jack B]

As strange as this sounds, check the ground strap where it connects to the a/c compressor. This is the ground for the 02 sensor circuit. You might be experiencing impedance issues since these 4-wire 02 sensors utilize the ground circuit to establish/vary the sensor voltage. That's why you can't use the narrow band output on the Innovate WB sensor (sadly enough) since the Viper doesn't use a straight 0-1v methodology, but voltage is influenced by some trickery in the ground circuit.

I replaced the a/c condenser and accidentally cut that ground wire, the car started to have intermittent idle hang. When I found the problem, I brought the ground out to the drivers side throttle body. On the pass side I did the same for the passenger O2. It has been rock solid since.

 

[Allan]

I replaced the a/c condenser and accidentally cut that ground wire, the car started to have intermittent idle hang. When I found the problem, I brought the ground out to the drivers side throttle body. On the pass side I did the same for the passenger O2. It has been rock solid since.

Wise to investigate this stuff. May be able to fix the problem with no parts.

 

[Allan]

Thanks! I appreciate all the input. I took it to a mechanic friend who works on European cars. His scanner showed voltages of about .2 for both O2s at idle with brief boost to .85-.9 with reving the engine. I will see if his scanner can do a graph (Snapon scanner)
Emissions were:
15 mph 38HC .08CO 1 NO
25 mph 44HC .58CO 0 NO (Max for HC 35 Max for CO .46)

O2 sensors are original, car has about 38k miles

Wow, they are stringent in Cali. or what....your not crazy out of whack, but still no pass. ...All the Snap-on scanners graph unless it's an older model (we call it the brick) -I still use one of those for older cars. If he's got a Solus, Modis, Verdict, or Verus, it will graph.

 

[jcaspar1]

Update. Replaced O2 sensors and no change. I think I am going to take it to the dealership and see if they can solve it. Will check grounds first.

 

[hiss highness]

am catless with headers/porting etc, found that removing the smooth tubes and going back to stock intake removed some exhaust smell and toned down the rumble, think the turbulence in the intake leaned it out a bit

 

[jcaspar1]

OK. Might be making some progress. Brought her to the local Viper tech. He confirmed the adaptive high on the left 11%. He flushed the fuel injectors and the adaptive dropped to 5-7%. Right side is still less but he feels this is significant. He also recommended changing the downstream O2 sensors as the readings were fluctuating. My understanding is that these only monitor cat efficiency but he said they had some effect on the mixture.
Does that sound right??

 

[EllowViper]

I would be screaming at the techs since these are well within normal ranges...given variances in injector flows and the FACT THAT YOU ARE USING 10% ethanol in the gas that will automatically cause an increase in LTFTs as the PCM compensates for the increased fuel needed to balance STFT/LTFTs AFRs. Folks always forget that these PCMs were tuned on non-ethanol blended gas. That's why the gov't can "get away" with the 10% mix since PCMs can manage that amount of fuel trim adjustments without setting a CEL on most cars. Flex fuel cars have a much more "adaptable" PCM. As a test, I'd get a tank of non-ethanol blended gas and see whare your trims come in at. Prove me wrong in other words.

 

[jcaspar1]

I think what was concerning was the difference in the adaptive between banks, 10.5% left and the right 0.8% and the fact the smog check suggested it is running to rich. Still wondering about the rear O2 sensors. They are not expensive but don't want to replace them if they have absolutely nothing to do with air-fuel mixture.

 

[EllowViper]

As you chase cause and effects, remember that all is not even engineered equal from the left bank to the right. Fuel enters the manifold on the left where it is initially exposed to the hot intake. It then is routed in the manifold via internal casting voids to the the right bank all while absorbing more and more heat...especially in a dead-head system like the Viper. The fuel density and pressure at injector 9 (closest to the fuel inlet) and injector 1 (opposite and distant) is different...yet they all receive the same fuel pulse width. If you must mess with the front 02's, please just put the left one in the right side and the right side in the left. Bet you get the same readings which indicate a non-02 issue and its just the way the engine purrs.

 

[jcaspar1]

Ok. I think I got it solved. Went to Dealership and they recommended flushing the fuel injectors and replacing the REAR O2 sensors. Did the first but not the second.
Rechecked smog today (first shop I went to wouldn't do Vipers..too complicated?!?) and PASSED!

After front O2 and new high flow cats, before injector cleaning
15mph HC 38 (max 51) NO 1 (419 max)
25mph HC 44 (max 35) NO 0 (706 max)

After injector cleaning
15mph HC 34 (max 51) NO 85 (419 max)
25mph HC 35 (max 35) NO 28 (706 max)

Thanks for all the advice

 

[EllowViper]

Jeff, SO what was the impact on your LTFTs since that was part of your original question?

 

[EllowViper]

..and good call on NOT doing the rear 02s They have nothing to do with your issues. In fact, I've turned mine "off" via reprogramming the engine controller and the engine couldn't be happier. Exact same emmission readings with or without the rear 02s.