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CA Smog: 2 ppm over the HC limit

I think I need to buy a more capable scan tool to get STFT and LTFT. What feature(s) does the tool need to have so I can sure it can measure fuel trim?
 



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OK, you convinced me. Should I spend the extra $15 or so for Motorcraft wires rather than Denso? If the Denso fit is not exact, that $15 would be cheap avoidance of frustration.

I guess I'll find some acetone too. That link was great.

I got Motorcraft wires at Amazon for $18, under the "used--Amazon Warehouse Deals" section. Mine were listed as "Very good," and they were basically new. It looked like someone played around with one of them (the grease was distrubed), but they were otherwise brand new.

They have one set in Like New condition for $30 right now. With Amazon's Warehouse Deals, I'd expect "Like New" to be completely unused--open box.

https://www.amazon.com/gp/product/B000BYD9TE/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
 






What are your fuel trims at idle and 1500 rpm. I also have a 96 and replaced the EGR valve because it leaks air thru the pintle.

I bought an ELM237 Wifi adapter and downloaded free OBD Car Doctor app.

Please post your best guess as to the root of the problem, if any, based on the following data.

Idle:
Bank 1 STFT oscillating about zero
Bank 2 STFT oscillating about -0.8
Bank 1 LTFT 12.5 steady
Bank 2 LTFT 12 steady

1500 rpm:
Bank 1 STFT oscillating about +1
Bank 2 STFT oscillating about -1
Bank 1 LTFT 1.6 steady
Bank 1 LTFT 1.6 steady

O2 sensor voltages
idle
O2 11 bank 1 0.14 steady
O2 11 bank 2 oscillating about zero
O2 21 bank 1 oscillating 0.16 to 0.8
O2 21 bank 2 oscillating about -4
1500 rpm
O2 11 bank 1 0.3 mostly steady
O2 11 bank 2 oscillating about +1
O2 21 bank 1 oscillating about +0.4
O2 21 bank 2 oscillating about -0.8

error codes even though I replaced all the O2 sensors less than 10k miles ago:
P0133 (slow bank 1 O2 sensor)
P1131
P1132
 






You have a vacuum leak. At idle ltft is high, but at 1500 rpm it improves. At idle a small amount of extra air makes a big difference, not so much at higher RPM. Remember you are adding fuel for that vac leak, so therefore more HC. It is not a serious leak but still...

Run propane or brake cleaner under the egr valve into the vents and watch the trims. There could be other leaks too but that is suspect. Next would be the plenum gaskets.

Do you have freeze frame data for those codes?

Also, look into forscan software, it should work with your wifi adapter. It is free and can read more specific pids.

I would like to know the BARO PID.

Bank 1 o2 sensor could have an issue. Was that the one you got on discount?
 












O2 sensor conventions are usually bank # then sensor #. So O2 sensor 21 would be bank 2 sensor 1 which is driver side post catalytic converter.

I may be wrong, but wouldn't sensor 1 be pre-cat?
 






O2 sensor conventions are usually bank # then sensor #. So O2 sensor 21 would be bank 2 sensor 1 which is driver side post catalytic converter.

I may be wrong, but wouldn't sensor 1 be pre-cat?
 






Steady precat o2 sensor on one bank at 1500 rpm is likely a bad sensor or a major lean condition affecting one bank(like a stuck injector). Being that the trims are so perfectly equal between the two banks it may be estimating one bank using the other. There is definitely some issues there.
 












Steady pre-cat o2 sensor on one bank at 1500 rpm is likely a bad sensor or a major lean condition affecting one bank(like a stuck injector). Being that the trims are so perfectly equal between the two banks it may be estimating one bank using the other. There is definitely some issues there.

I agree if the PCM is in closed loop which is normally within a couple minutes after engine start. As posted, the PCM can determine that a sensor has failed and then revert to the other pre-cat sensor. For good pre-cat sensors when the PCM is in closed loop the voltages should vary between less than 0.2 and greater than 0.8 for a constant throttle and engine load.

P0131 02 Sensor Circuit Low Voltage (Bank I Sensor I) pre-cat
P0132 02 Sensor Circuit High Voltage (Bank I Sensor 1) pre-cat
P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1) pre-cat

How many O2 sensors does your system have? Some exhaust configurations only have 3 O2 sensors.
 






I agree if the PCM is in closed loop which is normally within a couple minutes after engine start. As posted, the PCM can determine that a sensor has failed and then revert to the other pre-cat sensor. For good pre-cat sensors when the PCM is in closed loop the voltages should vary between less than 0.2 and greater than 0.8 for a constant throttle and engine load.

P0131 02 Sensor Circuit Low Voltage (Bank I Sensor I) pre-cat
P0132 02 Sensor Circuit High Voltage (Bank I Sensor 1) pre-cat
P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1) pre-cat

How many O2 sensors does your system have? Some exhaust configurations only have 3 O2 sensors.
96 OHV has 3. 2 pre 1 post. We have a Y pipe.
 






Run propane or brake cleaner under the egr valve into the vents and watch the trims. There could be other leaks too but that is suspect. Next would be the plenum gaskets.

I put a lot of propane all around the EGR valve and down the tube going to the rear and nothing happened. No change in rpm, no change in LTFT at idle. I put the propane everywhere I could reach around vacuum lines and the lower part of the plenum. Also no change. If I have a leak, it's really small.

Forscan Lite shows $4.99 price on my iPhone. OBD Car Doctor does not have BARO PID. Should I spend $5 for that?

I noticed that the O2 11 Bank 1 sensor was stuck at zero for 20 to 30 seconds after starting, then it gradually moved into the zone I listed above. Perhaps this is due to air in the exhaust pipes, but if so that's a lot of air.

I have bought new plugs and wires but I don't want to install them until after I decide whether or not to use the seafoam spray can that I bought. I don't want to break anything that's not broken.
 






I put a lot of propane all around the EGR valve and down the tube going to the rear and nothing happened. No change in rpm, no change in LTFT at idle. I put the propane everywhere I could reach around vacuum lines and the lower part of the plenum. Also no change. If I have a leak, it's really small.

Forscan Lite shows $4.99 price on my iPhone. OBD Car Doctor does not have BARO PID. Should I spend $5 for that?

I noticed that the O2 11 Bank 1 sensor was stuck at zero for 20 to 30 seconds after starting, then it gradually moved into the zone I listed above. Perhaps this is due to air in the exhaust pipes, but if so that's a lot of air.

I have bought new plugs and wires but I don't want to install them until after I decide whether or not to use the seafoam spray can that I bought. I don't want to break anything that's not broken.

1) Forscan is free for the PC and actually has more functionality. D/L from Forscan.org. If you need android d/l Forscan demo(free), you can view one PID at a time. It will also check if you can use Forscan Lite with your adapter.
2) You should be looking at STFT rather than LTFT for the propane test. LTFT adjusts to the STFT over time., Usually you would detect changes in idle quality, so maybe you eliminated that as a problem. You can also remove vac lines off the nipples, plug the port and see your fuel trim. The other alternative is a smoke test...
3) 02 sensors need a bit of heat to go into closed loop, so that isn't a reliable test. Engine should be at operating temperature for these tests.
4) If the 02 sensor drops out with a flat signal then comes back it can be flaky. Even new o2 sensors can fail. They can last 200K miles or fail in a week....
 






I paid $5 for the Forscan Lite iphone app. It appears BARO is not available from my 1996 Explorer or the ELM237 doesn't support it. So MAF trouble has not been ruled out, although I did use MAF cleaner on it 2 years ago. Also, a MAF problem should not generate an O2 sensor error on one bank but not the other.

I checked for an exhaust manifold leak using my bare hand on the passenger side manifold after starting the engine cold. I couldn't fell any air escaping anywhere.

My next step will be to follow the error codes as confirmed by Forscan and replace the upstream passenger side O2 sensor. (Forscan is great at translating codes into plain English and at showing Ford-specific information.)

I really appreciate all the help here, and I'm glad to have learned how to set up an use the WiFi ELM237. It's a great toy besides being useful.

I will report back after replacing that O2 sensor.
 






I paid $5 for the Forscan Lite iphone app. It appears BARO is not available from my 1996 Explorer or the ELM237 doesn't support it. So MAF trouble has not been ruled out, although I did use MAF cleaner on it 2 years ago. Also, a MAF problem should not generate an O2 sensor error on one bank but not the other.

I checked for an exhaust manifold leak using my bare hand on the passenger side manifold after starting the engine cold. I couldn't fell any air escaping anywhere.

My next step will be to follow the error codes as confirmed by Forscan and replace the upstream passenger side O2 sensor. (Forscan is great at translating codes into plain English and at showing Ford-specific information.)

I really appreciate all the help here, and I'm glad to have learned how to set up an use the WiFi ELM237. It's a great toy besides being useful.

I will report back after replacing that O2 sensor.

That is surprising because BARO works on my 96. The adapter should not matter as long as it can read Ford codes, maybe I learned something new. Are you using the PCM menu? There is also an OBD selection with less PIDS. You should have tons of PIDS to choose from, you can search for them.

Since you have equal trims on both banks I wanted to rule out a marginal MAF, or air flow issue, but the 02 sensor seems to be a culprit.

Check down on the Y-pipe for exhaust leaks too, I had mine welded recently. Being in CA though it is unlikely it rusted through.
 






That is surprising because BARO works on my 96. The adapter should not matter as long as it can read Ford codes, maybe I learned something new. Are you using the PCM menu?

Thanks! I found BARO on the PCM menu as you said. It's steady at 1.02 bar, or 160 Hz. The vehicle thinks it's at sea level and it is.

The upstream right side O2 sensor is upstream of the Y junction, but I will check it if I can reach it without raising the vehicle. I can't hear anything that sounds like an exhaust leak though. I expect to install the new O2 sensor next weekend. For what it's worth, I bought that sensor new 2 years ago. Only the downstream sensor was from Amazon warehouse deals.
 






I changed the upstream right side O2 sensor and my son drove it 1000 miles. No error codes. Bank 1 and Bank 2 numbers now look the same. Idle is still slightly rough. LTFT is 18 at idle and 7 at 1500 rpm.

STFT oscillates around 0.8. All 3 O2 sensors have voltages bouncing up and down in squarish waves between 0.3 and 0.8 volts.

Spark advance is 20 degrees at idle and at 1500 rpm, which seems high to me. I don't know how to adjust that.

I think the high LTFT means it's running lean. Does that point to an inaccurate MAF sensor? Or maybe an air leak between MAF and intake plenum? Or would the spark advance alone produce these results?
 






Spark advance is controlled by the PCM. The only way to change it is by tuning the spark tables in your strategy. The PCM uses spark advance to control idle speed because it can be changed much faster than the IAC valve is capable of. Is the spark advance at 20 degrees in Park when there is very little engine load or when in Drive?
 






It's in Park with no load.
 



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