CA Smog: 2 ppm over the HC limit

[myf16]

I read this article on fuel trim. It seems that long-term fuel trim is a measure of how much adjustment the computer needed to make from its nominal settings to achieve the right result. But the end result should be good as long as the computer is able to adjust and as long as the needed adjustment is not varying rapidly. So I think the smog values should be OK.

However I would like to eliminate some possible causes. I will look again for a vacuum leak and I will change the fuel filter (in case it's clogged) and the wires (150k miles on them) and the plugs (double platinum this time). Then I will cross my fingers and take the smog test.

Edited to add: a clogged fuel filter seems unlikely to produce a high long-term fuel trim at idle and a lower long-term fuel trim at 1500 rpm. In fact, it would be the other way around if the fuel flow is constricted. Spark would normally be stronger at low rpm than at higher rpm. So I'm down to vacuum leak or exhaust leak.

 

[96eb96]

18 is quite high, and since the number drops to less than half at 1500 RPM there is a vac leak somewhere. Not sure how that would affect smog, but it could affect gas mileage. Fuel trims control emissions are the expense of gas consumption. Cars actually waste some gas to keep the converters hot and keep emissions low. That is why the oxygen sensors cycle if you look at the graph. The strategy is to keep things at 14.7:1 air fuel ratio. Once the computer can't maintain that that the CEL comes on. So a trim in the low 20s would be game for for a CEL because the control limit is reached.

You may want to replace the intake plenum gaskets (I did mine, they were very compressed). Not sure if they made that much of a difference. My LTFT at idle varies from 3-7. Idle quality is good cold and excellent when it warms up.

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

How about STFT? A ford dealer told me that is a very common place on those engines to take in air. But don't change it unless you can verify STFT changes with propane.

Wires and plugs are a good idea too. Motorcraft if possible.

 

[myf16]

I put a LOT of propane everywhere today and the STFT and idle rpm were not affected. LTFT is 18 at idle and 8 at 2500 rpm. Does this sound like I need a new MAF sensor or could it be plugs/wires? I do have MAF cleaner spray and I will use it, but I don't expect it to anything it didn't do 10k miles ago when I tried it.

My plan is:
- Clean MAF and re-test LTFT. (now completed, no change in LTFT)
- Change plugs and wires and re-test LTFT. (now completed, no change in LTFT)
- Change MAF and re-test LTFT. If no improvement, give up. (completed, no change in LTFT)

Edit: I put half a can of Seafoam spray through the throttle body. Slight improvement in LTFT, to 14 and 11 at 820 rpm. Not nearly as much smoke as they show on the Internet, so probably the engine was in good shape. It doesn't burn oil.

 

[96eb96]

I put a LOT of propane everywhere today and the STFT and idle rpm were not affected. LTFT is 18 at idle and 8 at 2500 rpm. Does this sound like I need a new MAF sensor or could it be plugs/wires? I do have MAF cleaner spray and I will use it, but I don't expect it to anything it didn't do 10k miles ago when I tried it.

My plan is:
- Clean MAF and re-test LTFT. (now completed, no change in LTFT)
- Change plugs and wires and re-test LTFT. (now completed, no change in LTFT)
- Change MAF and re-test LTFT. If no improvement, give up.

Edit: I put half a can of Seafoam spray through the throttle body. Slight improvement in LTFT, to 14 and 11 at 820 rpm. Not nearly as much smoke as they show on the Internet, so probably the engine was in good shape. It doesn't burn oil.

You could have carbon on the valves absorbing gas. To compensate more gas is added. Try some good fuel cleaner or top tier gas. I use Mobil gas and it really helps my cars, there are articles about it. Not that other gas is "bad" but some gas has excess detergent and cleans the engine. It is not a gimmick because some car companies actually recommend owners to Top Tier Stations. It is not just one brand.

Beyond that you can get a smoke machine and smoke the intake. You can also plug off orifices from the brake booster, accessories, PCV, etc and see if there is a major change. The 4x4 system actually uses engine vacuum. There is vaccum line coupling on the passenger side around the intake manifold you can take off and plug.

 

[myf16]

I passed the test by only 1 ppm at 25 mph (30 ppm HC). I doubt that anything I tried had any effect other than replacing the defective O2 sensor. Maybe the catalytic converter is just too old at 150k+ miles for California's insanely low HC limit of 31 ppm.

I think the CA government just wants to force low-mpg vehicles off the road and they adjust the smog limits to achieve this stealthily and without legislation. What a waste of time and money.

 

[myf16]

I had a belated idea. When I first got this Explorer 4 years ago the temperature gauge was near the low end. I replaced both the sender and thermostat but the low reading remained. Would a higher temp thermostat bring the HC down and bring the gauge reading past mid-scale?

Another thing I learned while searching today is that a dirty or faulty Idle Air Control valve can allow excess air into the engine. There's a thread on how to clean that, so I think I will try that this weekend.

A third rather upsetting thing I learned today is that many California smog shops insist on stock tire sizes. I'm about to install 31-inch tires which are not huge but are a little oversize. I sure hope I don't have to buy a stock set of wheels and tires to pass next time. Or maybe I'll just sell the vehicle to someone who lives in a non-insane state.

 

[96eb96]

I had a belated idea. When I first got this Explorer 4 years ago the temperature gauge was near the low end. I replaced both the sender and thermostat but the low reading remained. Would a higher temp thermostat bring the HC down and bring the gauge reading past mid-scale?

Another thing I learned while searching today is that a dirty or faulty Idle Air Control valve can allow excess air into the engine. There's a thread on how to clean that, so I think I will try that this weekend.

A third rather upsetting thing I learned today is that many California smog shops insist on stock tire sizes. I'm about to install 31-inch tires which are not huge but are a little oversize. I sure hope I don't have to buy a stock set of wheels and tires to pass next time. Or maybe I'll just sell the vehicle to someone who lives in a non-insane state.

Mine is the same. Over the years lots of cooling parts were replaced for maintenance. I only use Ford Thermostats. I never saw the gauge go into the center(maybe a few times). Thinking of a Stant Super-Stat, but I don't think it will help. My gauge perfectly tracks what I see on Forscan. 172-181 deg , about 1/5-1/3 of the way.

Years ago there was a kit from Ford to bypass some coolant, some people have bridged the heater core lines. The engine has no external bypass, and there is a steam formation issue from what I understand. Another theory could be microcracks in the heads. Who knows. Raising temperature may help emissions, but technically anything over 160 is acceptable for emissions.

 

[lobo411]

I think the CA government just wants to force low-mpg vehicles off the road and they adjust the smog limits to achieve this stealthily and without legislation. What a waste of time and money.

I'm in the same boat re: a 1996 Explorer that is having an increasingly tough time passing smog. The rationale seems fair to me, though: a disproportionate share of the smog is created by old clunkers like ours.

 

[myf16]

Another thing I learned while searching today is that a dirty or faulty Idle Air Control valve can allow excess air into the engine. There's a thread on how to clean that, so I think I will try that this weekend.

I removed the IAC, which takes about 45 seconds. It was really clean, with just an ultra-thin soot deposit. However it had been mounted with no gasket whatsoever. I replaced it using the Felpro 71216 ($1.99 locally) as described in this thread: http://www.explorerforum.com/forums/index.php?threads/how-to-iac-valve-cleaning-thread-w-pics.84220/

No improvement in fuel trim. The values actually increased, which I believe will be temporary.

 

[Justinwht]

http://www.sciencedirect.com/science/article/pii/S2215098615302469

Interesting read, but the "The higher the flame speed is, the lower the tendency of knock occurs and, in turn, better performance obtained" has me confused.

A high flame speed causes pinging from premature ignition so an octane additive is used to delay the ignition, in other words slowing down the flame.

 

[Justinwht]

So O2 sensor 21 would be bank 2 sensor 1 which is driver side post catalytic converter.

21 would be the left bank upstream pre-converter. 22 would be bank 2 downstream post-converter.

Didn't look a my 4 L 2000 Explorer, but my 1996 ones have one cat converter, there isn't a driver side downstream sensor, i.e. 22.

 

[myf16]

OP here. Two years later it failed by 8 ppm at 25 mph. I was about to give up but the shop said they could fix it with $295 worth of intake and combustion chamber cleaning and checking the plugs. They were right! They cut the HC and NOX by 60% and the Explorer passed easily. I love the vehicle and I am delighted to be able to keep it on the road.

The shop said 2 plugs had incorrect gap. The plugs and wires have less than 30k miles on them, and I installed a new IAC and fuel filter (badly needed at 160k miles) within the last 6 months.

 

[96eb96]

OP here. Two years later it failed by 8 ppm at 25 mph. I was about to give up but the shop said they could fix it with $295 worth of intake and combustion chamber cleaning and checking the plugs. They were right! They cut the HC and NOX by 60% and the Explorer passed easily. I love the vehicle and I am delighted to be able to keep it on the road.

The shop said 2 plugs had incorrect gap. The plugs and wires have less than 30k miles on them, and I installed a new IAC and fuel filter (badly needed at 160k miles) within the last 6 months.

Probably save that in gas this year if it was that bad :lol: