Solved CA Smog was at the limit last time, would disabling overdrive help?

[myf16]

My 1996 Explorer 4WD was right at the HC limit at 15 mph last time, even after replacing spark plugs and wires. This time I expect it to fail. The vehicle has 180k miles but it runs perfectly and burns no oil.

I'm thinking that reduced diameter tires (I currently have 33-inchers!) would help by increasing rpms, or maybe disabling overdrive would help.

Any ideas? Is it possible to disable overdrive so that the smog test person cannot switch it back on?

 

[J_C]

How do they do this 15MPH test? Is it based on the (dyno-like with rollers?) machine measuring 15MPH, or is it based on your speedo measuring it, and if the latter, did you regear your speedo so it is accurate, or would the real vehicle speed have been higher because of the oversized tires?

If your speedo was not regeared for the larger tires, then the smaller tires should help. Disabling overdrive won't do anything until the vehicle is going fast enough to switch into it, AFAIK, not 15MPH?

If everything on your vehicle is original, you might try switching the EGR valve, O2 sensors, and clean the MAF sensor. Disconnect battery to reset PCM then follow the driving cycle needed to relearn PCM.

 

[Josh P]

Smaller tires, acetone in the gas cuts the numbers down.

 

[myf16]

It's a dyno test. What's the proper percentage of acetone?

I thought the EGR valve reduced NOx. Does it also reduce HC?

 

[Fix4Dirt]

cali still does the roller test? here in LA they just rev ir in park and at idle.

 

[Josh P]

It's a dyno test. What's the proper percentage of acetone?

I thought the EGR valve reduced NOx. Does it also reduce HC?

10%

 

[myf16]

Is acetone the main ingredient in "Guaranteed to Pass Emissions Test Formula"?

The dyno test requirement is, I believe, specific to the county in California or maybe to the vehicle model and year. In recent years my old cars get the dyno and new cars get OBD2 only. If your old car has AWD or traction control that cannot be disabled, you get a no-load emissions test which is pretty easy to pass.

 

[Flashflood]

Haha emissions.

 

[Josh P]

Is acetone the main ingredient in "Guaranteed to Pass Emissions Test Formula"?

The dyno test requirement is, I believe, specific to the county in California or maybe to the vehicle model and year. In recent years my old cars get the dyno and new cars get OBD2 only. If your old car has AWD or traction control that cannot be disabled, you get a no-load emissions test which is pretty easy to pass.

It's the main ingredient in many brands of fuel injector cleaner, the emissions passer, etc. Used to help increase mpg, doesn't do that with the stuff sold at the pump now

 

[Flashflood]

It's the main ingredient in many brands of fuel injector cleaner, the emissions passer, etc. Used to help increase mpg, doesn't do that with the stuff sold at the pump now

I get good mileage if I run 87 in my truck she gets about 21 to 23 depending maybe she just likes corn

 

[C420sailor]

If those upstream oxygen sensors are original, I’d replace them.

 

[Papa]

We had those tests here in FL a while back. I failed a few, older car, until I learned that changing the oil a day or so before the test was all I needed to do to pass the test.

You say you changed plugs and wires but I learned that many wires out of the box won't pass a resistance test as in a 1500 Ohm max resistance. That leads to poor performance right away. Just bending the wires during install can cause problems. I played around a stainless-steel wire in them and that gave me great performance but plaid hell on the distributor cap and rotor. but sure, upped my freeway mileage 5 MPG. This was on a car with a 4-cylinder engine and when I first started digging into the performance problems, hard starting was the first indicator, I found that the coil wire had over one megaohm of resistance. That’s the shortest wire one of the wires tested out at 15 megaohms. Yea that’s usually considered an open circuit. Better wires helped a lot.

 

[J_C]

^ Different ignition system, ours uses high resistance wires that are typically around 5K ohm per foot.

 

[myf16]

For test preparation, I cleaned the MAF, changed the plugs to nickel, and changed the oil. Downstream O2 sensor is fluctuating almost exactly the same as the upstream, so it's either running too rich for the converter to handle or the converter is not working. Long term fuel trim is close to +20 percent, so I suspect it's running rich. Fuel pressure is about 30 psi but steady on the original fuel pump. Vacuum gauge is normal and steady at idle, but the idle is not 100 percent smooth.

I put 22 inch diameter tires on the rear, but it still failed HC at about 1.2 times the very low limits. I discovered after the test that the parking brake had been engaged. Crap. The smog guys didn't blink an eye at 50-series tiny tires on the rear.

1. Should I pay for another test with the parking brake released?

2. Should I add 10 percent acetone for a retest?

3. Should I just take it to a smog shop and pay for diagnosis and repair, possibly a new catalytic converter?

 

[Josh P]

I think you have a fuel pressure issue

 

[J_C]

I suspect a vac leak, and you may be having occasional misfires as a result. Get LT fuel trim back where it should be and go from there. AFAIK, a bad cat won't increase the fuel trim.

 

[myf16]

I suspect a vac leak, and you may be having occasional misfires as a result. Get LT fuel trim back where it should be and go from there. AFAIK, a bad cat won't increase the fuel trim.

I sprayed starter fluid all around and the idle never changed. I must have sprayed half the can.

 

[J_C]

Okay, but the fuel trims still seem to point to the problem even if you haven't found it yet. Might be time for a smoke test?

 

[myf16]

Agreed. This other thread says starter fluid doesn't detect leaks on computer-controlled engines:

Vacuum leak testing the RIGHT way!

I've suspected I had a vacuum leak, but couldn't find it. I first tried using carb cleaner, but no luck. Then I tried using propane, and nothing. So I decided to test my test. I injected propane directly into a vacuum line, and literally could not hear any change in the engine at all. I had to...

www.explorerforum.com

I plan to buy a smoke tester and see what it reveals. Cheaper in money and time than replacing the fuel pump, plus I get to add another tool to my collection.

 

[Josh P]

Agreed. This other thread says starter fluid doesn't detect leaks on computer-controlled engines:

Vacuum leak testing the RIGHT way!

I've suspected I had a vacuum leak, but couldn't find it. I first tried using carb cleaner, but no luck. Then I tried using propane, and nothing. So I decided to test my test. I injected propane directly into a vacuum line, and literally could not hear any change in the engine at all. I had to...

www.explorerforum.com

I plan to buy a smoke tester and see what it reveals. Cheaper in money and time than replacing the fuel pump, plus I get to add another tool to my collection.

The fuel pump may not be bad, pull the vacuum line off the fuel pressure regulator and see if the fuel pressure changes. A common place for a vacuum leak is the upper intake manifold.