HELP: Why am I having a hard time passing emissions

[1Byounkin]

1991 Explorer 4.0
Ever since I've had this truck (8-9 years) I've always had a hard time passing emissions. I live in TN near Nashville we have to do emissions for the counties that touch Nashville. So not all people in TN might not know this. For me they do a tail pipe probe.

Every year I've upgraded something to hopefully make it better. Never have had a check engine light. Yes I've checked KOEO and KOER codes. Nothing with problems. Also replace the wires and plugs. The plugs always look clean. I know that the pass owner had the bottom end bored (.20) and rebuilt. Also with a high pressure oil pump.

4 years ago I had to put on a Cat. I had high HC which stopped that up, also replaced the O2 senor.
3 years ago I replaced all injectors with new rebuilt ones. Had HC again, up to 4,000 HC. The problem was a cracked valve. I replaced the heads with new ones from Alabama Cylinder Heads (Complete heads with valves). After the heads and driving for a few months I had to do the test again. This time 187 HC 1.08 CO 11.59 CO2. Which passes.

2 years ago did the regular tune up. Plug wires and stuff. Cleaning the MAF. Test came around again. Failed :/ This time I tried some for that Guarantee to Pass. Which did work. Got under by 1 point. 219 HC .98 CO 12.42 CO2.

Everything works fine and drives great. Starts fine.

This year failed again. This time did an oil change and more of a tune up before even going. Even ran a tank of 93 Oct gas. Still Failed again. 273 HC 0.91 CO 12.40 CO2.

1 - 187 HC 1.08 CO 11.59 CO2
2 - 219 HC 0.98 CO 12.42 CO2 < using Guarantee to Pass
3 - 273 HC 0.91 CO 12.40 CO2

Limits for TN > 220 HC 1.20 CO N/A CO2

I'm running out of ideas of why its doing it. Each year it slowly increases back up. I know I can cover it up each year, but its aggravating.

The only thing I can think that hasn't been replaced on the engine is the rockers and push rods. I know the lifters are good. When I did the top end rebuild with the heads, I noticed the worn rockers. At least on the valve side of the rockers. I know that valve clearances can make a difference on a motor. So this got me thinking. If the valves are not opening right than they are not let in or out the right stuff. Would it effect the running? I know the worn spots were about 1/16th deep on most. I know the rockers, before the head replacement, made noise on the passenger side. When I went back with them I put it on the driver side. Just to see of that changes anything. It do as in sound. I know driving down the road you can hear the taping noise, not like a lifter. But the worn rockers. I know you can hear a slight miss in the exhaust. Which Has always done that. Before heads and after.

>>So the main question is, Would replacing all the rockers and push rods help this problem. Going all new parts.

I know many might not of ran into this problem because of how the emissions are done here. Most things I've ran are just the ticking noise people hear. And read whear someone regained power back by doing it. Which that would put it back into the right area that the computer is made for. I think its over out putting the gas. Yes the FPR has been checked. Right before posting this. Also this model does not have an EGR valve.

Thanks for whoever could help me with this.

 

[1Byounkin]

My tags expired in May. So I'm having to figure out something soon.

 

[Tbars4]

..Check out the links of the first post in this thread while you are waiting for other replies..

http://www.explorerforum.com/forums/showthread.php?t=219411&highlight=smog

 

[1Byounkin]

Thanks. I've replaced all the vacuum lines with new ones. And have checked the other things too.

Lucky here its just an idle tail pipe test. No dyno testing or smog

 

[Tbars4]

..If you spend a few more minutes reviewing the "links" in the first post you will find one has information directly relating to failing "Emissions", aka "Smog" test, due to high HC's..

..My trucks still do the tailpipe, aka "Sniffer" test too, especially since my X get's a little bouncy on the treadmill..

 

[1Byounkin]

ok. I'll look at them again.

I'm still wondering if spending $230 to replace the whole rocker assembly, push rods and gaskets is needed since they are worn

 

[1Byounkin]

Tbars4 - After reading http://www.smogtips.com/failed-high-hydrocarbons-HC.cfm
I saw what number 6 says about low compression. My theory is IF valve are not opening to the full amount there would be less air coming in. Thus would be less air to compress but higher gas content. MAYBE????

 

[1Byounkin]

Anyone else know?

 

[Tbars4]

I see several things such as Leaky gaskets which are common, have you had your cats checked?

..What was your drive to the smog test? Did you let it Idle or did you let it cool down?

What was your compression test results?

I'm not sure why you are leaning to your rockers and pushrods but if you answer these questions perhaps you will get some more answers while you are searching the forum..

 

[1Byounkin]

Cats are good. Cato brand. All of the gaskets on the motor have been replaced. I did all of them myself. Using the master gasket kit. Everything has been torque to the right specs.

15 miles. To the testing center. I would rev it some while sitting in line.

I know after the heads most would read between 110 -120 psi.

True. That is just the last thing I can think that hasn't been replaced on the motor. Still has the original coil pack.

I'm just not sure what else to look for

 

[Tbars4]

How long were you in line and have you cleaned your MAF?

 

[1Byounkin]

Probably 5 mins. Yes I cleaned it the night before with MAF cleaner

 

[1Byounkin]

I'm just not sure what else to check or do. Read tons of things on the forum.

My thinking is: Is it running to rich and what could be causing it? New heads brought the numbers back down but are now slowly going back up. Weak coil? Also running double platinum plugs. All connection under the engine have die-electric grease, even the plug wires.

 

[1Byounkin]

What I have do so far is checking the MAF senor and the TPS. The MAF senor reads good for all values for each rpm range.

The TPS was reading .90v I made adjustment back to .964v. The idle seems smoother. so maybe that's what it needs.

For adjusting I used this page: http://www.explorerforum.com/forums/showthread.php?t=79362

 

[1Byounkin]

And this for check the MAF > http://www.explorerforum.com/forums/showthread.php?t=263750

 

[BKennedy]

Dump a gallon of E85 methanol in a half-full tank, drive it around for an hour, then go get in line at the smog place.
My Explorer passes smog very well, but the engine is basically stock.
I did the E85 trick with our Volvo S60.
I really don't know what would make it run rich.

 

[1Byounkin]

I was just guessing on running rich. Since adjusting the TPS. I've notice a better idle and even driving. Makes sense if they are checking at idle. Because I had to rev the motor to do a second test. The computer at the testing center thought the engine wasn't hot enough even driving it 15 miles to there. If the TPS is at a low volt like .8 or .92v it might think its running lean, maybe. But the rest of the ECM was trying to make it run different. I don't know.

 

[Tbars4]

I was just guessing on running rich. ...The computer at the testing center thought the engine wasn't hot enough even driving it 15 miles to there. ....But the rest of the ECM was trying to make it run different. I don't know.

..You just hit the key items of High HC's...

..Perhaps it wasn't warmed up...If your vehicle seemed like it was to cool for the test (when in fact it was truly warmed up) the concern would be the cats not working efficiently and are headed to their end of life...(again, I would have these checked at a muffler shop and it's free)

You do have the proper Thermostat and stock air intake set up I'm assuming?

..The other item is running lean...

..From a faltering MAF, A disconnected or failed thermostatic control valve, an air leak in the intake tube between MAF to Throttle body, or any random air, gasket, exhaust leak, or vacuum leak before your o2 sensors can give you this problem..

..These can give you a lean condition in which your computer reads these values as it needs to increase fuel supplied to the mixture..

This in itself alone would shorten the life of your cats..Excessive fuel

 

[1Byounkin]

Yes I have a new Thermostat and the stock air setup. I did check the MAF by using a voltmeter and see the volt with each rpm. Matched up just right. No skips. I have replaced all vacuum lines. Have check the FPR line for fuel in it (have that happen before) and the one coming from the Trans. No fluid in it ether. The one going to the air box used to be there but the rest of the tubing below was missing. And it always passed even when that was gone before I had it.

All the connections on the air duct tube are tight. I do know the O2 senor has came loose before. Might be what it is. Idk.

But I do know making that adjustment the exhaust smells better. Never had a rotten egg smell. Just a raw gas smell. Tonight smells alot better.

 

[Tbars4]

...A loose o2 sensor would do it..How many o2 sensors have been replaced on your X?