Failed smog

[FUN4ME]

Hi guys i have an old jeep it is a 1991 with 251949 miles on it. When i bought it i had it smoged and it had 251733 miles on ti then and it passed. I haven't done anything to the engine or emissions systems so i dont understand how it could fail after only about 200 miles on it. I used the same smog station both times.

I have checked the obvious things vacuum leaks exhaust leaks Etc and everything seems fine to me.

What could cause such a drastic change I'm wanting to have this fixed properly and not use a "smog guy"

Here's a picture of both smog results do you think the first one was wrong?

Any help would be appreciated thanks Erich

 

[lbhsbz]

It's a balancing act between NOX and HC. To cold of an engine and lower combustion temps / rich = high HC....to hot of engine and higher combustion temps / lean = high NOX. If it does a lot of short trips and never gets warmed up...chambers are probably carboned up...that results in higher compression ratios and higher NOX.

This thing looks like it spends its life sitting...any chance the thermostat was sticking or the fan is non-functional making it overheat/run hot? How old is the fuel? How far / how long did you drive it to warm things up before getting the smog check?

Is this carb'd or EFI?....I can't remember when they made the switch.

You might try the old de-carbon trick of spraying a mist of water (use a spray bottle) down the carb / throttle body while holding the idle at about 2000 rpms for a few minutes...that will clean things up nice, then give it an italian tune up and try the smog again.

 

[HitIt]

Drive it around and give it a workout. Get it hot. You could try SeaFoam if things are carboned up but it might take a while to burn off all of the shit that gets knocked loose.

 

[FUN4ME]

Never overheats runs below 210 (middle of gauge marked) all the time, fuel is about a month old, i drove it about 5 miles prior to the test to get it up to temp

 

[blackbart]

the erlyer jeeps are great for no failing probably has a small exhaust leake up by the headpipe or mainfold it looks like the converter is working because your HC and CO are great

 

[dribble]

That engine is EFI. It is not equipped with EGR. Nox failures are the result of high combustion temps. After checking the usual. Radiator, fan, thermostat , lean condition. Check your fuel pressure. An engine with that many miles could be carboned up. Based upon the CO2 numbers This could also be a marginal cat. I don’t know why it passed so well the first time. Are you sure the first smog was legit? SB Mech should have some insight on this.

 

[Fun Times]

Has the battery died while sitting at all?
Dead batteries generally tends to have an affect of passing or not without long drive cycles.
Edit: My misthought here regarding batteries...Please see post number 9 for correction.

 

[monkeyswrench]

Since you bought it, you didn't change tire size, did you? That can cause an issue, as the dyno speed will be higher than the motor is dialed in for.

 

[lbhsbz]

Has the battery died while sitting at all?
Dead batteries generally tends to have an affect of passing or not without long drive cycles.

OBD1 doesn't have monitors to run/pass...

 

[mash on it]

Does it need an oil change? If the oil smells like fuel, an oil change may help.
I'd also de-carbon with water as stated above, plus checking for vacuum leaks.

Dan'l

 

[badluck]

Hi no is a common problem. Needs more fuel as it’s too lean. Unfortunately I’ve yet to find a way to richen up. Have the same problem on a hesco conversion on a 4.2. I’ve tried everything listed above with 0 success.

 

[coolchange]

10 percent load of Methanol cools that deal right down! Lol

 

[BingerFang]

What motor is in your Jeep? Is it a renix?

 

[DLC]

Change the oil put good gas in it and drive it around work it!

 

[coolchange]

Change the oil put good gas in it and drive it around work it!

And no overdrive.

 

[Waterjunky]

Some seafoam in the tank and run it hard for a few hours. Then new fuel and try again.
between the cleaner and the harder running, it should burn out the carbon and clean out the cat some. Little to loose by trying these.

 

[HitIt]

Little to loose by trying these.

"Sorry honey, I have to go drive the shit out of the jeep for 4 hours. See ya for dinner. Whatcha making?"

 

[FUN4ME]

thanks for all the replys
4 liter ho engine
I just did an oil change 50 miles ago.
Ill try the sea foam deal
I baby it so i guess ill have to go work it hard

 

[FUN4ME]

What motor is in your Jeep? Is it a renix?

renix? dont know what that is

I believe it is the original engine

 

[LargeOrangeFont]

thanks for all the replys
4 liter ho engine
I just did an oil change 50 miles ago.
Ill try the sea foam deal
I baby it so i guess ill have to go work it hard

All the advice here is good. Don't baby it, go drive it hard, get everything hot.

 

[monkeyswrench]

All the advice here is good. Don't baby it, go drive it hard, get everything hot.

Where's that pick of the Jeep towing the gooseneck?
Don't think he'd pass smog either now

 

[blownbullet]

I have spent a lot of time trying to get the old jeeps to pass smog some things to consider make sure the oxygen sensor is switching rich to lean .1 volt to .9 volts and it’s not worn out. The jeep is lean you have to consider the fuel injectors it only takes one clogged injector to make the NOX high, also carboned combustion chambers cracked exhaust manifold check the fuel pressure 39-41psi. Also no vacuum leaks check the brake booster, PCV valve, if there are 4 x 4 vacuum actuators everything. Last thing with that kind of mileage if the camshaft is worn out there is no EGR on that car it relies on valve overlap it will never pass. Best of luck.

 

[BajaMike]

I know a guy in Riverside......j/k, I used to know a guy. My 2001 Silverado 2500 HD that I don’t drive much did that once. Mechanic said go drive it, I drove out I-10 20 miles and back, he re-tested it and it passed.

 

[badluck]

I have spent a lot of time trying to get the old jeeps to pass smog some things to consider make sure the oxygen sensor is switching rich to lean .1 volt to .9 volts and it’s not worn out. The jeep is lean you have to consider the fuel injectors it only takes one clogged injector to make the NOX high, also carboned combustion chambers cracked exhaust manifold check the fuel pressure 39-41psi. Also no vacuum leaks check the brake booster, PCV valve, if there are 4 x 4 vacuum actuators everything. Last thing with that kind of mileage if the camshaft is worn out there is no EGR on that car it relies on valve overlap it will never pass. Best of luck.

This is all perfect info! I’ve done all of the above with no success but these are pretty much the complete list of to do’s

 

[Echo Lodge]

There are six counties that require smog certifications within certain Zip Codes only. These counties are: El Dorado, Placer, Riverside, San Bernardino, San Diego, and Sonoma. If a smog certification is required and you have not had a smog inspection, you may still pay your registration fees to avoid any late fees.

Appendix 1C - Partial Biennial Smog Counties Zip Codes - California DMV

EL DORADO (09)95613-1495619956239562995633-3695643956519565695664956679567295682956849570995720-219573595762 PLACER (31)95602-04956269563195648956509565895661956639566895677-789568195692957019570395713-1595717957229573695746-479576596161 RIVERSIDE...

www.dmv.ca.gov

If you register it to a a zip code Like 92267 (Earp) you never have to smog it again.

 

[braindead]

Hi guys i have an old jeep it is a 1991 with 251949 miles on it. When i bought it i had it smoged and it had 251733 miles on ti then and it passed. I haven't done anything to the engine or emissions systems so i dont understand how it could fail after only about 200 miles on it. I used the same smog station both times.

I have checked the obvious things vacuum leaks exhaust leaks Etc and everything seems fine to me.

What could cause such a drastic change I'm wanting to have this fixed properly and not use a "smog guy"

Here's a picture of both smog results do you think the first one was wrong?
View attachment 992461

View attachment 992462
Any help would be appreciated thanks Erich

I went through this same issue with my Jeep last month, 93 XJ 4.0L stock gears and 33” tires, passed 2 years ago no problems, no work done to the car except oil change and the thing failed on me with high NOX also.

the biggest thing is the O2 sensor, everything I read said that Jeeps dont like anything other than the OEM sensor which is NTK 23023, $23 on the rock auto.

Order that and change it out, along with a 20-30 min cruise on the interstate at speed with the gear shift in 3rd, you want the revs up to get the engine hot and burn off any crap that may be built up.

before your test, drive it for about 15 mins to make sure everything’s up to temps, but keep your aux fan switched on, if you have done the bypass mod so you can turn it on when you don’t have the ac on, if not turn your ac on so that baby’s running to help cool your radiator.

when you get to the test station, keep it running with the aux fan going and pop the hood, you want to get the heat out of the engine compartment especially the radiator to help keep the cylinder head temps down, as Soon as you shut it off those engines start to heat up like crazy, pay attention next time you start it up after it’s been sitting for a couple minutes your engine temp will spike right when you fire it up and then return to normal once the coolants flowing.

follow these steps and you’ll be golden, as long as you don’t have an exhaust, I guarantee it!

 

[TITTIES AND BEER]

Pull it off , stuff a piece of #5 rebar through it , shake it out put it back on , worked for me when I lived in cal ,

 

[FUN4ME]

Thank everyone, looks like I got some work to do.
will report back on what I did and how it goes.

Thanks again Erich

 

[Crazyhippy]

200 miles in 2 yrs?

Bad Gas.

 

[rivermobster]

200 miles in 2 yrs?

Bad Gas.

Good call. Can't imagine what the inside of that fuel tank must look like. Todays fuel starts going bad in just a few weeks. Pull the fuel filter, dump it out and see what comes out of it. Most likely it will be brown (gas today looks like clean water straight outa the pump).

 

[FUN4ME]

So i have a new o2 sensor on order.
Should i replace it before i drive it hard or will after be ok?

Ill do fuel filter and new fuel.
Should i use premium fuel 91 octane?

Thanks again Erich

 

[rivermobster]

So i have a new o2 sensor on order.
Should i replace it before i drive it hard or will after be ok?

Ill do fuel filter and new fuel.
Should i use premium fuel 91 octane?

Thanks again Erich

Don't drive it at all until you replace the fuel filter, flush out the tank and lines. Bad gas can cause all kinds of engine damage. It can easily stick the valves in the guides.

Do another oil change after you get the fuel system done. Your HC readings look ok, but the converter could be cleaning that up.

Then take it on a nice long drive! Couple river trips maybe? Then get it tested again. If it doesn't test clean, then try the O2 sensor replacement.