Question about 1991 Ford Ranger Supercab

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Failed e-test in 91 ranger

My 91 ranger with a 4.0 failed the e-test badly in the nox section, it has a new exahaust sysystem including the cat, after the test i changed the plugs that were very bad and air filter that was also dirty, new wires were installed and i actually found two vaccum leaks, the tune up was done after the e-test! i also cleaned the maf, anymore suggestions?

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  • fonz27 Jun 02, 2009

    thanks, my wife is taking it in but it is a local ford dealer so i know the tester and i told him to run it hard for me before he does it, he said he would but the test is tommorrow morning and i don't have time to change the oil, it looks really clean though, wish me luck and thanks again you guys are great

  • fonz27 Jun 02, 2009

    It passed!! my wife took it out right before the test and ran it at 140kmh for a couple country blockes and backed it right into the dealers shop and it passed, barely the limit was 988of something like that and it tested 922 in the nox, thanks again this site rocks!!

  • Richard Delahant May 11, 2010

    Did you have the 02 sensors checked? It or they might be carboned up.



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Change the oil just before the test and get the Cat as hot as u can.

Posted on Jun 01, 2009

  • sharon currie Apr 16, 2011

    My 1991 Ranger 3.0, 6 cyl had similar problem; Failed emissions badly. I replaced the CAT and 02 sensor and retested and came out worse: HC (before CAT & 02 sensor) measured 209 at 15 mph, 102 at 25 mph (max allowed 124 at 15 mph, 104 at 25 mph), the CO (before CAT and 02 sensor) measured 1.18 at 15 mph, 1.52 at 25 mph (max allowed 0.75 at 15 mph, .095 at 25 mph). After New CAT and 02 Sensor, HC measured 473 at 15 mph and 168 at 25 mph, CO measured 6.69 at 15 mph and 2.01 at 25 mph. Any suggestions on that?


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If it was the Nox section, check the EGR valve. It that fails, your Nox will go way up. The EGR reduces Nox at cruise speed

Posted on Jun 08, 2009


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1 Answer

HOW To: tune up Geo Prizm 1995, myself.

wow ,no posted smog report, (the failed gases) now that makes this 10s harder, and for sure more expensive.....
many post,. why not just add to one post
click comments and add.
or edit one. post.
all engines that fail smog run fine. (so says all owners)
(fine means zero,) in the real world.
what's worse is owning a 1995 in USA, and must get sniff tested.
(cant fool that method) no report by you, (paper)

ignore all statements by all smog testers,
only one statement (it fails!)
all others are lies, guessing and BS.
after all if they were fully trained and skilled they'd have a real job.
a fact. (or they get huge retirements from the state?)
The car needs to be check by a pro.
it needs to be scanned, with a custom scan tool that is not sold in any auto store until 1996 happened.

but if that NOT IN THE CARDS./ no money for a real ASE tech?
then yes, do a tuneup..

1: spark plugs. and new wires, cap and rotor.
2: filters. and fresh engine oil, (the oil can be full of gasoline is why)
3: the cat may be ok, is spending a fortune on that good?
on a wild guess,? like your smog guy quipped?
that be your call. no? (shot gun method or testing) your call.

in a shop they would get the engine running perfectly.
in closed loop hot and light cruise.
A NEW front 02 sensor for sure.
then they test the cat last, the CAT is always last.
i think this car has 3 way cat too, so is really 3 cats in one.
all 3 must work. or you fail... (for sure)

what if only NOX gas failed.????
if yes, we fix EGR first. then CAT last. (they work as a team)
what gases failed matters
and was not stated by you.
in a real shop they can sniff front of cat and rear
and tell you ,
bad engine, or bad cat. in minutes.
or both, sure.

bad engine means
1:engine is bad.
2: EFI controls failing, (fuel or spark)
3: misfires. (even some humans cant hear, omg)
4: and many more. but no smog sheet posted, no savvy.

a pro shop knows the pre cat gas levels that are normal.
if they are, then the cat is bad.
end story.

Dec 28, 2016 | 1995 Geo Prizm

1 Answer

Failed MEAS

wow, no context but i can read your mind?
ok SMOG failed. right?
what speed, there are 2 in uSA, 15 and 25.mph.
so there are 3 tests, which one. all are PPM in usa.
parts per million.
but is that HC , CO, or NOX? or ?

based on your numbers is HC
hydrocarbons or in barstool, its raw gasoline leaving rear of car.
unburned fuel..

572 ppm is way too high 12-19 is normal
id say the CAT is bad.
but can be , engine is bad, and burned out the cat.
that is why all savvy mechanics, check the that the engines
holds closed loop status, (EFI closed loop) at the speed yours failed.
if not in closed loop the cat will burn up (rich)
that is first.
Once that is cured. you check HC again. if out of spec
you did burn up the can , new cat time.

that is the correct way.

Feb 19, 2014 | 1998 Toyota Tacoma

1 Answer

My 1989 Mercedes 260E has no EGR valve and CA emission test failed NOX. What's next?

You engine came with EGR, here is a picture of it, make sure it is functional.808daddd-23be-456e-979e-50a2188da73b.jpg

Apr 10, 2013 | Cars & Trucks

1 Answer

What is the meaning of a failing test with NOx(ppm)

Oxides Of Nitrogen (NOX)

Above 2500 degree engine combustion temperature
nitrogen bonds to oxygen to form NOX

The EGR Valve is supposed to allow a certain
amount of exhaust gases into incoming air to
control high combustion temperature and control

Bad Egr Valve
Engine operating too hot
Cat too cool at inspection station
Fuel mixture issues
PCV issues
O2 Sensor issues
Injector issues
Ignition issues

Jan 30, 2011 | Toyota Previa Cars & Trucks

1 Answer

I got a 95 corsica 2.2L failed emission test the carbon monoxide is too high the hydrocarbons passed but were higher than previous tests and the nox passed but were higher than previous tests...

sounds like a bad cat and o2 sensor. try a scanner, if the downstream sensor is attempting to make a 99% fuel trim adjustment, you can bet it needs changing along with the catalytic converter. get someone to follow you and accelerate hard, a rotton egg smell is a dead giveaway

May 28, 2010 | 1995 Chevrolet Corsica

1 Answer

1994 honda accord failed its emisions test.

i would say change the O2 sensors and a new cat ,these readings are well over the top ,could have a exhaust blow on exhaust as well which will throw out the O2 readings

Nov 07, 2009 | Honda Insight Cars & Trucks

1 Answer

Failed emissions....high nox

Sticking egr will raise everything except nox. Bad o2 bad cat hard to give an accurate diagnosis with out checking it

Oct 12, 2009 | 1994 Lexus LS 400

2 Answers

Emissions failing with high NOx

Change the lambda/oxygen sensor in the exhaust.

May 21, 2009 | 1994 Mitsubishi Galant

2 Answers

Emissions failing due to high nox

NOx emissions are the result of high combustion chamber temps pure and simple. NOx readings go up whenever there are hot spots that exceed about 2400 degrees. Things like lean mixtures contribute to high chamber temps, as does over-advanced ignition timing.Lean mixtures are usually caused by some failed components or by air (vacuum) leaks in the intake.
Poor fuel quality contributes to detonation, another cause of high chamber temps.
  1. Check to make sure the vacuum system is tight.
  2. Try a full tank of high octane fuel(run at least half a tank through before testing)
  3. Have the tester do the rolling tests with the trans locked in first gear.
  4. Make sure the oxygen sensors is working.
If you have done all of this and still fail, You will need a new catalyst

May 20, 2009 | 2000 Mitsubishi Galant

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