I have a 1992 Ranger with a 4.0 eng. in it and it runs great and I keep it upreally good bu here in Ca. we have those stupid smog checks (income for the politicians) and two years ago it passed but with los numbers in the NO ( nitrious oxide ) and this year (today ) it failed just that one thing. Max number allowed is 711 and mine was 969 in the 15 MPH range. In the 25 MPH range it was 613 max allowed and mine was 709 Does anyone know smog testing very well and can say what might be sending these numbers too high? Somebody has mentioned too much carbon? I'm open to knowlegable suggestions. Many thanks, Hank

 

Nox is controlled by the EGR. EGR reduces combustion temps, which in turn reduces Nox.

Was your HC high at all?

If your HC wasn't marginal, focus on the EGR.

If your HC was high, you may be heating up the cat too much.

If your HC was low, check for a vacuum leak which could lean your mixture out and raise combustion temps.

4.0s have a history of vacuum leaks at the o-rings sealing the intake. Cracked intakes are also possible. However, since you don't have a CEL or code, any vacuum leak would be pretty small at this point.

 

^ + 1 & you might try retorquing the lower & upper intake manafold fastners to spec, inspecting/replacing the PCV valve & its rubber hose if its time or never been done & having a good look at the condition of under hood vacuum lines & how tight their connections are.

If its using some oil, have a look at the EGR valve & the DPFE feedback port/orifice below it for carbon deposits that can restrict the exhaust feedback to the DPFE sensor & cause the computer to mess up the amount of EGR fed to the engine.

If you suspect intake side carbon deposits are leaning the air/fuel ratio to the engine a little, maybe run most of the current gas out, then add a 20oz Chevron Techron Concentrate Plus to the tank at the pump so you get good mixing, before filling up with Chevron, Texaco, CalTex, or now Shell, which have some PEA in them, so the extra PEA in Techron at the pump will raise the treat rate 10X above pump gas alone & should tidy things up in one tank.

During the treated tank, do the high rpm part of the Ford prescribed 4.0L decarb proceedure, with daily spirited driving at rpms above 3600 for 2-3 miles to blow out carbon loosensd by the Techron treatment & run most of the treated tank out.

Techron will remove fuel injector, intake valve, piston crown & combustion chamber head deposits, usually in one tank.

If you suspect the MAF sensor may be dirty & causing a lean air/fuel ratio, remove the battery B- cable to wipe the computers KAM & let the MAF sensor cool if its just been deiven, then carefully clean it with a non residual formulated MAF spray, like CRC or Valvolene MAF cleaner. Don't touch the sensor wire with the spray wand & keep it squeeky clean on reinstallation.

Then go through the Ford cold & warm idle & drive cycle relearn proceedures to reset the IM monitors.

More thoughts for consideration, let us know how it goes.

 

run it on alky right at the inspection? just enought to drive in, do the check then drive out.

 

This is a reply to 85e15031X4mTod No, the HC were very low Max allowed 15 MPH~~ 86, mine was 4. Max alowed ar 25 MPH~~Mine was 0 . What you are saying, that this suggest looking at the EGR valve and vacuum lines associated there. The smog check machine doesn't check the EGR valve but most everything else. I just had a fuel injector put in about 8 months ago and let a automotive shop do it as my mother just passed or I would have done it myself. They routed the acellerator/ transmission cable all crumpled between the firewall and engine and scewed up my alarm system to boot. They should have installed those o rings and intake manifold gasket whn they needed to remove that to replace No. 5 fuel injector. I'm assuming that they did the job right ? I probably should check the torqueing on the intake manifold as a precaution. Vacuum leaks sound promising though as well as the EGR valve, thanks Hank

 

[quote=capthank;11730901]This is a reply to 85e15031X4mTod No, the HC were very low Max allowed 15 MPH~~ 86, mine was 4. Max alowed ar 25 MPH~~Mine was 0 . What you are saying, that this suggest looking at the EGR valve and vacuum lines associated there. The smog check machine doesn't check the EGR valve but most everything else. I just had a fuel injector put in about 8 months ago and let a automotive shop do it as my mother just passed or I would have done it myself. They routed the acellerator/ transmission cable all crumpled between the firewall and engine and scewed up my alarm system to boot. They should have installed those o rings and intake manifold gasket whn they needed to remove that to replace No. 5 fuel injector. I'm assuming that they did the job right ? I probably should check the torqueing on the intake manifold as a precaution. Vacuum leaks sound promising though as well as the EGR valve, thanks Hank

 

I just checked into the emissions system in the Haynes Manual and as 85e150six4mtod sugested to focus on the EGR valve. but quoting fromHaynes manual 1090 and later 3.0L and 4.0L V6 engines are not equipped with an EGR system. Any new comments now on this ? Hank

 

Not sure where to go if no EGR. However, I looked for an EGR on NAPA and found one for that year and engine. Got anything connected to an exhaust manifold (driver side on my '98 SOHC) that looks like this:

NAPA AUTO PARTS

 

I see the Napa link will no longer take you all the way to the EGR. If you put your vehicle info in, they have a nice picture....

 

Usually the only thing that's connected on the exaust manifold is the oxygen sensor. You sure that's not what you are talking about ?

 

Don'tknow if I know theford cold and warm idle and drive cycle releanprocedure. the other part is understanable. Hank

 

Drive Cycle: Ford Motor Company Driving Cycle
Idle Relearn: Ford Truck Enthusiasts Forums - View Single Post - high idle problem

 

No, Oxy sensor is different. This gizmo works to meter the right amount of exhaust gas to make the EGR work. Just trying to see if your truck does have one.

If not, I want to think you have a vacuum leak that is leaning you out enough to raise combustion temps and give you those very low HC numbers. Although your HC numbers are not surprising based on what I recall about my HC numbers on a couple vehicles.

 

1992 ford Ranger 3.0 and 4.0 V-6 engines do not have an EGR valve but they do have a DPFE feedback port. I have loked for a vacuum hose leaks but have not found any so far. Did find the upper intake nuts not as tight as I figured they should be and tightened those. I saw in Pep Boys today, they have a new product called " Cataclean" It's expensive but it's susposed to clean your catalytic converter,oxygen sensors,fuel injectors and cylinder heads ? Tempted to try some! Gonna stick my code checker on this beast also. Hank

 

With low HC and clean CO (you didn't post CO but you passed, right?) I would say the cat is working fine.