Any smog/emission experts in here?

[69hondo]

My rv didn't pass smog. Hydro carbon way to high at idle. Any ideas? It has the cat still. This is a 2000 Worhorse chassis with the 7.4/454 mpi. No engine light on.

 

[DaveH]

start with a good old-fashioned tune-up.

i would pull all 8 plugs (definitely replace them) but more importantly look at the color/condition to see if they are all even. If one is darker then the rest that is a good indication of a cylinder that may be causing the issue.

given its age, I would also replace the wires. not sure if this is a distributor or coil packs.....either way, those items are also a potential issue requiring replacement.

if it has an 02 sensor, I would also replace that. you don't have to have a code..... a sensor is capable of reading incorrectly but not being in a "faulty" condition. an exhaust leak would make the sensor read lean and the computer adding fuel to compensate causing the higher HC reading.

also check your PCV system....thise valves get sticky with age and are cheap to replace.

probably also time for an air filter.

start with all that and see if it passes.

 

[69hondo]

PLugs, wires, cap, rotor and air filter all new prior to the test. I will check the PCV valve. forgot about that.

 

[hallett3]

If it has oxygen sensors change that. I just went trough this on my 2001 Chevy with no check engine lights . A mechanic buddy of mine said to do this has had success with it . I changed both right and left exhaust and passed no problems. And he said to be sure you get Gm sensors . Bosch and after market don’t cut it .

 

[73beast]

PLugs, wires, cap, rotor and air filter all new prior to the test. I will check the PCV valve. forgot about that.

Oil change too....

 

[LargeOrangeFont]

Was it warm? Or did you start it and drive it down the street to the smog test? You need to go drive it with some spirit and get the cat up to temp before a smog test.

Notice at 2000 RPM it’s perfectly fine, this is very likely a simple problem. If you did the full tune up already, look at the O2 sensors, they may need to be changed.

 

[HALLETT BOY]

Also check for a vacuum leak

 

[BigRedBryan]

HC's are unburnt fuel, look for anything associated with that, such as a fuel pressure regulator or even a stuck injector. Try and see if you can borrow a good scanner like a tech 2 and watch real time fuel trim, both short and long term. Being branded a gross polluter isn't a good thing... more than likely its something simple...

 

[BigRedBryan]

Smog an RV? Only in California. lol

2 speed idle test

 

[DaveH]

HC's are unburnt fuel, look for anything associated with that, such as a fuel pressure regulator or even a stuck injector. Try and see if you can borrow a good scanner like a tech 2 and watch real time fuel trim, both short and long term. Being branded a gross polluter isn't a good thing... more than likely its something simple...

definitely flow the injectors. especially if this is an RV that doesn't get used regularly......old fuel is murder on efi systems.

 

[rivermobster]

Oil change too....

Bingo. Do this first!!!

Then have em do a quick retest and see what you get. Change the air and PCV filter as well. If the oil hasn't been changed in awhile, this could easily solve the problem.

 

[SBMech]

Cold piped it IMO. Did he have to do the conditioning test? (hold it at 2500 for 3 minutes) If not something was wrong or he fucked you.

So either weak cat, open thermostat (not achieving closed loop) If it's got air injection maybe the valves are stuck? (should set a code).

If it's a medium duty rating chassis then many of the normal OBD2 monitors are disabled, so you won't get codes for some of this.

Funny enough, if it's been over a year, an oil change alone can drastically drop HC's, I'd start there myself. At 75k if you have never tuned it, plugs-wires-cap-rotor-filters will certainly be appropriate.

 

[overdue]

Any luck

 

[Your ad here]

I took a smog class at Saddleback College... a big thing was change the oil before getting any vehicle smogged.

 

[lbhsbz]

The beauty of modern fuel injection is that with scan data (and someone knowledgeable observing it) and a few pinpointed tests based on the scan data...it can be positively diagnosed. Where are you located?

 

[Big B Hova]

Sounds like your rv needs an .650 lift cam swap

 

[77charger]

Sounds like your rv needs an .650 lift cam swap

Rv cam

 

[69hondo]

Any luck

Wont be able to get to it until the weekend.

The beauty of modern fuel injection is that with scan data (and someone knowledgeable observing it) and a few pinpointed tests based on the scan data...it can be positively diagnosed. Where are you located?

High desert, Hesperia.

 

[dribble]

I’m looking at excessively high 02 levels at idle and cruise and thinking he has a major vacuum leak or something else causing a misfire at idle. I would first check for an intake leak with focus on all vacuum fittings and hoses as well as the manifold gasket. Then pull the plugs and run a compression check. HCs at that level indicate a cylinder not firing or not completely burning the fuel. Not sure if that’s a distributor engine or not but if not there could be a bad coil.

 

[LazyLavey]

It's obvious and nobody has suggested to change the prop?

 

[69hondo]

Update. Passed with flying colors. From 875 all the way down to an 8

 

[LargeOrangeFont]

what did you do?

 

[69hondo]

New fuel pressure regulator and new full exhaust.

 

[sintax]

New fuel pressure regulator and new full exhaust.

including a new cat?

 

[69hondo]

including a new cat?

Two new cats.

 

[sintax]

Two new cats.

nice, that never hurts

 

[cakemoto]

Ouch.. sure that was not cheap.

 

[HTTP404]

Ouch. I was hoping for the oil change fix.

 

[lbhsbz]

New fuel pressure regulator and new full exhaust.

Did you have an issue with longer than normal cranking time on a cold start? Or…does it fire now with shorter cranking time on a cold start? That would be an indicator the Regulator was leaking fuel into the plenum…could have killed the cats I guess…I’m trying to figure out if the cats and regulator were both bad, or maybe just one or the other.

 

[dribble]

Even an engine without cats should not have HC’s at that level. I believe he had a lean misfire at idle caused by low fuel
pressure. When the rpms went up the HC’s went to normal. The dumping of raw fuel in the cats at idle could have taken them out.

 

[Kachina26]

Two new cats.

Smog Depot, looks like we're neighbors. New cats can easily mask an actual issue. I've seen many a car come in for driveability concerns that had a new cat that some shop tossed on to get it through smog. Who recommended the cat?

 

[4Waters]

Even an engine without cats should not have HC’s at that level. I believe he had a lean misfire at idle caused by low fuel
pressure. When the rpms went up the HC’s went to normal. The dumping of raw fuel in the cats at idle could have taken them out.

Exactly, I'd like to see what the O2's are doing. Are the switching or are they are they pegged lean or rich

 

[69hondo]

The regulator killed the cats.

 

[Kachina26]

The regulator killed the cats.

Ah, I blew right by that post. Good deal.