emissions

[thndrwhls]

An 89 VG30, I have been trying to pass this thing since June with no luck. It would seem that the every time I fixed a potential problem the worse it would fail. The O2 sensor, new cat, the Temp sensor, the heater plate under the TBI and plugs wires etc.

 

The one thing that has yet to be fixed is the broken manifold stud which I have been told would have no efect on emissions. However today I was speaking to a local mufler shop about headers and replacing studs and was told that it could possibly throw off the O2 sensor due to sucking cold air through the gap.

 

I have always run this thing through inspection after running it to temp, not running the AC or anything else. Short of trying to trick the system I have tried everything that would apear to be a problem.

 

It runs great, I have been told though that with a gas analyzer it cold be made to pass the test however it would run like crap so I would have to bring it back to have it retweaked.

 

I have a hard time believing I will have to go through this everytime I have to have an inspection.

 

HELP!!!

[mws]

Don't have a lot to offer, but I know your pain. The TBI'd models seem to struggle when the miles get high.

 

On my '87, it would fail HC test at idle but pass fine at higher RPM. The guy doing the testing was pretty cool (he saw that I had put a lot of effort into making it run clean - new everything - and I go there for all of my vehicles) and he let me fiddle a bit while still hooked up.

By turning the idle speed up 50 rpm, the HC levels plummeted - from just barely out of limit to well under. Haven't figured out the why on that yet... Wish I could!

 

He was also kind enough to not notice the idle rpm was just a scosche over the defined maximum when he re-ran the test!

 

The moral: Try the test with higher idle speed.

 

The manifold leak is an intriguing possibility. Let us know if you see a difference from fixing that. I also have a leak, but only when cold. No audible leak once warmed up, but maybe it's part of my problem. I will be fixing mine before the next check and I'll be able to report if it made a difference, but that won't help you now. Sorry!

 

Also, that thingy bobby behind the drivers headlight (it's an air injector) will cause problems if not working right.

 

One last thing I'm considering is adding an MSD6 box. I have heard of other vehicles (like SBC's) getting better combustion and significant drops in HC emissions at idle with them.

 

Please let us know what you learn!

[FLApathy]

move to fla

[revgolem]

Not that I, and I assume NPORA, ensorses such things... but I've heard tell that it you flip the PCV valve upside down, it would pass with flying colors... though I don't know this for a fact.

[thndrwhls]

Man, I have tried the higher lower thing, aside from the fact that they have me run at higher RPM's for like 3minutes to blow out the system and it still fails. I dont seem to have a problem with the HC's it's the Carbon Monoxide thats killing me. I have been through like 8 times. I have gotten two tickets over this and have a pardon from the judge because of my efforts, and paperwork to back it up, until July of 06. I thought this kind of silly since my renewal is in June, but whos complaining if I get pulled over all I have to do is show the letter. Ha, I guess I cant complain to much but damn, I just want to pass the freaking thing.

 

BTW, Florida doesnt sound bad at all...

 

Peace Brutha's

 

Keep'em coming...

[nissandoms47]

it hasnt thrown codes? just get a new engine lol

[lgranch]

Go find a bottle of RXp. I know places like Autozone carry it. Dump it in the tank and run half thru. Get the engine good and warm (slightly overheating is good) and get the pathy tested. RXP does not fix the problem it fools the test equipment. The test equipmet should see CO2 not CO. However there are some states (california) that this may not work. Ohio, NJ, CT no problem.

[Slick]

in CA pathys are test station only....... :sniff:

 

my pathy failed CA smog bareely in the hc's also.. and i have new headers.. blah blah.. but my head gasket is shot.. and funny but my rpm's were also higher than normal.. and she still failed.... i guess it just depends how strict your testing is

 

good luck!

[Kn0xville]

i had a lot of trouble getting mine to pass! might wanna make sure your PC is sucking like it should, and replace the vavle. Also might wanna run a new ground from the MAF sensor. Im sure youve done the plugs cap and rotor? fresh oil change can help, new cat, o2 sensor. I have the manifold leaks too and i passed. i turned my timing WAY down to where she almost couldnt run on her own and thats what made it pass. I have to do it all again in a couple months.. cant wait! and ya, run a lower octane gas and some gas line antifreeze will help too! and be sure to run that engine until she gets good and hot and dont let em shut it off.

[mws]

Hmmm... I just noticed in your post that your problem is high CO, which is a very different critter than my high HC issues.

 

High CO is usually caused by an over-rich fuel mixture. So anything that could cause just a tiny bit too much fuel to be injected during the test could be at fault.

 

Possible causes I can think of:

 

- O2 sensor, of course! You already replaced yours... was there any change at all in results? There is always a slim chance that the new one is not working right for your engine. I have heard of some vehicles being sensitive to the brand used... I haven't heard that of Nissans, but just so you know - some cars will not pass unless they have OE or equally high quality sensors.

 

- Cat converter, of course.

 

- Computer (ECU) is thinking engine is colder than it really is and injecting too much fuel for the actual conditions (think bad coolant temp sensor - not the one for the gauge, but the one for the ECU)

 

- Bad or incorrect temperature thermostat. If it is opening too soon or not closing properly, the engine will not get up to optimal temp, and ECU will continue injecting an enriched mixture for that.

 

- Dribbly drooly or oversized or worn fuel injectors. If injectors can't squirt small enough quantities, it will always be too rich. Not as likely on a TBI vehicle as on an MPFI, but always possible.

 

- The leaky exhaust manifold thing.... I find it hard to believe it is leaking so bad it suck in enough air to upset the O2 sensor, but if it could, it could cause problems... Is it popping noticeably when warmed up? Most pop at start up and then seal as the engine warms up.

 

- Air flow sensor. If ECU thinks engine is getting more air than it really is, it will inject too much. The 02 sensor should help it re-correct that error, but if the error is too great, the logic algorithm won't compensate enough.

 

- Really clogged or malfunctioning IAC valve not letting enough air in...

[mws]

Another thought - Is the O2 sensor heater working?

 

Quick check: With engine cold, pull out sensor and gently clamp to side of exhaust. Turn key to on (don't start unless you like loud noises). Sensor should get very hot within a few seconds.

 

If it's not, check to see if you're getting 12 volts to it.

[thndrwhls]

Hey great, you guys are most helpfull. I have replaced the O2 sensor, the temp sensor and the heater plate undre the throttle body, and it seemd to get worse. I'm gonna try some of the other suggestion and see what happens.

 

 

Thanks,

 

Joe

[mws]

With high CO, I don't think your AIV is a top candidate (more so if high HC's..) but it is probably still worth a quick look.

 

It seems to be a relatively common culprit on older or high mileage pathys. It has a filter and some reed valves in it. When it is not working, it does not inject the extra air in the exhaust, which means the leftover HC's do not burn off like they should.

[barthel]

Silly question, anyone ever changed that filter in the AIV box?

[88pathoffroad]

Just a note, it's not possible to "flip the PVC valve" on a Pathy. It screws into the intake.