Jump to content

Need help passing smog check


shaggy
 Share

Recommended Posts

Posted (edited)

Hi guys... My '95 SE almost got through smog check (CA) today.

 

Only the low speed (15mph) NO check failed, reading higher than usual Nitrous Oxide (NO) levels (for this vehicle). All other checks passed.

 

I have a second try before DMV deadline next week and would really appreciate your suggestions.

 

A few particulars: There's a slight leak at the driver's side exhaust manifold, but it's been that way through all previous smog checks and passed OK. I keep it as tight as possible, and don't think it would have caused this fail.

 

I know that high NO is supposed to be from overheated combustion, caused most likely from a too lean mixture. So I wonder if the ECU is being wrongly informed by a bad sensor. MAP/ air temp sensor reading too high?

 

The oxygen sensor was replaced 5 years ago, don't know if that's worth a try(?), as they're not cheap. The plugs probably should be replaced, and could maybe make a difference.

Air filter too, perhaps. And maybe a long hard freeway run before taking it in again...

 

Any other ideas would be welcome

 

Thanks!

Dave

 

Edited by shaggy
Link to comment
Share on other sites

I would start by checking the MAF. It's a hot-wire MAF, so the crud that accumulates on the filaments insulates them from the passing air, making the computer think there's less airflow than there is. I messed with a Buick a while back that was running lean as hell, white plugs, went into limp mode if you stepped on it. The MAF was filthy. You can get proper MAF cleaner in a can, though I've gotten away with alcohol and the corner of a paper towel. Don't use anything that leaves a residue when it evaporates, and be very careful with the filaments. Also check the condition of your vacuum lines and the tube that connects the MAF to the throttle body. Damage to either will let in air that the MAF doesn't know about.

 

The exhaust manifold leak is pretty much standard on these. There's a test mode on the ECU for testing the operation of the oxygen sensor, it's in the EF&EC section of the service manual. These don't have MAP or air temp sensors, at least not for the VG30E (if there's an air temp sensor, it's for the climate control). General tuneup stuff like plugs and air filter aren't a bad idea if they're old, but I'd be surprised if either was the cause here.

Good luck!

Link to comment
Share on other sites

2 hours ago, Slartibartfast said:

I would start by checking the MAF. It's a hot-wire MAF, so the crud that accumulates on the filaments insulates them from the passing air, making the computer think there's less airflow than there is. I messed with a Buick a while back that was running lean as hell, white plugs, went into limp mode if you stepped on it. The MAF was filthy. You can get proper MAF cleaner in a can, though I've gotten away with alcohol and the corner of a paper towel. Don't use anything that leaves a residue when it evaporates, and be very careful with the filaments. Also check the condition of your vacuum lines and the tube that connects the MAF to the throttle body. Damage to either will let in air that the MAF doesn't know about.

 

The exhaust manifold leak is pretty much standard on these. There's a test mode on the ECU for testing the operation of the oxygen sensor, it's in the EF&EC section of the service manual. These don't have MAP or air temp sensors, at least not for the VG30E (if there's an air temp sensor, it's for the climate control). General tuneup stuff like plugs and air filter aren't a bad idea if they're old, but I'd be surprised if either was the cause here.

Good luck!

Thanks very much! I remember about the MAF now, it's been a few years. Will check it out. 

Link to comment
Share on other sites

Posted (edited)

OK, so I got a can of CRC MAFS cleaner and got the MAF sensor wire sparkly clean. Checked the air filter, which seemed OK. I replaced the old O2 sensor with a new Denso one. Found and patched up a nickel-sized hole in the muffler.

I can't easily get to the driver side exhaust manifold, but I did get the rusted-on heat shield out of the way enough to tighten down one loose nut, which helped quite a bit in making the leak less obvious.

I poured a bottle of Lucas injector cleaner in with a half tank of gas and will do a few hard freeway miles over the weekend before I take her in again for another try.

 

Tryin' to think of anything else that might help...

 

PS - This is promising. There's a very noticeable increase in power and throttle response immediately following the O2 sensor replacement. 

 

Edited by shaggy
Link to comment
Share on other sites

You may already know, but here are the usual tricks to help pass a smog: 

Change the oil before hand. Change the oil when the vehicle is "hot" so that more dirt and junk is in the oil.
Maybe change the oil a 2nd time several days later also. 
Change the oil filter. 
Change the air filter. 
Drive the vehicle around for half an hour or more so that everything is "warm" and ready for your smog check. 

Sometimes these tips are the difference between a pass and fail, and especially for a Pathfinder.

Link to comment
Share on other sites

Thanks for reminding me. I thought the oil was OK as I changed it not long ago. It sure gets dark quickly though. 

Taking her over again this afternoon. I think I'll get through this time. 

Thanks everyone for the suggestions. I'll post back later with an update.

 

 

Link to comment
Share on other sites

So, a last ditch attempt a day before the deadline, but my work paid off -  the PF passed smog with flying colors... notwithstanding the typical PF *minor exhaust manifold leak* (wink-wink). Took a second attempt at a different place, and another $100 smog fee, but I'm happy.

So if all goes well, I got another couple years keeping this old bus happily rollin' along. I hate to think about getting a newer truck - they just don't make 'em like this anymore... 

 

Thanks guys!

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...