91zxtt

Well f**king sh*t. Took my car to get it smogged this morning. F**king POS failed. It is now deemed a gross polluter at idle, so i have to take it to a referee once I get it figured out. It passed just fine at high RPM's, but the hydrocarbons were extremely high at idle. Max at idle is 120 ppm. Mine tested at 470 ppm (Gross polluter is over 270 ppm). At 2400 RPM it tested at 16 ppm. Max is 140. I'm perplexed. Hydorcarbons are basically a by-product of unburned fuel. Anyone have ideas? I'm thinking cats, maybe.....that could help explain why the car pulls real hard up to 5500 RPM's, but then seems to run out of gas above 5500 RPM's. Other than that it runs great. Smooth idle. No misses or backfires. No hesitation. My other thought is something to do with the idle control valve. If you guys remember a while back, I had a problem with a high idle that seemed to get progressively worse until I adjusted the screw on the idle valve. Now it idles at 700ish RPM's. Maybe I was just masking another problem, but what. I don't think I have a vacuum leak anywhere because Dad I checked the vacuum and it tested at 20psi of vacuum; which is strong. Timing's set at 15 BTDC. Just changed the plugs (NGk's) and fuel filter (factory). I do have that Seafoam stuff in the oil right now, but I don't think that could be contributing to it, or if it was, I don't think it would have that significant of an effect. I ran it through the brake booster and a bit through the fuel system, but I have a fresh tank of gas now. Suggestions???

CaptainZ

I had the exact same problem with my old 94 Pathfinder I used to have. Something was wrong with my temp sending unit so it wasnt allowing my engine to warm up properly. Plus I had about a million vacuum leaks. It idled real rough and would die if I let it idle for more than a minute. I got the vacuum leaks for the most part fixed, replaced the temp thing plus plugs, wires, cap and rotor, oil change etc. It still idled kinda wierd but it did pass. Before I had all that done it wouldnt pass, so what I had to do was go drive it kinda hard to warm it up a little more, and then have them do the smog test, and it would pass with flying colors. But after I replaced all of that stuff, passed just fine after that.

My Fairlady Z

i dont have to get smogged where I live

91zxtt

Captain-I replaced the temp sensor when I changed the timing belt 5k miles ago. And since I have 20 psi of vacuum, I don't believe I have any vacuum leaks. Obviously no cap/wires/rotor on these and since there's no misfire and it idles fine, then the coil packs aren't a problem. It was plenty hot. I had just driven it 15 minutes to work and it idled for a good 5 minutes before he tested it the 1st time. It was even hotter on the 2nd test because it had been running that much longer.

Fairlady....don't take this the wrong way, but f-you.

I spoke to someone at Z1 and he said it's probably the O2 sensors, but I'm not buying it because that would trigger an ECU error. Butch at Courtesy advised to tap lightly on the AAV with a hammer. He said that Carbon builds up in those and can cause the problem that I'm having. Maybe I can break the carbon loose with the hammer. Could explain why I had to adjust it. If not, then maybe I'll have to take it apart. Any chance of a TPS? I can adjust it either way and it doesn't seem to change anything. I'll work on the AAV when I get home.

CaptainZ

Hmmm. O2 sensor was my next guess. Faulty MAF??? Maybe

CanyonCarver

First bit of advice ...... Don't EVER take your car to a smog place in Cali that won't do a pre-test first. Unless, of course, they made you go to a test only center. I've heard that gross polluter deal is a real pain.

Now........ If you have the original cats, there's a good chance they're bad. If you have one of those infared thermometers you can check the cats with it. After running the engine for a while, the cats should be close to 400 degrees at idle. If they're cold, say 200 degrees replace them. I've been real surprised at how much new cats clean things up.

And.... for some theory and common sense (maybe experience). you said you had a idle problem? Check your ecu for codes. Especially bad o2 sensors. Bad o2 sensors can/will affect emmissions. On the seafoam deal, I can't see where it ever got to your iacv. Get some carb cleaner and go to it like I did last weekend. It helped the idle. Ideally, you'll clean things up with carb cleaner and then you'll have to readjust your idle speed to where it was before you messed with it. If you have the original injectors (I believe your thinking about replacing them?), when they get old, they start to leak. You can check them per the fsm. Pull one out, plug the connector back into it and apply fuel pressure (turn on the key to turn on the fuel pump only). It should not drip any fuel.

Lastly, get that air/fuel ratio gage. You probably would have known it wasn't going to pass if you had it. If your engine deviates very far from that perfect 14.7:1 a/f ratio, you're gonna fail.

I've learned to get the test done early, relative to the due date, so that I have time to order the replacement parts that I want instead of running around in a panic trying to get it done the day before the registration is due. I've also learned, that if I can't get it smogged in time, send in the registration fees on time anyway. If you get pulled over with out of date tags, but you paid your fees, and show the cop the failed smog test, they've always let me go without a ticket.

91zxtt

The place I took it offers a pretest, but there was nothing going on with the car that would cause me to suspect that there would be a problem, so I never even thought about it. I do have the orig cats. I have test pipes in the garage with hi-flow cats just waiting to be put on. There's a place 10 minutes away from wheere I live that does the smog diagnostics. I may just have to take it there. I think it's either the cats or the AAV. i checked the ECU a few months back because my check engine light came on. It returned code 51, so I guess I could have a problematic fuel injector. I try your TB cleaning technique 1st and cross my fingers.

The A/F gauge doesn't give you the air/fuel ratio. It just tells you lean/stoich/rich.

Not likely the MAF because it runs so well. No missing, no hesitation.

CanyonCarver

I'm not faulting how you get your smog checks done. I just found a guy that hooks the car up and gets an idea of how the car's running before he dials into the state. He'll tell me I need cats or need an adjustment beforehand. It's all part of his fees.

I'd get the new cats on anyway. Recheck the ecu codes. Did you do anything to actually repair the cause of the code 51? I'm not so sure a leaky injector would cause a code. The code 51 would come from a burnt out injector, a bad connection, or something where the ecu doesn't get a feedback signal. But then, if the injector isn't closing all of the way it might cause a resistance variation that the ecu sees. A real good sign of a leaky injector would be a spark plug with a lot of carbon buildup. Did you see any of this when you changed the plugs? Pull a couple again and check them.

Also keep in mind, A rich running condition will kill your o2 sensors and cats faster than anything else. Carbon buildup on your o2 sensors will actually short them out since carbon is conductive and they function from 0 to 1 volt. When they don't function you compound you problems. Carbon will also cover the reactive materials of your cats causing them to quit working.

"Not likely the MAF because it runs so well. No missing, no hesitation." Agreed

I know the average AFR doesn't show the actual ratio, but you failed at idle pretty badly. It probably would have shown something isn't right.

So in conclusion, If your plugs don't have any serious carbon buildup, and you don't have any ecu codes (including o2), I'd bet it's da cats.

I had a ford p/u that failed hc at like 650 ppm, new cats brought it down to like 140 ppm and a pass. Like I said you can check them with a infared thermometer.

DanZ32

I would agree with Canyon, although from my experience, when cats get clogged there is usually a sympton exibited. Hestitation (even slight), idle, sulpher smell as examples.
You mention in your first post you have Seafoam in the oil. How long have you had it in? I'm not suggesting you don't change the oil regularily (I wouldn't be so condescending). It may be time again because of the additive and the work it did. It couldn't hurt.
Good luck.

91zxtt

Well, this is what I'll be doing in the next few days....
1st-Clean the AAV's the way Canyon suggested.
2nd-Replace all the crap I was going to anyway; which includes new hi-flow cats w/midpipes from SpecialtyZ and O2 sensors. With any luck;when I take it to the referee, it'll pass and I won't have to worry about it. If you guys think of anything else, let me know.


Oh...as far as the plugs go, they all looked great. None of them appeared wet or to have excessive carbon.

91zxtt

Oh....the oil has 1500 miles on it. I've had the seafoam in for 150 miles. I'll probably change it. Since it's getting to be that time of year, I may switch over to 10/40.

91zxtt

Took it to the smog station again. Hydrocarbons have come down, but they're still way too high. I may have to bite the friggin' bullett and take it in to have someone else diagnose it. The only place up here is the Nissan Dealership. It goes against everything I've ever said or done. I may try changing the oil to see if maybe that seafoam stuff in the oil is the culprit. I've run it about 200-300 miles since I added it. It says to change it at 500-1000 miles. I can't imagine that's the problem, but it's just that it runs so well. Since I had the battery disconnected for several days, there aren't any stored fault codes. I'm at a total friggin' loss. Any other suggestions???

CaptainZ

Slip them a $50. Thats the only suggestion coming to mind that might help you pass

91zxtt

Ha! The guy that owns the shop is also a Police Officer. He's the person I've been talking to. That probably wouldn't be good. The thing is...I want to get it fixed. With the hydrocarbons that far out of whack, there's something wrong. I'll change the oil and try it again.

CaptainZ

What I cant figure out is if your are failing something is wrong, yet as you say, EVERYTHING runs perfect. Are you sure there is absolutly no hesitation, rough idle, smoking, noise, etc. I guess you can either just start replacing stuff untill you pass, or pay the $90 or whatever at the dealership to diagnose it. I am sure that even though the dealership is satan, they may be able to save you some time and possibly money by letting them diagnose it. Something to ponder.

topless93

My Z ran great also, so I didn't worry about emissions test either, but failed. After talking to some others about this. I was told I did what most people do wrong. I drove my car straight from the house (about 4 miles) to the testing station. This is not enough time to get the cats hot enough to burn the extra fuel left over from the engine, to pass the probe test. I don't know if this will help you, but this is what I did and I passed with flying colors.
1) put in brand new NGK plugs.
2) changed oil and filter.
3) new pvc valves
4) fresh tank of gas
5) new air filter
6) ran car on freeway for about 45 minutes @ 70 to 75 MPH
My Z is a 93 n/a with 60K, I don't know if this matters.
It pass with out a hitch. Maybe some of this will help. I'm like you, I could have payed someone to pass my car, but I also wanted it to run right. Good luck. LATER

Z_WRECKER

Wow... i never knew about that... thanx a lot man...91 you taking notes i hope you pass Jody

91zxtt

1) The plugs aren't even 50 miles old yet. (NGK PFR 6B-11B).
2) I'll be changing the oil.
3) PCV valves replaced a couple thousand miles ago (3k-5k tops).
4) I have 1/3 tank left. I'm think about running a tank of av gas through it. Can anyone think of a downside to doing this?
5) I cleaned the air filter around the same time I replaced the PCV valves.
6) I guess it's possible it wasn't hot enough. I know the engine was hot (cooling fan turned on), but maybe it hadn't run long enough to get the cats up to the proper temp. When it was 1st tested, I had driven it 15 minutes to work. It's a 2 lane freeway. It's 55-60MPH all the way and I don't usually get hard on the throttle. Today it was about a 10 minute drive. It's possible.



I have another idea....What if one of my connectors to either a coil pack or a fuel injector is semi corroded, or somewhat faulty??? It could allow electrical current through, but possibly not enough to generate a strong enough spark from the coil pack, or not enough current to open and close the injectors all the way. Am I reaching, or do you guys think this is a possibility. I'll bust out the ohm meter this weekend and see what I get. May be time for some new connectors. I'll change the oil later this week. I'm going to call the local Nissan dealerships (Chhico and Redding) and see if there's anyone in the service department that has had any experience with this car and/or motor. They do have the tools to run the proper system checks, so it could help me narrow down the search. Any other ideas?

bardabe

Yeah smog's here in caly really suck *** my car wuld not pass smog beacuse they said it was not grounding properlyso they charged me 190$$ to "fic" that problem and to pass the thamn thing

My Fairlady Z

dam cmon man type a little slower so we can make out what you are saying ffs quality not quanity man..

91zxtt

Ok guys,...I may be onto something. Pulled out the ohm meter and checked the coil packs. I checked 5 out of 6 (Didn't feel like fighting with the back one on the driver's side). 4 of them read 1.4 - 1.6 ohms. 1 read 2.4 - 2.6. That's a fairly significant difference (70% ish). Here's my thought.......That coil pack likely has a small short in it which is not causing a big enough difference to effect the overall performance (daily driving); however it is enough to where the spark is not strong enough to burn off all of the unburned fuel. This would cause a rich condition; however, the O2 sensor is trying to adjust the a/f by sending less fuel to that bank of the engine. The O2 sensor is trying to correct the problem, but can't adjust it enough to make it run properly, thus causing the other cylinders to run lean. The O2 sensor can't adjust each fuel injector. It can only adjust the left and right banks. That could be the cause of my smog problems. Everything tests fine except for hydrocarbons at idle. A lean condition causes increased hydrocarbons; whereas a rich condition will cause increased hydrocarbons and higher CO readings. My CO is fine. This could also be the cause to my pinging problem that I've experienced when the car is hot.

Here's what I need you guys to do.....if you have a multi-meter, please check a few of your coil packs. Remove a coil pack connector. You'll see 3 prongs in the coil pack.... I need you to place the multi-meter tips on the 2 left prongs. What readings are you getting???? Thanks in advance.

Riz Z Speed

So, your ECU isn't throwing any codes?

91zxtt

Nope. It threw code 51 several months ago. I had the battery disconnected while I did the work this last weekend, so it would've cleared it all.

91zxtt

I stumbled across this....

http://www.300zxclub.com/showthread.php?t=15586

It looks like people have had some success disconnecting the vacuum line from the fuel dampener.

I spoke with a Nissan tech who was actually quite knowledgeable about this car. He suggested that my TPS may not be adjusted properly....i.e., my car's ECU doesn't know when it's at idle. I'm going to play with that this evening.

Also, does anyone have any coil packs they're looking to get rid of. I thought I remember someone buying several in an attempt to solve a misfire above 3500 RPM's. If that person is out there and you still have those coil packs, let me know. I may be interested in taking a couple off your hands.

91zxtt

Well, crap.....My coil packs tested fine last night. I'm guessing that the resistence levels change when the packs are hot. It could still indicate a problem, but I'm not so sure anymore. I was also having a hard time getting any readings off of the TPS. I think my multi-meter may be a POS.

So, since the problem is caused by not enough fuel, then could an adjustable fuel pressure regulator make a difference? That would allow me to increase my fuel pressure and send more fuel to the engine. What do you think?