Every year I have hire an exorcist to drive the demons from my '90 N/A Z so it will pass emissions testing. Can anyone offer help? I can usually get through by changing the oil and adding Bardahl 'No Smoke' before going through. The car has only 114,000 miles and is in excellent condition, uses no oil and gets about 15 MPG city, about 24 HWY. It has recent platinum plugs and other wise runs great.

It doesn't fail badly, just about 50 ppm on the HC and about 1% over on the CO. The car smells just faintly rich at idle... and the tailpipe is a little black instead of grey. Could it be the O2 sensors? If so, how difficult to replace them? I have plenty of mechanic skills and have done most of the work on my cars myself.

I've tried all the other tricks such as the gas additives too. ANY help is greatly appreciated.

Thanks,
Johann

 

timing, PTU, 91 octane, warm engine, thas all I can think of.

 

Barbabe,
Thanks for your quick reply. I have tweaked the timing, run 93 octane gas, and run it on the freeway before testing to fire up the catalytic converter good. I'm not getting any trouble codes. Not sure how the Power Transister Unit would affect emaissions... or how to tell if it's faulty.

Thanks,
Johann

 

call nissan and give them your VIN number they will tell you if it was changed. if it was then don;t worry abotu that. if tehy didn;t then run over to the dealership and get it changed for free!!!!

 

Run ecu codes first. if all is well there, search for vaccum leaks. It's possiblr to have vaccum leaks without ecu codes. You can check your cats with a infared thermometer, they should be around 400 degrees at operating temp. Correct timing is important too. Then there's cleaning throttle bodies, IACV and all electrical connections and grounds.

 

Thanks to both of you for your suggestions... I will definitely check with Nissan on the PTU. I got my entire FI system replaced free in my old '86 Z when they had the recalls on the fuel leaks.

I'll look for vacuum leaks too. I already cleaned my throttle bodies. I don't have an IR thermometer to check the cat though.... I've also cleaned all my connections and have a new TPS. The thing that really gets me is this is the nicest car I have ever owned... yet it's the ONLY one which refuses to pass emissions....

 

Welcome to my world.

 

Anyone ever replaced the O2 sensors on the '90-'96 Z? How difficult?

Thanks,
Johann

 

Passanger side. remove th ebattery adn get the "02 Censor tool" Driverside well you gotta remove brake mastercylinder, get a long *** extension and the same tool as the other side. It's hella fun casue after removing teh BMC you gotta bleed teh brakes and if you don;t oreder speed bleeders... well it's gonna be fun.

 

To ease the loosening of the sensors, run engine up to operating temp, spray some penetrating oil around the mating faces and then loosen while hot.

 

On the driver's side you should try from underneath the car before removing the Brake Master Cylinder. I think it would be easier to have to drop the exhaust than messing with the BMC and bleeding brakes...especially if its 1 person doing the job. I own a TT so it might be different on your car...Im not sure. hopefully this helps.

 

Thanks Guys! That definitely will help if I end up replacing them. I figured it would be a bitch to do the job from what I have done on the car so far.

"The Japanese didn't loose WWII... it just took them 50 years to win"

Johann

 

If it still doesn't pass, then run 87 octane through it. It'll run like ****, but it'll pass. Run it almost out of 93 octane, then only put in a couple gallons of 87.

^^This is a temporary fix. You have another problem somewhere. If you've never replaced the O2 sensors, then that's what I would guess. Your city MPG isn't very good, but the highway mileage is great.

What kind of platinum plugs? If they're not NGK, then change them. How old is the fuel filter and the air filter?

 

Thanks for your help. I've never come across the 87 octane fix before... do you know the technical reason it works? I've had the car 2 years and never replaced the O2 sensors... I suspect them from what I've researched. The plugs are Bosch Platinum dual electrode... they only have about 5k on them. Air filter is about 5k too and I cleaned it recently. I have not replaced the fuel filter, but I don't suspect it since I am having problems with slightly rich mixture rather than lean. The car runs great and always starts instantaneously.

I have never had a car fail emissions before... even old ones with high mileage and in poor condition. I am mystified...

Danke,
Johann

 

if your o2's are bad, they'll throw an ecu code. Even still you can do a resistance check on them.
It looks like you're just barely failing, so it's prolly something small like a vaccum leak somewhere, Are you failing at idle or at a higher rpm? do they test it under load on a dyno?

 

They only test us at idle here. How do I perform the resistance check on the O2 sensors?

Thanks,
Johann

 

O2 sensors can become 'lazy' meaning that they react too slowly; which could be the cause to your problem.

If you don't have 87, then use 89 octane. The reason it works is because the fule burns more easily and more completely. That's why a car will ping with lower octane fuel. The fuel ignites too soon. You just don't want to run the lower octane fuel any longer tyan you have. The car will run fine under no load, but if you drive it a little hard, then she'll start to ping.

 

Thanks for your explantion... that makes sense. I may just try that and go through one more time. I've already been through 4 times... and I was about ready to go ahead replace the o2 sensors.

If this fails, I hope it is just the o2 sensors. I can get them for $67 ea. if I do the work myself. And, if they really are bad, it's worth it to have the car run properly. It'll eventually pay for itself if I keep it over a year longer.

"If it's got **** or wheels... your gonna' have problems out of it"

Danke,
Johann

 

To 91 zxtt:

I tried the 87 octane gas and went trough again... like you said, it ran like a 3 legged dog, but it passed!!!

Both HC and CO dropped dramatically:

previous test:
HC 282.91 ppm
CO 2.50%

Today:
HC 19.39 ppm!!! OVER a 1,000 % reduction!
CO 0.27%!!!

Pass this on to everyone.

Thanks to ALL who helped!!

Johann B

 

This is a major reason why California has limited our premium fuel to 91 octane. It burns cleaner than 93. There are a lot of people out there that think running a higher octane fuel gives more horsepower. It's not true. The car would need to be tuned to the higher octane. All these people are doing is wasting $ and polluting the air. You should run premium if your car requires it.

 

That's true about the octane values. Unfortunately, the N/A Z'z have 10.5 to 1 compression ratios... and require minimum 93 octane fuel. It was knocking pretty badly under load after I put the 87 octane in. I filled the rest of the tank with 93 as soon as I left the inspection station.

I know I have a minor problem somewhere, and probably should fix it so I won't have to resort to these kind of methods in order to pass. But you know how that goes... I think I need to replace my center support bearing now because I'm getting a very high frequency vibration at highway speeds... Sometimes I could SWEAR that I can hear my car saying: "Feed me... FEED ME!" Know what I mean?

Johann B