Help needed from smog tech's and 240 guru's

[OdessaS13]

Took my 1992 240 to go get smogged, failed. high measure's in almost everything. I read the high Nox thread in the archives but i think my situation is a little worse. Im seeling car so i need to figure this out asap and i have one more free re-test which i want to do ASAP. I really dont have time to make wild guesses on whats causing this so this is why im resorting to asking any smog tech on this board or anyone else that can offer any usefull info.

Notice my timing is way off so can that be causing these kind of measurements? and is it adjustable that much so i can get it back to stock 15- 20? What kind of results will lowering the timing have on the readings.

Once again any advice will be greatly appreciated.

here is a pic of what the reading look like, im ready to bang my head against the wall because im very pissed off. :(

cliff notes:
Cat was replaced at 126k
Timing chain was replaced at 140k
Can a walbro 255 cause this?
new spark plugs
new ngk spark wires
hks intake (dont have stock one)

There is nothing else i can think of that would have an effect on emmisions

http://i13.photobucket.com/albums/a283/VqNissan415/pic2.jpg

[Tomslide50]

NOX is most likely high because your timing is so advanced. Getting that properly set should take car of your high NOX readings. The HC's aren't really a problem on their own, because it's high CO's that are causing HC's to go up. CO is a direct indication of AFR. You're running rich. The walbro could be it if you're pumping more fuel than your system can effectively return. I wouldn't think that the stock return system would have a problem, but certainly if you have a stock fuel pump laying around throw that in. Have you tested the fuel pressure? How's your fpr signal line? Nissan released a tsb about those hoses burning on the egr piping. If that happened then your regulator isn't decreasing the fuel pressure to match the low pressure in the intake. This theory would be supported by the fact that the AFR gets better with rpm. At a higher rpm the vacuum is lower and so your higher fuel pressure becomes closer to what the engine acutally needs and the condition gets better. First step would be fuel pressure test. See what you've got. Fuel pressure at idle should be about 7-10psi lower than fuel pressure with key on and engine off(or at full throttle). Get that timing within spec too!

[Tomslide50]

What kind of results will lowering the timing have on the readings.

Forgot to answer this- Backing off the timing will effect NOX mostly. It will also have a small effect on HC's. HC's go up any time there is an incomplete or inoptimized combustion. This can be from a mechanical problem, ignition problem, or AFR problem. CO's are only effected by AFR, and when they're off it will make HC's go up. HC's aren't really the problem in a case like this, they're just reflecting the CO's(and to a lesser extent the advanced timing) which are the real problem.

[OdessaS13]

first off, thank you very much for that info (+1)
the shop that replaced my timing chain is going to set the timing back to stock tomorrow morning. I was hoping to take to take it to re-test in the morning. I didnt think iam running rich because I'm not smelling any fuel inside, the engine bay or coming from the exhaust.

this is a smog check about 10-15k ago with stock timing
http://i13.photobucket.com/albums/a283/VqNissan415/smogpass.jpg

notice how the RPM are also higher, iam assuming because the timing is right.

This theory would be supported by the fact that the AFR gets better with rpm. At a higher rpm the vacuum is lower and so your higher fuel pressure becomes closer to what the engine actually needs and the condition gets better.

So once the stock timing is back again the RPM will be higher at 15/25mph and the engine will receive the correct AFR. Ive done research and the stock fpr is suppose to handel the walbro with no problems.

Am i correctly understanding this or is there something iam missing.The mech at the smog station also said it may be my cat but it was replaced 20k ago and they should last 100+k

So setting the timing back to stock should in theory fix the majority of the higher readings assuming the stock fpr is working properly. Is there anything else you suggest i do after the timing to make sure i pass this re-test.

Again, Tomslide50 thank you for explaining this.

[Tomslide50]

Setting the timing back to stock will help a lot. It should(and most likely will) fix all your nox problems. It will help your HC's too, but it won't do a damn thing for CO's. It won't effect it what-so-ever. CO's are strictly air fuel balance. How many miles are on your O2 sensor? Even if it's not throwing a code it could be slow to react and be getting towards the end of it's life. If you have an analog Voltmeter you can backprobe it while the motors running(wait for it to heat up) and make sure that it's switching high and low enough. It should switch 10 times a second. Basicly we're looking for something that either A.) Results in too much fuel, or B.) Results in too little air. Since the problem is most evident at idle we can rule out things like a dirty air filter, because that would be more restrictive at higher rpms. You see where I'm going here? You just have to go down the list of factors. Typically at idle small problems show up more because you're dealing with smaller amounts of fuel and air. Is the car hard to start when the engine's hot? A leaking injector could cause this and that would be an indication. I agree with you completely that the stock fuel system should be able to handle that pump, but what if your return line has a bend or kink in it? You should check fuel pressure either way just to be able to cross a big player off the list. Pull out your injector rail with the lines still hooked up and the key on engine off. Put a paper towl underneath the injectors. Any one of them leaking? At this point we've confirmed fuel pressure is good (or not) and injectors are not leaking(or are). Those are your most likely culprits as I've said- but get your timing fixed, test the fuel pressure, make sure the injectors aren't leaking and assuming both those to be good you will have seriously narrowed down the possibilities. Usually with richness that gets better with rpm it's a leaking injector though. Let me know what you find.

[BigVinnie]

Well advanced timing will increase the knock signal, which will dump more fuel...
When I smog tested my engine it didn't pass at 23BTDC (which is the maximum limit allowed in California) due to this issue. Has alot more to do with the load, and advanced timing at X ignition that causes that issue. Mine was only HC related though, and it appears that you have a few other problems that may infact deal with the TPS,O2 sensor, and quit possibly the EGR assembly itself.
2 quick easy ways to spot the problem. Run the Actron code scanner to see if any smog emission devices come up on the ecu diagnostic, if not then you will need to go to step 2 and run what is called a Launch Diagnostic, an automechanic can find what ever problem for $60 if you by chance can't get your hands on the equipment. Launch is used to fine tune TPS,determine good or bad O2 sensors and MAFS or will let you know if a certain device is not functioning corretly.
If by chance you have swapped an 95-98 engine with 232/232 cams it will pretty much show all the problems that you just described with advanced timing.

[Tomslide50]

BigVinnie has a good point about the knock sensor. I was unnaware that the ecu richens the mixture to combat knock, I would have thought it would just pull timing out. I'm new to these cars so I don't know the adaptive strategies very well. The egr definitely effects the NOX production, but seeing as the timing is so high there's every reason to point to that and no reason to think the egr is causing a problem here. Although looking at your past test, and seeing how the NOX was borderline before, you might want to go in there and clean the carbon out of it. I also want to be very clear, OdessaS13- that the EGR has absolutely no effect on air/fuel ratio.

If the ecu dumps more fuel to combat knock as BigVinnie says, then that could definitely be the culprit. Hopefully he's right and fixing the timing will solve everything. Also- If I were you I'd be a really big dick and take that sheet back to the people who did your timing chain and make them pay for that inspection since you failed because they didn't reset your timing correctly.

[OdessaS13]

Yeah, i could be a dick, but i have a free re-test so hopefully the timing will help out. The shop is setting the timing back to stock for free and there pretty cool guys so i dont really care. The buyer checked out the car and we agreed that he will most likely buy the car as is. *knock on wood*. The EGR assembly has also been replaced so i doubt its the culprit however its possible. I will let you guys know how it turns out tommorow after timing is back to stock and what effect it had on the smog readings. :x:

[OdessaS13]

UPDATE.:

so i went to the shop today an had timing set to base 20, some how it mysteriously went down to 17TDC from the shop to the smog station
anyways results are, Passed smog (borderline at Nox but still passed)
TomSlide and BigVinnie thank you for your advice

HC

before at 15- 127
before at 25- 64

after at 15- 81
after at 25- 65

CO

before at 15- .81
before at 25- .49

after at 15- .49
after at 25- .61

NOx

before at 15- 1998
before at 25- 1064

after at 15- 794
after at 25- 633

[Tomslide50]

That's awesome! congrats!

[BigVinnie]

BigVinnie has a good point about the knock sensor. I was unnaware that the ecu richens the mixture to combat knock, I would have thought it would just pull timing out.
If the ecu dumps more fuel to combat knock as BigVinnie says, then that could definitely be the culprit. Hopefully he's right and fixing the timing will solve everything. Also- If I were you I'd be a really big dick and take that sheet back to the people who did your timing chain and make them pay for that inspection since you failed because they didn't reset your timing correctly.

Yeah it's all good man. I've been working on KA's for quite a few years now, and living in Cali pretty much have all the tricks to passing Cali smog.
Nissan ecu tuning is pretty simplified.
Advanced timing will always increase knock. Nissan ecutunes up until OBD2 always run the pulse width wider and slightly retards the timing, (kind of a decelerative process). This is done just to prohibit a destructive knock and ping (which leads to bent valves and rods). Nissan kind of over did it on fuel richness, Honda, Toyota, and DSM run much leaner in thiose instances.....

Good to know that you passed Odessa.....

[Tomslide50]

I come from the world of E30 BMW's where they don't even have knock sensors, but if anything bad happens they go the other way and lean everything out majorly. Crazy Germans!

[OdessaS13]

again, thanks guys,
handed over the pink slip today, so iam now officialy 240-less
it sucks, dont feel the same when i came back and no 240 in my driveway :(
what do you guys think about audi a4, ive heard about them having leakage problems and tranny issues but havent read anything on the audi forums to confirm that. Any ideas for a sporty sedan?

[Tomslide50]

2nd gear synchros are a common problem on that transmission. And VW/Audi in general is plauged by electrical problems. From my experiences with my mom's passat, and my buddy's experiences with his 2001 S4- I personally wouldn't buy a vw/audi. That being said I've heard that new ones are much better. The new GTI's are pretty cool cars(although minivan-ish in size), and I'd take a new RS4 in a heartbeat.

[BigVinnie]

what do you guys think about audi a4, ive heard about them having leakage problems and tranny issues but havent read anything on the audi forums to confirm that. Any ideas for a sporty sedan?

I am always Nissan at heart for reliabilty and power. I am not to pleased with VW manufacturing, although there is great after market support for Audi/VW.
If it were me I would look into a 350z touring edition, or the 350z nismo edition used and save $5000~$10,000 off the new price. For baller status a G35...
Really nothing beats the handling/power/price of a 350z/G35 at it's cost and is in competion with more expensive Bimmers. I've always seen Nissan as the poor mans bimmer since the days of the datsun 510.