dmg

My 96 Max failed smog badly (high NOx - 1500PPM). After going through the EGR system and finding all is OK, I checked the timing (should be fixed at 15 deg. BTDC), and found that the timing is jumping all over (between approx 18 and 22 deg).

I have had NO engine light or codes. Any idea what this could be? Crank Sensors? Cam Sensor?

I have the following mods since the last passed smog: UDP, Lightweight Flywheel, Y-Pipe, CAI.

Any help is greatly appreciated !

Dave

njmaxseltd

iTrader: (19)

How did you check the timing?

Clean your throttle body and throw a new set of spark plugs in. Go for a long drive before you have the smog test done and hopefully you should be ok.

dmg

I checked the timing by putting the ECU in "Code Mode" per the factory manual. I've checked / removed / cleaned the EGR components, which looked good, and work properly (per vacuum requirements), cleaned the intake, replaced the spark plugs, etc.

Should I be concerned about the advanced / sporadic timing at 18 +/- 2 deg.? I've heard that advanced timing greatly increases NOx, which is what failed. Per the manual, the timing should sit right at 15 deg, although many threads indicate other Maxima's have timing that "jumps" around...

Thanks in advance....

dmg

Any ideas? Is the sporadic / advanced timing normal?

Appreciate the help...

Ryan D

I'm having the same timing issue (on an ODBI Miata, but hey...). It's more stable with the ECU controlling the timing, but once I jump some connections to take the ECU out of the equation it bounces around a ~3deg range. Don't know what's up or even if it's a bad thing or not, but I'm trying to find out too.

edit: and i think advanced timing would kick up a specific part of emissions - i know some local guys would retard their timing by huge amounts to help it make it past the CA smog checks.

dmg

Anyone have any ideas?

njmaxseltd

iTrader: (19)

I don't think the timing has anything to do with your smog issue. Try a professional fuel system cleaning, not just a bottle of cleaner in your tank, but rather the real system. Nissan may offer that service or call a few local mechanics.

I think 3M or Champion makes the system. Basically you remove the source fuel line, disable the fuel pump, crimp the return line and run the car off a can of cleaner tapped onto your fuel rail. That cleans the injectors, intake valves and combustion chambers. The service should run you about $100 bucks and usually restores performance and lowers emissions.

dmg

Thanks. So can I assume it is normal for the Maxima to bounce sporadically between 18 and 22 degrees timing (even though the manual calls for 15)? Smog technician seemed to think that 7 degrees advance over the factory timing would equate to the NOx failure (about 4 times the legal limit).

The only reason I didn't do the cleaning is because the miles are relatively low, I get great gas mileage (29), and throttle response / smooth power has been good.

I'll check it out...

appreciate any input.

dmg

Any input regarding the jumping timing?

Thanks

njmaxseltd

iTrader: (19)

The crank shaft position sensors control ignition timing. They are magnetic sensors and tend to collect fine metallic dust. Take both sensors out and clean the dust off the magnetic pick ups, then check the timing again.

Mishmosh

iTrader: (3)

My 95 Nox was high as well, 1400. Could not find the problem after checking the EGR system for functionality.

dmg

THanks. I''l try removing the sensors and checking for dust. On another note, I tried bypassing the EGR BPT, and the EGR valve fully actuates (compared to before where it barely moved) ! After pulling the BPT valve, and applying vacuum to one port, while plugging the other and applying pressure to the bottom port, it seems to leak down slightly (which may be why the EGR doesn't actuate fully (vacuum leak). The book says that the valve should leak until pressure is applied to the bottom port. I'm just wondering if some leakage is allowed, or if it should completely seal, and allow full vacuum to go to the EGR valave.

Getting closer, and thanks again !

Mishmosh

iTrader: (3)

I would also check to see if the egr control solenoid actually does activate. I think it gets a 12V signal from the ECU (when EGR off) and gets 0V when signalled to activate the EGR system. For some reason, my ECU never activates the EGR system. The FSM says that if it doesn't like one or more of the inputs that determine activation, it may not do so.

dmg

EGR Control Solenoid works fine, once the engine warms up (and the EGR temp sensor sends the signal). I checcked the vacuum after the valve, and it is where it should be. My next step is to check how much the EGR valve moves on another Max., and if it is different (moves more than mine), I'll repace the BPT valve.

kcryan

iTrader: (1)

Fuel power has a great reccord with NoX

dmg

Unreal.. tried the smog additive, cleaned and tested the crank / cam sensors, and failed again (high NOx again).

Since the EGR valve actuates fine when I bypass the BPT valve, I'm going to replace the BPT valve. Here's the concern:

After talking to the smog technician, he claims that the aftermarket Y-Pipe may not allow the BPT valve to work properly, since it eliminates much of the exhaust backpressure (which actuates the BPT valve).

Has anyone else with a Y-Pipe failed emissions for NOX)?

Mishmosh

iTrader: (3)

I'm not buying the backpressure theory. When I activate the egr system at idle, the motor starts to sputter which clearly means exhaust is being introduced into the manifold.

I have already passed emissions handily twice with my Y-pipe (every other year thing) but unfortunately this year, I could not get it to pass despite my best efforts--NOx being around 1400-1500 no matter what I did. However on mine, the signal to the EGRC solenoid never changes as measured from the harness. In any case, I wouldn't go swapping back a stock Y-pipe thinking that that is the problem.

dmg

My engine sputters as well when the EGR is manually actuated. In fact, when I bypass the BPT (by connecting the vacuum line from the EGRC valve to the EGR), the EGR opens fully, and the engine runs rough, as it should). The Issue I've heard with the Y-Pipe is that it decreases backpressure in the exhaust manifold, which, in turn, doesn't apply as much pressure to the BPT valve, which in turn, doesn't close the valve as much to provide the vacuum to the EGR to operate.

I'm encouraged since yours passed with the Y-pipe, so hopefully, the new BOT Valve solves the problem. As far as your problem, did you try unhooking the EGRC valve during the smog test (so the EGR actuates normally)? Also, are the inputs to the ECM that control the valve opening working properly (temp sensor, speed sensor, TPS, etc.?)

Any other ideas?

dmg

Problem solved. BPT valve and / or vacuum line leading to it were bad. New BPT and hose routing...problem solved. NOx dropped from 1500 to 50.

Thanks for all the help.

Mishmosh

iTrader: (3)

Great to hear. Thanks for the followup. How much was the BPT valve and exactly what does "BPT" stand for?

themills

iTrader: (2)

you started 2 threads?? On the same exact thing??


http://forums.maxima.org/showthread.php?t=444387

dmg

Back Pressure Transducer valve....$50 from Nissan.

2 Threads...different header's / date's (one was generic, the other after the issue was narrowed down).

Mishmosh

iTrader: (3)

Thanks! Is this what people commonly refer to as "EGR valve?"

dmg

No, the BPT valve is in line right before the EGR valve.