91 240sx SE Fail SMOG!!!!!!!!!!!

[cd1921]

Hey all i just fail smog for the second time. The #s on the second time where alot better then the 1st time. but my NOX # are still too high.I changed cat , ful exhaust system, O2 sensor, full tune up, did the SeaFoam thing.Can anyone tell me what the problme is or what can i do to get my car to pass smog the car is a 1991 240sx SE. Also there is a strong odor of unburn gas on the engine bay and from the muffler tip..

here are the #

15 MPH Test @ 1807 RPMs

CO2 = 14.07O2 = 0.2HC PPM = meas 15 max(118)CO % = meas 0.00 max(0.75)NO PPM = meas 1028 max (799) FAIL

25 MPH Test @ 2027 RPMs

CO2 = 14.7O2 = 0.0HC PPM = meas 11 max(93)CO % = meas 0.01 max(0.63)NO PPM = meas 1098 max (738) FAIL
Modified by cd1921 at 6:45 AM 4/19/2006

[180fan]

just like everyone else's NOx failure, check the EGR.

[sleepyRPS13]

everything looks good, its not running lean either. definetly check the egr.

do you still have the stock fan?

[NISTECH]

Check the BPT hose under the BPT. see if its soft or has any tiny holes in it.

I ran your numbers in a lambda calculator. This calculator is used to determine what your fuel mixture out of the engine is looking. [weather its running rich or lean] Yours came out at 1.011 with an air fuel ration of 14.87:1 . Good range is .98 to 1.02 ideal is 1.0. Your engine is running perfect. So this does point to an egr problem.

[sleepyRPS13]

nistech i got a question!

are all 240sx manual/auto egr system are activated only thru certain constant back pressure??also what speed does egr turn on?

im asking this because my teacher said on certain cars egr is activated differently. ie: when tcc lock up egr is actviated, certain cars lock up 30+mph or on a rx7 you have to be on 4th gear to activate the egr.

[NISTECH]

All nissan conventional EGR systems operate on the back pressure transducer system. When the tps hard idle contacts open the egr solonoid is activated. This allows vaccum to go to the BPT. When exhaust back pressure is high enough [around 1.5 lbs] The bpt closes the vebt sending the vaccum to the egr. Some of the newer cars use a stepper motor egr system that the ecm controls under specific load conditions combined with TPS readings. on the conventional system if the wot throttle contacts are closed the EGR solonoid shuts off not allowing vaccum to the BPT. Hence no egr operation.

Same senario holds true on the newer system when the TPS voltage indicates wide open throttle, the step motor is reduced to 1step [rest position]

On niether system is trans input used.

[cd1921]

ok i checked the EGR hoses, they all seem to be ok, non had holes or leaking air. I checked the spark plugs and they had a black and white coating on the tip? I did the test where i push up on the EGR and the car almost stopped on me.What else could of be? Im lost now and confused!!!!!!!!

Please help thanks..
Modified by cd1921 at 4:50 AM 4/20/2006

[NISTECH]

possibly plugged passages. There are some allen had plugs in your intake manifold if you look down into the curl of the intake. You will see one plug on each runner and one at the end near the throttle body. Get a 10mm allen socket and remove the plugs. spray some chemtool carb cleaner in there and let it soak for 10 mins or so then start chisseling away on the carbon build up thats inside. when you start the car it will let off a huge cloud from all that carbon and chemtool. Just take note of the build up when you pull the plugs. If its just a little on the walls it may not be your problem. however if like #1 and 2 are almost completely plugged that would be your problem.

[cd1921]

ok i ll try this today and post the results.. then i ll post the results...

thanks again...

[hazw8st]

Nice.....

[cd1921]

ok i did that and nothing..Coult the fat that i have a CAI and HKS HI POWER exhaust system cause this? What else should i check

Also this are the # fromt he 1st run.Maybe this might help, then i had the other results after i put the new o2 sensor, cat and exhaust system and did the seafoam cleaning also..

here are the #s

15 MPH Test @ 1829 RPMs

CO2 = 12.9O2 = 2.5HC PPM = meas 166 max(118) FAILCO % = meas 0.63 max(0.75)NO PPM = meas 1223 max (799) FAIL

25 MPH Test @ 1997 RPMs

CO2 = 12.9O2 = 2.4HC PPM = meas 123 max(93) FAILCO % = meas 0.48 max(0.63)NO PPM = meas 594 max (738)

[hazw8st]

Go here.... zerothread?id=126437

[zer0c123]

Maybe your EGR isn't working correctly at all.

Last resort would be to remove all the EGR parts (egr valve, EGR-BPT valve, BPT tube, and EGR tube), and inspect to see if they are clogged with carbon. The job is a real pain.

[cd1921]

Maybe your EGR isn't working correctly at all.

Last resort would be to remove all the EGR parts (egr valve, EGR-BPT valve, BPT tube, and EGR tube), and inspect to see if they are clogged with carbon. The job is a real pain.

i did push ont he EGR valve and the car seem like it was going to died out. I dont know what else to look for..im puzzle here!!!!!!!!!!!!

[sleepyRPS13]

try putting back your stock exhaust, also.

[cd1921]

try putting back your stock exhaust, also.

hummmmmmm, thats going to be a problem... i no longer have it the stock exhuast was all jacked up...

[zer0c123]

The exhaust could be the cause, but i don't believe it would affect your emissions #'s that much. Your NOx is like over 1000, when it could be around 100 if everything is working right.

Actually your emissions #'s are about the same as mine, and we failed the same parts too. My problem turned out to be the EGR, and after it was cleaned out the NOx went down from 1000+ to low 100's. Also the #'s for the other gases went down too.

[cd1921]

The exhaust could be the cause, but i don't believe it would affect your emissions #'s that much. Your NOx is like over 1000, when it could be around 100 if everything is working right.

Actually your emissions #'s are about the same as mine, and we failed the same parts too. My problem turned out to be the EGR, and after it was cleaned out the NOx went down from 1000+ to low 100's. Also the #'s for the other gases went down too.

So u took out the actual EGR valve and cleaned it out, did u remove all the piping from the EGR??

can u email me so i can ask u more questions.. [email protected]

[zer0c123]

Well the smog tech was the one that cleaned it out. I failed smog twice, and after the 2nd time i just left it at a gold shield smog station for them to fix.

He diagnosed a weak vacuum in my egr valve, and it was due to clogged passages. I knew before hand that it could have been carbon clogging my egr passages, but some of components were so freaking hard to remove that i gave up hoping that replacing that little BPT hose would do the trick. Boy was i wrong and it costs me 200+ to fix.

Side story:Even though i passed the car didn;t run right. Jerked badly, and horrible has mileage. Took it back to them, they tried, but it helped little.

Eventually i got ticked off and replaced all the egr parts (bottom)

It seems they cut the top part of BPT-valve and jb welded it back together. ALso they replaced the BPT hose with some small *** generic hose that doesn't even make an L shape.

Think of this solution as a last resort. As i said before, the job is a PITA.
Modified by zer0c123 at 9:26 AM 4/23/2006

[cd1921]

anyone else, what else can i try.. Thank You all for the tips/advise so far.

[InsanityInc]

It probably isn't your EGR valve. My BMW doesn't even HAVE an EGR system, and it passed with like 135ppm NOx. EGR helps, but not that much.

My best guess is that your timing is a bit advanced. Have you checked the timing? Should be 20BTDC. Even if it is in spec, you can retard it to about 18BTDC (within the visual test limit) to drastically lower your NOx.

[cd1921]

It probably isn't your EGR valve. My BMW doesn't even HAVE an EGR system, and it passed with like 135ppm NOx. EGR helps, but not that much.

My best guess is that your timing is a bit advanced. Have you checked the timing? Should be 20BTDC. Even if it is in spec, you can retard it to about 18BTDC (within the visual test limit) to drastically lower your NOx.

when i took the car to get it retested , the tech guy said it was at 17BTDC. I ll take it to a real mechanic... LOL LOL

[NISTECH]

It probably isn't your EGR valve. My BMW doesn't even HAVE an EGR system, and it passed with like 135ppm NOx. EGR helps, but not that much.

.

This is incorrect info. The egr on a nissan makes a world of difference. The simple fact is the valve timing on a BMW is set up different on a bimmer and the pressure is lower. Most german cars do not use EGR. As a matter of fact I believe the germans were the first to discover the use of the aluminum head helped reduce combustion chamber temps which allowed them to go without an egr. This included compression differences as well as tuning differences.

From personal experiance I have seen a hole the size of a pencil tip in the exhuast of a 4cyl sentra cause the egr to not function at 15mph. This lead to a Gross polluter failure. This tiny hole in front of the cat was enough to raise NOx over 1000ppm from what it came down to after applying a small weld to seal up the hole. The final EGR readings were under 140ppm when performing my final pretest before sending her back to a test only.

[cd1921]

ok i went ahead and inspected the exhaust system that i had installed, i found out there is a leak before the CAT, can thi make my NOX # so high. im gonna take it apart tomorrow..

LMKI need to get this fixed..

Thanks...

[NISTECH]

you bet. Fix the leak.