280zx turbo failed smog. need advice to pass on retest

[stravi757]

Bought my second 280zx turbo couple days ago. engine is running pretty good, engine runs smooth all the way up to 6,000rpm. Put newer plugs, wires, cap, new chts sensor and o2 sensor. Checked and fixed vacuum leaks. I thought it was going to pass and it didnt.

 

I failed the 15mph test. here were my readings

 

M1: 15mph RPM 1676

%CO2: 14.1

 

%o2:0.8

 

HC: MAX:138 MEAS:161 FAILED

 

CO%: MAX:0.98 MEAS:0.67

 

NO: MAX:1136 MEAS:1447 FAILED

 

FAILED

 

 

25MPH test

 

%CO2: 14.7

 

%o2: 0.3

 

HC: MAX:77 MEAS:77 VERY CLOSE!

 

CO%: MAX:0.78 MEAS:0.16

 

NO: MAX 996 MEAS:240

 

PASSED

 

 

I suspect my failing HC has to do with the AFM. And My guess on the the failure for NOx is due to my egr system, either the valve has carbon buildup in it, or maybe my VCM wasn't giving it enough vacuum to open up. Really want to pass when I bring it in next time, you guys got any ideas or advice in what I should start looking at?

Edited March 23, 2011 by stravi757

[rayaapp2]

Your CO and O2 are close. I wouldnt touch the AFM! Its Most likely in GOOD WORKING ORDER!

 

I would suspect your kitty is is very old and needs to be put down. Hard to tell without putting my hands on it, but I suspect you passed the faster test cause you have a working EGR and the cat was getting nice and hot. I would take the car in and have them do a "cat efficiency test". You CO2 is on the low side during the 15mph run and picks up during the 25mph test. Another thing to think about is carbon buildup in the CC. That will attribute to some of your problem as well.

 

Just my 2 cents. Personally Id take the car to someone to have it really diagnosed. Otherwise its the toss the parts at the problem situation and hope it works. There are consequences in Cali now for replacing a cat and then having it fail again in 2 years so make sure your sure.

Edited March 23, 2011 by rayaapp2

[HowlerMonkey]

How long did the car sit cooling or idling before the dyno run?

[stravi757]

How long did the car sit cooling or idling before the dyno run?

 

On the way to the smog station I got on the freeway and did WOT. I really got on it around town. brought the car to the shop and it was idling for about 8minutes. And right before he tested it he was keeping the rev to about 3,000rpm for about 45 seconds to make sure it was warm.

[rayaapp2]

On the way to the smog station I got on the freeway and did WOT. I really got on it around town. brought the car to the shop and it was idling for about 8minutes. And right before he tested it he was keeping the rev to about 3,000rpm for about 45 seconds to make sure it was warm.

 

The tech went above and beyond what he was allowed to do for you. He actually cheated and can get in trouble for that. FYI.

 

I stick by what I said above.

[stravi757]

Your CO and O2 are close. I wouldnt touch the AFM! Its Most likely in GOOD WORKING ORDER!

 

I would suspect your kitty is is very old and needs to be put down. Hard to tell without putting my hands on it, but I suspect you passed the faster test cause you have a working EGR and the cat was getting nice and hot. I would take the car in and have them do a "cat efficiency test". You CO2 is on the low side during the 15mph run and picks up during the 25mph test. Another thing to think about is carbon buildup in the CC. That will attribute to some of your problem as well.

 

Just my 2 cents. Personally Id take the car to someone to have it really diagnosed. Otherwise its the toss the parts at the problem situation and hope it works. There are consequences in Cali now for replacing a cat and then having it fail again in 2 years so make sure your sure.

 

 

Well I suspect the EGR isnt working at the 15mph test. I hooked up a gauge to the hose right before the EGR valve, and at 1,500-1,700rpm I was getting no vacuum. Now when I reved the engine up to about 2,400-2,600rpm(RPM range of 25mph test) it started to read vacuum.

 

The cat on the car is definitely newer but it could be the cause( maybe I could take the cat off my other 280zxt that just passed smog and use that) The technician didn't even look for my cat, so i doubt I would have the replacement fail problem you were talking about.

Edited March 23, 2011 by stravi757

[stravi757]

The tech went above and beyond what he was allowed to do for you. He actually cheated and can get in trouble for that. FYI.

 

I stick by what I said above.

 

He was just revving it because he thought the engine was still cold since my water temp gauge isnt accurate. Is that really not allowed?

[rayaapp2]

He was just revving it because he thought the engine was still cold since my water temp gauge isnt accurate. Is that really not allowed?

 

Has to be at full operating temp so that is allowed. Some guys cheat and hold the throttle up to heat everything up.

[rayaapp2]

Well I suspect the EGR isnt working at the 15mph test. I hooked up a gauge to the hose right before the EGR valve, and at 1,500-1,700rpm I was getting no vacuum. Now when I reved the engine up to about 2,400-2,600rpm(RPM range of 25mph test) it started to read vacuum.

 

The cat on the car is definitely newer but it could be the cause( maybe I could take the cat off my other 280zxt that just passed smog and use that) The technician didn't even look for my cat, so i doubt I would have the replacement fail problem you were talking about.

 

That is what I would expect off the EGR on that car actually. So now you know the EGR system works. Im sure the tech would have done an EGR test on it as part of his funtional check. If it failed it would be on the paperwork. You can double check it with a vacuum pump while the car is running and see if you can stall or almost stall the engine at idle by applying vacuum to the EGR valve.

 

If you get a free retest Id say hell ya use the other cat and compare results.

For diagnostic purposes only of course.

Edited March 23, 2011 by rayaapp2

[stravi757]

That is what I would expect off the EGR on that car actually. So now you know the EGR system works. Im sure the tech would have done an EGR test on it as part of his visual check. If it failed it would be on the paperwork. You can double check it with a vacuum pump while the car is running and see if you can stall or almost stall the engine at idle by applying vacuum to the EGR valve.

 

If you get a free retest Id say hell ya use the other cat and compare results.

 

Well the reason I brought it up was I also tested it on my other 280zxt(that just passed smog) and It was reading vacuum at the lower rpm range.

 

How likely do you think my problem is a clogged up cat? If you really think it'll help, ill swap in on my car for sure, in fact I should probably just try swapping all the smog equipment from my other car.

Edited March 23, 2011 by stravi757

[rayaapp2]

Well the reason I brought it up was I also tested it on my other 280zxt(that just passed smog) and It was reading vacuum at the lower rpm range.

 

How likely do you think my problem is a clogged up cat? If you really think it'll help, ill swap in on my car for sure, in fact I should probably just try swapping all the smog equipment from my other car.

 

I dont have a FSM for that car, but you can bet that it will have very specific readings for EGR specs. Have a look and compare.

 

Personally I would not expect it to work a lot at 15mph and 50% load. Some do though esp older systems. Kinda cool that you have a good comparable vehicle. Verify with the FSM though.

[stravi757]

Okay well heres my list of things to do before my next smog attempt. Sound good so far? any suggestions?

 

Retard timing

 

switch cat with my other 280zxt

 

change the oil+filter

 

Buy new spark plugs and gap them

 

new air filter

 

new pvc valve

 

switch VCM with my other 280zxt

 

Run some seafoam in the tank and manifold, and oil before i change it.

[rayaapp2]

Okay well heres my list of things to do before my next smog attempt. Sound good so far? any suggestions?

 

Retard timing

 

switch cat with my other 280zxt

 

change the oil+filter

 

Buy new spark plugs and gap them

 

new air filter

 

new pvc valve

 

switch VCM with my other 280zxt

 

Run some seafoam in the tank and manifold, and oil before i change it.

 

Set timing at spec +- what ever it says on the hood... could be 0 with the ZX(some cars have 2-3 degrees of acceptable play). This is a pass/fail requirement for the functional check over.

 

New air filter, plugs(NGK plain copper cores), and oil change are always good before a smog... Usually Id say go for it. An oil change might actually do some good for you here.

 

PCV valve can help, but they only look to see if its on the engine not a functional check(visual). Its a good idea to change it esp if its really old.

 

Personally I stay away from seafoam for that kind of particular application. Im not one for pouring any liquid down the intake of a running vehicle. This is just MY OPINION!, but I feel it does more damage than good! It puts excessive forces on the bottom end bearings, pistons, and rods. I will use Seafoam for some of the other applications listed on the can, but not here. Again my personal opinion, there are people that swear by the stuff. Options for cleaning the engine for me are to run better fuels and maintain a good tune on the car, or tare the engine down and physically clean it. I know those options suck. I have no idea about the effects of seafoam when its read by a smog machine. So if you add it to the tank I would burn through a couple of tank before re-attempting a smog. This was probably already your thought to make sure it did its job, but just thought Id give you a second perspective.

 

Im not sure its worth the effort to dig the vacuum control module out to swap it(I remember those being buried under the AFM area). I would suggest a look through the FSM first(you can download it if you look around). It may be that your other car is missing the restriction in the vacuum line where the stripe is and it opens early, or it could be any number of other things influencing the EGR system... or it could be actually working correctly. The only way your going to be sure is to read up on it in the FSM and determine its operation. Nissan did an excellent job at clearly and concisely spelling out functional operation of each device on there vehicle with specs in the FSM.

 

As for the cat, Id give it a shot. Compare the CO2% between the two cats afterward. BTW, I dont think the cat is really going to look plugged up when you pull it either. The CO2% is still high enough that some of the capillaries will be plugged, but not completely melted down(gone Nuclear). The only way to tell to see whats really going on is to do that test I mentioned above.

[Gollum]

You can legally cap off the intake manifold plumbing for the Heat/AC control system, which is prone to leakage. I'd bypass that whole system first and see if your vacuum readings change.

 

And though the tech rev'ed your engine to 3,000 for a few moments before the test, that might not be enough to really heat up the CAT enough to "cheat". The real cheat is to stab the throttle over and over right before the test. This will richen the mixture and thus be blowing unburnt fuel into the exhaust, thus heating up the CAT very quickly. I wouldn't go telling smog tech's to do this though...

 

Your numbers are really close though. There's a good chance your car is working 100% fine, just a little tired. Couple that with a CAT that's going out and it's a recipe for smog dyno failure.

 

If the cat isn't welding in on either car, I'd swap it over. Bypass the air system vacuum system like I said, and then retest. Make sure your timing is what it should be (I think you can go 3 degrees from it, in which case to 2-3 degrees retarded), and go ahead and change your oil and such as you're planning on doing. Don't go crazy moving the AFM and such. That only changes transients for the most part.

 

Another interesting tidbit, is that the numbers you have to pass aren't totals for the time of the test, but rather an instantaneous rating (for one second I believe). So if the 15mph test goes really long it's likely you're failing. What will normally happen is that at the beginning of the test the numbers will be high, and then drop as the EGR and CAT start to do their work under a constant load. Then as the numbers drop the machine sees what's happening and passes you onto the next test. Quick smog tests are a good sign. Its usually those first few seconds that will fail you, and when you're over the smog machine keeps going for a full test to see what the engine is going to do, to see if they can reach higher peak numbers.

[rayaapp2]

You can legally cap off the intake manifold plumbing for the Heat/AC control system, which is prone to leakage. I'd bypass that whole system first and see if your vacuum readings change.

 

And though the tech rev'ed your engine to 3,000 for a few moments before the test, that might not be enough to really heat up the CAT enough to "cheat". The real cheat is to stab the throttle over and over right before the test. This will richen the mixture and thus be blowing unburnt fuel into the exhaust, thus heating up the CAT very quickly. I wouldn't go telling smog tech's to do this though...

 

Your numbers are really close though. There's a good chance your car is working 100% fine, just a little tired. Couple that with a CAT that's going out and it's a recipe for smog dyno failure.

 

If the cat isn't welding in on either car, I'd swap it over. Bypass the air system vacuum system like I said, and then retest. Make sure your timing is what it should be (I think you can go 3 degrees from it, in which case to 2-3 degrees retarded), and go ahead and change your oil and such as you're planning on doing. Don't go crazy moving the AFM and such. That only changes transients for the most part.

 

Another interesting tidbit, is that the numbers you have to pass aren't totals for the time of the test, but rather an instantaneous rating (for one second I believe). So if the 15mph test goes really long it's likely you're failing. What will normally happen is that at the beginning of the test the numbers will be high, and then drop as the EGR and CAT start to do their work under a constant load. Then as the numbers drop the machine sees what's happening and passes you onto the next test. Quick smog tests are a good sign. Its usually those first few seconds that will fail you, and when you're over the smog machine keeps going for a full test to see what the engine is going to do, to see if they can reach higher peak numbers.

 

Nathan, look at his O2 and CO numbers and rethink your vacuum leak theory... I still stand by my initial leave the AFM alone. It looks like he did a good job at finding any vacuum leaks. Good info just probably not relevant to this situation.

 

IF there is no timing spec "range" specified the tech's official position is that if its within 3degrees + or - of the spec its good.

 

Most techs wont rev the engine up and down when they cheat. "Most" cars will heat the cat up by free reving around 2500-3000 rpm. For TSI tests this is why there is a "cool down" period if the tech fails to stay in range. The long the tech is out of range the longer the timer will be for the cool down period.

 

Im honestly unsure how the machine determines what numbers to printout, maybe average or? Its kind of a big secret even to the techs. They do have the capability to preform continuous sampling with these old machines. If the machine "sees" what it likes it fast passes to the next test. If its seeing numbers that are close to fail or what ever criteria it has it holds it to the end of the test and its still a toss up whether it was a pass or fail.

 

 

BTW

Personally I have made a cat go Nuclear. Took a whopping 15 seconds. All I had to do was unplug the AFS and hold the rpms at 2500... cat was at 1422*F before I realized what happened. Luckily it was a training vehicle.

 

 

 

Here is something for you guys to check out. Lambda.

Lambda calculators are a cool thing. Take your 5 gas readings and plug them in and you can calculate your AFR before it was burnt!

15mph reveals a lambda of 1.013 which is 14.9AFR

25mph reveals a lambda of 1.006 which is 14.79AFR

 

Id say his air fuel ratio is ABSOLUTELY DEAD NUTS.

 

 

A Smog techs helpful tool

Lambda Calculator

Edited March 23, 2011 by rayaapp2

[stravi757]

Nathan, look at his O2 and CO numbers and rethink your vacuum leak theory... I still stand by my initial leave the AFM alone. It looks like he did a good job at finding any vacuum leaks. Good info just probably not relevant to this situation.

 

IF there is no timing spec "range" specified the tech's official position is that if its within 3degrees + or - of the spec its good.

 

Most techs wont rev the engine up and down when they cheat. "Most" cars will heat the cat up by free reving around 2500-3000 rpm. For TSI tests this is why there is a "cool down" period if the tech fails to stay in range. The long the tech is out of range the longer the timer will be for the cool down period.

 

Im honestly unsure how the machine determines what numbers to printout, maybe average or? Its kind of a big secret even to the techs. They do have the capability to preform continuous sampling with these old machines. If the machine "sees" what it likes it fast passes to the next test. If its seeing numbers that are close to fail or what ever criteria it has it holds it to the end of the test and its still a toss up whether it was a pass or fail.

 

 

BTW

Personally I have made a cat go Nuclear. Took a whopping 15 seconds. All I had to do was unplug the AFS and hold the rpms at 2500... cat was at 1422*F before I realized what happened. Luckily it was a training vehicle.

 

 

 

Here is something for you guys to check out. Lambda.

Lambda calculators are a cool thing. Take your 5 gas readings and plug them in and you can calculate your AFR before it was burnt!

15mph reveals a lambda of 1.013 which is 14.9AFR

25mph reveals a lambda of 1.006 which is 14.79AFR

 

Id say his air fuel ratio is ABSOLUTELY DEAD NUTS.

 

 

A Smog techs helpful tool

Lambda Calculator

Rayaapp2- I have been reading through the Fsm, don't want you think Ive been ignoring that. I forgot to mention, the tech did pump vacuum in the EGR valve to verify it was working. It didn't stall the engine but it came close to. Should I pull off the valve and maybe clean it?

 

So my A/f ratio is looking good then , So I think I will drop my timing a few degrees, the tech was really having trouble seeing exactly where it was through all that mess of things under the hood. So I bet i can get away with it without him noticing. Question is how much retarding will give me the best smog performance? Seems like retarding it will help reduce all of my emissions, but how much is too much.

 

Im hoping that changing my oil, plugs, cap, rotor, cat, and air filter will help reduce my HC enough. But Do you think changing my cat(which we don't know for sure is the cause yet) and pulling back the timing will be enough to get it to pass on the NOx at the 15mph test? Why is it so high at 15 then so low at 25? is it because of the EGR valve, or cat warming up, or both?

 

Also I keep reading about people saying running some alcohol in the tank made them pass. Is this true that it works very well, Do you guys think I should try it?

Thanks for the help so far guys, I really appreciate it.

Edited March 23, 2011 by stravi757

[stravi757]

double

Edited March 23, 2011 by stravi757

[rayaapp2]

Rayaapp2- I have been reading through the Fsm, don't want you think Ive been ignoring that. I forgot to mention, the tech did pump vacuum in the EGR valve to verify it was working. It didn't stall the engine but it came close to. Should I pull off the valve and maybe clean it?

 

So my A/f ratio is looking good then , So I think I will drop my timing a few degrees, the tech was really having trouble seeing exactly where it was through all that mess of things under the hood. So I bet i can get away with it without him noticing. Question is how much retarding will give me the best smog performance? Seems like retarding it will help reduce all of my emissions, but how much is too much.

 

Im hoping that changing my oil, plugs, cap, rotor, cat, and air filter will help reduce my HC enough. But Do you think changing my cat(which we don't know for sure is the cause yet) and pulling back the timing will be enough to get it to pass on the NOx at the 15mph test? Why is it so high at 15 then so low at 25? is it because of the EGR valve, or cat warming up, or both?

 

Also I keep reading about people saying running some alcohol in the tank made them pass. Is this true that it works very well, Do you guys think I should try it?

Thanks for the help so far guys, I really appreciate it.

 

Dont clean the EGR unless you think you can prevent the carbon chunks from going down stream and into the combustion chamber. If it trys to stall that is a good sign that its flowing okay. Try and apply vacuum to the EGR on your other ZXT and compare? The FSM should have a specific reading for vacuum applied to the EGR. My 82 maxima FSM has all that. Keep looking. You should be able to test and verify.

 

As far as timing goes follow whats on the hood label. Thats what their checking for. If its not specified how many degrees out that you can get away with, 3 degrees either way of spec. is acceptable. Thats about all I can tell you off hand.

 

"Why is it so high at 15 then so low at 25? is it because of the EGR valve, or cat warming up, or both?" Both was my guess and still is from my first post in this topic "Hard to tell without putting my hands on it, but I suspect you passed the faster test cause you have a working EGR and the cat was getting nice and hot."

 

The alcohol trick works on certain types of failures. Ive never done it personally, but have had friends try it. Im actually a Smog Tech, but I dont want to risk my license in this market

 

Id be more specific on timing and alcohol if I thought I could give a clear answer. Maybe someone else will tackle the ins and outs of those. I just got out of the ICU burn ward so my head a little fuzzy on some things on account of them pumping me full of pain meds for 13 days.

Edited March 24, 2011 by rayaapp2

[Gollum]

This site agrees with what I'd said earlier, you're allowed +/- 3 degrees.

 

http://www.smogtips.com/functional_inspection.cfm

 

I still wonder if he has a vacuum leak. Judging by the high HC he's probably running lean until the O2 kicks in (which takes a good 5 seconds after the test starts, I've watched it kick in).

 

The high nox is REALLY off the chart for an engine running well. I can only presume that it has to be EGR related. I know in my '81 which has dying rings and thus will only compression test just over 100psi in some cylinders, has a hard timing getting the EGR diaphragm fully open. My NOx is usually near the limit, but my motor also has obvious signs of nearing the end of it's life and the fact I get it to pass is almost a miracle.

 

If you can find a nice smog tech, I'd ask for some time with the car on a smog test run. Take a vacuum pump and when running at 15mph pump the EGR into vacuum and see if the NOx drops dramatically. If it does, then you're not getting enough vacuum to it from the engine, or if it doesn't move at all, you might have a clogged EGR system.

 

I agree though that fiddling with the AFM isn't the solution here. The engine isn't running right without the O2 is my bet. You need to find out why. My suspicions lie in the EGR from the high NOx.

[stravi757]

I passed! And didn't switch cats either

 

Here were my numbers this time.

15mph-%co2: 14.5 %o2: 0.4 HC: 123 CO%: 0.15 NO: 266

 

25mph-co2% 14.6 %o2: 0.4 HC: 75 CO%: 0.13 NO: 232

 

Heres everything I changed since the last test. Changed oil, I ran sea foam in the oil before i changed it, also ran some in the intake manifold. New spark plugs(Kind ray recommended). Re tarted my timing from 22 to 18 degrees. I drove my car like hell around the neighborhood and WOT pulls on the freeway, probably did about hour of driving in total. And the Big thing I did that I think reduced my NOx nearly by 1,200 was I disconnect the vacuum line going to the EGR valve. Instead I took the vacuum line from the purge valve which goes to the throttle body. I put a T connection and also used that vacuum source to my EGR valve. This way the Egr valve will open as soon as you start to open the throttle. Not recommending this but its just what I did and it looks like it worked. It was dogging my engine a little bit but other than that it looks like it helped bring my nox down to say the least.

 

Pretty happy, unfortunately the DMV is closed now so ill have to wait until Monday, But thanks for all of your help guys, happy to finally be past this smog stage.

Edited March 26, 2011 by stravi757