Failed smog test after adjusting timing -- help!


#1

I took my 1999 Nissan Quest for a smog test and it passed everything but the ignition timing (10BDTC). A day later a mechanic adjusted my timing to 15 and did a major tuneup, oil change, etc. The NEXT day I went back to the smog station and the timing passed (now at 12 BTDC less than 24 hours after seeing it at 15 BTDC with the mechanic). Fine, but now all the emissions numbers have tripled and thus FAILED the inspection. All the other numbers remained the same or very close. I’ve spent hundreds or dollars already and can’t afford a wild goose chase, and fear what huge repairs will be suggested on my car with 100,000 miles. How could my emissions numbers change so drastically in two days?


#2

Your mechanic made a mistake doing the “major tune up” (I really dislike this phrase,what does it mean?). I would like to review the timing set method (I love those cars you can’t move the timing,this started way back in the mid-80’s with BMW)

How did you get convinced to do anything but correct the timing since you did not have any other problems?

Has the tune up mechanic thrown up his hands and said you are on your own?

Was this work done by a professional mechanic at his place of business on the clock with a repair order created or was this a “side job”? you have recourse with the mechanic under most circumstances.


#3

possibly smog mechanic did not read timing right to start with. or repair mechanic has set incorrectly. take it to someone else to recheck the timing. I agree what a headache. you must be in california


#4

I went to a recommended mechanic but one who does not specialize in smog repair. It had been a long time since I had a tune up, so I thought I’d do that at the same time that I asked him to fix the timing. I showed him the smog results. Everything passed but the timing. I didn’t think it was a big deal. Just adjust the timing a bit and it would pass. I drove with him and saw the timing machine read “15” after he had adjusted it. I’m not sure HOW he adjusted I, but I believe it is adjustable. The tune-up mechanic does not seem to know what to do at this point and is consulting with other friends who are in the smog business.
At this point, do I give up and go to a test and repair facility and pay another $100 to diagnose the problem? (Nox emissinos too high) Perhaps unnecessarily get a new catalytic converter (as has been suggested by one or have teh EGR unplugged to the tune of $170 PLUS $100 for diagnstic? Help, I’m in a money pit and can’t seem to get out wiht the state smog due in a couple of days.


#5

Yep, I’m in California. I took it to another place that’s got a great reputation but no longer does smog repairs. The longtime mechanic there said it’s entirely possible that the emissions were off simply because the car hadn’t been warmed up long enough. He suggested taking it for a long ride before testing. I don’t know what to believe any more. If I had money (and my spouse hadn’t been laid off more than a year ago), I would buy a new car before I hit $1,000 in repairs. Alas, I can’t, so I search for answers to my car troubles on the Internet. Thanks.


#6

Consulting with others in the business is not bad so don’t give up with him yet (unless he wants to give up then its refund tiime for you)

The advice “car was not warmed up” is pretty basic but not impossible.

Don’t buy any more parts yet,the ball is in tune up mechanics hands,pressure him to make a move,remind him the only trouble you had was a timing problem.

My feeling is timing is incorrectly set.


#7

When you had the timing advanced 15 degrees, you should have noticed a BIG difference in the way the engine performed. Did you notice ANY difference in the way the vehicle drove??

This sounds more like computers telling lies to each other, resulting in a false failure. Then your mechanic “fixed it”, resulting in a REAL failure. Smog Tests. What a joke…


#8

When the engine computer is reset, or parts (like spark plugs) are changed, a lot of things (information) change for the engine computer. It has to relearn settings, and reset internal tables it relies upon to operate most efficiently. Your mechanic should have known this.
It takes driving, at different speeds and other conditions, for the engine computer to relearn and to set monitor systems. There is what is called a Drive Cycle which can be followed which will allow the engine computer to relearn and reset the quickest.
When you go to an emissions test, drive the car until it gets hot, and DON’T shut off the engine while you await your turn. If fact, if the engine starts to cool, it’s a good idea to speed up the engine and turn the A/C on.
A mechanic (IF s/he is really proficient), using a scan tool (MORE than just a code reader) can get so much information about how the engine is running that it’s not funny.
Don’t let a mechanic throw a catalytic converter at your vehicle just because “it might help NOx, or something”. The EGR valve not working can cause NOx to rise. In fact, that’s why it was invented. Overly advanced timing can raise NOx. Using gasoline with lower than recommended octane (by the car maker) can cause misfires and adversely affect emissions.


#9

So, are you saying I should have waited awhile and given my engine’s computer time to relearn the settings following the “major” tuneup (which included a transmission flush, coolant flush, etc.)?
I was told it was best to test it soon, but of course to warm it up first. But does warm it up mean 10 minutes across town or 30 minutes on the highway? I thought a tuneup couldn’t hurt but maybe it made things worse. Just kills me those NOx numbers increased so dramatically (after previously passing – eg. from 450 to 1200). My only probably after the first test was the timing didn’t pass (10BDTC). I fixed that and now I’m worse off. Now I’m taking to to a smog repair shop on Monday – Hope I win the lottery over the weekend 'cause I fear the potential repair costs.


#10

I don’t think your car even has this type of relearn need after sparkplug replacement. Drive cycles to make sure OBD2 Monitoring systems do exist but I have never seen one over 1 hour (other parameters besides time operating must be met to make sure monitors are set) but you did not fail due to a monitor not ready.

The most dramatic re-learn I have experienced is with OBD1 GM cars and it involved idle re-learn I usually took 20 min. Some BMW’s (and other high end cars) had adaptive and multiplictivly values to relearn but I have not experienced a car having a failing NOX value during this relearn.


#11

So then, could it be some simple like a loose vacuum hose? Or perhaps the mechanic accidentally failed to connect something after the tuneup, rear brake job and timing adjustment that caused those numbers to skyrocket when they passed the first time? Or, is it feasible that my original timing setting was so off that the NOx numbers jumped when the timing was adjusted to the right level? (They were on the border of passing on the original test.)


#12

Maybe the process of readjusting the timing was wrong. I don’t know off the top of my head the exact procedure on a Quest, but computer controlled timing vehicles often require a connector be jumped, TPS switch disconnected, wire lead grounded, or whatever.

If he did not do this then the timing will be artificially off; and quite possibly by a large amount.
Here’s what can happen if the timing is advanced too much. Advancing the timing has the effect of trying to lean the system out normally. However, with modern lean burning cars if the timing is advanced too much this may cause subtle misfires that you may not even notice.

Subtle misfires simulate an overly rich condition which means higher NOX, HCs, etc.
It’s possible that a vacuum leak could contribute to this problem since it means the engine controls will try to compensate by going rich. And it can only do this up to a point.

(Also count me as one of those who don’t like the phrase “tune-up”)


#13

Just another note here. The mechanic did a “major tune-up” and at 100k miles if he did not replace the plug wires maybe this is contributing to the problem.

The act of disconnecting and reconnecting old wires can screw them up even. In the old days plug wires were much less susceptible to problems like this.
Modern engines hover as close as possible to misfiring due to running so lean and it doesn’t take much to push one over the edge.
Even testing plug wires with an ohmmeter for resistance is not a sure-fire method of determining whether they’re good or not.
They can test fine and still be faulty to some degree.


#14

Wow, guess I should never have done a tuneup before a smog test, especially when I was so close to passing. Now my husband says I just chose the wrong smog Test Only station because those N0x numbers are so crazy (while the others remain very close to the original), but he is not a mechanic, so I don’t know what to believe any more. They did suggest the first time that he go next door to get it (the timing) fixed, but he said no. Then when I went back the numbers skyrocketed. But I guess it could be something even more complicated like a catalytic convertor or a malfunctioning EGR. I sure hope not. All the other numbers were OK. Sounds like timing could be the issue (even though it passed the second round). I don’t think the wire plugs were replaced. But he did replace spark plugs, Dist. cap and rotor adn air filter.


#15

FOLLOWUP: Unbelievably, another two days have passed and I took my car to a different smog and repair shop. They checked everything, found NOTHING wrong with my car and it passed with flying colors. Nox (NO PPM) numbers went from 1296 to 285 (15 mph) and from 1497 to 230.
How could they change so drastically in a couple of days with no one doing any work on the car? I spent an extra $200 on the car when nothing was wrong with it. Is it possible a 1999 Nissan Quest’s computer must relearn the new parts after a tuneup? Or is that not necessary? Maybe the first smog place ran it too hot, which threw the numbers off? How is this possible?


#16

Good! It passed the smog test with flying colors. The only way to have any idea as to why the figures at the two smog stations were so different would be to have comprehensive scan data immediately after the repairs were done and two days later (with the same scan tool) when it passed inspection.
It wouldn’t hurt to tell the CARB (California Air Resources Board) that you question the validity of the tests performed at the first emissions test station. Their equipment could be “out of tune”. Other people could be running into the same expenses if the test station equipment is in error.


#17

Doing a good deed does have its rewards but what if they want the OP to come back in and test again and her car fails? I say drive on and let others deal with a malfunctioning piece of test equipment,are you feeling lucky? stir the pot.


#18

Good advice. I sure don’t want to test again, but I do wonder if the first smog station was scamming me to get a kickback from the “next-door” repair shop – only several feet away (which I didn’t go to), or did he just rev up the car too hot and fail to run a fan? Or, maybe they are honest and I have some intermittent problem that I was unforutnate enough to have hit at the exact moment of the first test? I guess I’ll never know, but he did mention I could go next door for help.


#19

You can give me stars if you want. Just click those stars above “good advice” it is nice to hear someone liked your advice.


#20

Rationalization is fine for NOT doing something; or, is it? What if people before you had a similar misfortune, caused by errant people or errant machines, and did nothing? Would you think yourself justified doing the same nothing? Or, like most people, when it happens to YOU, that’s a whole different game? Oh, NO! Not Mwa!