# Emission Problems



## philritzert (Aug 20, 2010)

I apologize about the long message but I've done a lot to try to fix this and time is running out. This is my first new thread. I have read here for years, and recently got an account. I have searched here and read everything somewhat related to my problem and nothing helps too much. 

Basically, I first tested my emissions this year (req. for vehicle registration) two weeks ago. My Sentra was failing for NOx and HC. I checked/cleaned my EGR valve, and BPT valve. I replaced all my vaccum hoses including those to the fuel pressure regulator. This brought my NOx down slightly and my HC up slightly. My EGR solenoid switches the wrong vacuum lines than what it's supposed to so I compensated by swapping lines at the solenoid. Slight improvement on HC and again, the NOx went back up. CO is still at .5% which is pretty close to good mixture. 

I checked the wires to the solenoid and the wires are good, but the ground signal (105 at the ECM) is never cut by the ECM when the throttle is snapped (as it is supposed to). I check vacuum source and found that there is no port vacuum (checked while driving), but plenty of manifold vacuum. I re route the vacuum to supply the egr and canister from the throttle body. This brought NOx down tremedously (3200ppm to 700ppm) (limit is 1190ppm), but the HC is now 300ppm (limit 160ppm) and the CO% is 1.1 (limit is .8). My CO2% has stayed between 14.5 and 15% (min. is 6%).

I replaced my air filter, plugs, wires, o2 sensor, and coolant temp sensor. The plugs were kinda fouled but none of these repairs made a huge difference. I set the timing to 10 deg. it was about 12 before. No difference. Increased idle to 1200rpm from 650rpm and the HC went down some. Everything else stayed the same. I have run 4 cans of seafoam (not at the same time but 4 different consecutive days) and each time there are disgusting amounts of smoke. The car smokes for about 5-7 miles after running the intake cleaner. Two months ago, I pulled the intake manifold off and soaked it for four hours until it sparkled.

My fuel economy was around 40mpg highway (32 city) before any repairs. I now only get 25 in the city and haven't been able to test highway. Any suggestions? There are no fuel leaks and no vacuum leaks (pinch PCV hose while engine running method/spray everything with starter fluid, intake cleaner method). Please help. I can't afford this, and these emissions repairs are only killing my engine's efficiency. The acceleration has slowed since the repairs as well.

(Header, warm air intake routed behind battery)


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## philritzert (Aug 20, 2010)

Update: Repaired air regulator hose. (A split developed on this hose when I replaced another hose I guess). Retested yesterday and the HC went down to about 250ppm. still 1.1% CO and ~700ppm NOx. I drove to the inspection station with the ECM in diagnostic mode II (O2 monitor) and the check engine light would blink pretty quickly while cruising, turn off while decelerating and under heavy load. I left the ECM in this mode during the test and it was following the same pattern. This should mean that the ECM enters closed loop mode and that the AF is pretty good.

Any suggestions would be greatly appreciated.


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## tlhingan (Jun 8, 2009)

High CO usually means you're not getting enough air into the mixture. Clean your MAF and throttle body, it might help.


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## philritzert (Aug 20, 2010)

Thanks. They're pretty clean already, but I'll see what happens. The range on the TPS seems to be a little short (.75k ohms closed, 3.9k ohms WOT). Could this cause the problems? The MAF seems to test okay... 1v at idle, increases smoothly with throttle opening. 
I have an ignition coil coming in tomorrow, and maybe that will make a difference. The coil I have is out of spec (primary resistance is 1.4 ohms(.9 normal), secondary resistance is 12.84k ohms (13 normal)). Hopefully that shows improvement.
I guess I can also check for a leaking fuel injector. That will give me something to do.

Any other suggestions, keep them coming please.
Phil


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## philritzert (Aug 20, 2010)

Actually, I looked into it and when monitoring the O2 feedback, if the light is off, the car is running rich. That would mean that fuel is NOT cut off while decelerating. What could cause this? The Out of spec TPS? I adjusted it to where when the throttle plate is closed, the TPS puts out .5 k ohms and its still the same o2 readings. A 4-gas two-speed idle confirms the hc run at about 100 ppm at 2500 rpm. I release the throttle abruptly and as soon as the throttle closes, the HC jump to almost 4000 ppm after about a second, and slowly go down over about 10 seconds to stabilize back at about 120 ppm at idle. Any suggestions? I'm going to adjust timing and probably retest today.


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## jdg (Aug 27, 2009)

As far as your 1.4 ohm reading on the primary resistance... Did you check the resistance of the leads/tips and subtract that out? Sometimes that'll could be a better part of an ohm or two...unless they're gold and really clean. And the secondary resistance isn't THAT far out of tolerance. A bit low, yes. Shouldn't hurt anything being 160 ohms low out of tolerance. Might lower your spark voltage by a tad, and by a tad I mean a really really small amount. Couldn't hurt to swap it out though...
And I though the O2 feedback went the other way around. Light on = O2 low (=rich), light off = O2 high (=lean). Might want to double-check it.
Your HC numbers do look a bit goofy though. What does a compression check show? Anything useful?


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## philritzert (Aug 20, 2010)

I may have misread, but I think the FSM says light on = lean, light off = rich. That would explain my exhaust gas readings for the sudden RPM drop under no load. I may be mistaken though and I'll have to double check. As for the coil, I checked again, and with the coil out of the vehicle, the primary tests 1.4. and the secondary has dropped to 12.24 k ohms which is almost 6% out of spec. I think its worth replacing just to help, but may not solve the problem.
The compression test results show that the piston rings are starting to leak very slightly on cyl 3 and 4. Adding oil brought those numbers way up (plus pumped some smoke out the tail pipe after I finally started it back up ) The compression was within spec and I performed the procedure with each injector unplugged, the secondary coil wire was unplugged, all the spark plugs were out, and the throttle was wide open with a pedal depressor tool.
They sent me the wrong coil (completely different design that would damage my coil wire if I tried to hook it up), so I sent that one back and a new one is on the way. Hopefully on Monday I can pop that in.

Thanks for the help. Keep the questions and suggestions coming in.


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## rogoman (Dec 16, 2004)

A lean mixture causing misfiring will cause a high HC. Look for a major vacuum leak; test with a vacuum gauge. Also the fuel injectors may be leaking.


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## philritzert (Aug 20, 2010)

I was concerned that maybe the injectors might have a leak. I was going to check that this weekend. The intake has no leaks to my knowledge. I checked with a vacuum gauge and the reading is 22 in/Hg but it has a very rapid fluctuation of about 1 in. As I am informed, that type of fluctuation is most likely a fuel/ignition problem. The results of the compression test show that the valves and seats are likely in good shape. I would imagine the seals are pretty good as I have no oil in the combustion chambers (per spark plugs are dry). One of my tube seals is starting to go out as there is a minuscule trace of oil on the top of the #2 spark plug. Not likely a problem and definitely wouldn't affect emissions. Can anyone verify the vacuum fluctuation symptom? The fluctuation widens to about 4 in/Hg, still peaking at 22 in @ ~3000 RPM. Never drops from this and its a VERY rapid change... blurry almost.


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## rogoman (Dec 16, 2004)

philritzert said:


> Can anyone verify the vacuum fluctuation symptom? The fluctuation widens to about 4 in/Hg, still peaking at 22 in @ ~3000 RPM. Never drops from this and its a VERY rapid change... blurry almost.


Fluctuations by about that amount usually indicate one or more sticking valves or ignition misfire.


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## jdg (Aug 27, 2009)

Try doing a cylinder drop check...
Fire up the car, get it good and warm, let it sit idling for a few minutes. Turn the headlights on bright, turn the blower motor on full, turn on anything electrical you can think of. Disconnect the idle air control valve so the computer doesn't try to adjust the idle rpm for you. Then turn off everything that you just turned on. That way the idle will be a bit higher. If it's too high then skip turning everything on before disconnecting the IACV.
Note the rpm...
Pull one spark plug wire at a time noting how far the rpm drops. Don't forget to reconnect each plug after you read the rpm! May as well look at the vacuum gauge since you've got it out there.
The cylinder that is causing a problem (if it is just one cylinder) will change the rpm by the least amount (i.e. it's not contributing very much to the overall power output) and the vacuum readings won't change much when that cylinder is killed off.
Back in the day, a fluctuating vacuum gauge generally meant something is up with the valves (cracked valve, bad seat, etc), but as in the post above, sure doesn't rule out ignition problems.
You could probably do the same thing with the fuel injectors themselves, if they're accessible. That's one of the tests the Nissan CONSULT system (as well as others) do these days, but it's all computer controlled. Don't know if the CONSULT will work on a your model or not.


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## philritzert (Aug 20, 2010)

CONSULT would definitely work on my car. The DLC is located behind my fuse panel. I don't have access to a CONSULT, nor can I find one that works stand-alone. The real one is a dealer only part from what I have read, and these knock-off CONSULTs I find require a computer... I need a battery/charger for my lappy so diagnostics costs really add up doing it the easy way. (I would love to have a CONSULT and tomorrow is my birthday, hint hint. JK)
The weirdest thing about this is that I get excellent fuel economy. Hwy on avg is 40mpg on 87 octane and 44mpg on 91 octane. I was leaning toward ignition but all my ignition parts except the module and coil are new. The coil is only a little out of spec I guess, and I haven't tested the module... not sure if being a little out of spec on these would cause noticeable driveability issues.
What would be the cause of sticking valves? I have run 4 intake cleaners through and have noticed no gains. Just huge amounts of smoke. I have enough cleaner left for two more intake cleanings. I have fed 2 through the brake booster hose, and two through my PCV hose. Usually intake cleaner should clean the intake valves... what's the likeliness that exhaust valves are sticking? What would be the symptoms. My compression would have been lower if my valves were sticking, right?
The car is as peppy and economical as when I got it, but doesn't pass like when I got it.
I will try to do the cylinder drop test as suggested.
One last thing that may be a symptom of something: On two separate occasions just this past week when leaving work, after I got to the first red-light, the car hesitated like I was taking off in third. I got to about 5 mph and then she takes off. Doesn't happen the rest of the way home or on my way to work. It's only happened twice and there's no smoke. It's been cooler lately and on one of those occasions it was raining, but the most recent it was dry. The only transmission problem I have is 5-th gear pop-out so I am driving a "4-speed" until I can pass emissions and focus on this. Luckily these emission tests here on pre-96 cars are limited to a 25mph test, so no fifth gear is not an issue for them.
I appreciate all the help I have received so far and anymore I get. Thanks for the responses! If I get the car to pass, I will definitely post back. Perhaps advancing the timing might get me to slide for this year?


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## heathman (Sep 13, 2010)

This seems to be getting over complicated ... I would hook up the scanner and see what you short term and long term fuel trim is .... That will tell you whether you are lean or rich or maybee there is nothing wrong....the fuel trim or(block learn) should be at near 0 ... EXAMPLE if you short term is -4 and your long term is +3 you are near 0 and are o.k ... if short term is -8 and long term -8 ..you have a running rich issue...etc.. short term fuel trim is a response (fix)to a minor air fuel mixture problem it will add or reduce fuel. ... long term fuel trim is a long term fix, the computer realizes it requires that amout of fuel trim and remembers that and that is now the new perameter to try and bring the engine to run efficient. Good Luck !!


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## philritzert (Aug 20, 2010)

Without a scanner, I won't be able to perform this test. Good thoughts though. If someone knows where I can get a scanner capable of doing this on a 1992 year vehicle with OBD I, please advise. 
I appreciate the help, and I will consider your guidelines when I can get such a tool. Funds are limited and time is technically up. My registration will be late after tomorrow, but I must keep working on this because my Sentra is my only form of transportation to work 30 miles away.
I will be replacing the throttle position sensor tomorrow. If the ignition coil ships in tomorrow, that as well. Another symptom that I may be having is that when I suddenly release the accelerator while driving, I feel a jolt, as if the engine is swinging forward and the car drops forward. It's felt mostly in the pedal, but the shifter moves as well. All my engine and transmission mounts were replaced less than a year ago and are in excellent shape. I'm not sure if this is because the dog teeth on the other gears are worn down, but if it was, wouldn't I experience a pop-out in those gears as well.
I know its difficult to diagnose a problem without being here, so I appreciate all the effort that everyone is putting forth. Are there other sensors that I should test? Is there any way with a multimeter to check whether or not the ECM is using the input from the sensors? I have checked the wiring and every signal makes its way to the ECM and there are no bent/broken pins on the ECM. The wires are in excellent looking condition for their age, not to mention the resistance on those I checked are less than .05 ohms, which some of that resistance could be the leads and probes on my multimeter as suggested.

Thanks


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## philritzert (Aug 20, 2010)

I replaced my throttle position sensor. The coil comes in today... shipped late... not happy about that, but what can you do? The NEW TPS is out of spec too... I set it so the resistance was .5 at closed throttle and with ignition on it shows .34 v, BUT I retested yesterday. The numbers dropped. I'm getting close. 

2525 5015

HC 210/156 163/153
CO 1.1%/.8 .7/.8
CO2 14.5/+6 14.8/+6
NOx 860/1156 708/1189

Turned the distributor fully counter clock wise and brought everything WAY down. I passed! 53 HC, .4 CO, 15.5 CO2 and 115 NOx !! I still need to fix the car but I have more time now.


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## jdg (Aug 27, 2009)

How is your timing chain tensioner? Do you have the typical worn upper tensioner timing chain rattle thing going on? Distributor fully CCW surely isn't normal. What is your timing at with it fully CCW anyways? Whatever it is, can't be good!

As far as the new TPS being out of spec. Seems to me that a lot of things you're reading with your meter seem to be out of spec. Not to say that there aren't that many things wrong with the engine. But have you considered your meter might be out in the weeds?


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## philritzert (Aug 20, 2010)

I have not done an inspection of the chain in about 20k miles, however it was in good condition at that time. I need to pull the valve cover off anyway, so I might as well check it.
The timing I set the car too was definitely not good (exhaust backfires after every shift) but registration was due yesterday and this is my only way to work right now. I didn't check the timing with a light but I need to re-set the timing today, so I will find out for you. (The timing after the test was set by ear, and the engine ran just like it did before @ 10 BTDC). 
The timing was only set like that for about 2 minutes of idle before test, and the less than one minute it took to quick pass during the test. I immediately had the car shut off and rolled out of the inspection station where I turned the distributor back to almost where it was, started the car, and adjusted it by ear/feel. There were no knocks/pings during the test.
It is definitely a possibility that my meter is to blame for these readings, however there are so many other things that I check within spec. I definitely don't have a trustworthy/quality meter, like a fluke, but I was more concerned with the car than a meter so that's where my money went.
I appreciate the feedback and I will keep you posted on my findings


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## jdg (Aug 27, 2009)

philritzert said:


> (exhaust backfires after every shift)


You've got a vacuum leak somewhere. I would almost bet money on it (almost that is  ). The vacuum gauge might say you've got good numbers, the meters might say you've got good numbers, heck, the ECU might even tell you everything is working right....but only because it's able to compensate for it.
But I'd still bet good money that you've got a big ol' vacuum leak floating around in there somewhere...and of course the damn thing isn't going to step up and say "hey right here! vacuum leak!!!". Never does...(sigh)


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## philritzert (Aug 20, 2010)

I'll check it out. It didn't start backfiring until I adjusted the timing at the testing station. I have an exhaust leak, but its just a gasket. I guarantee after I replace the exhaust gaskets and fix the timing back to stock, it will go away. There may very well be a vacuum leak though, so I'll continue to look for it.

Thanks


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