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#1 Alex548

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Posted 02 April 2008 - 11:05 PM

Took a 1995 Chevy Lumina Minivan to a Test Only smog shop last week & it passed everything except NOx at the low RPM's (15mph). NOx was a bit high on the higher RPM's, but were within California's smog standards.

Since it failed on the low RPM's, I took it to a smog & repair shop. They told me my EGR valve was faulty. I paid $235.87 to replace it. Afterwards I went back for a retest & it failed again with no change at all on the results.

Took it back to smog & repair shop. . . they replaced catalytic converter and 02 sensor. They took it to a different Test Only smog station and this time it failed NOx at both Low and High RPM's (15mph and 25mph).
Not only that, it failed so miserably that it's now considered a gross polluter. I don't get it. . . .

Anyway, the other day they cleaned the fuel injectors, double checked the vacuum lines, and replaced some gaskets & other minor items. Again, he ran another test and although it's no longer a gross polluter anymore, it still will not pass smog.

The mechanic is now talking about replacing the throttle body and intake manifold.
I'm no mechanic, but a few guys here on these forums know quite a bit about repairs and such.
Would replacing a throttle body and/or the intake manifold decrease the amount of NOx being emitted?

Any other suggestions as to what the problem may be?

Items replaced so far:
EGR Valve
Catalytic Converter
O2 sensor
Gaskets
a couple evap related lines

Fuel injectors have also been cleaned.

Edited by Alex548, 02 April 2008 - 11:11 PM.


#2 lordvader129

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Posted 02 April 2008 - 11:14 PM

in IL if you spend a certain amoutn of money on rapairs and still dont pass emissions you basically get a waiver and dont have to pass

i know CA is a lot stricter but it might be something to look into, lol

#3 hamwbone

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Posted 02 April 2008 - 11:44 PM

make sure you are driving it on the highway for a while before you get it tested, get that cat rippin HOT! don't just bring it in cold

also, go to your local parts house and look for a product called G2P (guaranteed to pass) that usually works too =)

Edited by hamwbone, 02 April 2008 - 11:45 PM.


#4 raff18

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Posted 03 April 2008 - 12:13 AM

run the tank to almost empty then put in that g2p stuff then fill the tank just past half way ro mix it up dont fill the tank then go for a bit of a drive use about a quarter of that tank getting the cat rippin hot and then bring it to the smog test place theres no way it shouldent pass now i live in canada and we have to test our cars every 2 years ive done this to cars that would have to have to spent loads of cash to pass and they did the main ingredent in g2p is methonal alkahol you can just buy that but be very very very very carefull you can burn out the engine so easly pm me if the g2p doesnt work

#5 Alex548

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Posted 03 April 2008 - 01:18 AM

Prior to the first failure, I had driven cross town on the freeway to pick up my son, then back to the other side of town so that sucker was definitely warm. The van passed all emissions with the exception of NOx at 15RPM.

Now after a new EGR valve, Catalytic converter, and O2 sensor, it suddenly became a gross polluter which seems strange. Instead of the levels going down, it suddenly became worse. I know G2P will help with the Hydrocarbons, but I don't know how it affects the NOx levels so I'll look into it a bit further. I've also heard people mention using sea foam, but have no clue where to find it and how to use it. sad.gif


Oh and I just remembered. . . the mechanic also adjusted the timing. He said it was too far advanced so he moved it back a little.

Edited by Alex548, 03 April 2008 - 01:59 AM.


#6 raff18

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Posted 03 April 2008 - 02:29 AM

dont know why the timeing was out should have been fine you have done loads of work to your car and it should pass wonder what fuel ur running ive also heard of seafoam we sell it at the parts store i work at and have had costomers swear by it im going to try it this weekend to see if it helps my ford 3.0L with 300,000km on it get better gas mileage

#7 Alex548

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Posted 03 April 2008 - 03:18 AM

He said the timing was advanced to 14.
He set it back, but don't know to what. blink.gif

Fuel was regular 87 octane when it failed the first 2 times.
Afterwards, I filled it with 91 octane and it still didn't change anything.

Edited by Alex548, 03 April 2008 - 03:19 AM.


#8 StrictPuppet

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Posted 03 April 2008 - 05:30 AM

NOx is caused by high combustion temperatures, so the things that can contribute to high temperature need to be addressed/verified operational.

Causes of high NOx:

1: Lean air fuel mixture (O2 sensor, low fuel pressure, out of range map/maf sensor, out of range coolant temp sensor, restricted injectors, pcm fault)

2: Inoperative egr system (defective egr, plugged egr passages, vacuum hose routing, egr solenoid malf, egr transducer fault, {transducer not used on GM}, pcm fault)

3: High coolant temp (defective thermostat, low coolant level, plugged rad, defective water pump, inop rad fan)

4: High cylinder pressure (high compression pistons, incorrect valve timing, combustion deposits)

5: Excessive ignition advance (base timing set wrong, mechanical/vacuum advance faults, pcm fault)

6: EFE problem (thermostatic air cleaner control malf)

7: Defective catalytic converter (loose or plugged substrate, loss of precious metals, sulfur contamination)

8: Defective air injection system (vacuum/wiring faults, air injection valve faults, pcm faults)

It concerns me a bit that your mechanic appears to be just throwing parts at your vehicle as a guess without actually investigating the cause of the malfunction.
NOx failures typically are one of the simplest to diagnose as its just a quick order of elimination. In Canada at least, the 1995 Lumina APV, is equipped with a 3.1 TBI engine ( I assume that what you have since the PFI version has distributor less ignition and is therefore non-adjustable), so that is what I am basing my comments on.

All cats are not created equal, a cheap cat is exactly that...cheap and often lacks sufficient precious metals to work effectively. No matter how good your cat is, it cannot work to reduce NOx unless there is an absence of O2, so anything that is causing excessive O2 before the cat can render it ineffective. Things like exhaust leaks will actually allow O2 to enter the exhaust stream as it passes by between combustion pulses. Here we don't use an air injection system on that model, but if the cali-spec APV does, then a fault in that system which causes upstream air injection under load, will prevent the cat from managing NOx.

Egr valves. Yours should be a typical vacuum operated EGR w/o internal transducer. There is a pulse width modulated control solenoid that limits the amount that the egr opens by varying the amount of time that vacuum is applied versus time dumped. The pcm controls this function and inhibits egr operation until certain criteria are met ( coolant temp, gear position, vehicle speed input) This is a very simple device to test and need never be replaced in error. You can test the passages for blockage yourself just by manually lifting the diaphragm with your fingers. The engine at idle should nearly or preferably, actually stall out when the egr is fully opened. That tells you there is sufficient exhaust flow through the passage. If there is little to no difference when the diaphragm is lifted, then the passages are likely plugged with carbon, and the intake MAY need to be removed for a thorough passage cleaning.

Ignition timing is controlled electronically, and must be checked by disconnecting the in-line connector that is near the distributor (tan wire), and checking the marks at the harmonic balancer with an inductive strobe timing light. GM base timing is either set at 0 or 10 degrees depending on application with tan wire disconnected. Assuming that your HC and CO measurements were well within allowable tolerances, you WILL pass NOx with this connector apart, but CO and HC will increase (however the late ignition timing will now super heat the cat, so the post cat readings may not appear to increase). Engine power will be greatly diminished, but so will NOx.

Thermostatic air cleaner is easy to check, with the engine warmed up just look into the air intake(pull the duct off) and you should see a door that is open. If this door is shut then it is sucking preheated air from the exhaust manifold shield. Cant have low cylinder temp with super heated air going into the motor. It is a simple vacuum operated/or thermal pellet operated mechanical door, very simple to figure out. The door should only be closed during warm up.

Engine management (pcm). The pcm determines appropriate fuel mixture based on many inputs. Coolant temp, manifold absolute pressure, throttle position, and oxygen sensor are the main sensors. Coolant temp sensor can usually be ruled out, as they usually fail to the cold direction which would cause a rich/low NOx scenario. O2 sensors are a feedback to the pcm that tells it how well its doing with fuel management. They produce a voltage based on oxygen differential between exhaust gas and external air. Low oxygen in exhaust=over 800mv output, high oxygen in exhaust=under 200mv output. Typically when an O2 sensor fails it causes no voltage output which indicates lean exhaust, the pcm then tries to richen the mixture until it sees a voltage over 450mv. Bad O2 sensors very rarely cause high NOx, unless they short to voltage(voltage is applied to the sensor for an internal heater unless it is a single wire sensor which has no heater)
In saying this I find it unlikely that the O2 needed to be replaced for your high NOx failure.

Unless your mechanic has determined that the passages for the egr are plugged I see no reason to remove your intake manifold or remove/replace the throttle body assembly. Its unfortunate that he appears to be just throwing suspected parts in there without verifying the fault. A good mechanic should be able to tell you within 20 minutes what the exact fault is ( or at minimum, what it isn't), no guesses. There may be other reasons he deemed it necessary to replace those parts, I dont know I didn't look at them.

A glance at the test results tells you where to look.
Do you have the actual test result numbers, for all the exhaust gasses? They help in determining the fault. If Co is extremely low, then its running lean. If its average or high.... look to the egr system. If everything is high look at the cat (if a rich running engine fails NOx, the cat doesn't work). CO2 should be over ~14% at cruise if the cat works well, and there should be very little O2 remaining.


Post your emission test results if you have them, and I will give you my best over-the-internet diagnosis.

#9 Alex548

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Posted 03 April 2008 - 06:03 AM

Here's my first retest which shows just about the same numbers as the original test that was done a few days prior. This was after the EGR valve was installed. Since the results were nearly the same, the mechanic concluded the EGR valve was not the problem and reinstalled my old one & gave me credit for parts & labor. . . but since then, he's replaced the EGR valve again so there went my credit. sad.gif

After replacing the catalytic converter and o2 sensor, the van became a gross polluter. blink.gif
After adjusted timing, fuel injection cleaning and vacuum line checks. . . the numbers came back down, but still failed NOx at both high & low RPM's. mad.gif He mentioned the timing was at 14 & he moved it back down a little.

I might just have to cut my losses with this shop & pay what they say I owe & take it elsewhere.

Click here for my results.

Let me know if the image is too small. smile.gif

By the way, the fuel Evap passed on the original test, but failed on the second one. They told me it was a loose hose & I replace it with another one. It passed just fine on the 3rd & 4th retests. tongue.gif

Edited by Alex548, 03 April 2008 - 06:23 AM.


#10 StrictPuppet

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Posted 03 April 2008 - 06:25 AM

The 15% Co2 and 0% O2 says your cat works well (for HC and CO at least). I would have been very reluctant to replace the cat from those test readings. Further retarding the ignition timing should allow it to pass, as you still have quite a margin on the CO. Disconnecting the timing connector will turn on the Check Engine light, so if that is a fail, you dont want to go that route. I'll bet you a beer, 5-8 degrees less timing will allow you to pass. Also check the thermostatic air cleaner door as I mentioned above. I failed to mention that it should be checked with the engine actually running. Also, manually lift the egr and look for a considerable rpm drop @ idle.

Sorry for the twistedsymphony-esque post above.....hahahah


#11 Alex548

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Posted 06 April 2008 - 06:28 AM

Took a trip to the mechanic's shop the other day. He had already replaced the van's throttle body with a used one from a salvage yard. End result. . . no change in the smog readings. I asked about retarding the timing and giving it another try, but he told me something about California smog laws and having the timing no more than +/- 4 from TDC or something like that. . . don't really remember. I was just about to give up on this guy and tell him to give me a bill for work done & cut my losses then he tells me he's bringing over a buddy of his who knows significantly more about smog repairs than he does.

This afternoon I once again visited his shop and his buddy said the NOx readings go way down at higher speeds, but still have problems at the lower speeds. He seems to think there's not enough vacuum and told me he wants to try another throttle body replacement. Also said if that doesn't work, then there must be something wrong within the engine itself. blink.gif

At this point, my patience has nearly run out, but I had good news today. The mechanic said he's not gonna charge me for anything except the O2 sensor and the two failed smog tests if he can't get it to pass the next smog test. He said He'll give me my $235.87 back for the EGR valve and he won't charge for the replacement throttle body, catalytic converter, fuel injector cleaning, miscellaneous gaskets, and of course all his time. smile.gif

I hope he's true to his word since I wasn't gonna be able to afford the repairs anyway and would have stuck them on my credit card (again). I already owe about $12,500 on those things and it's primarily due to vehicle maintenance over the past 5 years. sad.gif

Will give another update probably Tuesday.
QUOTE
Disconnecting the timing connector will turn on the Check Engine light, so if that is a fail, you dont want to go that route.
Yeah, it's an automatic fail if the check engine light comes on at any time during the test. They also test to make sure the check engine light is working properly so disconnecting the timing connector and disabling the check engine light won't work. sad.gif

Edited by Alex548, 06 April 2008 - 06:31 AM.


#12 Alex548

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Posted 09 April 2008 - 02:15 AM

QUOTE(StrictPuppet @ Apr 2 2008, 10:06 PM) View Post

Causes of high NOx:
3: High coolant temp (defective thermostat, low coolant level, plugged rad, defective water pump, inop rad fan)


Bingo!

This Saturday I asked him if going with a cooler thermostat and flushing the radiator & adding new coolant would help any and he said he doubted it. I pointed out to him that I've had the van 3 years and I've only done Engine flush, Transmission service, and fuel injector cleaning. Never got around to doing a radiator flush.

Well, since he was out of ideas, he decided to check my coolant. It was pretty dirty so he took care of it.
He pulled it into the service bay today and I stood there and watched the computer. Not once did it go over 450ppm at both 15mph and 25mph. He also put it on the machine while cold so I have no clue what the numbers would look like if the van were nice & warmed up.

Anyway, he's gonna take it to a Test only station in the morning and try to get it certified (again). Hopefully it'll finally pass this time.

I need to get that thing out of there anyway since my 92 Eagle Talon is now having problems. sad.gif
The wife has been using it and it started knocking on Sunday. Sounds like it's coming from the Tranny (again). To top it all off. . . a chunk of metal hit the windshield (and cracked it) today while she was driving into town so now I have to deal with that. grr.gif

Edited by Alex548, 09 April 2008 - 05:15 AM.


#13 StrictPuppet

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Posted 09 April 2008 - 03:14 AM

I hope it all works out for you, Alex.

On a side note. If anyone is looking for a good mechanic in their area, a good place to check is IATN.

http://www.iatn.net/shopfinder/

I come up with these guys for you ... http://www.advancedsmog.com/

While it is not a guarantee of quality, it at least indicates a willingness of the shops/techs to strive for better repairs, by joining and having access to the largest group of auto technicians knowledge base available.

Edited by StrictPuppet, 09 April 2008 - 03:16 AM.


#14 Alex548

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Posted 09 April 2008 - 05:13 AM

QUOTE(StrictPuppet @ Apr 8 2008, 07:50 PM) View Post

I come up with these guys for you ... http://www.advancedsmog.com/


Thanks for the info. That's probably where I'll take the Talon when I get it back.

#15 Alex548

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Posted 11 April 2008 - 12:52 AM

Good news. . . NOx was within passing range at latest smog check.
Bad news . . . it failed Evap test. sad.gif






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