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Manik

Wont pass high speed asm emissions testing

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Actually have two issues, most important, the emmisions testing. On the dyno the high speed 02 and n0x are off the charts. The standard is 190 ppm and my pathy is running 2999 ppm. I purchased a new air filter, plan on changing the oil as well as the temp sensor. I'm not sure if that will correct the problem, but, gonna give it a shot. Problem 2, it takes 3-4 cranks before it fires up, this is a new issue that started about 2-3 weeks ago. Didnt have an issue with it up until this time. Did have a "stumbling" problem for a short while when it was cold out, that went away when it started to warm up, outside.

 

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High O2 and high NOx numbers indicate a lean condition. Can you provide the HC, CO, and CO2 numbers? That would help a lot. I have been doing emissions testing for about 17 years and most of those were done with a test and repair certification rather than test only, so have some experience reading the data. 

Your ignition timing is probably advanced a bit more than it should be, but the only adjustable part of the timing is the base idle. Might want to check the fuel pressure, intake and exhaust for leaks, the coolant temp sensor for accuracy and the MAF. 

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+1 for a lean condition. Check the MAF sensor for crap buildup on the filaments and check the rubber tube between the MAF and the throttle body for cracks.

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High O2 and high NOx numbers indicate a lean condition. Can you provide the HC, CO, and CO2 numbers? That would help a lot. I have been doing emissions testing for about 17 years and most of those were done with a test and repair certification rather than test only, so have some experience reading the data. 
Your ignition timing is probably advanced a bit more than it should be, but the only adjustable part of the timing is the base idle. Might want to check the fuel pressure, intake and exhaust for leaks, the coolant temp sensor for accuracy and the MAF. 
I can provide the numbers, at some point, like when I find the paperwork :-/ not gonna hold my breath though. I'm going to check the MAF sensor and the maf-to-tb intake tube for issues. Last year it passed without too many issues other than egr issue, which eventually got corrected. Just thankful for the last year of this BS testing!

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Took a quick look at the intake tube, it appears to be ok, will check with the old WD40 test later. The maf sensor had very little debris in it, I will clean it out tonight. What I did notice was a broken wire at the distributor. It is the single wire that connects to the side of the distributor right next to the cap. I know its a ground, but, any thought if this may be a little bit of the issue? What's the best way to set the base timing on the vg30e? If there's a thread, kindly point me to the at direction.

Thanks for the assistance.

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That wire is part of the motor grounding circuit and not really of concern. I suspect that there is pirate air getting in around the intake somewhere (yes.. very helpful, I know) but without a can of propane / something else that catches fire I can't help ya much. The only other thing I can think of is a blockage in the fuel delivery system (back to your "stumbling" problem) but since it runs super lean at revs it could be one of the hoses or the fuel pressure regulator that's going out. I would think you would smell fuel in the cab if there was a fuel rail/ injector problem sooooo... it must be either before fuel gets to the fuel rails or air getting into the intake after the MAF That's how I would attack the problem.

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Well, let me make a correction. I found the print out and I was mistaken, its not the high speed that it failed at, it was low speed.
The numbers are as follows:
HC - standard 147 - reading was 162
N0x - standard 990 - reading 2666
The high speed was just fine. There was only 100 rpm difference in the high speed and low speed and 10 mph... Well? Any clues..

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Posted (edited)

In that case: excess air is getting in and not being burnt if your HC is up, it's possible that the NOx is your intake air leak / pirate air. But knowing how easy it is to tear the bottom of the intake boot AND have a leaking injector I'm going to suggest that you have both problems until you can rule out positively that you have no air leak.

Edited by SpecialWarr
Ummm... dunb-ass wrote things backwards... because: cars!

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Look familiar? Does anyone know where I can get the clips for the air filter box?b150f0c668ed6b55886f3aaac26ce1ad.jpg

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I wrapped the thing in MULTIPLE layers of electrical tape. There was an immediate difference in the smell of the exhaust gas, it had almost no odor compared to before.. I changed the oil and air filter just for the halibut :) and on hopefully tomorrow the party gets its last proctology exam.

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Well second test, failed again. I'm starting to lean toward the egr valve. I am going to replace all of the vacuum lines to the EGR and test it. The guy that ran the test said something about the cat, but, its only a few years old and doesn't have 10k miles on it. Numbers dropped after repairing the inlet tube, but, not nearly enough for it to pass.

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EGR system is used to reduce the NOx, but at idle and light  loads, the valve should be closed. The intake leak you found may not be the only one. Check the pcv and breather hoses. I found one of mine had split on the underside sometime, but found it last month while working on getting mine ready for registration. It only expired 3 1/2 years ago. These trucks really don't like to just sit in the back yard. Lots of work to get it back to working again. 

 

If you can, try and find some low octane ethanol free fuel for your truck. The compression ratio is low and it won't burn the mid or premium fuel as well. The ECU is not calibrated for the E10 fuel either and so it tends to get the air/fuel  ratio wrong. Contrary to what the Government claims, ethanol is a poor fuel for our old cars and trucks that were not designed for it and it actually causes higher emissions because the engine can't burn it properly. 

 

To check your base timing, have the engine warmed up and at normal idle, with a timing light connected to #1 plug wire, make sure it is running at about 10° before top dead center. If your altitude is above 5k feet, add about 1° for every 1k higher as a rule of thumb. 

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EGR system is used to reduce the NOx, but at idle and light  loads, the valve should be closed. The intake leak you found may not be the only one. Check the pcv and breather hoses. I found one of mine had split on the underside sometime, but found it last month while working on getting mine ready for registration. It only expired 3 1/2 years ago. These trucks really don't like to just sit in the back yard. Lots of work to get it back to working again. 
 
If you can, try and find some low octane ethanol free fuel for your truck. The compression ratio is low and it won't burn the mid or premium fuel as well. The ECU is not calibrated for the E10 fuel either and so it tends to get the air/fuel  ratio wrong. Contrary to what the Government claims, ethanol is a poor fuel for our old cars and trucks that were not designed for it and it actually causes higher emissions because the engine can't burn it properly. 
 
To check your base timing, have the engine warmed up and at normal idle, with a timing light connected to #1 plug wire, make sure it is running at about 10° before top dead center. If your altitude is above 5k feet, add about 1° for every 1k higher as a rule of thumb. 
I appreciate all of the information. Sitting and idling and even off idle it runs great. I was in a similar situation, mine sat for almost 5 years waiting on me to get time to do an engine swap, long story short, I did it last year, did have some issues getting it to pass inspection and remarkably, it did quite well last year. I'm going to go through all of the vacuum lines and see if there's an issue there and replace likely most of it, but, am going to replace the EGR valve and O2 sensor in the process.

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Do you have the odd looking 2 valve egr setup? One is called the Back pressure transducer. I know it sounds like I just made that up but I didn't. Looks like this:

 

Image result for nissan back pressure transducer

 

I had to replace mine for the egr to work properly on my 1995.

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^^ Good thinking to check that. I think the BPT was standard for 94/95. I remember on my '95 the hose coming off the bottom of the BPT was all dry rotted and cracked in the back. Looked fine until I got it apart and went, oh, that's not supposed to look like that.

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Yes, mine has the BPT, seems a helluva lot like overkill. I had already ordered an EGR valve for it, but, it was a standard EGR that does not have the BPT port, I did install it last night and test drove it and damned if it didn't seem to wake up the little VG. One thing that I am going to do is fill up with ethanol free fuel prior to the next emissions test. One thing that I noticed last night was, this sounds very weird, after the test drive last night, the exhaust was actually hot, as compared to the last test, I could not smell it and the exhaust felt, not cold, but not as hot as I think it should have been and I could not smell it at all. This time  I could feel the heat and smell the exhaust as I should be able to. Weird I know, but, I think this will do it.

Another thing that I realized, when they did the emissions test, it had sat for nearly 3 hours, so, dead cold and had only been run for 10 minutes max prior to testing. With headers, I found that it takes much longer for the CAT to get hot and do its job.

We will see what happens this weekend. Oh yeah, fixed a leak at the header to EGR tube connection, I think it was sucking air and cooling the exhaust, dont know for sure, but, just my theory.

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Well, that is the purpose of the EGR system. It's job is to reduce combustion chamber temps to lower the NOx formation. If the exhaust is hotter now, odds are you might be able to get through the test. An air leak up by the manifolds will cause higher emissions readings because the air that gets pulled into the exhaust will give the O2 sensor a false reading, making it think it is running lean, just like the ethanol does. 

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The BPT valve is supposed to tweak the EGR operation based on the backpressure in the exhaust, regulator sort of deal. I'm not sure how much it actually does. I had a hell of a time finding an EGR valve with the right fitting for the BPT for my '95, ended up getting a used one IIRC. And yeah, getting the cat warm before you go in should help, I've heard of people taking a rig out and just running the hell out of it to get it good and warm before bringing it in to give the cat a fighting chance.

 

Good luck!

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Yea, where I have to get it inspected is a 35 minute drive from my house. Both times I went to get it inspected, it sat for 2-3 hrs until the guy showed up, so, this weekend it wont get shut off until the inspection gets done!

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Good news and bad news.. It finally passed on the high speed ASM test, it still failed the low speed, but, got a helluva lot closer to passing. I replaced the EGR valve and ran testing on ethanol free fuel. NOx dropped be 1000 points and HC has been just above the FAIL line at this point.
The guy at the station suggested retarding the timing about 2-3 degrees.
I checked the timing and it settled on the first mark on the pulley. I changed it to probably 20* I'm guessing. Runs great, but, would still like the definition of the marks. You know, 0,5,10,15 degrees and so on. Thanks again y'all.

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At least you're closing in on it! EF&EC-25 of the '95 manual has a diagram of the timing marks, showing four of them (TDC, 10, 20, and 30). The crank pulley on mine has additional marks in between those (TDC, 5, 10, 15, 20, 25, 30). Either way, the timing should be set to 15° +/- 2, right in the middle. Warm it up before you set the timing.

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At least you're closing in on it! EF&EC-25 of the '95 manual has a diagram of the timing marks, showing four of them (TDC, 10, 20, and 30). The crank pulley on mine has additional marks in between those (TDC, 5, 10, 15, 20, 25, 30). Either way, the timing should be set to 15° +/- 2, right in the middle. Warm it up before you set the timing.
My 95 has 6 marks and unfortunately my laptop was at work, it had tge FSM on it. I found kind of a definition on YouTube, but, it was all I had, so, I went with it. The timing was set on the very last mark on the right on the pulley, so, I knew it was way off. I set it at about 10*, going to give itnone last shot at emmisions later today.

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What's that old saying.. "Timing is everything"... The timing was advanced about 20 degrees too much, reset, reinspect for the LAST time and we are golden!

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Posted (edited)

Glad you got it worked out. I guess I just assumed you had the timing right, sorry I didn't think of that. I had a couple cars I had to detune for the emissions test then then turn them back up to give the performance I was after. My 77 200SX was a rolling violation most of the time. Since it was a Cali model, it had the electronic ignition and a catalyst. By the time I wrecked it, cat was gone, EGR gone, larger Webber carb, all vac lines gone but the distributor advance, brake booster and carbon canister purge, air injection system gone, and timing at about 38°BTC. Engine fan gone, replaced with electric.  Rough starting when cold, engine ran hot, but nobody could believe the power that little L20B was cranking out. Still miss that car. Almost lost it to my mom, she drove it for a couple weeks while I was out of town and her 79 620 King cab had a bad idler bearing. I came back and she was telling me how fun that car was. The woman who made me promise not to race on public roads before she would sign for my license was smoking tires at stoplights. Go figure. 

Edited by Mr_Reverse

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N..ko sweat, to be honest, I did/do have a timing light, just didnt check the timing because it passed without issue last year and absolutely no changes have been made to it since. Either or, it passed, from here on out, its safety only

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