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Smog Again: NOx

 
Old 02-13-2005, 02:40 PM
  #31  
pappy92651
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Originally Posted by Lorenfb
An intake leak would have to be fairly large, e.g. bypassing the MAF sensor.
Intake air leaks at the manifold have little to no effect off idle.

Most likely the problem, given all that's been checked/replaced, a bad/lean MAF sensor.
I've seen this as a source of high NOx at a few of my customers' Porsche shops.
Find a good MAF tester and check the CO before/after without the O2 connected.
Hello Loren,

The MAF is a good candidate. Look at my HC and CO numbers. Very low to non existent. All conditions that can be caused by a gross vacuum leak or bad MAF sensor.
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Old 02-13-2005, 03:15 PM
  #32  
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Steve
Here is my smog cert! It does appear an over-lean condition is the problem...which could also cause some more serious engine problems....in my 2 stroke R/C cars when you run them too lean they would pit the pistons really bad and inventually start to loose compression from the pits, or craters if they were really bad
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Old 02-15-2005, 11:25 PM
  #33  
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I passed smog. Failures were due to a combination of problems that required a number of man hours. The Ott X pipe with Random Technology CATs will pass smog and run very clean. DO NOT USE THE AIR INJECTION SYSTEM! Attach it to the X pipe and plug the diverter vacuum line or inject air after the CATs (not into the X pipe before the CATs). Please read my comments to Louie (attached).


"Hello Louie,

Thank you for all of the information and support. We solved the NOx problem
today. We had to establish a solid base line and this required the right
instruments. The car had problems. As we corrected each one the emissions
dropped. Attached is the PASS VIR from the smog test station. For a GT the
HC levels and CO levels are normal, but now the NOx levels are now extremely
low.


For the first test stock S4 chips were installed and the fuel pressure was
set to 48 PSI (vacuum line off). The car failed with high NOx levels. IR
Diagnostics at 2000 RPM:
The collector temp = 700F
X pipe exit = 400F
CAT inlet = 220F
CAT outlet = 200F
Muffler case = 120F
Tail pipe = 78F


For the second test we removed the custom exhaust and installed a stock S4
exhaust system. The car failed with all levels high. Exhaust elements were
at normal temperatures.


Next we re-installed the X pipe, Random Technology CATs, and DynoMax
mufflers. Diagnostics were conducted to determine AFR. The O2 sensor was
bypassed. We installed the Innovative Technologies Lambda gas probe in the
right pipe (where the O2 sensor had been). At 2000 RPM we measured the AFR
at 14.0:1. We switched the probe to the left pipe and measured 15.1:1 (a bit
lean). We located a bad fuel injector and replaced it. All spark plugs were
replaced. Compression was measured at 180 PSI +/- 5 PSI. NOx came down to
about 780 ppm but we still failed.
The collector temp = 700F
X pipe exit = 400F
CAT inlet = 260F
CAT outlet = 220F
Muffler case = 140F
Tail pipe = 80F

Finally we placed a bead in the air diverter vacuum line to shut off the
air. NOx fell to very low levels. We passed! AFR between pipes was 14.3:1 at
2000 RPM (Note the CAT temp increase).
The collector temp = 750F
X pipe exit = 420F
CAT inlet = 400F
CAT outlet = 500F
Muffler case = 180F
Tail pipe = 89F

Please change your instructions regarding the use of air injection. This
cools the CATs and they do not light off. The air line should be attached
but the diverter vacuum line plugged in order to meet smog in California.

My emissions failures were caused by real issues. They required attention
and repairs which also increased my HP. Greg dynoed me today at 337 rwhp =
406 crank HP (5900 RPM). These are numbers with bone stock fuel and ignition
timing maps!

A failing injector caused a significant lean condition in the left bank (and
the O2 sensor is in the right bank). If the O2 sensor were placed in the
center of the X the mixture might be better balanced.

If air is injected it should go in after the CATs. This could be done by
adding 2 bungs behind the CATs. It is not necessary if the original air line
is disabled (but is physically required in CA). Adding air before the CATs
will cause them not to light and NOx levels will be high.

The engine must be in good tune in order to pass smog. Your X pipe and CAT
design work rather well and are actually cleaner than the stock system. The
key to passing emissions is to ensure a properly operating stock engine
configuration and have the right tools to diagnose what's occurring. IR temp
meters and AFR gas analyzers are extremely useful.

Thank you,
Steve"
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Old 02-15-2005, 11:30 PM
  #34  
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Excellent!
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Old 02-15-2005, 11:41 PM
  #35  
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Steve, how did you locate the bad injector?
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Old 02-16-2005, 12:04 AM
  #36  
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Originally Posted by worf928
Steve, how did you locate the bad injector?
Attached is a useful tip. One injector sounded wrong and had the least effect on AFR when we pulled the connector! When we pulled the spark plugs out one had a white electrode. The others were brown in color.

"Fuel Injector Troubleshooting

As intimidating as it looks, the injection system is relatively simple to understand and you can do a few simple things to diagnose the problem.

1) Have a mechanic's stetoscope, and check each injectors individually. If one make a significantly different tapping noise you may have a pointer to your next step (see below, # 3 and 4))

2) You can also disconnect them one at the time. As long as you notice a change in engine behavior after disconnecting, you can skip to the next injector.

If you suspect any one injector to be faulty after these two tests, and before going to the next steps, you should give your Shark an extra dose of Chevron Techron and drive the car for a few days..(A full dose in half a tank did marvel once in my wife's BMW, without having to take anything apart)

3) If you decide you want to check some of the injectors a little closer, first get yourself the set of new O-rings (PN # 928 110 904 00 for a MY '87) You should NOT reuse an old O-ring, as most of the rubber parts under the hood are brittle after so many years and the last thing you want is a fuel leak while idling in traffic!

Handle the injectors very carefully as the nozzle is small and very fragile. Just in case, the PN for the MY '87 injectors is 928 606 119 02

4) with the whole rail out and the injectors mounted on it, you can do a simple leak test by activating the fuel pump (but without CRANKING the engine!!) and check if any of the injector leaks more than one small drop after about two minutes,. Use a soft clean light color cloth as protection for your injectors and to observe eventual leaks more easily.

Jacques Vuye
Sonoma CA
'87 S4 Auto Nougatbraun Metallic/ Tan"
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Old 02-16-2005, 12:21 AM
  #37  
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Thanks Steve. I figured it was something like that. I'm always looking for new tricks though.
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Old 02-16-2005, 01:11 AM
  #38  
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Steve--

My bone-stock '89 is on the ragged edge of passing/failing on NOx. Can you share a little detail on exactly which vacuum hose you plugged to get the cat to light off? I'll do the stethoscope on the injectors to see if any are not opeing, and will probably have them cleaned as part of the intake and cam cover refinish effort this spring.

Thanks for detailing your efforts and results.
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Old 02-16-2005, 01:54 AM
  #39  
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Hello Bob,

On the passenger side of the engine bay there is a diverter valve which connects four ways. The forward side goes to the air pump. The rear side goes to the air box. The downward side goes to a stainless line connecting to the third stage of the dual CATs. A rubber hose comes off the top. This can be plugged using a small plastic ball and it will direct the air pump air to the air box.

If you have a stock system the CATs are a three way type. Blocking the air will probably make your NOx worse. If your NOx is high it is likely that you have another problem, injectors, MAF, O2 sensor, or FP regulators. It is a lean condition which produces NOx. If your CO and HC levels are low but NOx is high you have a lean condition. The CATs require some unburned fuel in order to light off and make heat. Once the gas enters the final stage air is injected to catalyze the final reaction and then cool the gases. The stock system is different than the Random Tech system.

Note: You could install a new exhaust system and the problem might still exist. The stock CATs usually last forever. It is more likely that you have a problem other than exhaust. Determine the integrity of each system, fuel and ignition. Check your plugs, compression, wires, advance first. Next check your O2 sensor, vacuum, fuel pressure, and MAF. Do the pre test at a test only station to see the effect.

Your CATs should be running at 500F outlet t if they are working (IR meter). To test have a shop jumper your LH, remove the O2 sensor, and plug in a Lambda unit to determine your AFR at 2000 RPM. If your running at over 14.7:1 you may have a lean condition caused by one of the elements mentioned.
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Old 02-16-2005, 04:26 AM
  #40  
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A great ending results from great diagnostics! Your efforts should aid many in the future.
This thread exemplifies what forums are all about.

The shop you're opening in SoCal will be called ________???
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Old 02-16-2005, 03:18 PM
  #41  
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Many thanks to all those who commented and provided information. Emissions compliance is important. In large metro areas you can see the effect. Compliance makes the skys a little bit less brown with each coming year. You don't need to give up performance in order to run clean.
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Old 02-16-2005, 05:44 PM
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Steve
Great post! 337whp is damm good for a smog legal 5.0L!!! You should get a touch more with the chips! Your 0-60 should drop a bit now too....maybe 4.4?
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Old 02-16-2005, 08:59 PM
  #43  
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Originally Posted by IcemanG17
Steve
Great post! 337whp is damm good for a smog legal 5.0L!!! You should get a touch more with the chips! Your 0-60 should drop a bit now too....maybe 4.4?
Brian,

I put the chips back in and increased the fuel pressure. The car has incredible pull from 3000 RPM up to 6500 RPM. I should go back to the dyno once more. I noticed that the tires chirp all the way through first now. I am going to emissions pre-test the car when I'm done to confirm that I still pass. After that the SMT-6 computer will go in and so begins a third layer of testing.
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Old 02-16-2005, 09:01 PM
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Excellent going Steve...! Keep us posted.
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Old 02-17-2005, 04:56 PM
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I increased the fuel pressure to 51 PSI (3 over stock). The car really likes it there. The performance chips are installed. Filled the car with 91 octane pump gas. Temperature gauge was reading 1/2 during the test. We measured 349 rwhp at 5900 RPM. Idle is smooth and steady. No dead spots from idle to WOT. My emissions numbers changed slightly. At 1476 RPM, HC went from 73 to 80 PPM and NO went from 22 to 25 PPM.

My cousin has a new M3 which I run against on a regular basis. The cars used to be fairly even. Her 0 to 60 times range from 4.6s to 4.8s with a Gtech. We ran a few sprints this AM. Now I am solidly kicking her a$$ from 0 to 60. From 0 to 100 I watch her fade away.
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