Smog Again: NOx
02-12-2005, 08:06 PM
#17
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In 2004 my 84S failed for high NOx.
Replaced noisy air pump...FAIL .
Replaced O2 sensor...FAIL.
Retarded timing to spec...PASS. Dramatically lower readings.
Just tested again last week for 2005...PASSed with really low readings across all categories. I realize that you can not manually adjust your timing, but reinstalling factory chips just may be the answer. Good luck.
Replaced noisy air pump...FAIL .
Replaced O2 sensor...FAIL.
Retarded timing to spec...PASS. Dramatically lower readings.
Just tested again last week for 2005...PASSed with really low readings across all categories. I realize that you can not manually adjust your timing, but reinstalling factory chips just may be the answer. Good luck.
02-12-2005, 08:48 PM
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Originally Posted by WallyP
NOx is produced when combustion chamber temps exceed 2300 deg F. This is the only major factor in NOx production.
There are two strategies to reduce NOx output:
- Reduce combustion chamber temps, normally thru the use of exhaust gas recirculation(EGR), ignition timing, etc.
- Reduce NOx in a three-way cat. The fuel/air ratio must be very near stoichiometric for the cat to function properly, and there must be excess air in the cat - i.e., the air pump must be working in most cases. There are three-way cats that will function (at a less-efficent level) with no air injection.
Since your car doesn't use EGR, the only thing that you can do to reduce combustion chamber temps is to replace the standard chips to bring the ignition timing back to stock.
The only other major factors should be:
- Correct (i.e., three-way) cats installed.
- Air injection to cats working.
- Mixture controlled to stoichiometric.
The hot or cold ratings for spark plugs refer only to the mean temperature of the tip of the plug while operating. There is no effect on the combustion temps, unless the plug gets hot enough to cause preignition, or fouled enough to cause misfiring.
There are two strategies to reduce NOx output:
- Reduce combustion chamber temps, normally thru the use of exhaust gas recirculation(EGR), ignition timing, etc.
- Reduce NOx in a three-way cat. The fuel/air ratio must be very near stoichiometric for the cat to function properly, and there must be excess air in the cat - i.e., the air pump must be working in most cases. There are three-way cats that will function (at a less-efficent level) with no air injection.
Since your car doesn't use EGR, the only thing that you can do to reduce combustion chamber temps is to replace the standard chips to bring the ignition timing back to stock.
The only other major factors should be:
- Correct (i.e., three-way) cats installed.
- Air injection to cats working.
- Mixture controlled to stoichiometric.
The hot or cold ratings for spark plugs refer only to the mean temperature of the tip of the plug while operating. There is no effect on the combustion temps, unless the plug gets hot enough to cause preignition, or fouled enough to cause misfiring.
Originally Posted by Lorenfb
"Since your car doesn't use EGR, the only thing that you can do to reduce combustion chamber temps is to replace the standard chips to bring the ignition timing back to stock." - WallyP -
This is probably the biggest factor in reducing the NOx on an engine where all
other elements are O.K.:
1. a good CAT
2. proper fuel pressure
3. a good MAF sensor (fairly problematic)
4. a good O2 sensor
5. a good LH control unit (properly affected by O2 & MAF sensor)
6. good LH & EZK system grounds & powers
7. proper engine temp, e.g. correct thermostat, efficient radiator
Remember: Most performance chips just basically advance the timing to achieve
a "feel" of more HP, i.e. generally little to no torque increases occur on 928s
as the EZK with knock sensors maxs the ignition maps.
Bottomline: Performance chips overall
Benefits - ??????????????
Costs - MANY
This is probably the biggest factor in reducing the NOx on an engine where all
other elements are O.K.:
1. a good CAT
2. proper fuel pressure
3. a good MAF sensor (fairly problematic)
4. a good O2 sensor
5. a good LH control unit (properly affected by O2 & MAF sensor)
6. good LH & EZK system grounds & powers
7. proper engine temp, e.g. correct thermostat, efficient radiator
Remember: Most performance chips just basically advance the timing to achieve
a "feel" of more HP, i.e. generally little to no torque increases occur on 928s
as the EZK with knock sensors maxs the ignition maps.
Bottomline: Performance chips overall
Benefits - ??????????????
Costs - MANY
New O2 sensor
Installed stock S4 chips
Tested all grounds
Fuel pressure set to 48 PSI with vacuum off, 55 PSI with fuel relay jumpered
Verified air pump delivery
My readings came much closer to passing (attached). When I bumped the fuel pressure up to 55 PSI with vacuum line of, I almost pass. I'm thinking either a vacuum leak, fuel injector, or bad MAF, and not ruling out a bad LH. The car is running lean under all conditions, AFR = 15.1:1, unless I crank the fuel pressure above 56 PSI with vacuum line off. I also have a slight miss at normal FP, Hmmmmmmmm. More work to do. A lean condition is present.
02-12-2005, 09:05 PM
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Originally Posted by pappy92651
Working back through the suggestions I have so far covered the following:
New O2 sensor
Installed stock S4 chips
Tested all grounds
Fuel pressure set to 48 PSI with vacuum off, 55 PSI with fuel relay jumpered
Verified air pump delivery
New O2 sensor
Installed stock S4 chips
Tested all grounds
Fuel pressure set to 48 PSI with vacuum off, 55 PSI with fuel relay jumpered
Verified air pump delivery
I'm thinking either a vacuum leak, fuel injector, or bad MAF, and not ruling out a bad LH. The car is running lean under all conditions, AFR = 15.1:1, unless I crank the fuel pressure above 56 PSI with vacuum line off. I also have a slight miss at normal FP, Hmmmmmmmm. More work to do. A lean condition is present.
Grounds. Each side of the LH harness is grounded on the rear-top of the block. One side behind the throttle cable pulley and one under the regulator. Long shot. But, I did once find a 928 with one of those grounds loose.
Might not hurt to make sure that the new O2 sensor is well-plugged-in at the fuse panel.
02-12-2005, 09:14 PM
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Originally Posted by worf928
Hmmm... MAS is the only other component. However, it would be very unusual for a failing MAS to result in a lean condition. (AFAIK they read more air as they fail with the result that the LH pumps in more fuel, not less.)
Lean. And a miss. I'll place my bet on one or more of the 2-pole injector harness connectors. Since you replaced the injectors (with new I assume) in 2002 then normal-type wear and tear shouldn't result in injectors that are so clogged as to cause a lean condition. (Unless you almost always drive the car for less than ~30 minutes at a time.) I'd check each connector for a good, positive connection. Check the connector boot insulation. Perhaps disconnect each and examine for oxidation/corrosion, splaying of the female connector, or anything else that might gook-up the electrical connection.
Grounds. Each side of the LH harness is grounded on the rear-top of the block. One side behind the throttle cable pulley and one under the regulator. Long shot. But, I did once find a 928 with one of those grounds loose.
Might not hurt to make sure that the new O2 sensor is well-plugged-in at the fuse panel.
Lean. And a miss. I'll place my bet on one or more of the 2-pole injector harness connectors. Since you replaced the injectors (with new I assume) in 2002 then normal-type wear and tear shouldn't result in injectors that are so clogged as to cause a lean condition. (Unless you almost always drive the car for less than ~30 minutes at a time.) I'd check each connector for a good, positive connection. Check the connector boot insulation. Perhaps disconnect each and examine for oxidation/corrosion, splaying of the female connector, or anything else that might gook-up the electrical connection.
Grounds. Each side of the LH harness is grounded on the rear-top of the block. One side behind the throttle cable pulley and one under the regulator. Long shot. But, I did once find a 928 with one of those grounds loose.
Might not hurt to make sure that the new O2 sensor is well-plugged-in at the fuse panel.
I also forgot to mention. The car pings like mad at WOT with stock FP. I installed new fuel filters and new fuel pumps (they are running and pressure looks good on the dyno). I think the problem is under the hood but need to keep eliminating possibilities on the check list.
02-12-2005, 09:41 PM
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Originally Posted by pappy92651
The car pings like mad at WOT with stock FP.
I have had the same problem with my (ummm... CarChick's) GTS. Getting the in-tank pump working helped a little. Getting the injectors clean and balanced helped quite a bit. However, I still get a little pinging at WOT. But, the GTS scored triple-zero on a static (idle) emissions test.
In the case of CarChick's GTS the 10.4 motor is going to be very sensitive to octane and any build-up of crud in the combustion chambers. I'm about to start investigating procedures for a 'top-end cleaning.' The 'vette folks use a GM product that is fed directly in to the throttle body (so as not to foul the MAS) while the car is idling following by an overnight resting period.
The GTs like to run very rich at WOT. I've had the intakes off of both and there's a TON of buildup. If yours has a ton of build-up then the effective compression ratio could be higher and thus lead to pre-detonation.
BUT, since your A/F ratio is lean on a part-throttle rolling emissions test, then the finger's gotta be pointed back to too little fuel or too much air. I suspect that if you fix the emissions your WOT pining will also be fixed. After the harness connections your right to look for vacuum leaks. But, wouldn't you think a vacuum leak would lead to a too-high idle? What's your idle rpm?
02-12-2005, 10:17 PM
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Originally Posted by worf928
Well, that just ain't right. Was that with the chips? Or without? I know that on my '89GT when the cams were set at +3 the result was a 'knock-sensor' curve on the dyno chart. But, with freshly cleaned injectors I got no audible pinging noise.
I have had the same problem with my (ummm... CarChick's) GTS. Getting the in-tank pump working helped a little. Getting the injectors clean and balanced helped quite a bit. However, I still get a little pinging at WOT. But, the GTS scored triple-zero on a static (idle) emissions test.
In the case of CarChick's GTS the 10.4 motor is going to be very sensitive to octane and any build-up of crud in the combustion chambers. I'm about to start investigating procedures for a 'top-end cleaning.' The 'vette folks use a GM product that is fed directly in to the throttle body (so as not to foul the MAS) while the car is idling following by an overnight resting period.
The GTs like to run very rich at WOT. I've had the intakes off of both and there's a TON of buildup. If yours has a ton of build-up then the effective compression ratio could be higher and thus lead to pre-detonation.
BUT, since your A/F ratio is lean on a part-throttle rolling emissions test, then the finger's gotta be pointed back to too little fuel or too much air. I suspect that if you fix the emissions your WOT pining will also be fixed. After the harness connections your right to look for vacuum leaks. But, wouldn't you think a vacuum leak would lead to a too-high idle? What's your idle rpm?
I have had the same problem with my (ummm... CarChick's) GTS. Getting the in-tank pump working helped a little. Getting the injectors clean and balanced helped quite a bit. However, I still get a little pinging at WOT. But, the GTS scored triple-zero on a static (idle) emissions test.
In the case of CarChick's GTS the 10.4 motor is going to be very sensitive to octane and any build-up of crud in the combustion chambers. I'm about to start investigating procedures for a 'top-end cleaning.' The 'vette folks use a GM product that is fed directly in to the throttle body (so as not to foul the MAS) while the car is idling following by an overnight resting period.
The GTs like to run very rich at WOT. I've had the intakes off of both and there's a TON of buildup. If yours has a ton of build-up then the effective compression ratio could be higher and thus lead to pre-detonation.
BUT, since your A/F ratio is lean on a part-throttle rolling emissions test, then the finger's gotta be pointed back to too little fuel or too much air. I suspect that if you fix the emissions your WOT pining will also be fixed. After the harness connections your right to look for vacuum leaks. But, wouldn't you think a vacuum leak would lead to a too-high idle? What's your idle rpm?
Results are with stock S4 chips. Hmmmm, try stock GT chips (since I have GT cams)?
My idle wanders from 600 to 800 RPM. It did this before when I had bad vacuum lines.
GTs do like to run rich at WOT (especially with stock chips, I have a set). The high RPM pull with mods is incredible. The stock chips do not offer any low end torque though, all 4500 RPM plus. Time to generate my own fuel / timing maps.
I agree with your statement about too little fuel or too much air. I will dig deeper on Monday. It's BEER:30 and time to burn some red meat. I will let you know what I find next week (or sooner if I have a brilliant moment).
02-12-2005, 10:24 PM
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Originally Posted by pappy92651
My idle wanders from 600 to 800 RPM.
Have you had the intake off in the past?
... time to burn some red meat.
Good luck.
02-12-2005, 11:44 PM
#25
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Steve
I just checked my smog test sheet (08-2004), it doesn't have a NO section at all. The prinout is slightly different too. Both our zipcodes are considered "enhanced" smog check zones http://www.smogcheck.ca.gov/ftp/pdfd...p-Dec_2003.pdf
I wonder if the regulations for the current year are harder than before?
I just checked my smog test sheet (08-2004), it doesn't have a NO section at all. The prinout is slightly different too. Both our zipcodes are considered "enhanced" smog check zones http://www.smogcheck.ca.gov/ftp/pdfd...p-Dec_2003.pdf
I wonder if the regulations for the current year are harder than before?
02-13-2005, 12:30 AM
#26
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.
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.
02-13-2005, 12:56 AM
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Originally Posted by Lorenfb
An intake leak would have to be fairly large, e.g. bypassing the MAF sensor.
02-13-2005, 04:10 AM
#28
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PerryS4, his car has not failed badly enough to be classified as a 'Gross Polluter". If it had it would be CLEARLY spelled out on the VIR. You can test & fail as often as you like, they'll keep taking your money... 
It is much more efficient to do repairs and have a gas analyzer available to check your progress, but since we all don't have a spare $50K lying around... I know this sucks, but sometimes it just makes more sense to have the smog tech do the repairs. In cases like this it can be much less costly & time consuming. I know, I used to be a smog tech 
.
It is much more efficient to do repairs and have a gas analyzer available to check your progress, but since we all don't have a spare $50K lying around... I know this sucks, but sometimes it just makes more sense to have the smog tech do the repairs. In cases like this it can be much less costly & time consuming. I know, I used to be a smog tech .
02-13-2005, 02:23 PM
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Originally Posted by perrys4
How are you testing and failing without being marked as a gross polluter? Dont you only get a couple tries?
The Smog Check program has identified Gross Polluter (GP) vehicles as a significant source of smog emissions. Gross Polluter vehicles are chosen through these strategies:
Vehicles tested at licensed stations which exceed at least one of the gross polluter standards (twice the maximum emission limits)
Vehicles selected from the High Emitter Profile (HEP) database which have a high probability of failing the Smog Check inspection.
Once a vehicle is classified as a Gross Polutter it has to initially be tested at a "Test-Only" inspection station. If the vehicle fails this inspection it must undergo repairs and return to a Test-only, Referee or CAP (Consumer Assistance Repair) station for certification.
Vehicles, which are not classified, as gross polluters, do not have to seek a Test-Only inspection and can visit any local smog station. Once again, your DMV documents will state which type of test your vehicle requires.
As a result I can fail testing until I pass or meet the maximum repair cost required by the state of CA.
02-13-2005, 02:33 PM
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Originally Posted by IcemanG17
Steve
I just checked my smog test sheet (08-2004), it doesn't have a NO section at all. The prinout is slightly different too. Both our zipcodes are considered "enhanced" smog check zones http://www.smogcheck.ca.gov/ftp/pdfd...p-Dec_2003.pdf
I wonder if the regulations for the current year are harder than before?
I just checked my smog test sheet (08-2004), it doesn't have a NO section at all. The prinout is slightly different too. Both our zipcodes are considered "enhanced" smog check zones http://www.smogcheck.ca.gov/ftp/pdfd...p-Dec_2003.pdf
I wonder if the regulations for the current year are harder than before?
I don't think they have changed much for my car (attached). I am simply failing a test that I used to pass.