Emissions Question - NO is High
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
Hello Everyone...I've got a 77 Custom 100 with the 351M motor (It's either a 77 0r 78 motor, it has been replaced). Carb is a stock 2 barrel, Motorcraft 2500 I believe. During my recent smog check here in California, I passed on all regards with the exception of NO. Now the HC was on the high end, but passing, and the O2 was very low, as well as the CO, but the NO was over.
What are some possible causes for this? What can I do with this?
Any and help appreciated. I can provide more info if needed.
Thanks in advance
Dave Price
What are some possible causes for this? What can I do with this?
Any and help appreciated. I can provide more info if needed.
Thanks in advance
Dave Price
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
Emissions Question - NO is High
What were all the test numbers, measured and limit, at both idle and 2500 rpm?
High NOx is caused by excessively lean fuel mixture. The most common cause of overlean mixture is a vacuum leak.
If the EGR system isn't working properly, or if the EGR passages are plugged with carbon deposits restricting the flow, that could cause an overlean mixture and high NOx.
A combination of high NOx and high HC indicates lean misfiring.
High NOx is caused by excessively lean fuel mixture. The most common cause of overlean mixture is a vacuum leak.
If the EGR system isn't working properly, or if the EGR passages are plugged with carbon deposits restricting the flow, that could cause an overlean mixture and high NOx.
A combination of high NOx and high HC indicates lean misfiring.
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
I'll get all the details posted out tonight when I get home....I suspected a vacuum leak, or misrouted vacuum lines, but I'm having a heck of a time finding a good readable diagram.
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
Test Results as follows:
tEST 1 : 15MPH ,
CO2-14.1% ,
02-0.4% ,
HC-155 (MAX 199),
CO-0.76 (MAX 1.62) ,
NO-2386 (MAX 1520)
TEST 2 : 25MPH ,
CO2-14.6% ,
O2-0.2% ,
HC-118 (MAX 165) ,
CO-0.38 (MAX 1.42) ,
NO-1870 (MAX 1380)
Any and all suggestions welcome....
tEST 1 : 15MPH ,
CO2-14.1% ,
02-0.4% ,
HC-155 (MAX 199),
CO-0.76 (MAX 1.62) ,
NO-2386 (MAX 1520)
TEST 2 : 25MPH ,
CO2-14.6% ,
O2-0.2% ,
HC-118 (MAX 165) ,
CO-0.38 (MAX 1.42) ,
NO-1870 (MAX 1380)
Any and all suggestions welcome....
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
Emissions Question - NO is High
Like bubbaf250 said, first thing to do is check the EGR and make sure it's working correctly. EGR is designed specifically to reduce NOx emissions by lowering the combustion chamber temp. Second thing to do is check for vacuum leaks which may be causing misfires.
Make sure you check your spark plugs, air filter and change your oil before you get it retested. Also make sure you get it warmed up good before you test it.
If you still can't pass you may be looking at a new distributor and/or new cats.
Make sure you check your spark plugs, air filter and change your oil before you get it retested. Also make sure you get it warmed up good before you test it.
If you still can't pass you may be looking at a new distributor and/or new cats.
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
Well, when I get back from Chicago Friday night I'll get to work on that. I've got a new distributor already (that's a funny story in its self) and I was probably looking to change the cats anyway. Everything else was done prior to my test. Although, what is the correct timing on that year and motor? The label on the valve cover says 16BTDC, which is a far cry from everything else I've seen. Any ideas? Could that be a contributing factor?
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
Emissions Question - NO is High
Dave,
Yes, the ignition advance could be a contributing factor in the emissions test results. Too much timing advance can aggravate NOx formation by increasing the combustion pressure and temperature.
I'm not familiar with the ASM test protocol used in CA, and I'm concerned that you don't have a lot of room in the CO level for enriching the fuel mixture.
I think you have two things to check/try: timing and EGR.
Change the ignition static timing to about 10BTC or less. Check this URL for some truck M-block ignition timing specs:
http://home.earthlink.net/~bubbaf250/perf/perf10.html
I think you really should check the EGR, particularly the spacer under the carb and the EGR valve.
When you take off the spacer, make sure the hole going down into the exhaust crossover is clear, and make sure the passages in the spacer are clear. Also, make sure the EGR valve vacuum switching signal is functioning properly and that the valve is opening.
Yes, the ignition advance could be a contributing factor in the emissions test results. Too much timing advance can aggravate NOx formation by increasing the combustion pressure and temperature.
I'm not familiar with the ASM test protocol used in CA, and I'm concerned that you don't have a lot of room in the CO level for enriching the fuel mixture.
I think you have two things to check/try: timing and EGR.
Change the ignition static timing to about 10BTC or less. Check this URL for some truck M-block ignition timing specs:
http://home.earthlink.net/~bubbaf250/perf/perf10.html
I think you really should check the EGR, particularly the spacer under the carb and the EGR valve.
When you take off the spacer, make sure the hole going down into the exhaust crossover is clear, and make sure the passages in the spacer are clear. Also, make sure the EGR valve vacuum switching signal is functioning properly and that the valve is opening.
Trending Topics
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
I will plan on basically doing a tuneup, but also pulling the carb...I may have a lead on aquiring a brand new carb for nothing, can't beat that price.
I'll check out the EGR system as well, everything you say makes alot of sense.
It's the timing that has me baffled.....I can set it to 10 and the truck will run better, no pinging and such, but it would fail the test, because the sticker says 16. I just find it hard to believe that it is supposed to be set there, especially when it sounds as if it is going to shake apart when you hit the gas.
Such is life in California I suppose...
I'll check out the EGR system as well, everything you say makes alot of sense.
It's the timing that has me baffled.....I can set it to 10 and the truck will run better, no pinging and such, but it would fail the test, because the sticker says 16. I just find it hard to believe that it is supposed to be set there, especially when it sounds as if it is going to shake apart when you hit the gas.
Such is life in California I suppose...
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
Thread Starter
|
New User
Joined: Jun 2003
Posts: 19
Likes: 0
Emissions Question - NO is High
So I have pulled the carb and cleaned it, found it wasn't torqued down much at all (small vacuum leak), installed new gaskets and made sure the carb was tightened down right, pulled and cleaned the EGR ports and spacer, replaced all the vacuum lines (except one which caused another problem, but thats another thread), changed the spark plugs and wires, distributor cap and rotor, reset the timing to 8 BDTC, in accordance with the "new" valve covers I picked up, replaced the air filter and breather elements, de-gunked the engine and changed the oil and filter, and changed out my thermostat a few times.
I am hoping to get the emmissions test done this Friday afternoon. Based on what I did above, what are the opinions on if I am going to manage to pass or not?
Should I attempt to richen up the mixture at all to try and lower the NO?
I am hoping to get the emmissions test done this Friday afternoon. Based on what I did above, what are the opinions on if I am going to manage to pass or not?
Should I attempt to richen up the mixture at all to try and lower the NO?
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Emissions Question - NO is High
Congratulations! You not only passed the test but your truck will run a lot better now. Sometimes dark clouds have a silver lining...
p.s. -that is just one of the reasons for inspections...
p.s. -that is just one of the reasons for inspections...