My ZR-1 failed smog
12-28-2010, 08:25 PM
#1
Instructor
Thread Starter
My ZR-1 failed smog
Haven't been on here in a long time, so I don't know if some one else has had this problem also. Here's the story. My '91 w/about 41K on it failed CA smog because the NOX was too high. The tech suggested catalitic converter, but when I told him I thought I had a bad injector, he said that could be the problem. With the power key on, it feels like a bad plug, but without it, it runs fine, so a bad plug didn't seem like the problem, but I changed them anyway, but no difference. The old ones all looked great.
A friend has the magic box, so we checked it. No codes in the car, but it indicated that the right side was being leaned out by the computer because it was detecting a rich mixture. The O2 sensors indicated that they were working. We concluded that I might have a leaking injector. I did a fuel pressure test. 50 psi with the pump running and then down to 48 psi, which it will hold for a while but down to about 43 psi after 5 min. (Specs call for 48-55 psi) Then I pulled the plenum and checked the resistance on the injectors. All read 14 ohms except #7 which read 13 on the primary and 11 on the secondary. I plan to replace both, but this is not the side that was running lean.
So, any ideas? Did these injectors cause it to fail with the high NOX? Is there something else I should look at since I have it apart?
Thanks for any help
Ken
A friend has the magic box, so we checked it. No codes in the car, but it indicated that the right side was being leaned out by the computer because it was detecting a rich mixture. The O2 sensors indicated that they were working. We concluded that I might have a leaking injector. I did a fuel pressure test. 50 psi with the pump running and then down to 48 psi, which it will hold for a while but down to about 43 psi after 5 min. (Specs call for 48-55 psi) Then I pulled the plenum and checked the resistance on the injectors. All read 14 ohms except #7 which read 13 on the primary and 11 on the secondary. I plan to replace both, but this is not the side that was running lean.
So, any ideas? Did these injectors cause it to fail with the high NOX? Is there something else I should look at since I have it apart?
Thanks for any help
Ken
12-28-2010, 09:37 PM
#2
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St. Jude Donor '05
If you got one or two failing might as well replace the bunch.
Cats could be suspect also but start with injectors then try and do a pretest to see if you would make it through again.
Are you doing the smog test with the power key off? Thats the way to go.
Cats could be suspect also but start with injectors then try and do a pretest to see if you would make it through again.
Are you doing the smog test with the power key off? Thats the way to go.
12-29-2010, 12:05 AM
#5
Here's a post I made three years ago when somebody else failed NOx:
A leaking injector on one cylinder could cause the other three on that bank to go lean which could result in high NOx emissions. Do you have an aftermarket chip installed?
High NOx is caused by excessively high combustion chamber temps which can be caused by lean mixtures, too much ignition timing, and high coolant temperatures.
I see two things in your list above that may cause high NOx. The aftermarket chip may be giving you too much ignition timing. Do you still have the stock chip to put back in? The "alky" may be giving you mixtures too lean. Alcohol can reduce HC and CO emissions with the lean mixture it creates...you don't seem to have a problem with HC or CO, but may inadvertently be causing your high NOx problem. You also want to make sure your AIR pump isn't running all the time since the O2 in the fresh air stream will bond with the CO to give CO2 and prevent the nitrogen/oxygen bond from being broken to give its' oxygen to CO leaving the desired N2 and CO2.
If your coolant temp is high due to high ambient temps or a marginal cooling system, combustion chamber temps will increase and cause high NOx levels. Anything you can do to decrease coolant temps during the test will reduce NOx but make sure you don't get the temps too low in order to stay in closed loop. The test they do really isn't representative of the real world since the car is stationary and air isn't flowing around/under the car to provide the proper cooling. They may have a fan set up, but it isn't blowing at 40-50 MPH and certainly doesn't have the flow in CFM. If you can rig a manual switch for the cooling fans to keep temps under 200*F, that would help simulate real world driving and keep coolant/combustion temps down. Are they running it on a dyno to do a "cruise" test? If so, what speed and what gear are they using?
High static compression due to deposits on the piston may also cause high combustion chamber temps. There are products on the market that will reduce the amount of deposits. Cam timing can be altered to reduce dynamic compression giving the same result as lowering static compression, but that's getting pretty radical as a solution. If the timing isn't correct to begin with, then that's another story, but if your HC and CO readings are good, then it's likely your cam timing is too. With your engine running great to 7200 RPM, the cam timing has to be real close. I don't see changing cam timing a few degrees making a significant impact on NOx. The other stuff is easier/cheaper, go for the low hanging fruit.
Here are a few sites to get you going on the causes/interactions with the 5 different exhaust gases from an engine:
http://www.offyparts.com/Smog_Failure.html
http://www.asashop.org/autoinc/oct2004/techtips.htm
http://www.autoshop101.com/forms/h56.pdf
The last one is probably the best even though it's from Toyota. Happy reading and good luck.
I see two things in your list above that may cause high NOx. The aftermarket chip may be giving you too much ignition timing. Do you still have the stock chip to put back in? The "alky" may be giving you mixtures too lean. Alcohol can reduce HC and CO emissions with the lean mixture it creates...you don't seem to have a problem with HC or CO, but may inadvertently be causing your high NOx problem. You also want to make sure your AIR pump isn't running all the time since the O2 in the fresh air stream will bond with the CO to give CO2 and prevent the nitrogen/oxygen bond from being broken to give its' oxygen to CO leaving the desired N2 and CO2.
If your coolant temp is high due to high ambient temps or a marginal cooling system, combustion chamber temps will increase and cause high NOx levels. Anything you can do to decrease coolant temps during the test will reduce NOx but make sure you don't get the temps too low in order to stay in closed loop. The test they do really isn't representative of the real world since the car is stationary and air isn't flowing around/under the car to provide the proper cooling. They may have a fan set up, but it isn't blowing at 40-50 MPH and certainly doesn't have the flow in CFM. If you can rig a manual switch for the cooling fans to keep temps under 200*F, that would help simulate real world driving and keep coolant/combustion temps down. Are they running it on a dyno to do a "cruise" test? If so, what speed and what gear are they using?
High static compression due to deposits on the piston may also cause high combustion chamber temps. There are products on the market that will reduce the amount of deposits. Cam timing can be altered to reduce dynamic compression giving the same result as lowering static compression, but that's getting pretty radical as a solution. If the timing isn't correct to begin with, then that's another story, but if your HC and CO readings are good, then it's likely your cam timing is too. With your engine running great to 7200 RPM, the cam timing has to be real close. I don't see changing cam timing a few degrees making a significant impact on NOx. The other stuff is easier/cheaper, go for the low hanging fruit.
Here are a few sites to get you going on the causes/interactions with the 5 different exhaust gases from an engine:
http://www.offyparts.com/Smog_Failure.html
http://www.asashop.org/autoinc/oct2004/techtips.htm
http://www.autoshop101.com/forms/h56.pdf
The last one is probably the best even though it's from Toyota. Happy reading and good luck.
12-29-2010, 12:30 AM
#6
Instructor
Thread Starter
BennieC, I'm in Vacaville. Got it apart waiting for the new injectors, but I might take you up on that if it doesn't work.
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
12-29-2010, 11:12 AM
#8
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BennieC, I'm in Vacaville. Got it apart waiting for the new injectors, but I might take you up on that if it doesn't work.
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
I put RC engineering injectors in mine several years ago.
Good luck
ßill
12-29-2010, 01:30 PM
#9
BennieC, I'm in Vacaville. Got it apart waiting for the new injectors, but I might take you up on that if it doesn't work.
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
It does have a chip, but I don't know what it is as it was put in by the PO who bought the car new. However, it passed last time with the chip in it, so I don't think that is the problem.
I did check for leaking injectors per the manual (lift up the assembly and turn the power on) and the weak injector did leak for a few seconds, but all the rest look OK.
Where is the best place to get the injectors? Chevy has the secondary ones, but not the primary. Corvette Central has them as well as White Racing in FL. NAPA can get them also. I just don't know who is selling quality stuff.
Ken
Jon at FIC injectors is great to deal with and you can read about the many happy customers in the thread above as well as see videos he included.
After market chips increase ignition advance in the lower RPMs at part throttle which greatly improves throttle response in an area most used...unfortunately, it increases NOx emissions since combustion chamber temps also increase. If the new injectors don't help you pass the new emission standards in CA, try getting a stock chip to swap out when it comes around to test time. Good luck!
12-29-2010, 01:57 PM
#10
Instructor
Thread Starter
After checking around, all the aftermarket places want $90-$100 for the primaries and $70-$80 for the secondary injectors. I wanted to find ones not made in China. The guy at White Racing knew more than the others and said all are made by just a couple companies, mostly Bosch and Rochester. Also, and I guess most of you guys already know this, the originals were not designed for todays gasoline and foul quite often. Since I had ordered a new secondary from Chevy ($108 my cost) I just wanted to order one primary. However, if you order all 16 from White Racing they discount them to $850 for the whole set. (instead of about $1400) Since it would be costing me almost $200 for the two, and since I have it apart, I went for the whole package. Should be here Monday, (because of New Years) so I'll go from there. I'll let you know how it goes.
Ken
Ken
12-29-2010, 03:20 PM
#11
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St. Jude Donor '10
After market chips increase ignition advance in the lower RPMs at part throttle which greatly improves throttle response in an area most used...unfortunately, it increases NOx emissions since combustion chamber temps also increase. If the new injectors don't help you pass the new emission standards in CA, try getting a stock chip to swap out when it comes around to test time. Good luck!
12-30-2010, 12:56 AM
#12
Racer
Agree with Z51JEFF, if you bought MULTEC, you bought more problems.
I replaced the injectors (Multec look alike disc types from FIC) replaced the plugs (NGK Iridium) and loaded the stock GM PROM in July of this year. I just got my car this year and have a 1 year emmissions grace period - thought I wouldtry it while I still had time to fix any problems. Made it through with flying clours - my readings were as follows:
Driving Test:
Hydrocarbon ppm - 7.0 (88 allowed)
Carbon Monoxide % - .02 (.66 allowed)
NOx ppm - 5.00 (979 alowed)
Idle:
Hydrocarbon ppm - 8 (75 allowed)
Carbon Monoxide % - 0 (.42 allowed)
Well tuned - these cars can actually run pretty clean.
PS - my car has 40K miles on it.
Good luck.
I replaced the injectors (Multec look alike disc types from FIC) replaced the plugs (NGK Iridium) and loaded the stock GM PROM in July of this year. I just got my car this year and have a 1 year emmissions grace period - thought I wouldtry it while I still had time to fix any problems. Made it through with flying clours - my readings were as follows:
Driving Test:
Hydrocarbon ppm - 7.0 (88 allowed)
Carbon Monoxide % - .02 (.66 allowed)
NOx ppm - 5.00 (979 alowed)
Idle:
Hydrocarbon ppm - 8 (75 allowed)
Carbon Monoxide % - 0 (.42 allowed)
Well tuned - these cars can actually run pretty clean.
PS - my car has 40K miles on it.
Good luck.
12-30-2010, 10:40 AM
#13
Instructor
Thread Starter
The ones I ordered are Gp-Sorensen. The Accels are quite a bit cheaper. These are stainless. White Racing is dedicated to the ZR-1 and this is what they recommended. Here's their home page. http://www.whiteracingproducts.com/i...ain_page=index
Ken
Ken
01-11-2011, 03:13 PM
#14
Instructor
Thread Starter
Finally got it all back together, had to order the plenum gasket also. Took it to get smogged yesterday, and it passed with flying colors even with the chip in it, so I'm good for 2 more years! A lot more power. All the old injectors measured 14ohms, spec calls for 16. All the new ones measured 16 ohms, so I'm glad I decided to change them all as it looks like the others were weak.
thanks for the help
Ken
thanks for the help
Ken
