911SC w strange emissions numbers
06-24-2009, 02:25 PM
#1
I haddah Google dat
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911SC w strange emissions numbers
My buddy stopped by yesterday to borrow my LM-1, as his 911SC just failed smog.
I looked at the report, and it showed that he failed the HC section by 7 parts per million at 35mph. The CO number was 0.00, and the NO number was one-third of the allowed max.
I watched the computer while he drove the car, and I noticed at idle it was rich (14.4 afr), but at speed (2K+ rpm), it was way lean (16+ afr). I helped him richen in up to drive it home, but told him to get a can of starting fluid and start looking for vacuum leaks.
What else would cause this? Any thoughts? If it is a vacuum leak, the idle could be set at 1.0 lambda, and the mixture should stay near lambda right?
I looked at the report, and it showed that he failed the HC section by 7 parts per million at 35mph. The CO number was 0.00, and the NO number was one-third of the allowed max.
I watched the computer while he drove the car, and I noticed at idle it was rich (14.4 afr), but at speed (2K+ rpm), it was way lean (16+ afr). I helped him richen in up to drive it home, but told him to get a can of starting fluid and start looking for vacuum leaks.
What else would cause this? Any thoughts? If it is a vacuum leak, the idle could be set at 1.0 lambda, and the mixture should stay near lambda right?
06-24-2009, 06:13 PM
#3
I haddah Google dat
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hmm...ok so let's say that the system fuel pressure is 80psi for example, at idle.
If it's a fuel system problem, what am I looking for? I suspect fuel pressure would drop as load is applied, but by how much?
If it's a fuel system problem, what am I looking for? I suspect fuel pressure would drop as load is applied, but by how much?
06-24-2009, 06:30 PM
#4
Race Car
http://www.pelicanparts.com/911/tech..._Bosch_CIS.htm
Try that link.
IIRC, fuel pressure goes up as the car leans out, and down as it enrichens. CIS is not like your normal FI. There are several steps and you have to have the test guage set up in "series" btween the warm up regulator and the fuel distributor. However, then you have to rearrange the gauges to make other tests. There is a ton of info available on the tests and how to do them. I think some people and the factory would refer to this as a "test plan". it will seem overwhelming when reading the steps, but it is quit easy and straight forward. Follow the plan step-for-step and you will find the problem.
CIS is a foolproof and reliable system. Diagnosis is rather easy and most parts are readily available-some at a cost though. Warm up regulators and fuel pumps, as well as fuel pressure accumalators are usually tops on the list for known failure, but I think your problem may in fact lie in the warm up regulator.
I am totally shooting from the hip and would completely default to your test data for diagnosis.
If you run into problems, a competent shop should be able to make a sound diagnosis in an hour.
Try that link.
IIRC, fuel pressure goes up as the car leans out, and down as it enrichens. CIS is not like your normal FI. There are several steps and you have to have the test guage set up in "series" btween the warm up regulator and the fuel distributor. However, then you have to rearrange the gauges to make other tests. There is a ton of info available on the tests and how to do them. I think some people and the factory would refer to this as a "test plan". it will seem overwhelming when reading the steps, but it is quit easy and straight forward. Follow the plan step-for-step and you will find the problem.
CIS is a foolproof and reliable system. Diagnosis is rather easy and most parts are readily available-some at a cost though. Warm up regulators and fuel pumps, as well as fuel pressure accumalators are usually tops on the list for known failure, but I think your problem may in fact lie in the warm up regulator.
I am totally shooting from the hip and would completely default to your test data for diagnosis.
If you run into problems, a competent shop should be able to make a sound diagnosis in an hour.
06-24-2009, 06:36 PM
#5
Rennlist Member
I can safely say that the factory CIS test procedures are many pages long in the factory manual. What year is the car? I'm assuming this is an '80-83 car???
The basics are; (1) Does the car have the correct cat, (2) is the O2 sensor ('80>) hooked up, (3) what spark plugs are in the engine (Platinums can cause smog-test issues), (4) what is the idle CO% set at and at what idle speed? All four answers are needed before a diagnosis attempt can be made.
I learned in the USN that you should never try to fix equipment before checking if it's plugged in! Basics first!
The basics are; (1) Does the car have the correct cat, (2) is the O2 sensor ('80>) hooked up, (3) what spark plugs are in the engine (Platinums can cause smog-test issues), (4) what is the idle CO% set at and at what idle speed? All four answers are needed before a diagnosis attempt can be made.
I learned in the USN that you should never try to fix equipment before checking if it's plugged in! Basics first!
06-24-2009, 07:39 PM
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06-24-2009, 09:42 PM
#8
I haddah Google dat
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I can safely say that the factory CIS test procedures are many pages long in the factory manual. What year is the car? I'm assuming this is an '80-83 car???
The basics are; (1) Does the car have the correct cat, (2) is the O2 sensor ('80>) hooked up, (3) what spark plugs are in the engine (Platinums can cause smog-test issues), (4) what is the idle CO% set at and at what idle speed? All four answers are needed before a diagnosis attempt can be made.
I learned in the USN that you should never try to fix equipment before checking if it's plugged in! Basics first!
The basics are; (1) Does the car have the correct cat, (2) is the O2 sensor ('80>) hooked up, (3) what spark plugs are in the engine (Platinums can cause smog-test issues), (4) what is the idle CO% set at and at what idle speed? All four answers are needed before a diagnosis attempt can be made.
I learned in the USN that you should never try to fix equipment before checking if it's plugged in! Basics first!
Dr. Zimmermann, what can I say? You are a Porsche community treasure!
CO is the strangest part. The test result says 0.00 ppm, and NO is probably 33% of the max allowable. It is failing the HC at speed, and barely passing HC at idle.
The cat is suspect because there were overheating issues IIRC. Last year I found it was running really really lean, so adjusted to 14.4 AFR, or almost 1 Lambda @900 rpm.
The idle is currently 900-950 rpm, and mixture is 13.7 AFR, which is maybe .9 Lambda or so (due to the lean condition at highway speeds). I suspected a vacuum leak, but you guys have pointed out the complexity of this system.
And yes, I do believe I saw some empty Bosch Platinum boxes lying in the back seat area!!!
I don't have my Bentley 911SC manual with me right now. It's at the work garage, and I need to go out there tonight to get it. IIRC it has a test for system pressure, control pressure w engine off and fuel pump running, and a time test for the fuel accumulator.
I'll come back to this thread if I find out more. Hopefully this may help some poor lost soul in the future....
06-24-2009, 10:25 PM
#9
I haddah Google dat
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http://www.pelicanparts.com/911/tech..._Bosch_CIS.htm
Try that link.
IIRC, fuel pressure goes up as the car leans out, and down as it enrichens. CIS is not like your normal FI. There are several steps and you have to have the test guage set up in "series" btween the warm up regulator and the fuel distributor. However, then you have to rearrange the gauges to make other tests. There is a ton of info available on the tests and how to do them. I think some people and the factory would refer to this as a "test plan". it will seem overwhelming when reading the steps, but it is quit easy and straight forward. Follow the plan step-for-step and you will find the problem.
CIS is a foolproof and reliable system. Diagnosis is rather easy and most parts are readily available-some at a cost though. Warm up regulators and fuel pumps, as well as fuel pressure accumalators are usually tops on the list for known failure, but I think your problem may in fact lie in the warm up regulator.
I am totally shooting from the hip and would completely default to your test data for diagnosis.
If you run into problems, a competent shop should be able to make a sound diagnosis in an hour.
Try that link.
IIRC, fuel pressure goes up as the car leans out, and down as it enrichens. CIS is not like your normal FI. There are several steps and you have to have the test guage set up in "series" btween the warm up regulator and the fuel distributor. However, then you have to rearrange the gauges to make other tests. There is a ton of info available on the tests and how to do them. I think some people and the factory would refer to this as a "test plan". it will seem overwhelming when reading the steps, but it is quit easy and straight forward. Follow the plan step-for-step and you will find the problem.
CIS is a foolproof and reliable system. Diagnosis is rather easy and most parts are readily available-some at a cost though. Warm up regulators and fuel pumps, as well as fuel pressure accumalators are usually tops on the list for known failure, but I think your problem may in fact lie in the warm up regulator.
I am totally shooting from the hip and would completely default to your test data for diagnosis.
If you run into problems, a competent shop should be able to make a sound diagnosis in an hour.
And what about the low CO and NO numbers? If the cat was bad, would these still be low, or can we eliminate the cat as a problem for now? I know, I need to pursue the test plan, but I am thinking this all through right now. Thanks guys!
06-26-2009, 10:20 AM
#10
Race Car
Get rid of the platinum plugs. I have found that the good old Bosch copper plugs are the best in air cooled cars (early 911s had a early version of a Bosch platinum). I suspect someone will contend that NGK and Denso are great plugs and all that, but the 911 works great with the copper Bosch plugs - check your manual for specific Bosch number.
06-26-2009, 10:49 AM
#11
Burning Brakes
I had an 85 ZZZ 911 fail a northern Virginia rolling smog test some years ago. I replaced the cat, 02 sensor, changed the oil, and made sure the car was way warmed up when I arrived at the station. It passed the second time with flying colors, very low numbers.
Just a thought before you start deconstructing the FI.
Just a thought before you start deconstructing the FI.
06-26-2009, 11:16 AM
#12
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Whalebird, awesome post, my friend!
Dr. Zimmermann, what can I say? You are a Porsche community treasure!
CO is the strangest part. The test result says 0.00 ppm, and NO is probably 33% of the max allowable. It is failing the HC at speed, and barely passing HC at idle.
The cat is suspect because there were overheating issues IIRC. Last year I found it was running really really lean, so adjusted to 14.4 AFR, or almost 1 Lambda @900 rpm.
The idle is currently 900-950 rpm, and mixture is 13.7 AFR, which is maybe .9 Lambda or so (due to the lean condition at highway speeds). I suspected a vacuum leak, but you guys have pointed out the complexity of this system.
And yes, I do believe I saw some empty Bosch Platinum boxes lying in the back seat area!!!
I don't have my Bentley 911SC manual with me right now. It's at the work garage, and I need to go out there tonight to get it. IIRC it has a test for system pressure, control pressure w engine off and fuel pump running, and a time test for the fuel accumulator.
I'll come back to this thread if I find out more. Hopefully this may help some poor lost soul in the future....
Dr. Zimmermann, what can I say? You are a Porsche community treasure!
CO is the strangest part. The test result says 0.00 ppm, and NO is probably 33% of the max allowable. It is failing the HC at speed, and barely passing HC at idle.
The cat is suspect because there were overheating issues IIRC. Last year I found it was running really really lean, so adjusted to 14.4 AFR, or almost 1 Lambda @900 rpm.
The idle is currently 900-950 rpm, and mixture is 13.7 AFR, which is maybe .9 Lambda or so (due to the lean condition at highway speeds). I suspected a vacuum leak, but you guys have pointed out the complexity of this system.
And yes, I do believe I saw some empty Bosch Platinum boxes lying in the back seat area!!!
I don't have my Bentley 911SC manual with me right now. It's at the work garage, and I need to go out there tonight to get it. IIRC it has a test for system pressure, control pressure w engine off and fuel pump running, and a time test for the fuel accumulator.
I'll come back to this thread if I find out more. Hopefully this may help some poor lost soul in the future....
I have always preferred to set CO using an exhaust gas analyzer. The SC's CO% must be set pre-cat using the sample nipple on the outboard side of the front part of the cat (outboard at the flange). The spec is 0.6 +/- 0.2% with the O2 sensor plug disconnected.
06-26-2009, 12:30 PM
#13
I haddah Google dat
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Why is the mixture going lean at highway speed? Should I adjust the idle mixture to 1.0 Lambda (14.7 to 1 AFR), tell my buddy to change the spark plugs to WR5DC, install my cat just to be sure? The oil is new, same with filter, cap and rotor.
The car should have passed. It is only the HC number that is high, but the mixture is very lean above 2k rpm.
The car should have passed. It is only the HC number that is high, but the mixture is very lean above 2k rpm.
