1980 - 911 SC - Hard start with a warm engine
05-15-2010, 09:58 PM
#16
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No gas needed for the cold start, you can see I have my foot on the brake. (The Brake lights are on). The RPM's stay high for about 5 min after a cold start then they drop to just under 1k. During the warm start I only added some gas on the third try. I know you talked about a base CO before, but I'm not familiar with the term. What is a base CO?
05-15-2010, 10:52 PM
#17
Team Owner
Well if you didn't give it gas cold then all is good there .. i don't get the initial surge in mine so i was mistaken.
Base CO is a measurement of the Carbon Monoxide coming out of the tail pipe. You put a device there that can measure it ( LM1) , you measure it at idle with the car fully warmed up . It is then adjusted by adjusting the mixture. Sometimes this is all it takes. I borrowed an LM1 from a fellow lister. The Bentley Manual will tell you what it shoudl be , you have an SC so I can look that up for you if you would like.
This can be converted to a AFM ( air fuel mixture ) with a table as the AFM is usually what the meter puts out. You can even output it to an excel file and make a graph. If your car is O2 sensor equiped you have to diable it so it does not try and compensate ( after all thet is the O2 sensors Job. )
The issue I think is fairly minor as you are having no backfiring at all . Too bad you didn't live closer as i have bags of CIS parts and access to an LM1 .
Base CO is a measurement of the Carbon Monoxide coming out of the tail pipe. You put a device there that can measure it ( LM1) , you measure it at idle with the car fully warmed up . It is then adjusted by adjusting the mixture. Sometimes this is all it takes. I borrowed an LM1 from a fellow lister. The Bentley Manual will tell you what it shoudl be , you have an SC so I can look that up for you if you would like.
This can be converted to a AFM ( air fuel mixture ) with a table as the AFM is usually what the meter puts out. You can even output it to an excel file and make a graph. If your car is O2 sensor equiped you have to diable it so it does not try and compensate ( after all thet is the O2 sensors Job. )
The issue I think is fairly minor as you are having no backfiring at all . Too bad you didn't live closer as i have bags of CIS parts and access to an LM1 .
05-16-2010, 01:45 AM
#18
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It looks like the car is way lean when warm starting. It could be any number of things, and as noted, the warm up regulator is definitely suspect but it could be vacuum leak, bad mixture, clogged fuel filter, air meter out of adjustment, or others. You or someone needs to go through the diagnostic steps systematically.
05-16-2010, 10:17 AM
#19
Team Owner
Here i the outpot of the LM2 for my SC so oyu can get an isea of what I am talking about .. You can see it is VERY steady and even after bliping the throtle it comes back to baseline very quickly. Yours might be somewhat different as you have an 80 . But it gives you an idea.
Use the following table
http://www.perfectpower.com/technical_info/afr.asp
so can see my 13.5 AFR converts to about 2.7% CO and my car starts and runs perfectly under all conditions. This is why you check this first before swapping in parts as you could be chasing your tail.
You don't list your location so it is impossible to find out if there are any listers close to you that could help.
Failing all else at least you know what base CO means now and how you can use it to determine next steps.
Troy and I differ on opinions here but that is okay . Hard starting does not NECESARILY mean it is lean , it just means the AFR is not optimal for starting. When running lean often you get backfires through the intake as there is not enough octane in the mixture and it predetinates causing the backfire which you don't seam to have. Also rich engines tend to hunt as yours is doing. But regardless of this I think we both agree your Air fuel ratio or Air fuel mixture as it is sometimes called is just not at optimal in warm conditions for a good start.
Use the following table
http://www.perfectpower.com/technical_info/afr.asp
so can see my 13.5 AFR converts to about 2.7% CO and my car starts and runs perfectly under all conditions. This is why you check this first before swapping in parts as you could be chasing your tail.
You don't list your location so it is impossible to find out if there are any listers close to you that could help.
Failing all else at least you know what base CO means now and how you can use it to determine next steps.
Troy and I differ on opinions here but that is okay . Hard starting does not NECESARILY mean it is lean , it just means the AFR is not optimal for starting. When running lean often you get backfires through the intake as there is not enough octane in the mixture and it predetinates causing the backfire which you don't seam to have. Also rich engines tend to hunt as yours is doing. But regardless of this I think we both agree your Air fuel ratio or Air fuel mixture as it is sometimes called is just not at optimal in warm conditions for a good start.
Last edited by theiceman; 01-09-2013 at 10:13 AM.
05-17-2010, 07:12 PM
#20
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"When running lean often you get backfires through the intake as there is not enough octane in the mixture and it predetinates causing the backfire which you don't seam to have."
Lean mixtures burn slower. They can burn slow enough that when the intake valve opens, the exhaust gases are still burning and they ignite the mixture in the intake manifold which causes the back fire. Predetonation will cause knocking and can be caused by a lean mixture running the engine hotter but this is typically at load and higher engine speeds.
http://www.jcwhitney.com/fuel-inject.../p2008126.jcwx
here is the cheap pressure tester you need. Mine was made in China which I did not know because someone on the BMW forum told me theirs was made in Brazil. Mine seems to work fine which is surprising for a Chinese product. I also recommend you buy a Bentley manual for your car.
http://www.google.com/products/catal...CAcQ8wIwADgA#p
You definitely need to check your fuel mixture. The mixture could be overly rich and run better than fine when it is cold. When the car warms up it will not start or hunt then when the O2 sensor system turns on it will lean out the rich mixture and run great again. You can disconnect your 02 sensor when the car is warm and see if it runs poorly. You can also try and adjust your mixture by alternate methods until you find a AFR or CO meter. The 2nd best way to set it is to measure the duty cycle for the frequency valve if you have a dwell meter. The other option is to adjust the mixture till you get a reduction is rpm when you apply a light pressure to both top and bottom of the lever for the air flow meter plate.
I bought a used LM-1 on ebay for $200 but you cannot use it if you have a catalytic converter unless you switch it with the stock 02 sensor. I installed a second bung in my test pipe. The 80-83 cars are set to run a 14.2-14.3 afr at warm idle with the o2 sensor disconnected.
Lean mixtures burn slower. They can burn slow enough that when the intake valve opens, the exhaust gases are still burning and they ignite the mixture in the intake manifold which causes the back fire. Predetonation will cause knocking and can be caused by a lean mixture running the engine hotter but this is typically at load and higher engine speeds.
http://www.jcwhitney.com/fuel-inject.../p2008126.jcwx
here is the cheap pressure tester you need. Mine was made in China which I did not know because someone on the BMW forum told me theirs was made in Brazil. Mine seems to work fine which is surprising for a Chinese product. I also recommend you buy a Bentley manual for your car.
http://www.google.com/products/catal...CAcQ8wIwADgA#p
You definitely need to check your fuel mixture. The mixture could be overly rich and run better than fine when it is cold. When the car warms up it will not start or hunt then when the O2 sensor system turns on it will lean out the rich mixture and run great again. You can disconnect your 02 sensor when the car is warm and see if it runs poorly. You can also try and adjust your mixture by alternate methods until you find a AFR or CO meter. The 2nd best way to set it is to measure the duty cycle for the frequency valve if you have a dwell meter. The other option is to adjust the mixture till you get a reduction is rpm when you apply a light pressure to both top and bottom of the lever for the air flow meter plate.
I bought a used LM-1 on ebay for $200 but you cannot use it if you have a catalytic converter unless you switch it with the stock 02 sensor. I installed a second bung in my test pipe. The 80-83 cars are set to run a 14.2-14.3 afr at warm idle with the o2 sensor disconnected.
05-20-2010, 12:55 PM
#21
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Sounds like you losing residual pressure. It could be Fuel Accumulator, Fuel Pump Check Valve or Warm Up Regulator. In my case it was the WUR.
Start with the basics. Ignition timing, CO adjustment, etc.. Let the car cool and even better, let the car sit overnight. Then connect a gauge set to the Fuel distributor and WUR. Run you tests. I bet you 50 cents you are losing Residual Pressure.
Good luck,
Ed
1977 Carrera 3.0
Start with the basics. Ignition timing, CO adjustment, etc.. Let the car cool and even better, let the car sit overnight. Then connect a gauge set to the Fuel distributor and WUR. Run you tests. I bet you 50 cents you are losing Residual Pressure.
Good luck,
Ed
1977 Carrera 3.0
05-23-2010, 10:05 PM
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05-25-2010, 02:40 AM
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05-25-2010, 09:40 AM
#26
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I have not folowed this thread in a while as I have been away. I hope you have checked your fuel pressures and confirmed you in fact need a warm up regulator. If not, throwing parts at your car like this with CIS can get expensive fast.
That being said if that is the route you want to take why not try to see if you can get a used one from DC automotive or maybe a refurbed one. you of course need a specific WUR for your year I think they changed after 79, there should be a number on yours, the Bentley i believe also specs this out.
That being said if that is the route you want to take why not try to see if you can get a used one from DC automotive or maybe a refurbed one. you of course need a specific WUR for your year I think they changed after 79, there should be a number on yours, the Bentley i believe also specs this out.
07-03-2010, 09:47 PM
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Hey guys! So I replace the warm up Regulator. It helped to fix the problem, starting up is not so bad. Replacing it was super simple, I might have some pic / video of it, soon. But One thing that I'm wondering is what is this gold foam thing in the intake for the WUR?
I left it in, because I thought it might be a filter that the old one did not have. If it's not supposed to be there it might enplane why it only kinda fixed the problem. Thanks again guys!
I left it in, because I thought it might be a filter that the old one did not have. If it's not supposed to be there it might enplane why it only kinda fixed the problem. Thanks again guys!
07-03-2010, 10:12 PM
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That is a filter. It is a different type of filter than I remember having on mine. My filter had clogged with rust when I bought my car and caused excessive fuel control pressure. Cleaning it out fixed the problem. I think it was just a wire screen.
