SC Injection experts only
03-21-2003, 11:19 AM
#1
Instructor
Thread Starter
SC Injection experts only
I posted the following last week and got zero response and wanted to throw it out again.
I have replaced my fuel pump with a new Bosch and can't seem to get the idle set to a point that the car will start and idle while warming up and then idle correctly once warmed. I have to rev the car when cold during the first 30 seconds or so and once warm, the idle hunts around between 300 and 1300 and occasionally stalls after abruptly letting off the throttle. I have adjusted the idle and the mixture and can't get it right. I know that I have seen this topic written about over and over and over again. I've seen lots of suggestions but I don't think that I have ever seen anyone post "I did .........and it worked for me". I have also seen something regarding the AAV (auxilary air valve) and it's removal in improving the idle on SC's. Do I completely remove the AAV or just plug it? Is it like a gall bladder, really needs to be there, but you can live without it? <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />
I have replaced my fuel pump with a new Bosch and can't seem to get the idle set to a point that the car will start and idle while warming up and then idle correctly once warmed. I have to rev the car when cold during the first 30 seconds or so and once warm, the idle hunts around between 300 and 1300 and occasionally stalls after abruptly letting off the throttle. I have adjusted the idle and the mixture and can't get it right. I know that I have seen this topic written about over and over and over again. I've seen lots of suggestions but I don't think that I have ever seen anyone post "I did .........and it worked for me". I have also seen something regarding the AAV (auxilary air valve) and it's removal in improving the idle on SC's. Do I completely remove the AAV or just plug it? Is it like a gall bladder, really needs to be there, but you can live without it? <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />
03-21-2003, 11:54 AM
#2
Did the engine run ok before you fitted the new pump? Have you checked the warm up regulator?
If not look at this
<a href="http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm" target="_blank">http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm</a>
If not look at this
<a href="http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm" target="_blank">http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm</a>
03-22-2003, 07:00 PM
#4
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Gregg,
What year SC ? It very well could be your warm up regulator, this is a also symptomatic of a timing/fuel air mixture problem. A 4 gas analysis
would tell you.I can tell you that on my 83SC, My searching idle was cured by a (new) remanfactured Warm up regulator.My idle wdould go between 500 and 1500 rpm during warm up and be ok when warm.
Good luck with it !
Oh, Yea....
I just have to ask,
You did replace with the EXACT factory Bosch pump didn't you ?
What year SC ? It very well could be your warm up regulator, this is a also symptomatic of a timing/fuel air mixture problem. A 4 gas analysis
would tell you.I can tell you that on my 83SC, My searching idle was cured by a (new) remanfactured Warm up regulator.My idle wdould go between 500 and 1500 rpm during warm up and be ok when warm.
Good luck with it !
Oh, Yea....
I just have to ask,
You did replace with the EXACT factory Bosch pump didn't you ?
03-24-2003, 03:08 AM
#5
To be honest, mine does something like yours. Though mine does it from running a hair too rich. I have my idle set at over 1000. More like 1,200, because if any lower while the engine is cold, the idle will go up and down, up and down and so forth. Until it reaches optimum temperature. If I had the idle set lower, it would conk out. I could easily rectify the problem by running leaner, but I run mine very rich for the extreme heat I track the car at. I don't know what your exact problem is, but I will at least put in some thoughts. These things do go up and down in the rpms when cold if they are on the rich side. On mine, I just raised the idle. If really rich, they will even do it while hot. If it does it hot, then it is either still way rich or something else in the injection is off. There aren't a lot of parts in CIS and they seldom go bad. So check the stupid, free basics first.
As far as mixture, I do it by ear. I usually go counterclockwise till the point where the engine slows down and starts getting choked. From there, I start turning clockwise until the up and down idle starts. Then I back up a hair until I just have a slight up and down when warm. From there I set the idle at just over 1K. If next morning the up and down idle is excessive, I go counterclockwise by amost a quarter. I always try to keep the idle set at around 1K. If you can't get a solid idle no matter how lean, then you have a problem with some other part.
As far as mixture, I do it by ear. I usually go counterclockwise till the point where the engine slows down and starts getting choked. From there, I start turning clockwise until the up and down idle starts. Then I back up a hair until I just have a slight up and down when warm. From there I set the idle at just over 1K. If next morning the up and down idle is excessive, I go counterclockwise by amost a quarter. I always try to keep the idle set at around 1K. If you can't get a solid idle no matter how lean, then you have a problem with some other part.
03-24-2003, 06:24 PM
#6
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I'm not a 911 CIS expert, but in years past I fixed a few VWs and others with CIS with this problem. I am assuming it is straight CIS and not CIS-E.
The problem is most likely the warm-up regulator, which can be replaced. It can also be tweaked if you have the ability to take apart and make careful measurements. I did this due to being pissed about people just wanting to replace parts without thinking about anything, and these are relatively expensive.
I removed the regulator and took off the cover. There is a pin which closes the valve when the bi-metal strip heats up. It has its own heater and it gets heat from the engine to close the valve. If you shorten the pin it will close the valve later and let the engine run richer for a bit longer. I overdid it once and had the engine way too rich for one tank, but a newly made pin a bit longer solved that. I would take it down in increments of .003"-.005" until you get good cold starting. If you take it too far it will be rich all the time. Note your measurements just in case. The pin is about 1/16 dia x 3/4 long. The worst part is getting it back together without thi pin falling over. My solution was to set the pin in some grease so it stands up as you assemble. If it does not seat the car will be REALLY rich.
This is all pretty simple stuff, so I would not hesitate to try it. Worst case is you buy a new one. This solution came out of poverty, but I would still use it if I had a CIS car.
Art
The problem is most likely the warm-up regulator, which can be replaced. It can also be tweaked if you have the ability to take apart and make careful measurements. I did this due to being pissed about people just wanting to replace parts without thinking about anything, and these are relatively expensive.
I removed the regulator and took off the cover. There is a pin which closes the valve when the bi-metal strip heats up. It has its own heater and it gets heat from the engine to close the valve. If you shorten the pin it will close the valve later and let the engine run richer for a bit longer. I overdid it once and had the engine way too rich for one tank, but a newly made pin a bit longer solved that. I would take it down in increments of .003"-.005" until you get good cold starting. If you take it too far it will be rich all the time. Note your measurements just in case. The pin is about 1/16 dia x 3/4 long. The worst part is getting it back together without thi pin falling over. My solution was to set the pin in some grease so it stands up as you assemble. If it does not seat the car will be REALLY rich.
This is all pretty simple stuff, so I would not hesitate to try it. Worst case is you buy a new one. This solution came out of poverty, but I would still use it if I had a CIS car.
Art
03-24-2003, 06:51 PM
#7
Rennlist Member
Had the same cold-start symptoms to the point of stalling each time unless I blipped the throttle a hair, so I leaned (CCW) the mixture by 1/8th a turn. The problem for me was solved. I had the idle screw set a little high (1100 rpm) to help with the cold stalling, but I've since return the idle to 950 rpm for that slow, pleasant rumble sound. Now I announce my presence with authority at a stop light instead of a wimper.
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03-25-2003, 06:31 PM
#8
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I should add that it is worth checking some of the basics, injector 0-rings, aux air valve for smooth operation, throttle body clean, etc.
Fuel/control pressure check is a good idea too, but tough without the guages. I made my own fuel pressure guage with an old british oil pressure guage and some fittings that allowed it to be hooked to the test port.
Art
Fuel/control pressure check is a good idea too, but tough without the guages. I made my own fuel pressure guage with an old british oil pressure guage and some fittings that allowed it to be hooked to the test port.
Art