Am I doing any harm?
10-30-2002, 03:29 PM
#1
Racer
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Am I doing any harm?
I was wondering if starting my car and then keeping the RPMS up to 2000 or less is damaging anything. Without doing, the engine fights for life and backfires a bit. I have tried everything except replacing the Cold start valve which can be a pain. So instead of waking up the neighbors, I start the car and as soon as it turns over, I keep a bit of gas on to keep the RPM's up to 2000. I do this for probably 15 - 20 secs. then take my foot off the gas and the RPM's drop to 900 with no backfiring. Am I ruining anything?
Thanks in advance.
Thanks in advance.
10-30-2002, 03:59 PM
#2
Technical Specialist
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David,
Some might say starting the engine is the hardest thing you'll ever ask it to do. There's no oil distributed, frictions at it's highest point, etc.
What model 911 do you have (CIS-based?), and what have you done?
Some might say starting the engine is the hardest thing you'll ever ask it to do. There's no oil distributed, frictions at it's highest point, etc.
What model 911 do you have (CIS-based?), and what have you done?
10-30-2002, 04:34 PM
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Hi Bill, 77 911 3.0 ROW. I have tried adjusting the WUR, the mixture control unit, changed all the filters. Any other suggestions? I have kept away from the cold start valve because of it's location. I thought by giving gas, I would basically be doing what I think the start up valve is failing to do.
While your listening, I recently found out that my engine was rebuilt about 20k miles ago. The car gets terrible gas mileage (way less than 20/gallon) but I have been told that it has a lot more I guess power and responsiveness that than it should. Unfortunately, the way I found out that the engine was rebuilt was by calling the person who had the car three people before me. No receipt, but the guy he sold it to said that he was told it was rebuilt and it ran so good he just believed it. His mechanic then confirmed a rebuilt was done and whoever did it did "knew what he was doing". He then went on to tell me that after selling this car and doing the 928 and 924 Turbo thing that he bought a 87 Carrera. His exact words were that"the 77 would blow the doors off his 87". Any ideas what could have been done. It does have SSI's but I don't think they produce that much more power to constitute "Blow the doors off". Also, my neighbor who has a 78 SC mentions how much power this engine puts out. Any ideas what could have been done?
Thanks for your time.
While your listening, I recently found out that my engine was rebuilt about 20k miles ago. The car gets terrible gas mileage (way less than 20/gallon) but I have been told that it has a lot more I guess power and responsiveness that than it should. Unfortunately, the way I found out that the engine was rebuilt was by calling the person who had the car three people before me. No receipt, but the guy he sold it to said that he was told it was rebuilt and it ran so good he just believed it. His mechanic then confirmed a rebuilt was done and whoever did it did "knew what he was doing". He then went on to tell me that after selling this car and doing the 928 and 924 Turbo thing that he bought a 87 Carrera. His exact words were that"the 77 would blow the doors off his 87". Any ideas what could have been done. It does have SSI's but I don't think they produce that much more power to constitute "Blow the doors off". Also, my neighbor who has a 78 SC mentions how much power this engine puts out. Any ideas what could have been done?
Thanks for your time.
10-31-2002, 01:24 PM
#4
It's not your cold start valve. Your warm-up mixture is too lean. To resolve this, you'll need to buy a CIS fuel pressure tester ($65), and set your cold control pressure to the proper specs. If you've already done the pin modification to the WUR, then it will be easy. Then have your CO level set to around 2.5-3.5%, and your car will idle properly during warm-up, and not backfire. Changing your cold start valve is a pain, and it will not solve the problem you are describing.
Rob
1980SC
Rob
1980SC
10-31-2002, 06:33 PM
#5
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David,
Rob hit the nail on the head when he says to check the pressures (as a related aside, I have a CIS pressure tester I bought and didn't use before I sold my SC, if interested email me). The approx pressures you're looking for are:
Cold: 50 deg outside temp, 20 psi; 75 degree, 32 psi; 100 degree, 49 psi.
System: 65-75 psi
Warm: 39-45 psi
At rest after 10 minutes, 19 psi
At rest after 20 minutes, 16 psi
Other things that might be contributing would be if your auxilliary air valve wasn't opening, that would prevent your idle from naturally rising when cold.
On the poor gas mileage, things to check are idle speed, timing, idle mixture, cold start valve leaking, fuel injector(s) leaking, fuel pressures are off (control pressure warm is too low), the airflow sensor plate is out of adjustment, or there's a sticking control plunger in the fuel distributor. If you find you do need to pull the cold start injector, see the article on tech.rennlist.com under 911 engines on the partial engine drop. Sounds scary, but it's easy, and it gives you decent access to the backside of the engine.
Rob hit the nail on the head when he says to check the pressures (as a related aside, I have a CIS pressure tester I bought and didn't use before I sold my SC, if interested email me). The approx pressures you're looking for are:
Cold: 50 deg outside temp, 20 psi; 75 degree, 32 psi; 100 degree, 49 psi.
System: 65-75 psi
Warm: 39-45 psi
At rest after 10 minutes, 19 psi
At rest after 20 minutes, 16 psi
Other things that might be contributing would be if your auxilliary air valve wasn't opening, that would prevent your idle from naturally rising when cold.
On the poor gas mileage, things to check are idle speed, timing, idle mixture, cold start valve leaking, fuel injector(s) leaking, fuel pressures are off (control pressure warm is too low), the airflow sensor plate is out of adjustment, or there's a sticking control plunger in the fuel distributor. If you find you do need to pull the cold start injector, see the article on tech.rennlist.com under 911 engines on the partial engine drop. Sounds scary, but it's easy, and it gives you decent access to the backside of the engine.