TWO QUESTION: IAC SETTING AND FUEL PRESSURE

Tom Kelly

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Jun 23, 2016
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I've been wondering about two things. One is my IAC setting. I have no trouble setting a warmed up engine to an IAC setting of 10. It will stay there for days and then one day it will be at 35. Next day it might be back to 10. So I am wondering what might affect the reading after it is set. Weather? Or does this indicate the the valve is beginning to fail? Or is this completely normal?
My other questions relates to where to set idle fuel pressure. The recommendation I read is usually around 43 hose off, then +/- 3 for adjustment. In my car, 43 hose off results in 35 hose back on. I've been told that this is too low. So I set it at 46 hose off and therefore 38 hose on. The car seems to run the same no matter where I set it. So how do I decide which is best for my car?
 

No disintegrations

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Dec 27, 2015
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If the fuel pressure gauge is liquid filled they give different reading hot and cold. Built up pressure inside them can be released by prying the little rubber cap back.
 

Ttype6

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Aug 17, 2004
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Flint,Michigan
I've been wondering about two things. One is my IAC setting. I have no trouble setting a warmed up engine to an IAC setting of 10. It will stay there for days and then one day it will be at 35. Next day it might be back to 10. So I am wondering what might affect the reading after it is set. Weather? Or does this indicate the the valve is beginning to fail? Or is this completely normal?
My other questions relates to where to set idle fuel pressure. The recommendation I read is usually around 43 hose off, then +/- 3 for adjustment. In my car, 43 hose off results in 35 hose back on. I've been told that this is too low. So I set it at 46 hose off and therefore 38 hose on. The car seems to run the same no matter where I set it. So how do I decide which is best for my car?
What your fuel pressure does at 43 is exactly what it is supposed to do. Leave it set at 43. Your IAC is also acting as it should. It will change with temp changes. It is perfectly normal.
 

Tom Kelly

Member
Jun 23, 2016
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72
What your fuel pressure does at 43 is exactly what it is supposed to do. Leave it set at 43. Your IAC is also acting as it should. It will change with temp changes. It is perfectly normal.
Thank you for your reply. So I guess if IAC is affected by temperature then it should be set when the temp is 60 degrees (standard day)? And as to fuel pressure, I take it you meant that I should ignore what the pressure drops to with the hose back on and set it at 43 vacuum off regardless. Okay. But I was wondering about adjusting it. Some posts say refer to scanning tool results to fine tune it. I am not clear as to the relative roles of changing the WOT fuel parameter via scanmaster and turbotweak chip versus adjusting fuel pressure to change a/f results. In other words, when would you adjust fuel pressure as opposed to just changing the fuel parameter? My gauge shows fuel pressure up by 1 for every pound of boost under WOT as well as normal increases as vacuum drops under light to moderate acceleration. Thanks for any input on this.
 

Ttype6

Well-Known Member
Aug 17, 2004
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Flint,Michigan
Thank you for your reply. So I guess if IAC is affected by temperature then it should be set when the temp is 60 degrees (standard day)? And as to fuel pressure, I take it you meant that I should ignore what the pressure drops to with the hose back on and set it at 43 vacuum off regardless. Okay. But I was wondering about adjusting it. Some posts say refer to scanning tool results to fine tune it. I am not clear as to the relative roles of changing the WOT fuel parameter via scanmaster and turbotweak chip versus adjusting fuel pressure to change a/f results. In other words, when would you adjust fuel pressure as opposed to just changing the fuel parameter? My gauge shows fuel pressure up by 1 for every pound of boost under WOT as well as normal increases as vacuum drops under light to moderate acceleration. Thanks for any input on this.
The chip adjustments should be all you need to adjust WOT fuel. When you get to the end of your fuel injector's capabilities,you can then raise base fuel pressure to get more fuel into the engine. If a chip adjustment increases or decreases fuel supply too much,you can fine tune with fuel pressure. Running higher fuel pressure does atomize the fuel better.
 
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Tom Kelly

Member
Jun 23, 2016
138
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The chip adjustments should be all you need to adjust WOT fuel. When you get to the end of your fuel injector's capabilities,you can then raise base fuel pressure to get more fuel into the engine. If a chip adjustment increases or decreases fuel supply too much,you can fine tune with fuel pressure. Running higher fuel pressure does atomize the fuel better.
Thanks again. I have 60lb injectors and an upgraded fuel pump. Do I understand that you are saying that increasing/decreasing fuel pressure by 1 psi can fine tune in between one increment adjustment to fuel on the scanmaster? If so good to know.
 

Ttype6

Well-Known Member
Aug 17, 2004
3,340
253
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60
Flint,Michigan
Thanks again. I have 60lb injectors and an upgraded fuel pump. Do I understand that you are saying that increasing/decreasing fuel pressure by 1 psi can fine tune in between one increment adjustment to fuel on the scanmaster? If so good to know.
Exactly.
 
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