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  #1  
Old April 24th, 2004, 04:40 PM
Nuke_Danarchy Nuke_Danarchy is offline
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Strange occurence today. While warming up my truck today this morning I started fooling with the windshield wipers. They have strong vacuum and I noticed that when I disconnected the hose it made the idle smooth out considerably, and I wouldn't say it was rough before!
What gives? Is it a sign of Fuel Pump problems to come? Pump works fine and has good flow. Anyone else ever noticed this?
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Old April 24th, 2004, 07:43 PM
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sounds like it may be idling a little rich. have you tried adjusting carb mixture screw to see if it makes a difference?
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Old April 25th, 2004, 08:23 AM
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My idle goes rough when I unplug the wipers. My fuel pump side of the vacuum pump has been broken since I got the truck. I don't know why a seperate accessory should change the idle. Good question.
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Old April 25th, 2004, 08:49 AM
Nuke_Danarchy Nuke_Danarchy is offline
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Dave-I have adjusted the carb.(and completely rebuilt it) on the lean side and on the rich side before coming to what I thought was the smoothest idle I could achieve. Then I unplugged the wipers?
Does the vacuum work off of two sides of the same diaphram or are there two diaphrams on the stock fuel pumps? I haven't ever had one apart, anyone?
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Old April 25th, 2004, 12:08 PM
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Default *update* M715 spotting on MCAS in North Carolina

I'd guess it's a touch rich at idle and unplugging the hose creates a vacuum leak that'll bring it to being lean.

The pump has two seperate sections. The vacuum side kicks in when it senses a drop in vacuum like when you accelerate so it can keep the wipers up to speed.

Chris
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Old April 26th, 2004, 01:37 PM
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I have noticed the same thing with mine. It runs better with the wipers disconnected. FYI, I am using the mechanical fuel pump side still. I thought that this was a totally seperate pump, anotherwords having nothing to do with crankcase vacuum.
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Old April 26th, 2004, 02:10 PM
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Default 100 amp rectifier

There is an input line to the vacuum pump from the motor...at least stock there is...might have been changed later if you dont have it now...
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Old April 26th, 2004, 05:49 PM
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Like Jon said,

It has an "in" side from the intake manifold and and "out" side to the wipers. When the vacuum signal at the "in" side drops, the pump will keep the vacuum up high enough to run the wipers.

Chris
 

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