tach issues
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Junior User
Joined: Feb 2010
Posts: 77
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From: rathdrum idaho
tach issues
ok i did a 94 500hp cummins into a 91 f359 i hooked all the wires up they way they should be. it idle im turning 800RPM when i het the marker lights in at 600RPM when i turn the low beems on im at 400RPM and high beems on im at 200RPM when i turn all the lights off its back to normal 800RPM any thoughts?
Cargo Master
Joined: Mar 2006
Posts: 2,789
Likes: 5
From: Sand GAp, KY
My tach does the same thing just about. It sits at about 700 at idle then drops to 300 with the headlights and zero with the heater fan with or with out the lights on. I was told to check for a bad ground but couldn't find any that were bad. If I give it fuel it will jump right up with the lights on to normal but will run about 300 low while driving with the heater fan on. Have you tried it while driving to see if it does the same thing as mine? If you figure this out let me know lol.
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Junior User
Joined: Feb 2010
Posts: 77
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From: rathdrum idaho
weel of couarse its gunna go up when you drive it because your really turning more RPM when your driving it im gunna try adding some more graound wires to see if i can eliminate this issue. a 500hp cummins needs to be accurate on the tach
Cargo Master
Joined: Mar 2006
Posts: 2,789
Likes: 5
From: Sand GAp, KY
Ya i know it will go up lol. I was wondering if the slow reading stayed consistant like mine does. It will always run 700rpms slow with the fan on no matter what speed the engine is turning, it is always the same rate.
Cargo Master
Joined: Mar 2006
Posts: 2,789
Likes: 5
From: Sand GAp, KY
ya mine is as well. I mean does the rate it runs with the lights stay consistant? in other words, if you are driving and it is at 2500rpms and you trun the lights on high does it drop down to 1900rpms? I use this number as you said it drops from 800 to 200 at idle.
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Junior User
Joined: Feb 2010
Posts: 77
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From: rathdrum idaho
dont know havent driven it yet just got the steering done tonight all thats left is to bleed the brakes then i hues i will kknow more. i know i need to add more grounds i only have a main from the batery to the chassis and a main from the battery to the engine. i know i need more just havent gotten around to it yet
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