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Whats the spec on powering up the Lift pump?

banzaitoyota
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anoldbiker

anoldbiker

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Can't help on the specs, sorry, but I did check my truck after reading your comment, and as soon as I turned my key, the lift pump started. After thumbing through my manual, nothing was indicated as to this issue.

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Mopar1973Man

Mopar1973Man

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My lift pump takes 20-25 seconds to get power; I think thats too long. No Codes. Sign of Fubar PCM?:banghead:

ECM...

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ECM is in sole control of the lift pump circuit... No relays unless you got a aftermarket...

G107 is behind the starter if your wondering so you'll have to remove the starter to get that ground... :duh:

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jumpjg

jumpjg

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I have a '99 that has a similar problem. I purchased the truck last November & at first my pump powered up as normal; ~2 second pulse as soon as key was turned on, 25 second run time if starter is bumped. At sometime during this past winter it changed to no discernible pattern. Occasionally I'll get the pulse as soon as the key is turned, but not often. Most the time if I wait like you (~25 sec) it will pulse. Sometimes it won't pulse unless I bump the starter. I've tried starting the truck without waiting for the lift pump to turn on; a cold engine won't start but if I had recently shut it down (like at a fuel fill-up) it will start without transfer fuel pump pressure. As soon as the engine starts the transfer pump stays on-line and performs as normal. I suspect that the problem is a glitch in the ECM and perhaps could be sorted with a "re-flash" from a dealer. Keeping my fingers crossed that it doesn't leave me stranded.Joe in St Louis

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mrtowman4u

mrtowman4u

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I have 2 of the 98.5 24v, and if the wts light doesn't come on, the truck just turns over! But as soon as the wts light comes on the lift pump fires and the truck will crank and run! I've had my ecm reflashed an it didn't help on my truck! I've been dealing with this for several years now, and haven't found the answer! :doh:

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Mopar1973Man

Mopar1973Man

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What would happen if you just wired the lift pump to the battery with a switch? :shrug:

Well if you turn on the pump before you start the truck you'll have hard starting issues. Then if you forget to turn on the pump after you start the engine then you VP44 will be ruined... During cranking the lift pump is modulated at 50% duty cycle till you release the key to prevent excessive pressure during starting.
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jumpjg

jumpjg

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During cranking the lift pump is modulated at 50% duty cycle till you release the key to prevent excessive pressure during starting.

Don't follow what you mean by 50% duty cycle. I would get a 2 second pulse, then pump would turn off until engine started. If I bumped the starter the pump would run for 25 seconds then shut off, but it would start fine anytime during the 25 second run. How is "duty cycle" modulated on the big pumps like Airdog, FASS, Raptor, etc. that are wired through a relay?
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Mopar1973Man

Mopar1973Man

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Don't follow what you mean by 50% duty cycle. I would get a 2 second pulse, then pump would turn off until engine started. If I bumped the starter the pump would run for 25 seconds then shut off, but it would start fine anytime during the 25 second run. How is "duty cycle" modulated on the big pumps like Airdog, FASS, Raptor, etc. that are wired through a relay?

When you cranking on the starter the ECM send a on - off - on - off - on signal ot the lift pump at exactly 50% off and %50 percent on.

http-~~-//www.youtube.com/watch?v=NCJjMzRImpA

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jumpjg

jumpjg

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Mike, Thanks for the video. Never saw that on my gauge, but then I never have cranked mine over with the relay removed. Once I get a pulse from the fuel transfer pump, it starts instantly like your truck. It is just that sometimes I don't get any power to the pump unless I bump the starter. Other times it gets a quick pulse as soon as the key is turned on, or it may take 5 seconds or so before it pulses. No real pattern I can discern.Joe in St Louis

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MnTom

MnTom

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is it relevant that on my '01, if I turn the key on, no pump action occurs? But if I bump the starter, the pump will 'prime' for about 5-10 secs?

Your LP should run about 25 seconds if you bump the starter, otherwise you have a 'normal' truck.
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