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I6FREAK

Lift pump is not powering up in the on position

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I have a 99 5.9 24 valve 2wd, auto..... My fuel pump is not powering on anymore, when the key is placed into the on position. With the fuel heater on my "On Position voltage is around 11.8 to 12.0 volts.....it has been around 45 in the mornings here, and my grid heater/s are cycling normally. My issue is that my fuel pump only starts running when I start the engine. There is no lag time, it starts normally and the grid heaters stop cycling after about 30 seconds plus or minus. I do not have any fuel leaks and am running 17 psi at idle as soon as both fuel pressure gauges (electric and mechanical) top out about 1 second give or take after it starts...... this is not what it did for the last 4 years.....Also when it is bumped it turns on for a split second and shuts of right away, it doesn't even get to 10 psi and pump shuts off. there is no voltage going to the pump... it is not the pump's issue... can anyone shed some light.... everything else is functioning normally and no light has turned on.Thanks,Will

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Have you upgraded your trucks ECM software recently?I know that later VP trucks (if not all) would just have a short prime then shut the pump off until the motor was running. The VP doesn't like to start with high inlet pressure.

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I have not upgraded recently, shouldn't it always have the lift pump run around 25 seconds if the starter is bumped....Not sure if there is a PCM issue or what? My battery voltage is 12.6 volts, 13.98 to 14.00 running after the heater/s turn off. Please forgive this stupid question.... How often should this update be done... I was familiar with an update but that was around 8 ish years ago.... what causes this need for an update?I know these questions are maybe old news but I am still learning the details on the 98.5-02, and would appreciate anything you guys got..Thanks,Will

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Actualy I've seen where the ECM have failed internally from lock rotors in the the lift pump and cause excessive current flow through the ECM which fries it out... So I would bump the starter and check the lift pump connector with a DVM and see if 12 volt is seem if so then the lift pump is dead most likely...

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Actualy I've seen where the ECM have failed internally from lock rotors in the the lift pump and cause excessive current flow through the ECM which fries it out... So I would bump the starter and check the lift pump connector with a DVM and see if 12 volt is seem if so then the lift pump is dead most likely...

Thanks so much, I will try it.... it is running at normal pressures when it starts... is it still a possibility that the air dog 100 is having a strain to work or at least more than it should?

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What your fuel pressure from idle to WOT @ highway speed? :shrug:

just drove 160 miles today through up hills and down hills..... Idle at stop 17 psi-WOT @ 70 to 75 14.5 ish(elecrtrical)....19psi at idle and 15.5 ish at WOT(liquid filled mechanical gauge) at around same speed.... I have been using both, I think i mentioned this but cant remember, just to make sure there isn't something getting damaged.... What do you think.... I am usually around 14 volts while charging. I also checked fuses and relays.

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Actualy I've seen where the ECM have failed internally from lock rotors in the the lift pump and cause excessive current flow through the ECM which fries it out... ...

Ahaah! one good reason to relay the lift pump to run directly off the batteries. Good to know this can happen.:stuned:

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This is going to be tough to test eletrically. My lift pump only runs a few seconds... maybe 5... when the key switched to 'on'. Since it runs after starting, my conclusion is the pump & wiring is good. My AD kit runs the power off the batteries through a relay which came with the kit (now screwed to the firewall). The ECM must be the trigger. I'd have to guess that it's not triggering for some reason. If it's in the electronics... Codes?

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Run your own wires from the lift pump, turn on the key and then hook them directly to the battery and see if it runs continous and brings up full pressure. That's what I would do. I'm not the brightest bulb in the light shop but might give some kind of clue.At least this would show if the L/P is running right or not. Second thing is perhaps the relay is going out / has burnt contacts.

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Here's the deal.... I checked voltage first thing in the morning while bumped starter.... 8.5 volts at pump....voltage at the relay is 12.59 volts... drove for about 20 miles.... same result after the truck was shut off for 15-20 seconds.....The good news is I figured something out..... I wanted to see if disconnecting the batteries would do anything for about 5 minutes.... all connections are clean..... I hooked cables back to posts, and it is totallly back to normal.... I went through around 8 cycles of key on-see pressure for 5 seconds-start-drive-turn off... it is back to normal...Not so comforting that I do not know what the issue is... no codes, and running exactly the same....lift pump has 12.55 volts in the on position for 5 seconds, and same for when it is bumped...I ran all the functions of the electronics(a/c, blower motor to max...etc..) to see if something is drawing excessive voltage causing the ECM to lower voltage after a code is triggered.Everything is fine now, but if we could still work on this I would really appreciate it.

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Might do a voltage drop test... http://mopar.mopar1973man.com/cummins/general/voltage-drop/voltage-drop.htm This test can be done on any wiring the same way... But to see lower voltage at the pump is a concern... :ahhh:

When I disconnected the battery cables and reconnected them after five minutes the voltage to the pump is back up to 12 volts and the pump is on when the key is turned in the on position, like it always has...I will do the test tomorrow when I get off work..

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This is going to be tough to test eletrically. My lift pump only runs a few seconds... maybe 5... when the key switched to 'on'. Since it runs after starting, my conclusion is the pump & wiring is good. My AD kit runs the power off the batteries through a relay which came with the kit (now screwed to the firewall). The ECM must be the trigger. I'd have to guess that it's not triggering for some reason. If it's in the electronics... Codes?

P0230 - Transfer Pump (Lift Pump) Circuit Out of Range Basically either the lift pump is pulling to much amps (lock rotor, shorted wiring) or to little amps (open connector or armature issues inside the lift pump)

When I disconnected the battery cables and reconnected them after five minutes the voltage to the pump is back up to 12 volts and the pump is on when the key is turned in the on position, like it always has...I will do the test tomorrow when I get off work..

Now as for my power lead to the AirDog they are NOT hook to the battery. My connections are done off the studs in the power distribution box to prevent acid/corrosion to the wiring. As for my battery cables I keep them coated with engine oil and NEVER had to clean them nor had weak connection issues ever!

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I'm having similar problems. On a cold motor it may take 10-15 seconds after the ignition key is turned on for my lift pump to give the 5 second pulse. Sometimes it closer to the normal operating scenario but still delayed. Most times on a hot motor it won' give any pulse at all but starts easily. Normally I can get the 25 second pulse with a starter bump.

Here's the deal.... I checked voltage first thing in the morning while bumped starter.... 8.5 volts at pump....voltage at the relay is 12.59 volts... drove for about 20 miles.... same result after the truck was shut off for 15-20 seconds.....

Wonder if the low voltage at the pump is caused by the "reduced duty cycle during cranking" we discussed here a while back? Was that the battery side of the relay or the fuel pump side? If the latter I'd be checking connections from the relay to the pump or be looking for a high resistance through the relay.

The good news is I figured something out..... I wanted to see if disconnecting the batteries would do anything for about 5 minutes.... all connections are clean..... I hooked cables back to posts, and it is totallly back to normal.... I went through around 8 cycles of key on-see pressure for 5 seconds-start-drive-turn off... it is back to normal...

I'll have to give that a try on my truck to see if it clears up the problem - thanks for the clue! Joe in St Louis

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So this morning the truck started normally with the gauges showing pressure upon the turning to the on position......but when I got off work... it was back to no pressure when turned to on position... it was 65 degrees outside.... Mike, I trouble shot the using all the standard voltage diffeential checks in the link you posted, and I had a 0.00 volts at all juncture points...

I am getting a new relay just to see what happens.....not sure if there is a safe way to wire the air dog using an independant 12.6 volt circuit.... Anyone have any ideas without running the risk of running too much juice to the pump/system/sensors...etc????

--- Update to the previous post...

I'm having similar problems. On a cold motor it may take 10-15 seconds after the ignition key is turned on for my lift pump to give the 5 second pulse. Sometimes it closer to the normal operating scenario but still delayed. Most times on a hot motor it won' give any pulse at all but starts easily. Normally I can get the 25 second pulse with a starter bump.

Wonder if the low voltage at the pump is caused by the "reduced duty cycle during cranking" we discussed here a while back? Was that the battery side of the relay or the fuel pump side? If the latter I'd be checking connections from the relay to the pump or be looking for a high resistance through the relay.

I'll have to give that a try on my truck to see if it clears up the problem - thanks for the clue!

Joe in St Louis

Hey Joe,

Let me know how and if it works, thanks for letting me know that you are dealing with similar simptoms...

Will

--- Update to the previous post...

Hi I6,

When it happened to me it was just my crank sensor. I have an extra.

Let me know,

Dave

How much do you want for it?

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the pump should not be running when the key is just turned to the on position. it does bump the pump for a brief second but then goes off and the pressure drops back to zero quickly. mine for about a 1/2 second and some folks here get near 5 seconds. if you bump the starter it should come on for about 25 seconds and then turn off again, but it does not run just because the key is on. you might have had a weak connection at the batteries that cleared up when you took them off and reconnected them.

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the pump should not be running when the key is just turned to the on position. it does bump the pump for a brief second but then goes off and the pressure drops back to zero quickly. mine for about a 1/2 second and some folks here get near 5 seconds. if you bump the starter it should come on for about 25 seconds and then turn off again, but it does not run just because the key is on. you might have had a weak connection at the batteries that cleared up when you took them off and reconnected them.

Yes I understand and have experienced the 2-3 second pressurizing up when first turning to the on position and 25 seconds when bumping for around 5 years now..... what I am experiencing now is no pressure at any time turning the key to the on position and only .5 second pressure increase from 0 psi when bumped. It maybe gets to 10 psi during this brief time. I'm pretty sure that all i have to do is find the item that is drawing too much current...creating the voltage spike that tells the ECM to lower the voltage.... what do you think?

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my apoligies. i thought you were looking for constant pressure while the switch was on. had to go back and do some rereading. Do you atleast still have 12v at the pump when you bump it?

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my apoligies. i thought you were looking for constant pressure while the switch was on. had to go back and do some rereading. Do you atleast still have 12v at the pump when you bump it?

No apologies necessary.. I would've said the same thing... for the split second it happens, I didn't get an accurate reading.... at that point it was getting a little too dark and I kinda wanted to post to see if anyone knew what was goin on, ya know..... I could sit there and measure voltage at different points chasing wires, but all that would do is fuel frustration.... I think I will try the idea you had to see what the voltage is when being bumped...to see if it is in fact 12 or if it is 8.5 like is is when turned to the on position at his point. thanks so much, Will P.S. I am jealous of your truck.... 6 speeds are really hard to come by in CA.

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Yes I understand and have experienced the 2-3 second pressurizing up when first turning to the on position and 25 seconds when bumping for around 5 years now..... what I am experiencing now is no pressure at any time turning the key to the on position and only .5 second pressure increase from 0 psi when bumped. It maybe gets to 10 psi during this brief time. I'm pretty sure that all i have to do is find the item that is drawing too much current...creating the voltage spike that tells the ECM to lower the voltage.... what do you think?

Well if you got a AD or FASS then there is no load on the ECM just that the ECM triggers the realy for the pump so there is virtually no serious amp load there. I so I would check the stock ECM leads for voltage...

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Well if you got a AD or FASS then there is no load on the ECM just that the ECM triggers the realy for the pump so there is virtually no serious amp load there. I so I would check the stock ECM leads for voltage...

I actually am using the rapter which plugs into the stock wiring harness....I would really like to hook a 12 volt switch up to give it a full 12 volts to be sure... Do you see an issue with this? Also.... Did u remove your grid heaters? Did it set a code, and how cold will the truck start at.... I noticed that I get voltage fluctuation between 13.2 and 13.75 within the first minute... Which I thought were the grids, but it was 74 degrees...what do u think is the deal?

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I actually am using the rapter which plugs into the stock wiring harness....I would really like to hook a 12 volt switch up to give it a full 12 volts to be sure...

You can but leave the switch off during cranking. If the switch is on during cranking the pressure will be too high and the truck will fail to start. Hence why the cranking voltage is modulated to 50% duty cycle to reduce lift pump ressure.

Do you see an issue with this? Also.... Did u remove your grid heaters? Did it set a code, and how cold will the truck start at.... I noticed that I get voltage fluctuation between 13.2 and 13.75 within the first minute... Which I thought were the grids, but it was 74 degrees...what do u think is the deal?

My grid heater as in place but disabled electronically. No code... As for the grid heater they maybe active because the manifold air is colder yet. Remember the cast iron block hold cold for a very long time. As for cold start with my grid heater disabled I can start down to 30-32*F easy without missing a beat... But the coldest I can start from is +25*F and then it starts to miss and shake getting going. At that point I trigger the grid heater with my high idle switch before I turn the key on...

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You can but leave the switch off during cranking. If the switch is on during cranking the pressure will be too high and the truck will fail to start. Hence why the cranking voltage is modulated to 50% duty cycle to reduce lift pump ressure. My grid heater as in place but disabled electronically. No code... As for the grid heater they maybe active because the manifold air is colder yet. Remember the cast iron block hold cold for a very long time. As for cold start with my grid heater disabled I can start down to 30-32*F easy without missing a beat... But the coldest I can start from is +25*F and then it starts to miss and shake getting going. At that point I trigger the grid heater with my high idle switch before I turn the key on...

Dumb question, but..the air dog powers either from battery or alternator per the instructions....so is there an issue with the Rapter pump getting 14 volts? How would you wire it?

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