Lift pump is not powering up in the on position

[I6FREAK]

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.

[Mopar1973Man]

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...

[I6FREAK]

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?

[Mopar1973Man]

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...

[I6FREAK]

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?

[gassernomore]

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?

I have mine wired to the alternator. Have not had any problems with it this way. That was the recommendation from the instructions when I installed it! p.s. IMHO There is NEVER a dumb question! Good luck!

[Mopar1973Man]

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?

No problem...

I have mine wired to the alternator. Have not had any problems with it this way. That was the recommendation from the instructions when I installed it! p.s. IMHO There is NEVER a dumb question! Good luck!

I put a twist on this and hooked up right on the studs there in the PDC for the battery lead. This way I did have wires going all the way to the alternator like Gassenomore and not hooked directly to the battery like you I6Freak but the say clean on corrosion free like Gassernomore.

[JAG1]

Post deleted... for redundant question

[I6FREAK]

Just wanted to say thanks to you guys who helped me out here....If any of you find out what would causes the ECM to not power the pump during the first second when you turn the key into the "On Position" please let me know.....at this point all I care about is that I have 12 volts at the lift pump, and I do.... thank you very much and Happy late Thanksgiving!!!Will

[Mopar1973Man]

All I can say is a internal ECM problem because once the ECM is replaced the problem goes away...

[I6FREAK]

All I can say is a internal ECM problem because once the ECM is replaced the problem goes away...

I don't know if this has anything to do with it, but in addition to the symptoms I've talked about the wait to start light is on longer than it ever has, about 15 seconds, and it the time it stays on doesn't change based on temperature... It has been up to 85 and as low as 26 in the mountains and it is on for the approximate 15 seconds....not sure if this was vital to what anyone was thinking about... In my opinnion it just adds more validation to Mike's ECM conclusion.

[Mopar1973Man]

In my opinnion it just adds more validation to Mike's ECM conclusion.

Sounds about right...

[jumpjg]

I don't know if this has anything to do with it, but in addition to the symptoms I've talked about the wait to start light is on longer than it ever has, about 15 seconds, and it the time it stays on doesn't change based on temperature... It has been up to 85 and as low as 26 in the mountains and it is on for the approximate 15 seconds....not sure if this was vital to what anyone was thinking about... In my opinnion it just adds more validation to Mike's ECM conclusion.

Strange symptoms with my truck too. This morning the ambient was 34 deg F when I got into my truck - been sitting overnight. Key on, no fuel pump pulse nor wait-to-start light for about 5 seconds, then the light came on & pump pulsed for about one second. The light stayed on for about 20 seconds then went out; truck started right up, fuel pump turned on & stayed on upon start-up. After pulling away from home a block or two the grid heaters had quit cycling. About a mile into my drive I shut the truck down & re-started about 15 seconds later (Ultra-Gauge reset). Key on and no pulse from the FP & no wait-to-start light; truck started right up. At this point the coolant temp was about 100-110 F, but after restart the grid heaters started to cycle again. I would have expected the heaters to stay off line. The other day I had taken a short drive but the weather was warmer & coolant temps were up to 180-190. Same thing; shut the truck down & restarted within a few minutes & the grid heaters were cycling. Hard to establish any pattern. I noticed with my Juice w/ Attitude that I can monitor fuel temp, I presume at the VP. Wonder if that parameter plays into the grid heaters being turned on. This morning it was reading 34 at start-up & got up to 79 after a 17 mile drive city/highway. Fuel pressure came up 0.5 to 1 psi over the drive. I will continue to monitor but won't take any action (like replacing the ECM) until it prevents reliable operation - keeping my fingers crossed. Joe in St Louis

[Mopar1973Man]

Remember grid hater actions are based off of 3 sensors...

[*]ECT - Engine Coolant Temperature

[*]IAT - Intake Manifold Temperature

[*]BTS - Battery Temperature Sensor

Like on my truck I've seen this a million times. Run to New Meadows, ID and got a full head of temp 195* ECT. Then stop some where for like a soda shut jump out get your soda and fire right back up. Maybe shut down all of 2-5 minutes tops. The IAT and ECT and well above trigger point for grid heaters. But still the wait to start comes on voltage falls (grid heaters are active). Then after you fire up it pulsing grid heaters after your running again. The only reason I can see this occuring is the BTS being cold enough... Even in the FSM they mention that there is a relationship between the IAT and BTS sensors.

[AH64ID]

I don't recall the temp on 2nd gen's, (66°F for 3rd gens), but if the IAT is above that the WTS doesn't illum but if the ambient temp is low the grids will cycle after engine start. If the IAT is below the threshold the WTS will illum (time is based on temp), and the grids will cycle after the engine starts. In either case they will operate for up to 2 minutes or until you hit ~18 mph. I have no clue what the cutoff is for coolant temp (if there even is one on 3rd gens) as I have never seen it not operate from a hot truck.. just that 66° IAT number.

[jumpjg]

Remember grid hater actions are based off of 3 sensors...

[*]ECT - Engine Coolant Temperature

[*]IAT - Intake Manifold Temperature

[*]BTS - Battery Temperature Sensor

Like on my truck I've seen this a million times. Run to New Meadows, ID and got a full head of temp 195* ECT. Then stop some where for like a soda shut jump out get your soda and fire right back up. Maybe shut down all of 2-5 minutes tops. The IAT and ECT and well above trigger point for grid heaters. But still the wait to start comes on voltage falls (grid heaters are active). Then after you fire up it pulsing grid heaters after your running again. The only reason I can see this occuring is the BTS being cold enough... Even in the FSM they mention that there is a relationship between the IAT and BTS sensors.

Thanks for the explanation, Mike. So the fuel pump is not tied into anything controlling the grids/WTS light - makes sense. I was not aware of a battery temp sensor; where is that located, in the battery tray(s)? Sounds like a tough environment.

[Mopar1973Man]

I don't recall the temp on 2nd gen's, (66°F for 3rd gens), but if the IAT is above that the WTS doesn't illum but if the ambient temp is low the grids will cycle after engine start. If the IAT is below the threshold the WTS will illum (time is based on temp), and the grids will cycle after the engine starts. In either case they will operate for up to 2 minutes or until you hit ~18 mph. I have no clue what the cutoff is for coolant temp (if there even is one on 3rd gens) as I have never seen it not operate from a hot truck.. just that 66° IAT number.

AH64ID the will come on every time for a bulb check. It just do you see the voltage gauge fall or not. (Grids being active or not).

Thanks for the explanation, Mike. So the fuel pump is not tied into anything controlling the grids/WTS light - makes sense. I was not aware of a battery temp sensor; where is that located, in the battery tray(s)? Sounds like a tough environment.

Driver side battery tray is the battery temp sensor.

[AH64ID]

AH64ID the will come on every time for a bulb check. It just do you see the voltage gauge fall or not. (Grids being active or not).

Same on the 3rd gen up thru 05, no bulb check on 06+ if the grids don't fire.

Depending on the year the volt meter may or may not bouce with the grids. My 05 it stays low thru the entire cycle, but I can watch the volts change on my SG and in the headlights. My dad's 06 bounces with the voltage.

Driver side battery tray is the battery temp sensor.

[ATTACH=CONFIG]3298[/ATTACH]

BTS plays no role in grid heater operation on a 3rd gen, it's only uses for charge rates.

--- Update to the previous post...

This is out of the 01 FSM.

The BTS is used to determine the battery temperature

and control battery charging rate. This temperature

data, along with data from monitored line

voltage, is used by the PCM to vary the battery

charging rate. System voltage will be higher at colder

temperatures and is gradually reduced at warmer

temperatures

[Mopar1973Man]

Well Dang... I'll have to find the document again about how the IAT is compared to BTS sensor at key on... I knew I read it somewhere but now I can find it... :banghead:

[I6FREAK]

I decided to wire a custom relay system to power the lift pump where the relay is activated by a 12volt circuit from ignition system and is powered by alternator. I don't see a problem with the lift pump being power when the key is in the on position being that the pump has an internal regulator and if there is an over pressure situation the 14.2psi valve will open, relieving any pressure that would build if the regulator goes out. This would be very similar to bumping the starter and starting it half way through the cycle. Other than a good prime does anyone see a problem with this?