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Discussion Starter · #1 ·
I'm in a spot. I'm an old school Mopar guy. I can help you with a prostrate or drag car. Well a friend of mines Ram left him stranded 75 miles from home. Great guy, I'm not charging him to work on his truck.
Ok I have his 04 Ram in my shop. He told me his fuel pump was out. So I checked a few fuses and relays. All seemed to be normal. I dropped the fuel tank. Pulled the fuel pump regulator assy. Ohm checked to pump. It showed a complete circuit. So I put 12 volts to it and the pump feels strong. So I'm not a parts changed. Reinstalled the tank, the truck fired right up and ran for a good 20 mins. Then slowly died. I pulled the connector on the pump and this is what I found. Cycle the key on and sometimes you get 12 volts some times no. I noticed that when it put out 12v it was only for about 3 seconds. Then dead. I'm stumped. Newer computer trucks arnt my bag. No engine codes.
So any ideas would be welcome. I'm sure it's a glitch in the electrical system. But where?
Is that normal operation? For the pump to run a few seconds then another circuit takes over?

I'm ready to put a fuel pump switch in the truck, if I can't find the problem soon.
The truck has 140,000 miles on it. Any help would be greatly appreciated. I need this thing out of my shop ASAP!!!!
But I would like to find the problem and correct it. Maybe the ASD system is acting up? Got me.
 

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. . . . Ohm checked to pump. It showed a complete circuit. So I put 12 volts to it and the pump feels strong. So I'm not a parts changed. Reinstalled the tank, the truck fired right up and ran for a good 20 mins. Then slowly died. I pulled the connector on the pump and this is what I found. Cycle the key on and sometimes you get 12 volts some times no. I noticed that when it put out 12v it was only for about 3 seconds. Then dead. I'm stumped. Newer computer trucks arnt my bag. No engine codes. . . .
When you first turn the ignition switch to the RUN position the PCM (powertrain control module) energizes the ASD and fuel pump relays for 1 - 2 seconds. If the PCM does not detect any rotation of the engine crankshaft, it drops power to the ASD and fuel pump relays. This is a safety feature such that if the engine stops running for any reason, the electric fuel pump is not left to continuously run and pump fuel.

After several iterations of turning the ignition switch to the RUN position without engaging the starter the PCM logic remembers and will not continue to energize these relays. You have to engage the starter, the PCM detects crankshaft rotation, and then energizes the relays.

You need to attach a fuel pressure gauge to the fuel rail on the engine and determine if there is adequate fuel pressure when the engine dies and you attempt to restart. That will pinpoint if the fuel pump is the culprit.
 

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t sure looks like its i need of a new fuelpump. If it stalls again try whacking the fueltank with somethin and se if it runs again.
 

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Discussion Starter · #4 ·
Yea, we tried hitting the tank. Nothing. I believe it to be in the ASD. I'm thinking maybe a bad flywheel trigger sensor..??
 

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Discussion Starter · #5 ·
I have a efi test kit. I never put it on. I knew the pump wasn't running. After I put the tank back up and turned the key on. I checked for fuel on the left rail. It blasted fuel pretty hard. That's when it ran for about 20 mins.
What kind of pressures should I see? 35-55 psi?
 

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Around 50 psi is good.
I would diagnose this first. A good OBDII scan tool should show you ASD and Fuel Pump relay states (on or off).
Is this a 3.7L, 4.7L or 5.7L?
The tool should also tell you if the crank position sensor signal is present or lost. If the crank sensor is lost, it may not set a fault code and you will lose spark and fuel pump. The fuel injectors are synced by the cam position sensor.
It may tell you that the PCM has shut down the fuel pump and why?
 

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Discussion Starter · #7 ·
It's a 5.7 I have a spare 5.7. I traded out the cam and crank sensors. But it looks like the fuel pump gave up the ghost. It must of been on the weak side. I have to go to the part store and pick up a new 180$ pump now. I'll let you know if this straightens it out. Yea, I wish I had a scanner. But I try not to work on these computer vehicles in the first place.
Thanks for the help and comments.
 

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AllanC called it right on the function of the ASD. If the only time it drops power to the fuel pump is after the second try of turning key on without cranking, that's normal.

Try starting and running it with the fuel filler cap off. See if it starts, and continues to run indefinitely. That will tell you if there is a pressurization problem at the tank that's affecting the pump.
Wondering also if this fuel pump has a sock, or the tank has baffles, and if either one is preventing fuel from reaching the pump pickup.

Check fault codes before you pull the pump again, using the keydance method:

Chrysler, Dodge, and Jeep Computer Error Codes
 

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Discussion Starter · #9 ·
This is the second time I dropped the fuel tank. I cleaned it the first time. Just a few small things in it. Pretty clean. But like I said the pump completely failed now. I guess it was going and testing it put the final touch. I'll have a new pump on it this afternoon. If that doesn't fix it, I'm going to burn it down
:)
 

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How did you determine that it failed completely? Did you put 12V directly across the pump terminals? If not, please test it that way.
 

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Discussion Starter · #11 ·
Well I screwed up and let the truck owner insert the test leads from my fluke meter.
He broke a pin off a lead in the FP connector. I noticed it wasn't seated. Pulled the plug apart. It looked like a pin from the FP broke off. So we dropped the tank. The FP pins were fine. I pulled the pin off and saw it was from my fluke.
Yea, I used a battery and jumped across the pump, with 12v, it ran for a few seconds then died completely. So I replaced the pump and the trucks running fine. I never checked the pressures. But the owner noticed an improvement in performance. So looks like we had a weak pump that checked good. It final just stopped working.
Thanks for all the help and suggestions guys. Now I understand the fuel system better on a modern RAM.
 

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Glad you found the problem; Just for info.

If the car was in a big collision, a fuel line could break open, the engine would of course stall (which an engine driven fuel pump would stop and not pump gas out of the tank) but the entire contents of the gas tank could pump out on the ground with an electric fuel pump. Not exactly a comforting thought if you're trapped in a wrecked car with broken wires that might spark. So, for safety, if the PCM sees the engine is NOT rotating, it will turn off the voltage to the fuel pump. To start the engine, you need the fuel rail pressurized, so when you first turn the key the PCM will run the fuel pump for a few seconds to pressurize the rail and shut if off, waiting till it sees the crankshaft rotating before it turns the fuel pump back on. And anytime the engine stalls or the crank is NOT moving, the PCM will shut off the voltage to the PCM (turning the key to on without starting the motor several times within a minute, the PCM won't continue to energize the fuel pump again until some time passes). That explains what you were seeing during your checks.

Checking fuel pressure is a big clue. Check a reference for what the pressure should be, most EFI systems in the last few years use around 50PSI, early systems had varying pressures that were lower. The way EFI works, it monitors the A/F ratio with the O2 sensor, it then adjusts the injector pulse width (how long the injectors is opened), to correct the A/F ratio. If fuel pressure is low, less fuel would be going through the injectors, but the PCM will adjust to that by holding the injectors open longer and you won't even notice you have fuel problem, until the motor needs more fuel than can be supplied at that pressure, then the engine would stumble or go lean. That explains why the motor seemed to run OK, except stalling, but seems to run so much better with a new pump. The PCM could adjust to the lower pressure and make due most of the time, but obviously run better all the time with the proper fuel pressure.

I bet the fuel pressure was low or inconsistent while you were stalling from time to time with the bad fuel pump. It likely didn't stall from low fuel pressure, more likely the failing fuel pump motor was overheating and shutting down, when it cooled off, it would start running again, that is not uncommon for failing fuel pumps, and low or surging fuel pressure is common for a bad fuel pump as well. Sometime the fuel pump just dies and never comes back to life.

The fuel pressure should stay steady with the motor running, including if the motor is rev'ed or load changes. A bad pump or bad filters/accumulators/dampers in the fuel system, the pressure will surge up and down. I had an EFI motor that seemed to run ok, but the fuel pressure gauge needle was blur moving up and down +/- 10PSI from the spec pressure. The fuel pump failed a year later, after putting the new pump in, the fuel pressure needle was steady as a rock at the spec 55PSI, and didn't move with rev'ing or load changes; and like your friends truck, the engine ran much better.
 

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And to address the overheating issue, these pumps rely on the fuel around them to cool them slightly. So don't consistently run the fuel lower than about 1/4 tank. People who run the tank to 1/8 or below all the time are more likely to have fuel pump failures. I tank up at 1/4 full routinely, to extend pump life.
 

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But, I think for most vehicles after 2000, they switched to a built in reservoir for the fuel pump. So instead of the fuel pump being mounted in the tank, there is this drum like unit you insert into the opening, the drum is the reservoir with the pump inside it. So as long as you have enough gas that you're not sucking air, the fuel will be sucked up and fill the reservoir that will keep fuel around the pump to cool it.

I think the idea is less chance of running out of fuel/sucking air on a hill or slosh from acceleration/deceleration when the tank is nearly empty. Maybe it just makes the fuel pump motor more reliable by keeping it cooled?

Keeping the tank closer to full is good idea, less problems with condensation, contamination and fumes, etc...

But I think newer vehicles with the built in reservoir negates any heat problems for the fuel pump, regardless if the tank if full or nearly empty, a little drum that is full of fuel is always around the fuel pump until the tank runs completely bone dry.

And Bob did NOT say this, just no one confuses it, a motor going bad can run and not run intermittently because as its failing it can overheat and that causes it to die, not poor cooling, once it does cool down it might run again until it overheats again from its own internal breakdown. But keeping the motor cool will help it live longer, that was what Bob was getting at. If your late model car has a built in reservoir type unit for the fuel pump, I speculate tank level won't make a difference in keeping the fuel pump cool, unless you're habitually running the tank to bone dry and getting stranded running out of gas.
 

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Rick - regarding failing fuel pumps I've never been lucky enough to have them continue working after banging on the tank or letting it cool down. In my experience once the fuel pump quit it was kaput. And usually I don't get any warning. One minute it was working and the next it wasn't.
 

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That is the experience of most, yet I read more than a few posts of an engine dying and restarting 20 minutes later, it becoming more and more frequent, and the owner finally narrows it down to the fuel pump. Anecdotal, but it seems to happen enough, its a possibility. A bad Crank Position Sensor seems to often fail with these same symptoms as well.

My experience, one of my vehicles, it just didn't start one day, finally narrowed it down to the fuel pump. It ran fine all the way up to the end, and lucky for me, didn't quit while driving, it died in its sleep and never awoke the next morning when trying to start the car.

Another, the pressure check showed the pressure surged up and down rapidly above below spec pressure, but the motor seem to run fine, so I thought nothing of it and it ran fine for more than year with the pressure like that. Then one day the engine started to surge or loose power, from time to time, over a week or two, it got worse and was harder to start. Then one day the motor died when I came to a stop, I could barely get it restarted, and it barely idled when it did restart, just to quit again. I get it towed home, check the fuel pressure and it was at 10PSI, install a new fuel pump, and it ran better than every. And the new pump, the fuel pressure check showed the needle dead steady at spec pressure, no surging up and down, so that pump had some sort of problem and took years to finally die.
 
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The fuel pump in my '06 Ram 1500 failed about a mile from the house on a Saturday about 6 months ago. No warning. As it died I was able to coast into a Wa Wa convenience store. I tried banging on the tank, but that didn't make a difference. Another Dodge truck owner was nice enough to tow me back to the house. Not fun with no power steering and no power brakes.

I suspected the fuel pump and to confirm it I removed the intake hose from the air cleaner and sprayed a liberal amount of carb cleaner in and then tried to start. It stumbled so that confirmed the ignition was working and pointed to the fuel pump.

Monday I had it towed (insurance covered it) to a local shop 2 miles away. He installed a Carter fuel pump (took a day to get it since no one in the region carries them. Had my truck back by Wednesday. The charge wasn't too bad - ~$480 parts & labor. Firestone wanted nearly $600 and the dealer was outrageous at $800. Firestone would have installed an Airtex brand pump (reputation not so stellar) or for $400 more (for a grand total of $1,000) they'd get a Bosch.

I checked all the local parts stores and all of them had Airtex as the preferred brand. None had Carter.

The only other vehicle that the fuel pump failed was my '92 Acclaim. I was driving home from work through southern MD on US 301. Just passed the turn for Budd's Creek it just died - about 3.5 miles from the bridge. I was able to confirm the timing belt was good since a failed timing belt would exhibit the same no start conditions. If memory serves I had just replaced the timing belt. Had it towed to the same shop - $391 later I had a new pump. This was back in the late 90's. Car had about 145K miles.
 

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Discussion Starter · #18 ·
It was my fault, the pump was working very weak. That should of been enough for me to just change it out. But after it ran fine for 20 mins, I started thinking of bad sensors. Like I said, I have a few spare 5.7s laying around. I just canblized the crank and cam sensors. Which I'm sure are good. I'll just stick them back in the 5.7 I robbed them from.
I just want to tank everybody for the input. Fast and on point. Bravo.....
 

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Discussion Starter · #19 ·
One morning my Wife tells me her 13 pickup has some lights on the dash. So we take it to the dealer. I get a call a few hours later. Mr. Snelling, it looks like some rodents ate some wires under the cab of your truck. 300$ bill to repair the wires. Which wasn't that bad. It had a few more things that need the dealer's attention. I tell the service manager I know the two rodents that ate the wires. Two Bluetick **** Hounds, Pepper and Cookie. That's the second time I've had pups chew on wires under one of my trucks. LoL
 

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Discussion Starter · #20 ·
This repair took three days of chasing causes. I should have known it was the pump from the weak stream of fuel it was putting out. I spent 270$ on parts. Pump was 180$. Trans filter and oil. And just a few things to clean the truck up.
I rebuilt the 9.25 rear gear alittle over a year ago. It spun the front pinion bearing. I had to hunt down an oversized bearing. And have it machined. Put the crush sleeve delete in it. Seems these crush sleeves cause enough problems on their own. But the owner doesn't work on his truck till it breaks. And he's in a spot. So I bought him a trans filter and oil. I didn't change it. Just gave him the parts. 140k miles, rebuilt rear gear and never changed the trans filter.
 
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