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1998.5 4X2 Dodge 2500
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Discussion Starter · #1 ·
Hi all, fighting a issue with my truck. 280k, 4X2 std trans completely stock original owner. About 4 months ago I was on a trip and about 3 hours onto the trip I felt a bucking at 70 MPH. pulled over and shut it down. Everything looked fine. Drove to the destination and picked up a boat. Started bucking real bad, thought I would be stuck there. Pulled into a Advance and changed the fuel filter in the parking lot. Drove 3.5 hours home pulling the boat no issue. Got home and cut the filter open, it was spotless inside so I knew it wasn't fixed. Fast forward to last weekend, again about 4 hours into my trip felt the bucking again. Pulled over to check and everything looked fine under the hood. Picked up a 8k lb boat and drove 5 hours home with no problem. Not sure what to do. VP was replaced about 2 years ago. Lift pump is one of those FRRP 150 Airdog pumps. APPS was also replaced. Injectors are original and ECM is original. No codes, no smoke. I hate to just throw parts at it since everything is hundreds of dollars. Seems as if when I cycle the key it goes away. But its so intermittent going to be tough to figure out. Any help greatly appreciated..
Tony
 

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I see that you have an AirDog FRRP pump. Was the VP44 replaced before or after the stock lift pump was replaced? Do you have a fuel pressure gauge? Is the bucking you're describing due to dead pedal?
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #3 ·
I replaced the lift pump with the injection pump when I did it. Doesn't feel like a dead pedal. I can accelerate fine, the more throttle the worse the bucking. I had a gauge in the filter housing for a year after the pump replacement. It never dropped below 15psi. I was thinking of driving with the gauge in till it acts up again. Now I'm scared to take it on any long trips. I have one of those cheap OBD2 apps on my phone and was watching the APPS voltage while it was bucking. Seemed smooth tho... I am thinking of just replacing the APPS:confused:
 

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Have you tried recalibrating the APPS?
 

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You may want to try that. Here is a link to APPS Reset.
 

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Had the fuel filter been replaced lately?
I had same issue once and that was it.
 
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I'm having a similar problem with my 08 3500. Will this help my year and a 6.7.
And what is APPS ?
 

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2003 Ram 2500 5.9L NV4500
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Do you think this could be a clutch issue
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #11 ·
APPS is the "Accelerator Pedal Position Sensor". I have replaced the filter, it was clean. And I also thought of the clutch. Its the original. Just doesn't make sense why I could cycle the key and its goes away..
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #12 ·
Hi all, yes, after two months I found the problem. Now I need to figure out why. So I installed a gauge in the filter housing two months ago to monitor the fuel pressure. When the bucking happens the fuel pressure will drop to zero or near zero. No codes, no smoke. Just bucks. Here's what puzzles me. If I stop and cycle the key just for a second the pressure returns to 15 PSI and the problem is gone. Now my fuel gauge in the dash has been wacked out for a while. Looking at the wiring diagram, the fuel level sensor is tied into the PCM and the fuel pump control module. I feel like its the transfer pump but any other ideas appreciated,,,, Thanks, Tony
 

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Hi all, yes, after two months I found the problem. Now I need to figure out why. So I installed a gauge in the filter housing two months ago to monitor the fuel pressure. When the bucking happens the fuel pressure will drop to zero or near zero. No codes, no smoke. Just bucks. Here's what puzzles me. If I stop and cycle the key just for a second the pressure returns to 15 PSI and the problem is gone. Now my fuel gauge in the dash has been wacked out for a while. Looking at the wiring diagram, the fuel level sensor is tied into the PCM and the fuel pump control module. I feel like its the transfer pump but any other ideas appreciated,,,, Thanks, Tony
Sounds like you are losing power to the lift pump. I believe you have a problem with the ECM. Quickly cycling the key and the lift pump starts running again seems to back that up.
 

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Does your wait to start light come on every time you turn the key to ON for at least a second? Does it start on the first cylinder hit every time you start it? Pull codes with a better scan tool. Sounds like you are having heat issues with the ECM or VP. Check fuel lines betwen teh lift pump adn tank for looseness or places it may be sucking air? Does it do it with a full tank? Does the tach ever drop out to near zero when it is acting up?
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #15 ·
All is normal on the dash as far as the wait to start light. Starts with a half of a crank no matter how cold it is. I had a air leak at the fuel heater but took care of that. Im using a snap on solaris. What controls the lift pump? Is it the PCM or the ECM? I dont think the pump is turning off completely but I could be wrong. The pressure goes to zero but will come up to 15 if you just let the truck idle. It will float around 8 to 10 psi. Then as I said with a cycle of the key its a solid 15. Shouldn't it be zero if the pump turns off?
 

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It is controlled by the ECM if stock. Yes it sounds like the lift pump is worn out not electrical. Electrical could be checked by hooking a voltmeter up to the hot wire on the lift pump and running the wire to it in the cab and monitoring while driving. If voltage drops off itis ECM or wiring, If pressure drops but voltage does not, it is in the lift pump.
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #17 ·
Im going to rig that up. Just what I was thinking... The problem is so intermittent it may be a while before it happens unless its getting worse. Thanks for the help, I will let you know.
T
 

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You can also monitor the apps same with the same set up by porbing pin/wire #3 on the apps plug. I tshould read about .5 volts at idleand smoothly graduate to 3.8v at WOT and hold fairly steady at any held throttle position.
 

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1998.5 4X2 Dodge 2500
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Discussion Starter · #19 ·
My son took the truck on a trip of about 2.5 hours. I rigged a LED on the power wire to the lift pump and the gauge he can read all the time in the cab. Hel be home Wednesday. Thanks for the help. I going to get to the bottom of this...... :geek:
 

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I do not know if that would show a minor voltage drop like a 5 dollar harbor voltmeter would. Does it have a fuel pressure gauge? Good luck on his trip.
 
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