I posted about my issue here about 6 months ago and it has driven now up the wall! Nobody can tell me what's going on!

Truck:
2004
Dodge Ram 2500
Manual 6spd
4x4
Quad Cab
6.9TD
Stock with Edge Aptitude box.

Problem:
Engine cuts out at idle.

The truck runs great otherwise, pulls like a freight train without abnormal noise or smoke. However, when put it in neutral or idle it will sputter and die sometimes immediately, sometimes 20 minutes later. This often happens as I am rolling up to a red light which cuts out my brakes and steering – this makes for lots of fun in an 8000lbs vehicle that is often pulling a 5000lbs load! The thing that is really nutty is that I can leave the truck running in my driveway, it will go for half an hour then without cause just choke. Other times, I have problem getting it to idle for 10 seconds. The computer tries to save it and sometimes it is able to rev it up, but usually the problem happens so suddenly that neither the computer nor I are quick enough to add gas.

The problem does not seem to happen on immediate cold start-up. I assume that the computer is doing something different for a warm-up start, but I have had it happen within 2 minutes of a cold-start.

I can keep the problem from happening by lightly pressing the gas pedal and raising the RPM - it never happens out of idle. Likewise, if I hear it start to choke, I can rarely save it by flooring the gas pedal.

The problem has been coming and going for over a year now. Sometimes it will go away for a few weeks, other times the truck all but refuses to idle.

I thought that the issue was linked to moisture or sea level as the truck seemed to cure itself, or get better when I would leave my home in Seattle for higher and dryer Idaho, but I now think that it was a coincidence because it goes away in Seattle and started to happen in Idaho.

The worst part is that nobody can tell me where to even start looking! I took it to a dealer and another shop. They all began guessing at the problem and I got the impression that I will be paying them to randomly swap parts.

I have an OBD2 scanner and used it to monitor various sensors hoping to see something abnormal when the problem happens. Everything looks to be in spec.

I have tried various modes on my Edge box, I mostly keep it in Stock 0 mode - the other modes have the same problem. I am hesitant to cut the Edge box out of the system because I really doubt that it is the cause.

I ran a few cans of SeaFoam though the fuel to no avail.

I changed the air and fuel filters without any noticeable change whatsoever.

I don’t think that it’s an injector problem - the truck would run like crap all the time if they were clogged and I would not have the top end power that I have.

There is one idea that I have: I read somewhere that the lift pump in these trucks uses variable voltage - the voltage is lower at idle than at WOT. I have seen this on other cars. Given that the system recirculates anyway I have no idea why the hell car makers do this! It is possible that due to some minor wire corrosion the lower voltage current is not getting through as well as it should. It's possible that the pump is tired and although it works well at full voltage, it does not crank at reduced... I don’t know! The problem is that my truck seems to be a rare bird in that my lift pump IS NOT on the back of my fuel filter! I read that some of the 2004's were retrofitted with an in-tank pump (WHY!?) I have been unable to find any relays or fuses for this in-tank pump. I cannot find any documentation about the in-tank system - all of my books show that my pump should be on the fuel filter...

I’m going crazy here! Does anyone know if this truck really does do variable voltage on the pump? How can I check this? Where can I tap the pump circuit? Does anyone have any other ideas????

 

It only does it while in neutral right? Have you checked the neutral/clutch safety switch for shorts? Or mabey even a bad brake light wire shorting out if it only does it when the brakes are applied. If it only happens when you have a trailer hooked up, i would look at the trailer wiring/elec brakes. If it is something electrical, i would think there would be a voltage drop right before the truck goes wacky.

The LP on the fuel filter were prone to malfunction so they switched to a more reliable in-tank setup. Everything now is run by a computer setup, so there are very few fuses and relays. If you really think its the LP, then an aftermarket FASS or AirDog would be the way to go. To rule it out, you need to hook a fuel pressure guage up and monitor the pressure.

 

My truck is stick shift, so no neutral switch. It does it in gear or out - its RPM and load sencitive. Has nothing to do with brake lights. As I said sometime just leaving it running in the driveway, it will run for 5, 10, 15 minutes and just suddenly cut out for no reason.

 

do you have a fuel pressure gauge? if not get one...

also do you have a rail pressure gauge? again if not, get one...

if input pressure to the CP3 drops it can cause rail pressure to drop which means lift pump is failing...

if rail pressure drops but fuel pressure from lift pump stays the same, means either your CP3 is failing, or you have an injector issue.

 

If its a pressure issue, how does the truck run fine under load and had the problem at idle? Does this vehicle have a variable voltage lift pump??

 

yes. at idle and while starting the lift pump is given lower voltage to reduce pressure to the injection pump to aid in starting the engine. At least that is true on the 2nd gen 24v's and 12v's. not 100% sure on the common rail 24v's...seriously though check your fuel pressure and rail pressure. it sounds like a fuel delivery issue.

Diesel engines are very simple. piston goes down with intake valves open, air comes in, valves close, piston goes up and compresses the air, fuel is injected into the cylinder causing an explosion forcing the piston back down, exhaust valves open and piston goes up to clear the cylinder. exhaust exits and runs through the turbine side of the turbo causing it to turn. now the intake side is compressing air and helping force air under pressure into the cylinder....

the one and only thing controlling your throttle is the fuel. there is no air intake butterfly...your entire air intake is wide open 100% of the time (with the exception of the intake valves) there's no spark, no air fuel mixture, none of that. fuel is the ignition source. so either your ECU is having issues, an injector is cracked or sticking, rail pressure is dropping off, injection pump is failing, or input pressure to injection pump is not feeding it enough fuel.

 

The last thing I need or want is a bunch of gauges in my truck to troubleshoot a one-off problem. Does the truck have a built-in fuel pressure sensor? I read that it does, but my ODB2 scanner does not seem to have the function to read it. I also read that I need a special banjo bolt with a sensor port to get pressure out of it. Since the problem happens in idle, I would rather just use an under-hood pressure gauge version. But then again, it sounds like I need to find this banjo bolt...

Again, I doubt that the problem could be in the injector - if it were cracked, I would assume that higher pressures under load would make it run worse - the truck runs like a dream when out of idle.......

 

Update: By jacking the truck up and squezing my head between the rear tire and the wheel well, I was able to get at the fuel lift pump plug on top of the tank. I mesured voltage with the truck running. It gets full voltage at idle - not a variable system. Given that the pump keeps up with fuel demand under load, I think this clearly rules out the fuel lift pump as the culprit.

 

Did you get it fixed? My daughters truck is doing the same thing.

 

they will all have full voltage at idle...they will only have lower voltage when starting/not running to aid in starting.

even my airdog is effected by the PCM lowering the starting voltage.

I get 15psi while starting and soon as the truck is running pressure rises to 20psi.

having full voltage doesn't mean squat when it comes to fuel pressure output. you really need to hook up a couple pressure tester gauges and test both input and rail pressure. borrow a pressure tester from the auto parts store.

if you want your injectors tested for failure, take it to the dealer and tell them you want them to perform an injector kill test. that will tell you if it has a bad injector and tell you exactly which injector(s) is bad.