24 valve rough idle and hard to start hot or cold

[rth0006]

Hey guys,I'm new on here but I have a question that I haven't been able to find a good answer for. When I first crank my truck it is hard to start whether hot or cold. When it does crank it idles fine. After driving maybe 5-10 miles and stopping at a red light the idle becomes real choppy. If I shut it off, it will fire up normally and idle just fine, but 5-10 miles down the road the same thing happens again. I have a fuel pressure gauge and for some reason when I was pulling a load it jumped around and then stuck maxed out. Every now and then it will jump around but I never get a normal reading like I did when I first put it on. I do not have a snubber or needle valve on it, so that is probably the problem as far as the gauge goes. Any suggestions? BTW, the injection and lift pump was replaced in march of 2010.Thanks for your time,Ryan

[Mopar1973Man]

As for the fuel pressure gauge sounds like the sender is damaged from water hammer pulses... Did you install a needle valve and set it properly? As for the choppy idle could you hook up a OBDII scan tool and read the error codes? But if there is no error codes you might have to pop test the injectors it might have a damaged pintle needle and sticking some after it gets warmed up. But a pop test would most likely show this too...

[rth0006]

I did not install a needle valve, a mistake that I realized a couple of months ago. Can I pick one up at lowes or home depot? and how do I set it properly? As for a pop test I've never heard of that? I haven't hooked it up to a OBDII scan tool. There isn't a check engine light on, but I know that there are "silent codes." Can advance do this for me? or another parts store? Thanks in advance,Ryan

[Mopar1973Man]

Well I got you cover then... Go to NAPA and get a WH6820 it cost about $8 bucks... Needle Valve Adjustment

 

 

As for pop testing. (Basic)

http-~~-//www.youtube.com/watch?v=7jXX_rGqgGo

 

Edited February 11, 2022 by Mopar1973Man

[rth0006]

Well, I got my fuel pressure gauge squared away, and I'm running 9-10 psi WOT. However, the truck still has a rough idle after running for a few miles. If it's parked with uphill, the system has to be reprimed. If its parked level or downhill, it will start everytime. The rough idle will go away if the A/C kicks on or if you shut it off and turn it back on. It shouldn't be the VP44 (it and the lift pump were replaced March '10.) I've read that its most likely an air leak in the return fuel line, but I can't figure out where it's coming from. Please help, this is driving me NUTS!!! :banghead:

[Mopar1973Man]

Return line shouldn't cause problems... It would be a suction lines from the tank to the pump more than likely... Those line rarely ever leak outward but seen to suck air in and drain the prime easy. Then while running they suck more air reducing the fuel pressure.

[rth0006]

So how would you go about seeing if this is the problem? Just replace them?Thanks in advance,Ryan

[pepsi71ocean]

the first thing is you say 9-10psi at WOT, is that towing or is that sitting and free reving?also are you gaining oil? did you tighten down the T fitting on the back of the motor? it seems however your eratic idle is computer based i would think. also what fuel pump did you put in when you replaced everything, is it a OEM pump or is it aftermarket ie fass airdog or raptor?

[Mopar1973Man]

So how would you go about seeing if this is the problem? Just replace them? Thanks in advance, Ryan

Well the only way I found was to pressurize the fuel tank and check all the fittings to see if they are wet.

[MnTom]

If it's parked with uphill, the system has to be reprimed. If its parked level or downhill, it will start everytime.

Classic symptoms of the rubber lines that go from the cab to the engine. 12 valve engines have the same problem. 12" of 5/16" and 12" of 1/4" diesel rated fuel hose is all that is needed. Just don't forget the clamps!

[pepsi71ocean]

Classic symptoms of the rubber lines that go from the cab to the engine. 12 valve engines have the same problem. 12" of 5/16" and 12" of 1/4" diesel rated fuel hose is all that is needed. Just don't forget the clamps!

it is also a sign of a shot front end on the VP-44, my current one developed a temperature sensitive leak that would cause hard starting up hill or on level ground when cold, but if i plugged in the truck she would start up hill. once the weather broke i stopped gaining oil, however the Vp-44 didn't like it

[rth0006]

9-10 psi when driving, and as far as gaining oil, I don't know what you're talking about. I have normal levels of oil when I check it. I have not tightened the t on the back of the motor, and it was replaced all OEM. I don't believe it is the injection pump. It was replaced march of last year, and hasn't lost fuel pressure at any time. Everyone else has said its something to do with the rubber lines. I'll check those and let you all know.Thanks,Ryan

[pepsi71ocean]

9-10 psi when driving, and as far as gaining oil, I don't know what you're talking about. I have normal levels of oil when I check it. I have not tightened the t on the back of the motor, and it was replaced all OEM. I don't believe it is the injection pump. It was replaced march of last year, and hasn't lost fuel pressure at any time. Everyone else has said its something to do with the rubber lines. I'll check those and let you all know. Thanks, Ryan

gaining oil as in you have mixing of diesel fuel and oil. the only real way to tell is to do an oilo change and see the greenish tint coming out of the motor. (you can also check for dilution with a paper towel and your oil dipstick. since you said it was replaced.... my advice would then be to use baby powder and sprinkle it on on the fittings you will have it change color if it is attracting diesel fuel. When the "stealer ship" changed my return tube (when they replaced the Vp-44) they didn't tighten down on the return line enough, so here we are a few years later where the tube was loose as hell and even came off when i went to replace the check ball valve on the VP-44.

DANGER!

i wouldn't put t much faith in the "rubber lines" as they are not really rubber bur more like hard plastic, however with a stock lift pump putting out 9-10psi of fuel pressure i would advise you replace your lift pump soon. You can kill two birds with one stone this way.

I live on the rusty east coast and my fuel lines are fine, granted i would east stock lift pumps like there was no tomorrow because they were crap, and my truck when hauling would put a tremendous strain on them i can tell you that the drop from 15-12psi was quick, it hangs here for sa while then when the pump's bearings go your psi will drop pick, but by then it will be to late. Take my advice replace your pump now, and prevent a VP-44 failure, i have lived through many VP-44 replacements because of said OEM lift pump. My fass 95 has outlived both stock OEm pumps to date, if she died tomorrow i feel i got my money's worth:smart:

[rth0006]

Well this may make sense because I noticed the rough idle started after I delivered a load of hay. As far as lift pumps go, what would be a good replacement option? Raptor? Thanks again,Ryan

[pepsi71ocean]

Well this may make sense because I noticed the rough idle started after I delivered a load of hay. As far as lift pumps go, what would be a good replacement option? Raptor? Thanks again, Ryan

in my opinion it depends on what you do with the truck. as someone who hauls everything with this truck i went with a aftermarket FASS 95 pump. it has a pair of filters on it, and came with larger fuel lines. the fass is more expensive then the raptor but the fass is a upgrade from the raptor (which replaces your stock fuel pump, and uses the stock filter and pump. My fass system came with a wiring harness and replacement larger fuel lines and a draw straw. Once installed i have to report that i see 15-17psi non stop winter or summer. I have also added other goodies like a fuel heater, and used USCG fuel line to help keep the draw down to a minimum. Now you can do the same with a raptor, but you will need to buy a 1/2inch fuel line and all the needed parts and then your restrictions will still be the stock filter system. Since i town heavy i wanted a fuel pump (and thew harness and larger fuel lines) to help with high demand fueling. I have noticed that under heavy acceleration i can draw the fass down to 14-15psi hauling about 20,000lbs ratherwise she is as stable as a rock with anything under 10,000. Now before when i had the in tank pump conversion (suppose be better then block one) i was going from 13-14psi down to 10. If your at 10 empty i wonder what you were under load?

[rth0006]

Well, now the truck doesn't haul much of anything, but I used to haul hay, which was loads in the 15k range, not counting truck and trailer and it would draw down to about 8. I had a typo, the fuel pressure stays around 11-12 and 14-16 at idle.

[gassernomore]

Not to step on pepsi71ocean's remarks.But Raptor pumps come with all the extras if you buy it from a diesel shop(at least the sites i have looked at). When I've seen them on EBAY that is when it is just the pump.

[banzaitoyota]

I bought my Raptor 150 from Glacier Diesel Products. Thay have always treated me fairly

[rth0006]

Hey guys, thought I would let everyone know that I FINALLY fixed the problem. It was the injectors. Bought some new Bosch RV275s from diesel auto power threw em in and the problem went away. Just my .02 DO NOT buy injectors from Pensacola Fuel Injection. The ones I took out looked horrible and only had 70K on them. Ryan