Engine/Transmission (1994 - 1998) Truck Vibrates Bad

[seagrave2001]

My buddy has a 1994 dodge 2500 diesel, w/ an auto transmission, everything stock except he has the silencer ring removed & the star wheel turned in for a little extra power. He has it turned to just where it barley smokes.



A few years ago one of his injection lines was leakingat the top of the pump, and the shop he took it to wanted to replace the injection pump. Well he didn't want to pay the money so they put a washer on one on the injection lines and ever since that the truck has a slight vibration at idle, but it gets a lot worse around 1000 rpm. Then above 1000 it stops...



A few months ago he replaced his fuel filter, and when he was manually priming the system, he heard a loud hissing noise. . Well he started his truck & the vibration was gone. But a Day or Two later it came back. Is there a piece of dirt in there or something else?



Thanks for the Help...

 

[Andy Redmond]

See below. .



>>>A few years ago one of his injection lines was leakingat the top of the pump, and the shop he took it to wanted to replace the injection pump. Well he didn't want to pay the money so they put a washer on one on the injection lines and ever since that the truck has a slight vibration at idle, but it gets a lot worse around 1000 rpm. Then above 1000 it stops...



Likely a sealing washer on the supply or the return. The vibration. . likely normal. Many p-pumps do this. Its likely just coming off the idle springs and transitioning the the next spring pack (governor operation) 900-1100 rpms.



>>A few months ago he replaced his fuel filter, and when he was manually priming the system, he heard a loud hissing noise. . Well he started his truck & the vibration was gone. But a Day or Two later it came back. Is there a piece of dirt in there or something else?



Hissing was likely the overflow valve bleeding off excess pressure after it was primed. Aeration in fuel or an air leak can cause roughness as well. Assure curb idle is at least 800 rpm, low idle causes roughness too. (0 then 500 then 750. . 3rd mark on the tach).



The fuel pickup can get a pin hole in the tank (tank module). Rubber supply line (3/8" id) can deteroriate. Return line (5/16" id) is notorious for splitting and allow prime loss and air entrainment. Both of these are more easily changed by removal of the starter and fuel filter.



Weak fuel transfer lift pump (leaky check valves), weak spring in the overflow valve (makes low fuel psi or allows an air entry point). S/B 20 psi after the filter at idle and 25-35 under load off idle rpms.



The fuel heater (mounts to ds of engine block alongside the transfer lift pump) has several gaskets on/around it which can allow for air entry and or fuel leakage.



Now go forth and verify!



On the injection pump and replacement, a really good fuel pump shop might make some adjustments/calibration efforts so that you don't see this complaint so much at your complaint rpm zone.



>>Thanks for the Help...



Your welcome a Cummins troubleshooting manual or the factory service manual will allow easy guides and pics. /illustrations to follow thru what was discussed.



Good luck

Andy

 

[seagrave2001]

Thanks Andy, I will pass this information on to him... I think his idle is around 500 or so... At least thats where I thought i saw it. . And I have been reading a lot about that rubber fuel line deteoriating and maybe its time to replace that short section...



Could there be air geting in and causing the engine to not fire right & vibrate, but not enough air for it too loose prime?

 

[Andy Redmond]

Yes, the idle s/b what we discussed with the vehicle in drive, a/c on, lights on etc.



Yes, it can get mucho air and maybe not lose prime. It will eventually leak fuel. Find some marine grade diesel rated hose if you can. I've also had better luck with fuel injection hose that meets the 30r9 specs. vs. 30r9 rubber fuel line. Get 2. 5 ft. of each (supply and return) and you'll have enough for a mis-cut or a spare set for a next time if any.



Its similiar to changing out the fuel filter, it can cough and sputter until the air is purged thru the injectors. I'm lazy and get tired of pumping on the transfer lift pump. I use the starter judicially (cooling periods) and a nut loosened slightly on an injector. Then once it pukes fuel and trys to fire, tighten the nut up.



Good luck and post your results if any of this helps, if not we'll back up and try again.



Andy