before i start dismanteling i just purchased a 95 6.5 dually with a complete jasper engine.
the engine has about 32k miles according to all the paperwork that came with the truck and per previous owner. i purchased truck in nc and had about a four hr ride to get to sc. any ways truck fired right up and it was about 30 deg that day. it had just under 60 psi cold. i drove it about a mile for test drive and seemed fine. on the way home oil pressur dropped to about 20 psi on hwy cruising. at a dead stop ideling it drops to 10 psi.
oil looks to be really fresh with no shavings. not black like they get in diesels after even a few weeks.
i am leaning towards pump. or could the pressure gage be bad and do this. there does not seem to be any knocking and i dont think bearings would act like this?? of course the jasper warrenty is out.

 

check gauge and sending unit and hook up a manual gauge and check real pressure. is the lift pump running because if the sending unit goes out on a 95 the lift pump wont work anymore

 

is there two oil sending units? on my 92 it went bad and was very hard to start but once it staeted the oil pressure gage read normal about 45 psi on that truck. the oil pressure switch was the problem there

 

no i just said the wrong word. i meant oil pressure switch.

 

hi we have been having trouble with a 6.5,we know the switch is malfunctionining and cutting the feed to the primary fuel pump,does anybody know which 2 wires of the 3 to cross to get the thing running while i wait for a new sender unit?? (i live in uk and it takes a while),,thanks in anticipation Tim

 

1st. don't do this unless your really, really , really, REALLY sure that you HAVE oil pressure.

locate the sending unit relay. use a wire to jump it from an accesory feed to the output of the relay. if you don't jump it from the accessory feed (thats a 12v feed thats only active with the key in the on position.) it will never turn off.

sending unit relay is in the relay box under the hood. it's labeled fuel pump i think.


if you do. that the sender will work like a charm. but if for some reason oil pressure drops to far down say goodby to about $10000 for a new motor.

 

hi thanks for that,ive found the oil presure sender unit in the block,,it has 3 wires going into it,i,m presuming 1 will feed the oil pressure gauge on dash,the other 2 bang together when the pressure builds and make contact inside the unit,which then gives signal to pump/via the relay,Ive checked with 1st position on ignition,that the pump works for about 4 seconds ,then switches off,this is the prime position,which is correct,when cranking the pump is still ticking,after a short while when the engine fires and runs,the pump(primary) stops working(presumably because the sender unit has failed)this is intermittent, and the main pump still draws fuel until the filter bowl runs dry,when she stops.if i undo the filter housing bleed ther is a vacuum ,as if a blocked fuel line,if i then switch ignition to on,fule pump ticks and send fuel up for a few seconds and switches off,if i do this 2 or 3 times to prime system,she starts again,then the electric fuel pump switches off,and she agin stops due to no fuel,I was intending just by passing system until i can get a new sender unit,,I really dont want to be junking a super sweet 6.5,,this is the only problem ive had with her,ive replaced PMD,and have realised nothing has changed,,its the OPS which is giving head aches,,I thought crossing the wires ,or opening the OPS unit up and joining the 2 contacts would give the same result,(subject to good oilpressure)?? thanks for your help,,any info much,much needed,,Thanks Tim

 

heres the diagrams from my 1999 6.5td

 

Many Thanks Sir,I have put a jumper wire on to the fuel pump today,which has cured 90% of the problems i have been having,we now have a constant fuel feed,I have an obd2 reader coming in the morning,so I can start to pinpoint faults,truck feels strong again,but seems to have an on/off as if the fuel solenoid on injection pump is being switched on and off,then clears ,then starts doing it again.Until I get a clearer picture with the code reader,I,m waiting,but I suspect either the fuel shut off solenoid is suspect,or whatever feeds it or controls it is suspect,I have found several suppliers in Uk who have most parts in stock,so code read,and take it from there.Many thanks for your help,,the wire diagram is great,Regards Tim