• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Help me to find the problem!

valyidol

valyidol

Active Member
Messages
316
Reaction score
112
Location
Russia, Moscow
Hi!
My friend ask me about help. His truck 1995 6.5 diesel no running good. Sometimes it running very bad it seems as someone is holding it by the tail. Sometimes it running very good. Sometimes the engine is running at idle speed is unstable and may even stall. What is it? Words SOMETIMES is the worst!
 
Easy thing to check is fuel pressure at T-valve on front top center of engine. No pressure here means no lift pump fuction. With engine idling open this valve. You should see diesel fuel flowing from the exit. If no fuel and engine shuts off, check the lift pump and associated controls.

A plugged fuel tank screen can cause similar faults.

Your friends engine injection system is also electronically controlled with the infamous PMD module which can be quite contrary to diagnose.

More info about this truck would be nice, also.
 
Yes, I also think about the lift pump and about dirty fuel tank.
About this truck.One year ago I replaced the engine to this truck. PMD I put on the left of the engine cover on the radiator. But it's not the PMD. I tried to put another PMD but no changes.
Sorry, but I don't understand what is T-valve? My English is not so good. Where is T-valve?
 
T valve is the brass valve on the front passenger side of the engine. There should be a short rubber hose attached to it. This is the water drain valve for the fuel filter.

Sent from my Studio 5.0s using Tapatalk
 
You need to supply electricity to the lift pump with the engine off. hook up a fuel pressure gauge after the filter, and before the injector pump. Turn on power to the lift pump and read the pressure. Then get a reading with the engine running. This is to verify a bad lift pump, or loss of electricity to the lift pump (usually a bad oil pressure sending unit). Search the stickys here for ops mod.

By the description above your lift pump is bad, and when you opened the t valve with the engine running, it sucked in air causing cavitation of the injector pump. You need to bleed the air out of the injector lines at the injector nuts while cranking the engine to evacuate the air (known as bleeding the injectors). Repair the lift pump first, or you might have to bleed it again.
 
Will L. said:
You need to supply electricity to the lift pump with the engine off. hook up a fuel pressure gauge after the filter, and before the injector pump. Turn on power to the lift pump and read the pressure. Then get a reading with the engine running. This is to verify a bad lift pump, or loss of electricity to the lift pump (usually a bad oil pressure sending unit). Search the stickys here for ops mod.

By the description above your lift pump is bad, and when you opened the t valve with the engine running, it sucked in air causing cavitation of the injector pump. You need to bleed the air out of the injector lines at the injector nuts while cranking the engine to evacuate the air (known as bleeding the injectors). Repair the lift pump first, or you might have to bleed it again.
Click to expand...


I concur

Verify power to the lift pump.


A quick check, IIRC, Key in the start position will over ride the OPS and provide power to the lift pump. (Someone correct me!)
Pull the S wire from the starter to prevent it from cranking.
have someone turn the key to start and verify voltage at the lift pump. ( or that its running)

There are a couple quick and easy checks before heading off to buy a pump and / or an OPS.
No meter or test light? use a small fuse and and some wire wrapped around the ends. Stuff the wires in the pump power plug. Hit the Key, blown fuse, have voltage.
Or short the plug and check for a blown the fuse in the fuse block. (last resort)

Suspect the pump, but check for power first, to be sure.
 
Ok. I understand OPS is Oil Pressure sender/switch. Buy I don't understand which there is a connection between the fuel pump and OPS? Do I need to see an electrical diagram?
 
You must log in or register to reply here.
Back
Top