derceg

Had hard start issue so I ordered a new $2000 pump. Didn't fix my problem. It still won't start when hot and pops off when cold. Now the weird part. I happened to open and close the water separator and it started. Duplicated it and again it starts. How weird is that. What's causing my issue. I replaced the valve thinking that was it and it wasn't. Literally can crank it for 30 seconds and it won't start. Walk out, open and close the water depart or valve and truck pops right off. Any ideas?

johnh

too much fuel pressure from your lift pump!!!!

derceg

I thought about that, but why all of a sudden. I've been running the same setup for 8 years. Factory lift pump in tank and fass up front. Pushing 30 psi at injection pump. We were going to pull the lift pump out, but the tank is full. Was hoping it was something else easier. Lol

johnh

pressure should be not more than 20 psi, http://www.cumminsforum.com/forum/98...-pressure.html

derceg

Even with the high pressure, why would it become an issue after 8 years

johnh

"Your starting problem is most likely because the fuel pressure during engine cranking is too high. This issue is more common than people realize after replacing the VP and fuel pump, and you'll generally hear bogus advice telling you somethings wrong too.

The reason its happening is because the VP fuel solenoid and timing ring lock up under higher fuel pressures during cranking as the VP heats up and the internal tolerances change.

The ECM regulates the pressure from the fuel pump by alternating power to the fuel pump while cranking the engine which effectively reduces those pressures, Even though its still receiving the alternating power, it will pump more pressure that the VP wants as the engine is starting. In saying that, the VP prefers zero fuel pressure while starting as long as the fuel system prime is retained.

Here's how to check if this is the cause of your hot starting problem..... pull out that single fuse for the lift pump and fass then try starting again. I'm betting a buck that it starts right up like normal.

Now, if it does then just be sure to IMMEDIATELY reinstall that fuse or shut the truck off so as to not run the engine for more than a couple seconds without fuel pressure. All you care about at this point is if this works or not.

johnh

KATOOM said
3)" Aftermarket fuel pump pressure to high. The stock lift pump is barely capable of supplying the needed fuel pressure so replacing it with something better is more common than not. Unfortunately though the higher volume/higher pressure fuel pumps place too much initial pressure on the VP fuel solenoid and timing ring while the engine is trying to start. The high pressure during that engine cranking will then cause those components to momentarily lock up until the pressure bleeds off, causing extra cranking. Again, this ONLY happens when the engine is at full operating temp AND if you have an aftermarket fuel pump.....and.....usually a re-manufactured VP in combination with that fuel pump. For whatever reason the factory VP's dont seem to be as affected and probably due to greater internal tolerances and wear."