hard start - only on warm engine

sidebrake · **Posted:** Wed Aug 18, 2010 2:57 pm

I’m looking for some assistance from those who have dealt with air in fuel and similar problems. I have a hard start situation that, on the surface, looks like a classic air in fuel problem. I’ve read dozens of threads indicating the best resolution is either the new fuel head assembly or a lift pump. Unfortunately, my symptoms are slightly different and these may or may not apply. I don’t want to throw money at the issue, only to find out it won’t fix the problem. (There was another member on LOST with a similar issue and a lift pump did not help. http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=53207&hilit=battery) This will be a long read, but any advice on additional tests to perform or things to check before spending money will be greatly appreciated.

Issue: 2005 KJ CRD will not start or is very difficult to start only when engine is warm. Higher ambient air temperatures seem to exacerbate the problem, but it has occurred on cool nights as well.

A couple weeks back I replaced the fuel filter and removed the fuel heater relay. This seemed to cure the problem initially, but it has come back and steadily seems to be getting worse. I have also tried a number of fuel suppliers to determine if fuel contamination was an issue and it doesn’t seem to be.

When issue occurs/symptoms:

Engine is warm (does not have to be full operating temp), engine has been running for more than a couple of minutes, glow plug light does not come on (even for a split second), there is little to no fuel at the injectors or rail, there is air built up at the head which can be purged thru the bleed valve. No CELs, other than ORM. I do have the new fuel head and it does not appear to be leaking from the common location.

I can prime the fuel head and build up very good pressure, but a couple seconds of cranking leaves it soft again. Purging all the air from the head with the bleeder valve does not really help. Again, I can build up good pressure, but after a couple turns of the engine, its soft. I have successfully started it after 15 – 20 minutes of the “prime, crank, prime, crank” dance, but it’s not consistent. The only real way to get it to fire up every time is to let it sit for 3 or 4 hours and completely cool. I have also had success running the engine a very short amount of time (not allowing it to reach operating temp), shutting down, then restarting. This is the only way I’m able to stop to get fuel, actually.

Does not occur when the engine is completely cold (water temp gauge pegged at the bottom and glow plug light comes on for a second). It always starts perfectly for me first thing in the morning and it always starts when leaving work in the afternoon. No hesitation, no difficulty. I will also note that once started, it runs perfectly fine in all conditions… no loss power, no hesitation, etc…

In addition to the common air in fuel issues/solutions that have been discussed at length in this forum, I do have another theory that I’ll do a second post for below.

Any additional theories or tests I can perform before spending the money on a lift pump will be greatly appreciated.

Thanks

sidebrake · **Posted:** Wed Aug 18, 2010 3:01 pm

My father-in-law, who is a former diesel mechanic, believes the problem is with the Cascade Overflow Valve inside the Fuel Injection Pump. He thinks that, for whatever reason, it’s stuck in stage 3 after shutting down, simply pumping fuel back to the tank (instead of on to the high pressure pump). Potentially once the engine cools or sits for a long enough period, the valve closes back to stage 1, allowing starting. Unfortunately the FSM doesn’t really provide any testing procedures, and short of replacing the pump (which I imagine is very expensive) I don’t know how to verify or discredit this theory.

Cascade Overflow Valve, per FSM:

Quote:

Cascade Overflow Valve Instead of using an electric
supply pump, this fuel system uses a gear supply
pump located inside the rear of the high pressure
pump. The pump is driven by an eccentric on the end
of the high pressure pump shaft. The gear pump
draws fuel from the fuel tank through the fuel filter.
The pressurized outlet side of the gear pump provides
pressurized fuel to a branched circuit internal
to the high pressure pump flange, which supples
both the fuel quantity solenoid and the cascade overflow
valve. Because the gear pump increases fuel
flow and pressure as the engine rpm increases, the
pressure is regulated by the cascade overflow valve.
The cascade overflow valve and gear supply pump
are not serviced independently of the high pressure
pump.
The cascade overflow valve has two functions:
² Regulation of lubrication fuel to the internal
moving parts of the high pressure pump
² Regulation of the fuel pressure being supplied to
the fuel quantity solenoid
The cascade valve has a machined center piece
that has three drillings. One for overflow, one for
lubrication and one for supply. The valve works in
three stages based on the pressure entering the inlet
of the valve.
Stage 1 When the fuel pressure entering the tip of
the cascade valve is between 0 and 3 bar (44 psi), the
spring force is not overcome and fuel only flows
through the center drilling. This drilling always
allows fuel flow through to the pump center ring and
lubricates the pump bushings and internal moving
parts. This circuit also allows air to bleed during initial
cranking and returns the air to the fuel tank.
The cascade valve is only in stage one during cranking.
Stage 2 When the fuel entering the cascade valve
exceeds 3 bar (44 psi), but is less than 5 bar (73 psi),
the center piece of the valve moves against the
spring force aligning another passage for lubrication
purposes. Stage 2 can be reached during cranking
and initial start up.
Stage 3 When fuel pressure exceeds 5 bar (73 psi),
the center of the valve aligns with the overflow passage.
This stage relieves the pressure into an overflow
circuit that sends the fuel back to the inlet side
of the gear pump which limits maximum fuel pressure
to 5 bar (73 psi). Lubrication fuel also continues
to flow though the other ports during this stage.
Excess is sent back to the fuel tank through the
return circuit.
High Pressure Pumping Plungers The fuel quantity
solenoid supples three high pressure pumping
chambers. The pumping chambers have one way
inlet valves that allow fuel to flow into the chambers.
The valves then close during compression of the fuel
and cause the high pressure fuel to overcome a ball
and angled seat outlet valve.
All three pumping chambers are tied together in
one circuit internal to the pump and provide high
pressure fuel up to 1600 bar (23,000 psi) through a
steel line, to the fuel rail.
The pump is driven at 1 :1 engine speed and is not
responsible for injection timing. The pump is only
responsible for providing high pressure fuel while the
ECM controls the injection timing.

dkenny · **Posted:** Wed Aug 18, 2010 5:34 pm

can you install a vacuum pressure gauge in the fuel line feeding the CP3? YES it must be a vacuum pressure gauge.
I did some testing on my wifes jeep before it died..it would pull 20 inches of vacuum with no problems. hopefully you don't see this much vacuum.

do you know/ have a picture of where this cascade valve is located on the CP3?
I one sitting on my bench in a few major parts. I haven't tried to get at the 3 pistons that make up the pump. I have removed the gear pump and some other parts. I'm asking because this pump was the cause of my wife's jeep no start problem. this valve might be cause. the code that I read before it died was P0093.

-dkenny

hard start - only on warm engine

Who is online