03 CR hard starting

[tgee43]

Ruled all out as to why it was hard to start, ran great once running. Spent the money and put injectors in it. Starts right up, still runs great. What was wrong with the injectors?

 

[cerberusiam]

The injectors have fuel return circuits that cool the solenoid. Its a constant return that is orficed to return a set amont of fuel based on duty cycle. Constant exposure to high pressure liquids eventually will eventually erode the toughest metals. Add to that solids in the fuel greater than 3 micron and the wear accelerates. Filtration, filtration, filtration, its not a gimmick. Solids not only cause scarring problems in close tolerance moving parts they also accelerate wear thru any orfice or port in the system.

The other issue you run into are the cross over tubes. Constant heat cyles cause expansion and contraction in the tube. That tube is seated on a beveled edge into the injector. Enough expansion and it wears a groove into the tube that does not close until it warms. A couple thousandths will cause enough leakage cold to drop rail pressure on startup.

The starter only spins the engine at about 200 rpms. Enough fuel bypassing in the injectors and\or cross over tubes and rail pressure cannot build high enough fast enough to start normally. You get long cranks and cold start problems. When the wear gets excessive you get no start cold. All expansion\contraction does not happen evenly either. Depending on the make up of metal in the tube and radial exposure to heat sources the expansion\contraction will vary around the diameter and it warps. Same problem then as the tube does not seat square in the inejector bevel and leakage occurs. The kicker is it may be the tubes and not neccessarily the injectors causing the problem but it is almost impossible to diagnose without changing parts. The injector return and tube leakage is in the same gallery so high return flow can have multiple sources.

Nature of a high pressure fluid handling system. They simply take more care and feeding when running at 15-20k instead of 3-5k of pressure, these HPCR systems are even worse because they are kinda cheap. Nothing new in concept, just application in the diesel automotive world.

 

[BIGNASTY]

Cerb
I have wonder about that on my truck I KNOW with the amount of filters that is not a problem. But often wondered about the return to tank line I have the AD100 and im Stock HP could the return line NOT be enough and cause a problem with back pressure not being able to return the greater amount of fuel that the stock lift pump COULD NEVER HAVE PUT OUT.

 

[cerberusiam]

For all intents and purposes the gear rotor pump on the CP-3 will limit how much fuel is available for return from the pump. Your not going to push any more than what the pump will flow at a given rpm past it. There is a limit to what it will flow at max and the return line should be sized to handle that flow. The return from the pump is orficed also so going from 8-9 psi like stock to even 25-30 psi should not increase the flow enough to matter. It will just insure the cooling\lube circuit is running at maximum all the time which is a good thing. The AD or FASS are both regulated so excess is returned from there to the tank so it never sees the pump return circuit.

 

[tgee43]

Thanks, cerbersusiam, that was a good explaination of what was going on. I am an old school diesel mechanic. Common rails tend to trip me up a little