Hard start after sitting

[mopartechnician]

Cut the red wire of the raptor wiring that runs to the stock lift pump connector

http://www.cumminsforum.com/forum/98-5-02-performance-parts-discussion/619526-fass-keeps-running-after-priming.html

Edited June 30, 2014 by mopartechnician

[mulcher812]

So there should be 4 wires on the relay.

Ground

Power from the battery

Power to the pump

Power from the wiper fuse

[dave110]

First of all I want to thank everyone for their replies. Mopertech, I never would have thought my problem was a too much LP pressure while cranking but that was exactly what it was. Thanks to LIVE OAK for confirming this from Blue Chip’s page…..

HARD START COLD, LONG CRANK TIMES, AND INSTANTLY RUNS SMOOTHLY

This is typically due to a cracked or broken diaphragm inside the Injection Pump. To test for this try disconnecting the electrical power from the Lift Pump BEFORE turning the key on, and see if it starts better. This happens because the electric lift pump pushes air which is always in the fuel chamber inside the VP44 pump, through the crack or break in the diaphragm, into the mechanical high pressure pump and it becomes air-bound until it rotates enough times to bleed out the air. If it starts better without an electric Lift Pump, it is because the electric Lift Pump hasn’t forced air into the mechanical high pressure pump through the crack or break in the diaphragm, which is what separates the fuel chamber from the high pressure pump. This failure requires a VP44 replacement to fix the problem.

This was my symptom EXACTLY. I tried starting the truck after sitting over night and it would not start. Pulled the fuse for the Raptor and it started instantly. It’s hard to deny Chip Fishers claim about this with all of the VP44’s he must have torn apart. It’s also hard to dispute Mike’s finding…. No diaphragm in the pump he disassembled. So if there is no diaphragm, what is it then that causes these pumps to suddenly not start when the LP is running? I never had this problem before with the 2 VP’s that I’ve had on this truck so something changed to give me this problem, and it changed pretty quickly too. Like the diaphragm had a little crack and gave me long cranks and the crack kept getting bigger until it would not start at all until the LP was disabled. I can’t help but think this fix is nothing but a Bandaid, I did not fix the problem and I would like to know what the cause is. For those of you who did this how long have you been running this way?  I’m not sure I trust my truck now but at the same time I hate to drop $1000 plus into a VP if I don’t have to.

One more thing. I did not like the way the LP was wired to the wiper fuse in the schematic for 2 reasons. 1) In an accident the LP would run until the key was turned off. 2) In the winter when the heater grid is activated the LP would be running at the same time for 25sec. or so before even trying to start. That’s a lot of draw on the batteries before the key is even turned to start. So I put a relay in the feed wire that goes from the battery to the original relay and triggered it off of the wiper fuse. That way the ECM still controls my LP, it will turn off when the engine quits, but it is still disabled during cranking.

Sorry for the long post but I hope this will help someone else and look forward to hearing what the real problem may be.

[mopartechnician]

Ive had brand new vps do it.

[dave110]

Good to know. Worry's me though why mine did not do it and then all of a sudden it does

[mopartechnician]

Thats the thing, these all happened months later. I dont understand it, I know its probably a band-aid fix but it has worked for almost a year on the one pickup I did it on

[Mopar1973Man]

Well, on Friday it started like normal after sitting overnight so I thought I fixed it. On Saturday I had another long crank with a puff of white smoke so I guess I didn't fix. I'm thinking a cracked diaphragm from reading Blue Chips diagnostic page but I've also read there is no such thing as a diaphragm so now I'm confused. Is there a diaphragm in the VP 44 or not? I guess my next step is to disable the LP during startup but again I'm confused because I've read that is only during a HOT hard start and I have a COLD hard start problem. HOT starts are normal. After that I'll check injector tube O-Rings. Would I be able to see if they are leaking by pulling the valve cover? I'm not getting any fuel in the oil that I can tell.

 

Correct there isn't any diaphragm.

 

This is a harden steel plate with a plastic back to hold the o-ring. The days of diaphragms are long gone.

[dave110]

So instead of the diaphragm cracking would you say the O-Ring is leaking or the plastic back has cracked? Would this shorten the lofe of the pump?

[Mopar1973Man]

Neither will happen. Plastic is most likely never going to break being its backed up with harden steel metal disc molded to it. O-rings typically would last a very long time before failure being it never moves. So the whole cracked diaphragm is all a Internet myth now.

 

Here is all the guts... Mine you all parts are harden steel.

 

Here is the rotor unit.

 

[mopartechnician]

I could see the o-ring going bad, have seen many connector tube o-rings crack or flatten and they dont move

[Mopar1973Man]

Yeah that true... But few different things there is much much more heat in the cylinder head and the backing plate of the rotor is much much tighter fit than cross over tube. Hard to see it but the plastic lip comes all the way around the outside filling the void. It just the whole cracked diaphragm is out of date for the most part.

 

What I've found on the hard starting is excessive cranking pressure. The lift pump should be modulated at 7-12 PSI during cranking. If greater than about 14-15 PSI hard starting occurs because of excessive advanced timing. This why the stock lift pump is modulated 50% duty cycle to reduce lift pump pressure during starting. Problem is most people get carried away with running pressure that they create the starting issue.

[dave110]

 

 

. The lift pump should be modulated at 7-12 PSI during cranking.

 

How is this done?

[MnTom]

Dave, the stock ECM cuts the power to the lift pump. A lot of guys will wire their lift pump into the power window circuit so that when the key is in the start position the power is shut off to the lift pump.

[dave110]

Well, so far so good since I wired relay to wiper fuse. Still wondering though how this all of a sudden starts to happen after 2+ years with this VP. If it's a fuel pressure causing timing advance issue I would think it would have done it from the start cause I'm running the same 20psi now as then. It wonders me how the ecm can cut pressure with no regulator but maybe it's not doing what it used to? Something changed and that's what bugs me..... I'd like to fix it right.

[Mopar1973Man]

ECM uses a modulated signal that is a 50% duty cycle. So the ECM during cranking is going OFF - ON - OFF -ON in a rapid pulse. Cranking pressure should be 7-12 PSI optimally. So you need a mechanical gauge to see the pulse because most electric gauges or digital gauges filter the pulse so you don't see it or don't function during cranking.

[dave110]

Thanks. Good to know how that works. Maybe mine quit doing it's job causing my sudden hard start issue.