phal

Hello guys,

I recently replaced the stock lift pump with a Fass DDRP due to death of factory unit. The truck has always started like a champ, fires after a second or less of cranking.

Now I can go out in the morning to a cold truck and it starts perfect. Once it is warm though, you have to crank, shut off then crank again and it will start. Once started there is no loss of performance with the truck, it runs great with good acceleration and no missing at idle.

I have lost all confidence in the truck and am wondering if the loss of the lift pump damaged my VP.

When I replaced the LP, I had some bad banjo washers and the only ones I could find locally were thicker to the point that I could barely get them on. Could having a thicker washer cause me to pull air into the line?

I went through the fittings sunday and checked all for tightness and did the same for the injectors, no help. I changed the fuel filter at the time of the LP change

Any other things to look at such as the Crank Position Sensor?

Thanks...gary

MATTIEBOB

I Have Heard To Much Fuel Pressure Can Cause Hot Hard Start Issues. It Have Also Heard The Ect Sensor(by The Thermostat Housing) Can Cause The Same Thing

rebal

Your Vp44 was probably damaged from low fuel pressure, and that is a typical sign .to test it when it hot un plug the fass and see if it starts. If it starts shut it off fast . now you will need a hobbs oil pressure swithch that will turn the fass on after it builds oil pressure,it will plumb in to the oil port on the filter head and to your power wire for the fass.

PaulDaisy

Too much pressure during cranking.
I had the very same issue last summer when my Walbro was wired directly do the Run-Start circuit. I was tired of that and switched the LP power to the Run only circuit (fuse 7 or 2 on the cabin fuse panel). Problem solved, no hard starting this summer at any engine / outside temperature.
Of course you also have zero fuel pressure when cranking but this seems to cause no problem that I can see. Zero FP only lasts half a second before the engine starts and FP kicks in.

bent valves

The hard start problem when hot is why Cummins programmed the ECM to run the lift pump slower when the engine is cranking. This limited the lift pump fuel pressure to about 7 psi. Maybe the Cummins engineers knew that there may be a problem starting with full pressure. When the HO VP44 came out the ECM program was changed again to just bump the lift pump when the key was turned on. Older trucks with the SO VP44 ran the lift pump for a couple of seconds at full pressure then dropped pressure to about 7 when the engine is cranking.

If your truck has the HO VP44 take PaulDaisy’s advice and drop the pressure for a quick start. Even with the SO pump it is not a bad idea.

phal

So, it may not be the VP? Boy it will be a happy day if it is not.
Here is what I think you are saying:
The new lift pump may be supplying too much pressure for startup. If I unplug the Fass after the truck is hot and crank it and the truck starts immediately like it does when it is cold, then I need to wire the Fass into the run only circuit in the cab. Right?

Can you tell me how to find out if the VP is an HO?

thanks...gary

steven.m.coon

I had this problem as well except it was my vp44. The orings were cracked. When it was cold it would start because the orings in the vp44 would not be expanded but soon as you ran it they would get hot and expand so when you went to start it would suck a little air making it hard to start. Fix was getting a new pump.

1882

Mine does it with a brand new VP, my FP runs 21 psi

82shovel

After I switched the to Airtex lift pump, the truck would have a hard start if I had too much fuel pressure. (trying to immediatley start as sson as the lift pump was energized, I'd have 20psi of fuel pressure... after a couple seconds it drops down to zero, and starts no sweat)

So, I would wait a few moments before I put the key in the "start" position, and everything was fine.

Twice over the past 2 years I've had the same hot-start issues as the original poster. I ran 16oz of Power Service Diesel Fuel Supplement and both times it solved the problem. It could be something as simple as dirty injectors.

phal

I drove the truck for a half hour home from work today, then unplugged the fuel pump and it started right up. That was the first time since installing the Fass that it started correctly when hot.

You guys are great!

thanks...gary

madmax44

I have a fairly new IP and Airtex LP probably installed in the early spring of '09. And with the temps in the 90's and running around town shutting it down and restarting every once in a while it will crank for about 4 seconds before it turns over. I'm installing a fuel pressure gauge this week so I don't have any idea what's going on yet.

phal

[ QUOTE=PaulDaisy;2543948]Too much pressure during cranking.
I had the very same issue last summer when my Walbro was wired directly do the Run-Start circuit. I was tired of that and switched the LP power to the Run only circuit (fuse 7 or 2 on the cabin fuse panel). Problem solved, no hard starting this summer at any engine / outside temperature.
Of course you also have zero fuel pressure when cranking but this seems to cause no problem that I can see. Zero FP only lasts half a second before the engine starts and FP kicks in.[/QUOTE]

I have tried both of these fuses and I cannot get the truck to start. I cut the wire that was originally powering the pump and wired it to an "add a circuit" fuse block and took it directly to the cabin fuse box. I have tried 7 and 2 and neither will work.

The truck actually ran out of fuel when I tried fuse 2 first. Is this why it will not run now?

Is there another fuse I could try to make the pump run?

...thanks....gary

PaulDaisy

Mine is set up this way:
I have a Bosch 30-amp relay which coil side is powered by the original LP circuit. I mounted that relay under the hood. The power side of the relay is connected to fuse 2, goes to Walbro and returns to the ground. When I turn ignition On (run position), I see fuel pressure rise (to 18 psi in my case) and drop after 2 seconds. When I am cranking, the LP circuit will activate the relay but there is no power provided to it because fuse 2 is not powered while cranking. The engine starts basically w/o any fuel pressure. Once I release the key, the pump activates because there is now power on the relay main circuit.
P.S. If you ran it out of fuel you will need to bleed the fuel system before it will start again. Loosen the injector lines that you have access to and crank in s10-15 s intervals until you see fuel spray. Tighten the lines and crank again to start.

phal

The motor used in the DDRP must be run with the green lead to the power supply or it will run backwards.

I originally thought I had somehow reversed the polarity on this motor. polarity reversal can be done to certain styles of AC motors by touching positive lead to negative side of power then grounding other wire on case.

But no, they are just running the motor backwards in this application.

I finally swapped the wires and hooked green to fuse 7 via an "add a circuit" and it works great!

Thanks for all the help guys....gary