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Multiple LP failures now hard starting when hot


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Last November my original LP and IP failed. Both were replaced at the same time.  The LP was a Napa stock replacement.  It failed when I got home from a 900 mile trip. I took it to a shop and they diagnosed the LP failed.  When I got it back with a new LP and pressure gauge, the LP failed after 2 weeks.  I took it back to the same shop, it's under Napa's warranty, they replaced the LP again.  Got it back, 2 weeks later the LP failed.  Being fed up with the Napa LP dying, I researched online on aftermarket pumps.  I settled on the FASS 95gph mounted close to the fuel tank.  Got it started and running great.  This past weekend, I drove it to pick up a heavy load of wood, the weather was warm but not hot.  After I loaded the wood I tried starting it, it took a longer crank than usual, but it did start.  When I got home I tried it about an hour later, same thing, longer crank time than usual.  I have another long trip in a couple of weeks and don't want to be stranded.  Is it possible that the IP is going out or that the LP has too much fuel pressure for the IP?  I have the add a fuse connected in the cab of the truck to fuse 9.

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I would look over the fuel system from one end to other and see if you leak some where too. A leak will let air into the fuel system and can cause partial loss of prime and cause hard starts. Watch your fp gauge the next time it hard starts and see what pressure your getting. It should bounce alot but stay in the 7 to 12 psi range.

I would definitely do some more trouble shooting before throwing an $1100 part at it and hope it works. Just so you know there are only a few re builders of the VP44 and many, many sellers as NAPA is just one seller. How much does NAPA get for one?

Edited by JAG1
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It starts fine when cold.  They rebuilt the original VP44 pump that came on the truck. It's not a Napa part.  Napa VP44 pumps start at $1750 not including core.  When I start the FP is around 14psi then build up to around 16.  I'll see if I have the issue again this weekend, we will be hitting around 100 degrees here in CA.  

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21 minutes ago, dripley said:

How much does NAPA get for one?

 

Screenshot from 2020-08-14 14-59-22.png

 

I just sold a DAP VP44 injection pump for $1,100 here in the valley plus the labor. Nice to have my vendors @dieselautopower and my sale tax permit I get these pumps at cost and make a bit of profit. I can't tell you my price because I'd have to kill ya when you hear my price. :gun:

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Posted (edited)

 

This weekend I got it up to normal temp.  I tried starting it after about 5  to 10 minutes.  it started as normal.  I waited for 30 minutes or so, and tried again. Cranking was longer to start.  I tried running cool water over the VP for a few minutes, still longer cranking time. I removed the fuse to the FASS fuel pump.  It started as normal. I put the fuse back in, longer crank time.  I waited for about an hour to try again. Longer crank time if I waited for the Please Wait light to go out. I tried cranking without waiting, it started as normal.  How can I rectify the long crank time when hot?  I've seen wiring diagrams on adding another relay to delay the LP from starting while cranking.  I'm not really mechanically inclined or electrically inclined either.  Does someone have a step by step with diagrams on how to do this?  I have a friend who is a mechanic and does know a little about wiring that can help me.

Edited by DoggyDiner
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Do you know how your lift pump is wired? Sounds like too much pressure like Mike mentioned since it starts fine with the pump disconnected and hot. Do you have a fp gauge?

Edited by JAG1
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Yes i wired the FP myself.  I went by the FASS instructions.  wired it to the pump, battery and to the fuse box in the cab.  The pump comes on when i turn the key to run.  The fuel pressure is around 15psi or so.

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Cant figure why FASS and apprently AD both got away from the wiring harnes with relay that is controlled by the oe fuel pump pigtail other than to save themselves money. Using a relay controled by the ECM reduces fuel pressure during cranking for this very reason. The older FASS and AD's used to come with a wiring harness and relay.  The oe pigtail connected to the harness so the ECM was still in control. Then power for the pump would come from another B+ source. 

You could wire in a switch to the pump to turn off during starting or @IBMobile has an article on making your own harness that would use the oe fuel pump connection for control. I cant link it o. This tablet so maybe he will pop in and help. I am good enough with wiring to burn your truck down to the frame.

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I wish FASS had kept the wiring for the OE fuel pump to make things a lot easier.  If someone could detail how to wire the FASS to the oe fuel pump pigtail, that would be great.  I don't like the idea of a switch, because my wife drives it and she could forget to flip the switch to turn the pump back on. I'm a "dummy" when it comes to wiring myself.

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You need to have your mechanic friend remove the add a fuse and wire from the relay at fuse #9 in the cab; then connect it to the yellow/white wire that was used to power the other fuel pumps you had on the truck.  This will put the fuel pump control back to the ECM.   

 

  

 

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2 hours ago, IBMobile said:

You need to have your mechanic friend remove the add a fuse and wire from the relay at fuse #9 in the cab; then connect it to the yellow/white wire that was used to power the other fuel pumps you had on the truck.  This will put the fuel pump control back to the ECM.   

 

  

 

I believe he needs this whole set up. As I understand @DoggyDiner is just wired to a key on hot with no relay. Key on pump on. That is correct is it mot Mr DD?

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Look at it this way the the ECM should control the lift pump for safety. If your in a accident with a key hot pump then the pump will not know to shut down because the engine has died (impact damage) which now could have a fire up front after batteries or electric shorts. The lift pump will continue to feed the fire will you burn alive in the cab possibly. 

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21 hours ago, DoggyDiner said:

The FASS has an inline fuse and a relay before the wire to the fuse box and FASS fuel pump

I missed the part you have relay. I lost it in the translation somehow. What IBMobile says above is what you need to do. That will take it off of a key on hot that runs the pump constantly and put the ECM in charge. Sorry for any confusion I caused.

Edited by JAG1
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Posted (edited)

Everyone explains it very well and has their LP wired like it's supposed to be for safety and easy fast starts. Only thing I can add is that the relay is controlled by the ECM, but the power comes directly from the Batteries. If you let the ECM (power) the LP, like the factory harness, you risk frying the ECM when you get a LP failure due to possible electrical overload. Relay allows power from the batteries, but the ECM can still control how much power, for lower starting pressure and when to give full connection for full fuel pressure or shut down when in an accident.

Edited by JAG1
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59 minutes ago, DoggyDiner said:

OK,

 

so now i'm confused. should I not connect the wire I have run to the fuse in the cab to the yellow and white wire on the old LP pigtail?

 

  1. Disconnect wire in cab from fuse in cab.
  2. Remove wire from cab.
  3. Attach wire, that you have removed from cab, to the yellow and white wire on the old LP pigtail.
  4. You're done; go have a drink.
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