New VP44 - Engine requires excessive cranking when hot

[Leaky88]

Hi,

Installed reman VP44 from DAP, no codes, no problems.  But engine now requires excessive cranking to start when hot.  It fires right off when hot.

Truck has FASS 150 that provides 20psi all day and I've always used a protected isolation relay between ECM and the FP.

In preparation for a trip last weekend, and with limited time, I modified my existing isolation relay by adding the NC relay and using the B+ from brown solenoid wire to hold FASS150 at bay during cranking. Moparman  has an article on it. 

No noticeable improvement was seen.

I switched to a FASS DDRP-02 I have as spare (circa 13psi) and truck fired right off.  Suspect problem is too much FP from FASS 150.

But I want to retain the FP 150 for the FP it provides to VP44. (The one I just replaced.)

I have read that one can change a spring in the 150 to reduce FP.  Again, I like the 20psi for the VP44 and would rather not dink with the FASS 150.

Since the FASS runs for 10 secs when key is turned on, I am entertaining getting B+ for the newly added NC Relay shown below - from another source than the solenoid, and installing a NC spring loaded  switch to control the LP NC relay until engine fires. This procedure would only be done/needed when engine is hot.

 

Anyone see a problem with this?  It seems like a harmless mod but given the problems these trucks have with AC noise etc. I need to ask.

 

Thanks.

 

Leaky

 

As soon as I get this done, I need to find out why I have a TC Lock/Unlock issue that magically appeared during my trip.  

 

  

 

 

[dripley]

A couple things I see as strange is a 10 second fuel run at key on. That shouldn't  be but a quarter to half second blip of the pump on. The ECM shoild cycle the lift pump on and off to reduce pressure for cranking, you should see around 10 or 12 psi while cranking. Your second lift pump at 13psi letting the engine start is telling me the ECM is not doing that. 

 Not saying your work around of the problem wont work. That is above my paygrade.

[dave110]

Agreed 10 sec. seems strange. If I am understanding right I ran the same setup as you on my last VP when it developed a hard start. 2 relays. 1 triggered by the ECM and 1 triggered by the power window fuse to kill power while cranking. A new VP cured the problem but your's is new so not sure what to think there. I would try pulling the fuse to the FASS to kill power and then try to start and see if it helps. Plug it back in when it starts and no harm done. Some don't like high pressures when starting but 20psi is not excessive in my book. Also check Blue Chip's website for trouble shooting info.

[Tractorman]

I agree with @dripleyregarding the key on scenario - about one-half second. 

 

I am not so sure about the performance of the ECM modulating the output voltage to the lift pump during engine cranking when a relay is involved.  With the OEM fueling system the ECM modulates the lift pump directly, so I can see how that would provide reduced voltage to the lift pump. 

 

But, with the ECM modulating the voltage to a relay coil, I am having a hard time believing that the mechanical portion of the relay would be rapidly opening and closing its contacts to reduce voltage to the lift pump.  It would seem that the relay contacts would have a very short life if this is so. 

 

I can see a reduced voltage to the lift pump with or without a relay during cranking just because battery voltage will be reduced to around 10.5 volts during cranking.  That alone will reduce the rpm's of the lift pump which would result in a lower pressure reading while cranking. 

 

Can anyone demonstrate proof that a lift pump relay controlled by the ECM actually does reduce pressure by rapidly turning the lift pump off and on?

 

@Leaky88, your wiring diagram looks like it should work to keep the lift pump out of the loop while cranking the engine.

 

- John

Edited July 10, 2019 by Tractorman
As usual, I forgot something.

[dave110]

Can't prove it but I've read here that it can be seen on a gauge if you look close. I'd be tempted to pull the fuel relay in the PDC  so the truck won't start and crank it and look. Otherwise my truck fires almost immediately and it would be hard to see.

[Leaky88]

Thanks guys.  Some very good points.   The FASS I have is putting out every bit of 20 psi and maybe more. When I turn on the key, that gauge immediately swings up.  Conversations with others indicates they have LP putting out 20 with no problems.  Then I hear the VP44 has such close clearances it does not like too much fuel pressure.    From what I read, the causes of the hard start when hot are due either to a damaged diaphragm in the VP44 or too much FP.  I hate to crank the starter any more than necessary given the amps and work it has to do.  I figured the switch would be easier for me to control the on/off situation given the location of the fuse for the FASS. Thanks again for the replies.

Leaky 

[Tractorman]

2 minutes ago, dave110 said:

Can't prove it but I've read here that it can be seen on a gauge if you look close.

 

@dave110, thanks for your response.  I would expect to see reduced voltage to the lift pump (consequently lower fuel pressure) even if the relay doesn't cycle because there woud be significantly reduced voltage to all electrical components (including the lift pump) during engine cranking.  My question is:  Does anyone know if the ECM controlled relay actually makes the relay contacts cycle rapidly to reduce fuel pressure? 

 

- John

[Mopar1973Man]

2 minutes ago, Tractorman said:

Does anyone know if the ECM controlled relay actually makes the relay contacts cycle rapidly to reduce fuel pressure? 

 

Yes. It does. Mirrors the same signal from the ECM.

[JAG1]

Sometimes I bump the starter and while watching the gauge go up as soon as it hits 9 p.s.i. I hit the starter. My truck also starts very quickly all the time though.

 

Have you tried a hot start with the fuel cap off?

 

Have you removed the screens on the fuel module? They tend to hold hot return fuel near the fuel pick up tube or draw straw esp. if they are clogged or varnished.

Edited July 10, 2019 by JAG1

[pepsi71ocean]

1 hour ago, Tractorman said:

Can anyone demonstrate proof that a lift pump relay controlled by the ECM actually does reduce pressure by rapidly turning the lift pump off and on?

 

I see it with my fass 95.

 

To the OP, you can get another spring, or cut a little off of your spring. I think the 150 is overkill, I have a fass 95, and it works fine.

 

My VP-44, will do he same as they have reported starting issues between 20-23psi. I'm actually running 18psi a idle and about 10 at cranking. I also run a fass 150 spring that was custom cut to the psi. I see 18 a idle and maybe 16/17 under WOT load with that spring.

[dripley]

Let us all rember that if the ecm is used to run the lift pump and that there is no factory relay to the stock lift pump. The FASS and AD both come with a wring harness with an after market relay. If connected to the ECM pigtail to the aftermarket lift pump the ECM still has control. It should cycle the lift for lower pressure during starting. Mine still does after 8 years with the AD.

 I would ask the OP what fuel pressure you see when your truck has the hard starting issue? Could be the ECM loosing control.

[pepsi71ocean]

19 minutes ago, dripley said:

Let us all rember that if the ecm is used to run the lift pump and that there is no factory relay to the stock lift pump. The FASS and AD both come with a wring harness with an after market relay. If connected to the ECM pigtail to the aftermarket lift pump the ECM still has control. It should cycle the lift for lower pressure during starting. Mine still does after 8 years with the AD.

 I would ask the OP what fuel pressure you see when your truck has the hard starting issue? Could be the ECM loosing control.

 

I did take note that the OP, said 

Quote

I need to find out why I have a TC Lock/Unlock issue that magically appeared during my trip.

 

I suspect that things are indeed electrical issue based. It sounds like the alternator has massive blow by, or the ground cables are bad..

[Leaky88]

Ground cables are new/clean and AC noise is .015 - .020 measured with a Fluke like Mikes video shows.  I do intend to pull ALT fuse from PDC and 2 wire connector from back ALT and test drive to  see if the TC problem remains.

 

 (It’s always good to have 2 problems going at once so I can alternate between them. Reduces the boredom/stress.)

 

Thanks for all the replies. 

Leaky

[NIsaacs]

Do not pause in the run position before start. Go instantly from off to start when hot.

[dripley]

6 hours ago, pepsi71ocean said:

 

I did take note that the OP, said 

 

I suspect that things are indeed electrical issue based. It sounds like the alternator has massive blow by, or the ground cables are bad..

I had go back and reread the original post. I dont remeber seeing that the first time I read it. Pretty important clue.

 

@Leaky88 its time to get the volt meter out. And you ought to think about doing Wt's ground mod.

Edited July 10, 2019 by dripley

[JAG1]

Hey guys what if Leaky poured cool water over the PCU to see if it starts up without problems? Would that be any kind of test to see if he got a bad VP44 before his warrantee expires?

[dave110]

Not PCU, but PSG (on top of VP44). That's probably what you meant, just wanted to clarify

[dripley]

I talking with @Leaky88 about the issue he tells me he has another lift pump that only runs 13 psi and when he put that on it fires right up hot or cold. The pump he has on there now puts out 20 psi and that one hard starts when hot.

[01cummins4ever]

3 hours ago, JAG1 said:

Hey guys what if Leaky poured cool water over the PCU to see if it starts up without problems? Would that be any kind of test to see if he got a bad VP44 before his warrantee expires?

I wouldn’t call it a bonafide test, but I had a hard start when hot several years ago, and tried the pouring water on it, and surprisingly truck fired right up, Don’t know if it was just a coincidence or not,  I ended up replacing VP and problem went away, It was a Reman VP that I got a couple months earlier.

 

I wouldn’t think 20 psi. at start up would kill a VP, but you never know, but it’s defently  wise to have no more than 5-7 psi at start up.

 

IIRC the ecm is programmed on first click of key to give a 1 sec. burst of fuel, 2nd click 1 sec, and 3rd click about 10 to 15 sec. At least that’s the way mine worked when I had an electric pump.

 

[dripley]

Mine has always been key on about 1/2 second bump, bump the starter, no engine start, about a 25 second lift pump run.