Intermittent non start no fuel pressure

[JVackiner]

Hello Gentlemen
Been awhile since I been here
Need to rememedy that

I have a 99 that on occasion will not cycle the Fass engine mounted fuel pump when I turn on the key, I have pre and post filter, fuel pressure gauges and I don't hear the pump come on
It is always the first time trying to start in the morning and if it doesn't then, it will not start the rest of the day.
Generally the next morning it will start fine. A few times not
If it starts, it will start the rest of the day.
Recently replaced the VP44, injectors and exh manifold and pigtail to the Fass
It really runs and pulls great for 345xxx miles
This is the first time it has acted up since early last fall. Started great all winter
But it has done it so many times over the years, I can't trust it to leave the ranch and shut it off away from home.
I assume something is keeping the fuel pump from getting power but don't know where to go from there.

Any ideas?

 

[petersonj]

Just in case you are not familiar with lift pump operation, I will mention the following for OEM lift pump operation:

* Key in "Run" position will activate lift pump activate for approximately 1/4 second (hard to detect sometimes).

* Key turned to "Bump Start" and back to "Run" (not starting the engine) lift pump will activate for approximately 20 seconds and then turn off.

Can you confirm this operation?

The ECM sends power directly to the lift pump.

- John

 

[JVackiner]

Thank you for responding so quickly

Yes I am familiar

In normal operation when I turn the key to on, (not bump start) I can see the fuel press gauge needles "blip" up briefly and I know it will start.

However, when the needles don't move at all, I know I am in for a non start

If I try to bump start, no needle movement either on these rare occassions.

Also I use the bump start when changing fuel filter to fill it, I put a schrader valve on top to bleed off air easily

 

[petersonj]

The next question: Is the Fass engine mounted lift pump still wired in the OEM fashion. If so, you may be having an ECM issue.

Many, if not most, of this era of VP44 trucks by now have been modified to an ECM triggered lift pump relay operation to remove the electrical load from the ECM.

Can you verify what you have?

- John

 

[JVackiner]

Yes, I believe it is wired into the factory pigtail

Please explain the "ECM triggered lift pump relay"

I assume a relay that gets it's voltage directly from the battery to power the lift pump and is "triggered" (contacts pulled in) only by the ECM?

 

[petersonj]

I assume a relay that gets it's voltage directly from the battery to power the lift pump and is "triggered" (contacts pulled in) only by the ECM?

That is correct. This reduces the electrical load on the ECM to about 150 milliamps.

Before condemning the ECM, I would check the wiring from the ECM to the transfer pump (including the connector) and check the ground wiring from the connector to G107 on the engine block. You could also have a faulty lift pump.

There are other grounds to check as well, such as the ECM ground.

- John

Ground location below fuel transfer pump.

 

[JVackiner]

I will check those out sir
I do know bad grounds can do funny things
And also there was a time I could manipulate the connector and get it to run, as is why I put the new pigtail/connector on
But everything is such a tight fit and with years could have gone bad again
You have given me some homework and can't get at it till Tuesday but will tackle it then
thank you again for your time

 

[JVackiner]

I think also no matter what I find I would like to go with the relay
Do you have a recommendation on what I should get?

 

[petersonj]

Here is an example of what could be used (from Amazon). Note that the relay coil has a diode which will offer voltage spike protection for the ECM. You will need to install a 20 amp fused unswitched circuit to the relay.

If the lift pump connector is still OEM, then this connector can be used for replacement. You could also use this connector to build a jumper lead for testing the lift pump operation.

- John

 

[JVackiner]

Looks great John

Hit the key this morning and it fired right up

But I will be fixing it right so hopefully it won't happen again.

Thanks for the links

Jeff