2nd Gen Non-Engine/Transmission 1999 24V wont start without throttle

[j31975]

Intermittent starting problem becoming more frequent. Won't start without applying some throttle, after it fires up a surge in RPM's like it just got a massive shot of fuel. 1999 24V with a FASS that's a couple of years old pushing 215k on the truck. No other issues at the moment.

 

[JLandry]

Is it safe to assume you're monitoring the fuel pressure? If yes, what is it pre and post-start?

How old is the Bosch VP44 fuel injection pump?

How old are the fuel injectors?

Is there any smoke immediately after starting?

Regards,

John L.

PS: Welcome to the forum. Please fill out your signature with more info about your truck.

 

[j31975]

I do not have any fuel pressure gauges. The VP pump has about 100k miles on it, its a rebuild, and the injectors are factory originals from 99. I have seen a little black smoke immediately after startup for some time now and heavy soot deposits on my bumper. I will check pressure this evening and repost.

 

[JLandry]

I do not have any fuel pressure gauges.

On these trucks you definitely want to monitor the pressure where the fuel enters the VP44. After you connect a gauge, do the following tests:



As you turn the ignition key to the run position (but don't engage the starter), you should see a very brief spike of fuel pressure as the fuel transfer pump (your FASS) is energized briefly.



Next, bump the starter (but don't start the engine). The fuel transfer pump should energize and run continuously for approx. 25 seconds. Ideally the fuel pressure should be between 10 to 20 psi. Fuel pressure over 20 psi can cause hard starting.



Not related to the starting problem, but you never want to see the fuel pressure drop below about 5 psi under load at full power.

The VP pump has about 100k miles on it, its a rebuild

That's getting up there in miles and the starting problem could be the result of wear.

and the injectors are factory originals from 99

I'm not sure if they're contributing to the starting issue, but with that many miles on them, I can guarantee you those injectors are worn to the point where they're not completly shutting off the flow of fuel anymore. When tested at 90,000 miles, the original injectors in my truck were already "*******" fuel from the tips well below the pop-off pressure. I mention this because you might want to go ahead and replace the injectors as a preventive measure. Again, I'm not sure if it would help or hurt the starting issue.



Best regards,



John L.

 

[j31975]

Here's what I have today:

Key on no pressure
Cranking engine no pressure
Bump start pressure runs up to almost 30 then immediately bleeds off to zero
Bump start does not always turn on the lift pump for some reason. I have to cycle the switch all the way to off then try it again.
Checked the overflow valve and it appears to be functioning best I can tell with the air compressor I'm using.
Checked the return line and did not locate any visible leaks.

I can bump start and prime the VP then the truck will start and run good pressure ~17 at idle ~12 at WOT.
I can also restart the truck within 30 seconds of shutting it down after that I have to re-prime.

How long should the fuel lines stay pressurized after the lift pump has shut down?
Should I check the ecm to lift pump voltage?

 

[JLandry]

Bump start pressure runs up to almost 30 then immediately bleeds off to zero

Does the lift pump run for the full 25 seconds?

Bump start does not always turn on the lift pump for some reason. I have to cycle the switch all the way to off then try it again.

Having to turn the ignition switch all the way off before the lift pump will energize when bumping the starter sounds normal.

I can bump start and prime the VP then the truck will start and run good pressure ~17 at idle ~12 at WOT.

I can also restart the truck within 30 seconds of shutting it down after that I have to re-prime.

Assuming the FASS is working correctly (a little hard to tell based on your descriptions), then it sounds like either your VP44 could be getting weak (possibly due a ruptured accumulator diaphragm) or the injectors are so worn they're loosing pressure, or a combination of the two.

How long should the fuel lines stay pressurized after the lift pump has shut down?

Not very long. The fuel line after the lift pump should stay full of fuel (i. e. : no air leaking into the line) but it generally won't stay pressured once the lift pump shuts off.

Should I check the ecm to lift pump voltage?

That definitely can't hurt. You might as well rule out the low cost options.



You may want to start shopping around for new injectors and a new VP44... just-in-case. Or you can just live with it.



John L.

 

[j31975]

No the lift pump is only running about 9 seconds.
I don't think its running when the key is turned on either.

I unplugged the lift pump and cranked for 10 - 15 seconds and the truck started. I had the same results with the lift pump plugged in.

 

[Missouri Mule]

The VP44 pump has a mechanical fuel/lift/transfer pump inside of it. You don't want it pulling fuel solo needs a stronger pump feeding it (Vp44).

Blue Chip Diesel has info how to verify problems of Vp44 system. www.bluechipdiesel.com