Engine/Transmission (1998.5 - 2002) hard start fuel pressure question

[ESims]

99 24 valve with 250,000 on original vp 44. all of a sudden got a starting problem. If i hit the key and fuel pressure guage doesn't go to 15 psi or so truck won't start. If i turn key off and try to restart as long as fp guage moves truck will start. Is this a key switch,relay or other problem. Basically my question is what tells lift pump to start pumping when you hit the key? Thanks

 

[JLandry]

Basically my question is what tells lift pump to start pumping when you hit the key? Thanks

The ECM supplies power directly to and controls all lift pump operations. There are no external fuses or relays for the lift pump.



When you say the truck won't start, do you mean the engine cranks normally but won't run?



When the lift pump is running (as when you bump the starter and leave the ignition key in the on position), is the fuel pressure normal and adequate?



Have you replaced the fuel filter recently?



Have you checked for diagnostic trouble codes?



Good luck,



John L.

 

[ESims]

The engine cranks normally but wont start. fuel filter last month. no cel but have not checked using a code reader and when lift pump runs i have between 14 and 17 psi. Lift pump is relocated and easy to hear when running and the hard start is hit or miss. When i hit the key if the fp guage moves the truck starts, if no movement of guage then truck will crank for maybe 6 or 8 seconds and either start or i will release key. Could it be a key switch problem?

 

[JLandry]

Could it be a key switch problem?

Ya know I don't think so. The ignition key doesn't have a direct tie-in to the lift pump. The ECM receives power when you turn the ignition on and it controls the lift pump's operation via its internal programming.



You may already know this, but it's worth mentioning that the ECM is programmed to only operate the lift pump for 2 seconds when the ignition key is first turned on before the starter is engaged. Per the Dodge service manual, this behavior is to prevent too much fuel pressure at the VP44 inlet before starting. This 2 second burst from the lift pump will normally result in only a brief pressure spike on a fuel pressure gauge and the pressure doesn't normally hold (at least on my truck it never does). When the starter is engaged, the lift pump is supposed to operate continuously for up to 25 seconds while cranking.



With that many miles, I'm wondering if your VP44 could simply be worn enough internally to need the higher inlet pressure to help create enough injection pressure to actually force the injectors to open? Remember, the VP44 is turning relatively slowly during cranking and if worn, I could imagine it having trouble building adequate injection pressure to operate the injectors properly.



I think if it were my truck at this point I'd do the following...



1. Verify you don't have any stored TDC's with a code scanner.



2. Verify the fuel pressure behavior at the VP44 inlet by using a fuel pressure test gauge if you can't trust your current fuel pressure gauge 100%. You want to positively rule out the lift pump as being the source of the problem.



3. If there's any doubt about when the lift pump is operating, also verify it's indeed receiving power when it's supposed to (2 seconds when turning the ignition key on and approx. 25 seconds when the starter is bumped). This will rule out that the ECM is acting up.



If all of the above check out, then you're pretty much closing in on the VP44 as being the culprit and it's probably time to start shopping for a rebuilt unit.



Best regards,



John L.

 

[ESims]

the only reason i was thinking key switch is if lp doesnt come on and i cycle key once or three times eventually lp will come on briefly and truck will start. I know i am on borrowed time with pump, it has been tapped with drag comp since about 20,000 miles and currently has 150 hp injectors and a ht2b

 

[JLandry]

the only reason i was thinking key switch is if lp doesnt come on and i cycle key once or three times eventually lp will come on briefly and truck will start.

Well that's a good point... if the ECM isn't getting an ignition key on signal, then it won't power the lift pump. When I get a chance I'll find out which wire leading to the ECM you should check to verify this.



Regards,



John L.

 

[grimesja]

You might want to check your fuel lines also. I had a cracked fuel line and it caused the same sympthons that you are having. The cracked line evidentily let air in the system casuing some bleeddown from the VP-44. Just food for thought.

John G.

 

[JLandry]

Well that's a good point... if the ECM isn't getting an ignition key on signal, then it won't power the lift pump. When I get a chance I'll find out which wire leading to the ECM you should check to verify this.

To verify the ECM and PCM are getting power when the ignition key is in the run and / or start positions, use a multimeter and check for 12 volts at:



Pin 5 of the ECM connector. This pin will be toward the center on the top or bottom row of wires in the large 50 pin ECM connector (I can't remember if pin 1 us up or down). This is an 18 gauge Light Green wire with a Black stripe.



Pin 2 of the PCM C1 (black) connector. This pin will be located toward one of the corners of the connector and it's also an 18 gauge Light Green wire with a Black stripe.



But, I really doubt that's the problem because if either wasn't getting power reliably, I'm sure you'd be getting all kinds of trouble codes when the engine is operating.



Best regards,



John L.

 

[ESims]

thanks, i will check it out.