Archived Long Crank times and jumpy fuel pressure

[mongoose]

1999 2500

Truck used to start almost by looking at key. Now sometimes it starts right off, sometimes has to crank for 3-8 seconds. When all this started, I noticed my fuel pressure gauge acting wild. Pressure would jump around almost all the time. Changed LP, no change in pressure or starting. Changed Crank position sensor, no change. No codes set. Could I be experiencing a bad VP44?



Daniel

 

[JLandry]

Daniel,

Are you still seeing this jumpy fuel pressure both when cranking and when the engine is running with the new lift pump?

Have you verified the fuel pressure using a different gauge (getting a second opinion so to speak)?

Jumpy fuel pressure is usually caused by air in the fuel line (as when the tank is starting to run empty or when air is being sucked into the fuel line).

Once started, does the engine operate normally in every other way?

A suggestion: You may also try swapping out the ASD (Auto Shut Down) relay, which is located in the PDC, with another non-critcal one such as the wiper relay. If this fixes the problem, replace the relay.

If the lift pump is truly operating erratically, it's possible something is wrong with the ECM (which controls the lift pump). In that case you could try rewiring it to run continuously when the ignition key is turned on. Read this thread for more info and ideas.

Good luck and please keep us posted,

John L.

 

[mongoose]

have not tried a second gauge, but will. Engine seems to have a slight miss at idle. Just enough that you can see the tach needle move as it misses and it seems down on fuel mileage some.



I'll try the relay trick and if that doesn't help I'll move on to wiring the lift pump. If that doesn't help, i'm thinking that I need to try the #6 and #7 wire jump on the injection pump to see if that makes any difference on starting.



Thanks for the suggestions.

 

[JLandry]

Engine seems to have a slight miss at idle. Just enough that you can see the tach needle move as it misses and it seems down on fuel mileage some.

Well not meaning to add more confusion to this, but if you have a sticking or leaking injector (or two) that could account for a miss at idle, decreased fuel economy, and hard starting.



Just trouble shoot and eliminate one thing at a time and you'll ultimately nail it down.



John L.

 

[mfburns]

You might want to check the fuel lines for leaks. It could be getting air in the line and delaying teh start and also the rough idle. Just a guess on my part. It seems to me the lines last about 10 yrs before they start to degrade.

 

[mongoose]

Thanks guys, what is the easiest way to trouble shoot the injectors?

 

[JLandry]

Thanks guys, what is the easiest way to trouble shoot the injectors?

The best way to verify the injectors are all working properly is to pull them out and send them off to be pop tested and adjusted. But because this can involve some significant down time, most people opt to simply replace them with new ones... especially when they have lots of miles on them.

You can conduct some rudimentary testing to assure the injectors are at least functioning on a basic level. The easiest way to do this is using a Chrysler DRBIII scan tool or Cummins Insite software to selectively kill (turn off) injectors one at a time. But without those tools, with the engine at idle you can loosen one injector line at a time at the cylinder head to do the same thing.

When you kill a properly functioning injector, the engine idle quality will become rougher and have a "loping" sound to it. When you kill a faulty injector, there will be no significant change in the engine idle quality.

John L.

 

[mongoose]

Thanks John!