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In this episode of WTF is wrong.. - Fuel Pressure


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I'm confused as can be, and this'll be long-winded..

 

Subject: 1998.5 2500 Cummins 24V 5 speed RCLB 4WD.  115K miles

Complaint:  He (good friend of mine, and neighbor) stopped by the other day with it poppin', stumbling, hazing, and no power.  Also, fuel gauge is not correct, and reads very inaccurately.

 

I checked the FP at the injector pump..  KOEO, 12psi.    KOER, idle 10,   At 1500rpm, 5-6psi.    Fuel filter was changed a few months back, truck's been about 1500 miles since.
I could barely hear the in-tank pump (it's had the dodge conversion from block-mounted to in-tank lift pump).

 

Codes: P1693, P0216..   (dun dun dunnnnn)

Inspected all the fuel fittings/lines, nothing looks suspect. So I decided "let's start with a replacement in-tank pump, and check for crap in the tank."   Ok.   Ordered parts (including a new overflow valve).  Dropped the tank, and noticed when I removed the return line, the tank took a big ole gasp of air; it was under vacuum..   Once I got the tank out, I noticed a shipping plug still on the rollover valve of the sending unit..  Also noticed the tank was deformed along the bottom and sides, as if it were sucked in for a long period of time, and it was holding that shape now, even after venting.  When I talked to the owner, he said "I replaced that in-tank assembly about 8 yrs ago.   And off and on, I've noticed over the last couple of years, that when I refuel, the tank has vacuum when I remove the gas cap."  So apparently, this vacuum issue has been a problem for a number of years, with most recently, getting noticeable.

 

I replaced the pump/sender assembly, and reinstalled the tank, then cleared codes.  Tested pressure..

KOEO, 16psi

KOER, 10psi

1500:  8psi

Idling, it still constantly hazing, and "missing".

 

So I ran a length of 14g wire back, cut the green 16-18g in-tank pump wire, spliced in the test wire, and went direct to battery..  I also replaced the Overflow valve at this time, and cleared codes again..

KOEO, 20psi

KOER, 12psi

1500: 8-9psi

 

And that's where I'm at now.  Would the VP44, if failing, act this way?  Could it be leaking internally?    I don't understand why the pressure drops so much, even at idle.

Thoughts on a solution?

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Demand volume is out weighing the supplied volume. Need a pum with more volume to keep up. Then you need plumbing with less restriction. Stock lift pumps are about 60 GPH pump which are too small from the get go. The stock plumbing is less that 1/4" its 6mm ID. Very restrictive.

 

Quote

Q: How much volume does a stock lift pump provide?
A: Approximately, 35 GPH

 

Even to this day AirDog 150 pump I'm only a 2 to 3 PSI drop from idle to WOT at 100 MPH with about 500 HP with of mods. This just points out you need a better fuel system. Make sure the tank vent is not plugged up you could clean it up and the route some vinyl tube to a higher place where mud and dirt won't plug it.

 

VP44 is done and need to be replaced with that P0216 code the timing piston is ruined. 

 

  • Quadzilla Adrenaline 180 HP
  • DAP 150 HP Injectors (7 x 0.010 @ 320 bar)
  • HX35/40 Hybrid Turbo 60/60/12 producing 47 to 49 PSI boost.
  • AirDog 150 with a 4G AirDog 165 pump. Idle at 17 PSI and WOT at 14 to 15 PSI @ 100 MPH.

 

Edited by Mopar1973Man
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1 minute ago, Mopar1973Man said:

Demand volume is out weighing the supplied volume. Need a pum with more volume to keep up. Then you need plumbing with less restriction. 

 

Even to this day AirDog 150 pump I'm only a 2 to 3 PSI drop from idle to WOT at 100 MPH with about 500 HP with of mods. This just points out you need a better fuel system. Make sure the tank vent is not plugged up you could clean it up and the route some vinyl tube to a higher place where mud and dirt won't plug it.

 

VP44 is done and need to be replaced with that P0216 code the timing piston is ruined. 

So here's my question, concerning you saying the demand vs supplied..
If it's a new OE pump, OE lines, truck is 100% stock, how/why would the demand be higher than the supplied, even at idle?  I could see it with a hotrod VP pump, etc, but not 100% stock.

The tank vent?  You mean the rollover valve?  That's the only "vent to atmosphere" fitting on the tank assembly, and it's clear and unobstructed.  The entire sender/pump assembly is new, so that shouldn't be an issue.  The one I replaced had a capped nipple on the RO valve, the new one is opened.

 

My old 01 had a 0216, and it's cause was a plugged up, jerry-rigged filter setup the previous owner had done.  I cleaned that catastrophe up, and my 216 code went away.

I'm not saying the VP pump isn't bad, especially with how long it may have been ran with restricted (vacuumed) flow, but I don't wanna throw a $1200 pump on if it isn't needed.

 

How does a timing piston (if that is, indeed, the issue) cause fuel pressure to drop that much, or be that low to start with?   Not arguing, more trying to understand..

 

 

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9 minutes ago, Rogan said:

So here's my question, concerning you saying the demand vs supplied..
If it's a new OE pump, OE lines, truck is 100% stock, how/why would the demand be higher than the supplied, even at idle?  I could see it with a hotrod VP pump, etc, but not 100% stock.

 

Because the OE lift pump was too small from the start, why most of us upgrade to larger pumps. If pressure is dropping out then the pump is too small and the plumbing is too restrictive. I was here a very long time ago with the very same problem where I ran Carter Campaign pump on the frame rail and fought to barely reach 11 to 12 PSI at WOT and 14 -15 Cruise pressure. Still to this day I still see stock fuel system barely pulling 5 to 7 PSI at WOT and just shake my head. Doesn't even need to be modified to be be low in pressure hence the whole reason for lift pump market for our truck it never went away. 

9 minutes ago, Rogan said:

I'm not saying the VP pump isn't bad, especially with how long it may have been ran with restricted (vacuumed) flow, but I don't wanna throw a $1200 pump on if it isn't needed.

 

Might have too though... If the timing piston is galled up and stuck there is absolutely nothing you can do. I just done a VP44 that would start cold and run fine but shut it down it would never start again with a warm engine. P0216 code present and the timing piston is STUCK ADVANCED so the engine will never start. After a new VP44 truck run great and starting issues is over. If you can't get proper timing there is a host of weird things that pop up from not starting or just running will super low power. Even my last VP44 was stuck full advanced and was rattling hard core. P0216 code and only could do about 25 to 30 MPH top speed home. 

 

To remove this piston I had to heat the pump body with a propane torch and expand the body to even pull it out. 

ecm or ecu diagnosis - 2nd Generation Dodge 24 Valve Powertrain -  Mopar1973Man's Dodge Cummins Forum

 

Additional info...

 

 

Yes I've already been done this road long time ago...

Edited by Mopar1973Man
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If you get it to resolve the P0216 code and stay cleared after a tank of fuel I would still watch it like a hawk. Kind of like saying if the oil pressure minimum is 10 PSI at idle and the engine oil pressure is actually 8 PSI at idle and barely 25 PSI at 2,000 RPM. Do you expect the engine to last as long? Most likely not. 

 

Being the fuel is your lubricant and coolant for the VP44 when you short change for pressure now your return is closed being the over flow closes at 10 PSI completely this means all your cooling and lubing ability of the fuel has stopped. Now this goes farther being now the cooling has slowed way down now the fuel temperature rises (Flow is roughly 2.5 GPH at 55 MPH). I've had a discussion with some that have 140 to 150*F fuel temps. While with my setup I struggle to even reach 130*F. Typically more like 90 to 110*F fuel temps. VP44 PSG is very happy here. Being the fuel pressure never drop below 14 PSI this means optimal cooling and lubing. Meaning longer life. 

 

Yeah you can run a VP44 on as little as 5 PSI as BlueChip so quickly announced you can still make MAX HP. But I'll note the longevity is greatly shorten on the VP44 from the lack of cooling and lubing. 

Edited by Mopar1973Man
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So what lift pump is your recommendation for an OE truck?  As for VPs, I see Scheid has the VP stock for $1200..  From a lift pump perspective, everything I see is 3-600$, then a big line kit, I've not found yet..

I'd assume a 95gph pump like Raptor or FASS would be plenty?

Edited by Rogan
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AirDog or FASS is a complete kit. 

 

Then mechanical pump that are belt driven the only thing I don't like is there is no priming pump. Kind of like yesterday I forgot to take my line clamp off and the truck ran out of fuel and died. Bump the starter a couple of times prime it up and start fairly easy. But mechanical pump will not be able to do this. You'll have to use a drill and pull the pump and belt and spin the pump to get the system primed. 

 

Also make sure to KEEP the stock filter. Like myself I change filters at 60k to 70k miles now. 15k is a waste being the filter still look brand new. The factory can filter is a 7um filter and it catching more that the 3um Donaldson is passing. I just changed my fuel filter and going to cut it open later today. 

 

Being my fuel temps are much lower I don't get the large amount asphaltene like people with lower fuel pressure so my fuel filter stay cleaner longer than most. 

 

15k mile Fleetguard 3um filter. (AirDog 150 filter)

Am I filtering fuel enough? - 2nd Generation Dodge 24 Valve Powertrain -  Mopar1973Man's Dodge Cummins Forum

 

60k miles on both... (Stock can filter 7um, and fleetguard 3um AirDog 150 filter)

54k Fuel Filters - 2nd Generation Dodge 24 Valve Powertrain - Mopar1973Man's  Dodge Cummins Forum

Edited by Mopar1973Man
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I did just over a year on the in tank pump from Dodge. Had couple issues and took it to shop and the only thing they found was low fuel pressure. 5 at at idle and 0 at WOT. They are worse than the block mounted pump in my experience. That pump only cost me $1k. Made the AD look like a bargain at the time.

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So for shitsngigglez, I threw an old block pump inline, tandem the pumps, for a test..

 

24psi KOEO

20 psi KOER @ idle

15-16psi @ 1500-2000

 

 

Truck still hazing/smoking, though, so I'm guessing a VP is in order, AS WELL AS and AD/FASS pump, and trash the in'tank + block pumps.

Thanks for all your input, guys!  As always, it's greatly appreciated.

 

edit:  he really needs a new tank, too.  this one is so distorted; I am guessing due to the vacuum the tank has lived in, over the last 8+ yrs...  lol

Edited by Rogan
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