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Engine/Transmission (1998.5 - 2002) Unigue Fuel pressure Problem I think!!

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Engine/Transmission (1998.5 - 2002) gettin hot !!!!!!!!!

Engine/Transmission (1994 - 1998) Vacume pump leak

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Okay the long story. Last July 4 weekend fuel pressure went to 0 between La Junta Co. and Taos NM. Hope I did not screwup the VP! :{ Change to my spare FP in Taos pressure back up to 14 idle, around 13 cruise and 10 WOT. 3 weeks ago fuel pressure got erratic. :{ Be cruising along 13 psi then all of a sudden pressure drop to 9 even done to 6 sometimes and stay for awhile then jump back up to 13 no change in engine sound or performance.



Installed Vulcan big line pump relocation kit yesterday and pressure went to 15 idle around 14 cruise and 12 WOT. Pressue rock solid until I had to slow and turn on a road at the bottom of a grade. Accelerating up the hill, the pressure jumped down then back up to 12 then down again 3 times(a short hill) after topping out it went to rock solid 13 psi cruise. :eek:



What do you think OEM fuel pump from Cummins I installed last July, electric Autometer gauge sending unit, something else? By the way what does everyone use for a mechanical pressure gauge for testing pressure. :confused: I have another pump on order but won't have it before my trip to Vegas this weekend. Hope that does not turn out to be a mistake. I need to cure this problem before towing my 14,000# 5er to Phoenix for the NASCAR race in April. Oo.



Thanks for any help.
 
Are you running the stock filter and did you run the big line kit to the filter or did you also run it from the filter to the VP? What is the condition of the filter?
 
Running the Fleet Guard filter and changed it yesterday while I was installing the Vulcan kit. I ran the big line kit to the filter then to the VP.
 
Bob

i had a simular problem with my autometer (electric) sending unit. it would jump all over the place. i installed a rubber hose between the FF housing and mounted the sending unit on the firewall. this worked for a bit but i think i messed up that sending unit so i bought another one and its been fine ever since. and i also put a small shutoff valve in between the FF canister and the sensor to better protect it from any spike in the Fuel pressure from the vp44.
 
When I open my fuel system an I get a little bit of air in it I get that split second needle bounce, then steady as the air is passed through the system.



I think you are going to see the split second bounce for about 2 - 3 weeks then it goes away as truly ALL the air bubbles are really out of the system.



In you big line kit install I know you purged the system of air as the last step, but I find a little bubble will hang on some internal connection and pass fuel fine, but not dislodge the bubble. Then a bump in the road, a unusually fast corner left or right, higher than normal flow (towing in my case), just some little quirk that dislodges a tiny bubble and the gauge reports it correctly.



IF you think the lp pump is cavitating you could put a bypass valve on it (like the RASP pumps have) and that would keep it from cavitating (ie the flow going regardless of fuel demand).



Just some thoughts,



Bob Weis
 
As a follow up, I get the same phenomenon with my FASS... I also attribute it to the FASS capturing the air in the filter that is then released when you hit a bump... as the air passes through the return line it causes the pressure to drop rapidly for a moment as it passes through the checkvalve... air compresses and flows differently than fuel.



In your case, the air is causing the pump to cavitate and drop pressure... in mine, it causes my low pressure light on the dash to flicker every now and again.



Just my thoughts... it might be absolutely normal, it also might be an indication that you have a fitting/line leaking somewhere that is allowing some air in under the vaccuum of the pump...



steved
 
Keep the thoughts coming it is appreciated. Oo. lets see first I have braided stainless line to the Autometer sending unit and also installed a snubber in line at the sending unit to prevent spikes. This was done when I installed the gauges several years ago. Air in the system is scary!!! :eek: Bleed the system after Vulcan install the the VP probably a gallon diesel. Also bleed fuel at the Autometer sending unit. I don't think there is any fuel leaks at the fittings but will look closer tomorrow and let you know. Also I had erratic pressure before the Vulcan kit install it is just better now.



Here is another tidbit. :confused: Took the truck out of the garage to wash it before going to Vegas Saturday(muddy here). :rolleyes: Anyways pressure was at 15 PSI. After washing truck pressure after start was 11. 5 PSI. Note by the way I greased all elelctric connections before reattaching them. Pulled into garage and shut truck down, Immediately restarted truck and pressure back to 15 PSI!!! :(



I also noticed that every time the intake heaters cycle the fuel pressure drops I assume because of a drop in voltage. I was thinking this is normal does everyone elses trucks do this? Mine has every since I put the gauges in. Could it be a voltge problem to the gauges or lift pump? I notice also that when voltage up I can hear the pump run but when the heaters cycle on the pump does not make as much noise so it must not be pumping as much. Of coarse cannot hear the pump when accelerating. :-laf
 
Mundgyver - I only wish it were that easy. :-laf Though seems to me I read someplace in here there was a discussion the voltage fluctuations could cause erratic fuel pressure perhaps from the ECM.



Thought I had a OEM on order but fouind out it was the in tank one!!! :{ Don't want that one so will be going to Cummins first change I get. Perhaps I should try the Carter 4600 is it from NAPA? I just have a hard time justifying getting a FASS because my truck is stock and really have no intention of souping it up have enough problem as it is stock. :D
 
I know what you mean. The grid heater are interesting though, I am not sure what amount of current they draw, but I know it causes the lights on my truck to dim when I have just started up and am idleing.



I put on a FASS 150 GPH about 150,000 miles back and replaced the inlet banjo bolt with a straight in fitting that I drilled out to 3/8 ID. The banjo bolt restricts flow and I wanted the volumn to the VP. I do know that when I put on the FASS, my motor smoothed out. I think that is because I am now keeping the air out of the fuel lines. My fuel pressure runs a steady 15 psi.
 
Steved - I checked and no leaks in the installation.



Mundgyver - Is the FASS a plug and play or did you have to do electrical work to make it work? May still ultimately have to go with the FASS though it seems over kill for basically a stock truck.



Off to Vegas tomorrow for my Nephews wedding on Monday. Wish me luck, may have to go by Cummins Monday morning in Vegas for a new pump as I need a spare at any rate. Wish me luck!! ;)
 
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Steved is right,sounds like you are pulling air,If you still have the existing fuel module,install the updated intank pump,in addition to the outside lift pump. The old intank module is prone to restricting the suction line and leaking air.
 
Huf N Puff - The intank module was replace around 30K. Don't take this wrong but would not the pressure change its erratic behavior depending on how full the fuel tank is if pulling air? Seems to be the same no matter how full or empty the tank. Thanks for the thoughts though. Arond 420 miles and am in Vegas and the gage was jumping around so much thought about putting tape over it. The last 100 miles or so the gauge did not jump around as bad and ran either 7 psi or 14 PSI steady most of the time. Need to get over to Cummins tomorrow so I at least have a back up should it decide to go to ZERO!!!
 
The FASS was a plug and play. I mounted it back on the frame up into the pocket formed by the fender liner and the front of the bed on the drivers side. The electrical harness plugged right into the plug for the stock lift pump. I am at 164,000+ miles now and have no problems with fuel delivery. I also installed a fuel cooler to help keep the VP temps down. I still have my original VP and it shows no signs of dying. ;)
 
Mine did the 13. 5 psi and just drop to 5-6psi thing on my last pump.



It was not air in the system, it was a bad lift pump. Also, a bad overflow (sticking) can cause this.



For those that think that air in the gauge line causes a lower reading, it is not true. Air compresses, just ata different rate than diesel. If you have that much air in the line to have the pressure drop and stay at 5-6- psi for 20 minutes, I would tell you the truck would not even run right.



I could get the pressure back up on my dying pump by going to WOT for a second. That's why I thought I had a bad overflow. I figured the lowered pressure in the feed line was allowing the overflow valve to close. It was actually allowing the stock pump to get some traction on the pump shaft and spun the vane harder.



Dave
 
Mundgyver - Thanks for the FASS info. ; bought 2 new pump kits(4090046) from Cummins in North Las Vegas this morning. The 2 kits was like $139 and very popular as I called them this morning and they had 16 in stock and when I walked in their was someone on the phone asking about the same kit. I doubt they have 16 in stock anymore as when I asked for 2 he said let me look!!!! I did not get the name of the person on the phone if he was TDR or not but probably. So won't be using the FASS yet but someday. Hope my exisiting one gets me home as I rather work in the garage than in a parking lot or side of the road!! When I have time will figure out how to make a low pressure LED next to my guage since this pump came with the switch for it.



Fishin Guide - I agree with you and when I change the pump to the $70 one I will let you and everyone else know if the problem stopped. If it doesn't will go to correct the overflow possible problem. I have to do a search on how to do this unless you know and it is easy right off the top of your head.



Thanks for all the input it is awesome.
 
Bob Cochran said:
Fishin Guide - I agree with you and when I change the pump to the $70 one I will let you and everyone else know if the problem stopped. If it doesn't will go to correct the overflow possible problem. I have to do a search on how to do this unless you know and it is easy right off the top of your head.



Thanks for all the input it is awesome.





You need a regulated air supply a tapered tip air gun and a piece of hose.



Pull the overflow out of the VP. Slip one end of rubber hose over it. Now jam the tip of an air nozzle int he the other end. I actually built a manifold with a gauge to read actual air pressure. Looks like a 'TEE'. Start with the pressure low or off. Slowly increase air pressure until valve opens. I like to do this 1 psi at a time. You know it's open because air will be leaking through the center and not just through the air bleed port. I usually plug the air bleed with a toothpick.



Once it's open, slowly lower air pressure until the valve closes. These are you opening and closing pressures. It should hold at least 12 psi before opening, but 14 psi is better. If it is tripping at 8 psi, it's junk and needs to be replaced. Also, if it is hanging open, it's also junk. Sometimes a little debris from the fuel system can cause an issue. And a solvent bath will sometimes clear up the issue. But it's usually scoring on the check ball or body that causes the most grief. And there is no cure for a weak spring that I am aware of.



Dave



Dave
 
Huff N Puff & Steved - After getting home from Vegas I found waht appeared to be a small fuel leak on the FF input loosened and retightened the AN fitting. I also foudn the the water drain was leaking on the FF(I hate that thing I have had this happen before) and it was dripping. For all I know this was being thrown up on the bottom of the FF canister making it look like it was leaking but everyting dry now. Still having erratic fuel pressure readings.



Fishin Guide - You maybe right about the over flow valve. I noticed if the pressure got bouncing/jumping between 7 to 11 psi if I give just a little throttle(no were near WOT) it would stop and go back to 14 psi cruise pressure. Will have to look into this possivlity.
 
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