Engine/Transmission (1998.5 - 2002) Fuel Presser--At start up on cold days.

[MatthewW]

My 01 Ram truck when I start it up for the the first time in the morning has low fuel pressure. then after I run the truck for 15 miles or so will then level off at what i consider the norm on my truck. . My question is this: Do the lift pumps take a bit to warm up as with the rest of the truck components in the morning?



stats that I have. .



Morning Temp's- single digits-teens

Start up fuel presser- 9psi

Fuel Pressure almost wot- 2psi



After driving for 15 miles... ( my normal readings when warm)

fuel pressure- 13psi

fuel pressure at wot- 5-6psi



Or is this maybe a lift pump going out and or on its way. .



matt

 

[Steve St.Laurent]

My bet is that it's because the heater grids are cycling in combination with thicker fuel being it's cold. The heater grids pull a LOT of juice. Now that it's winter your grids are coming on when you turn your key on. Notice how your lights dim when they activate? The power to your lift pump is lowering too.

 

[Sixpack]

With a mechanical gauge and isolator the diaphram is cold (stiffer) and therefore maybe not as responsive to the pressure until it warms a bit. JMTCW

I notice mine is lower as well until the truck warms up. And I have a new lift pump.

 

[Hohn]

I have lower pressure in the cold and I run no isolator on my mech gauge.



It will idle @13-14 when first started, and at 17 when fully warmed. Recirculation of the warmed fuel from the engine is mostly responsible for the higher readings when warm.



Second Steve's point. Notice that you still have low pressure once you get going faster than 20mph and the grid heaters turn off? That's just the cold.



I am doing the Wildcat upgrade soon. i don't like the idea of feeding cold fuel through those tiny holes.



Justin

 

[DLausche]

Mine is doing something very similar on cold mornings. Starting at +5* I will get pressure readings that jump randomly between 0psi and 12psi. Slight throttle and the pressure goes to zero. Release throttle and it might take 10 to 30 seconds to move off the 0psi mark. After driving for 15 miles or so, the fluctuating pressure symptom would disappear and pressure would remain near normal (13 idle, 6 wot). Took it to the dealer to get replaced under warranty. This was a difficult one to explain to them and it took a long time to convince them that something wasn't right. They would bring it in their shop (warm) and test it and of course it would check out within spec since it had warmed up enough so the symptoms didn't show. Ended up leaving it there overnight since the temps were going to drop down again overnight. Went in just this am, grabbed the service manager and started up the truck out on their lot. After he saw the gauge jumping all over and the 0psi with any amount of throttle he finally believed me and started the paperwork for a new LP under warranty.



MatthewW, The number that sticks out in your post is the 2psi at wot when cold. To me this indicates that something isn't right with the LP. The 5-6psi at wot when warm also seems to be a bit lower than it should. The heater grids cycling will drop the psi due to lower voltage and increased fuel demand, but I wouldn't think that will affect it much at wot. Assuming you are driving when you hit wot, the grids shouldn't be on anymore. I think they stop cycling once you hit 15mph or something like that.



If you are under warranty, then you should be able to take the service manager for a ride when it is cold and show him/her the 2psi reading. I would think they would then agree that it needs to be replaced.



Sorry for the lengthy response. I wish you the best getting this one taken care of.



-Deon

 

[MatthewW]

That sounds just like what mine is doing... Let me know how the new pump works for ya. . This morning it was around 7* here and it did just as you said. . I started the truck and idled at like 7psi and tapped the gas to say 1500rpms and the fuel pressure went to 0psi. . and slowly came back up. . let Idle for 5-10 min and took down the road and once warm the pressure went back up to the norm for me. .



Let me know how it works out for ya... If it does I will be going to the ******* to get it repaired...



mattw

 

[DLausche]

A quick update on how mine is turning out. Dealer confirmed yesterday that their gauge was showing same as mine. Before replacing the LP, they want to confirm that there are no air bubbles in the fuel line. They had to order some sort of clear fuel line in order to do this check. I assume this clear line connects inline at the quick release connecter at the inlet of the LP. I can see that air in the line might cause the low pressure problem, but not really sure why the low ambient temp would trigger the problem.



-Deon

 

[CCOLLAR]

I experienced an extreme case of this on Saturday. Went out to start the truck at -45F below. Truck started immediately (love those Optimas!). Hit the high-idle, then went in side the house. About a minute later, the truck dies. Now I get worried. I start the truck (again, starts right up), and notice the fuel pressure is below 0, as in no voltage at the guage at all.



I figure the diaphram of the isolator stiffened up. I let the truck run for 30 minutes to warm up, then drove it. After 10 minutes or so, the pressure started coming up.



So I think a couple of things are happening: 1) the diaphram of the isolator is not as responsive/accurate (or even operates) in very cold weather; 2) the fuel thickens up, and the LP has to work harder to lift the fuel to and through the filter until the fuel warms up; and 3) the LP doesn't get all the current it needs to do the added work because the heater grids are drawing so much current, so the fuel pressure is lower.



At least that is what I hope is happening!



Craig

 

[MatthewW]

I can see it being any of the above. but I want to figure out which it is cuz that cant be good to be let'n our rigs running with 0psi on the pump... more or less starving the pump ya know. . hmmmm???

 

[CCOLLAR]

My point was that just because your fuel pressure guage reads 0 doesn't mean the actual fuel pressure is 0. The problem could be in the sender due to cold weather and thick fuel.



So, I would suggest that you prepare your fuel for cold weather use -- add a fuel anti-gel/conditioner (Howe's, Stanadyne, etc. ) with every fuel-up. Find out if the fuel you buy is a cold-weather mix, e. g. , #2 mixed with #1 diesel, not straight #2. Ensure that the fuel heater in the filter canister works. Use strong batteries.



If the problem is more in line with the problem DLausche is experiencing, you might want to check your fuel pressure with a mechanical guage (assuming you are currently using a sender/electrical guage).



Good luck.



Craig

 

[WestTN]

cold...

It takes the fuel heater a while to catch up. Until it does, the pressure drop across the filter will be higher because of increased viscosity of cold fuel. If your filter is a little dirty this effect will be worse.

 

[JFinke]

At anywhere from 0 to -45* listed I doubt that the pump needs any return flow for cooling purposes! Mine is up to 5-6 PSI by the time the truck will read 140* in 0 to -10*F weather. I never drive below 140*. A mile or so down the road it is at it's normal pressure.

 

[DLausche]

Dealer called me back today and stated the LP is within spec because of the amount of fuel it delivers (not psi). I can understand the fuel pressure being lower when cold and the filter condition affecting the pressure. Their gauge was showing the same as my dash gauge and they measured on both sides of the filter element. They basically told me today that it is fine and normal for it to run with 0psi for however long it takes... Took over 25 minutes and 15 miles the other week at 0* for it deliver any fuel pressure at all.



Could this be considered normal at 0* with a fairly new filter and fuel considered to be decent??? I've been thinking the dealer is crazy for saying that there is no problem. Am I the one in the wrong here? Now they want to charge me $$$ for diagnosing nothing wrong with it. I'd certainly agree that the dealers shouldn't be doing diagnostic work on vehicles with no problems for free, but I don't think I fall into that category.



-Deon

 

[MatthewW]

Deon that truely sucks... I can see they dont want to be replacing the pumps for no reason. . just doesnt seem rite ya know. . I guess I am going to look into running duel lift pumps, one in the back by the tank to help out the other on the motor. .



read an article on this and they are getting upwards of 25psi of fuel after doing this on there trucks. . I just would hate to starve the injection pump myself. .



Must just be cuz of the cold weather and thick fuel, only cuz we are running gauges we see it. . going to start running some good additive to my fuel to, tring to thin it out a bit ya know. .





my regards and good luck with the dealer. .



matt

 

[CCOLLAR]

Deon,



You can always buy a new pump and replace it yourself, or have a Cummins certified tech do it. Its an easy-to-moderate install, and it will provide you 1) peace of mind, and 2) a spare lift pump. The pump run about $140. Labor should be 1 hour or less.



In re: the 25 lbs of pressure -- the injection pump is very peculiar about the fuel pressure it receives: too little, it'll wear out rapidly, too much, it won't start the truck. I think I remember 17 psi being the maximum reliable pressure.



So, just for your sanity, buy a new LP and slap it on there. Having the peace of mind will be priceless!

 

[DLausche]

My problem solved.

Went to dealer today to get truck back and they had figured the problem out! Diagnosis: bad LP! Will be covered under warranty after all.



More here: https://www.turbodieselregister.com/forums/showthread.php?s=&postid=822237#post822237



Matt, I hope yours turns out positive as well. Have a positive attitude with the dealer, be firm, and give it time at the dealership, if possible, as it might take some time like it did for me.



Thanks for everyones help.



-Deon

 

[PLaFrombois]

I'm in the same boat. I noticed that the pressure was low, and thought it was time to change the filter, or even bad lp. I was watching the gauge closely and was only seeing 7-8, I could even get it below 2. I turned around to come home and see if the filter was bad, and looked at the gauge and it read 12. I think as others have said, when it's cold the gauges don't read correctly until the fuel is warmed up. It's been single didgits here the past week, and doesn't look to warm up anytime soon. I'm just glad that I've normal reading, because I really hate to work on vehicles outside in this cold.

Paul

 

[daveshoe]

After seeing this thread, I decided to watch my gauge at startup. It usually comes right up, but now took a couple of seconds to get to 15psi. Normal is 15 to 17 , but when I kicked the idle up, it went to 21. My stock LP is probably one of the better ones in an '02. but I also notice that it reads less in very hot weather.

Haven't been using additives,but probably should