Engine/Transmission (1998.5 - 2002) Low FP

[Ramboy]

Since the beginning of winter, I have had very low fuel pressure readings on startup. When first started, gauge reads 2 psi. After everything gets nice and warm under the hood, gauge reads 12-14 psi. On warm days, on startup I will get 10 psi or above. I have a Nordskog digital gauge and I am suspecting the sender may be the problem. Anybody else with a Nordskog unit experience this problem?

 

[Wheaties]

I've been getting low fuel pressure on cold cold mornings too. But only for a few minutes, then it comes right up to normal. The fuel filter is heated, and a significant amount of fuel passes through the injector pump and returns back to the tank. I suspect that this may be the onset of fuel gelling? I haven't checked or drained my filter in quite awhile, water could also be a factor.



Matt

 

[Bob Wagner]

I've been having the same problem. but if I plug it in for a couple of hours then the low fp is gone



stsrt up cold snd is 8 psi max and drive down the road can drag it down to zero, but plug it in and its good to go with no fp drop at all



btw westach gauge and sender and all pressures check with a Rip mechanical gauge

 

[fmj]

I'm running a Norskog gage and have noticed that I have "lost" a pound while running since the temp has gone from hot to cool. I'm no where near as cold as you guys. My pressure used to run at 12 all day long. Now it can get to 11. Not much difference, but I thought that I was beginning to see a LP going. I have a new one under seat, but haven't changed as it warmed up and the pound came back. I think that you guys are seeing a more dramatic change because of the real cold. I'm running my gage post filter. I wish someone had a clear idea on this.

 

[Mad Bomber]

LP?

That's how my LP started going down hill. It did that for a week or two but then it died. Eric

 

[Bigsaint]

IMHO it's fairly normal to see a slight drop of FP when the fuel is cold. Every pump I have tried, with the exception of the PE4100, which failed, always had lower psi's, to the tune of 1-2 psi's until I was about 30-45 minutes underway. The 4200 I'm using now appears to be extremely prone to lower psi's when the fuel is cold.



Ramboy, to eliminate the possibilty of a failed sender, pick up a small mechanical gauge and plug into your port where the Nordskog sender is located. You can pick a 1 1/2" gauge from Summit Racing or Jegs for about $20. 00. Even less for a generic psi gauge from Graingers. They have a 1/8" NPT fitting on the back of the gauge, and you can use some 1/8" tubing and 2 compression fittings for your temporary test gauge. Total cost maybe $25. 00.



A swing from 2 to 12 psi's is a bit much, and I'd be concerned about pulling vacuum numbers when cold, if it is your pump and not the sender.



Scott W.

 

[Mad Bomber]

F P

I agree with Scott W but the cold weather brings it out more. With a new pump it was a lot safer psi's for the injection pumpeven in the morning cold.

 

[Wheaties]

Interesting, I confess, I didn't look at your location Ramboy when I first posted, because this sounded exactly like what I am experiencing in the "Great White North". How cold does it get in New Mexico?



My lift pump did the same in the summer, just before it failed.



Matt

 

[John Berger]

I'm getting the same behavior as you. I don't this occuring in winter prior to this year, but it has been colder than usual down this way. Once it runs for a bit, my inlet pressure stays right at 7-8 cruising.

 

[wlowe]

I have the same problem with my FP. My sender is remote mounted with a two foot line coming off the banjo at the bottom of the Fuel filter. When it's 50 degrees or above I get a startup pressure of about 12 psi. But when it drops to the 30's or low 40''s my start up idle pressure jumps between 4 and 8 psi, sometimes jumping up to 11 then back down. After 5 to 15 minutes it returns to a constant 12 psi at idle and finally tops out at 14 psi when fully warmed up. Warmed up WOT runs about 9. 5 - 10 psi. I haven't tried WOT with the colder psi but I'm pretty sure it would be close to zero. I figure I will baby it for now, keeping an eye on startup psi to see if it gets worse. As long as it shows a positive startup psi I am hoping there will be no damage. If warm psi starts to drop I will definitely be replacing pump.

 

[pwr2tow]

I have been reporting this to people all winter. Are lift pumps are week to say the least and if your using #2 fuel the viscosity thickens with colder temps and is harder for the lift pump to pull and push. Mine acted like it was going to die and then I thought I would try a blend of 50% #1 and #2 fuel and have had no problems in the last three months and the temperatures have been down to -30 F.



Any thing a person can do to improve the viscosity of the fuel will help the lift pump live longer.



Ron

 

[pwr2tow]

Also if i am not mistaken the ECM controls the lift pump cycles and upon start up the pressures will be lower, than as long as the heater grid is cycleing the lift pump pressures will be lower until it stops cycleing, slowly increaseing in pressure until it tops out at normal pressures.



Ron

 

[pwr2tow]

The ECM pulses the current so fast that it is undetectable to the human ear but that is how it lowers the fuel pressure.



Ron

 

[pwr2tow]

geessss, I'll get all in here soon.



Hence the colder it is the the longer the heater grid cycles the longer it takes for fuel pressures to come up to normal. This coupled along with thicker fuel from colder temperaturs leads to the problems some are haveing.



Ron

 

[Ramboy]

Wheaties,

It was in the low 20's at night when I was experiencing this problem. The lows have warmed up to around 40 and I don't see the problem anymore. It seems that either the LP or the sender is temp. sensitive but I still don't know which one. I think I will get a mechanical gauge and try that.

Phil

 

[Goddard]

ramboy that is the same thing i have been having with mine

after it has run for a while then no problems. when it is cold like 20's or under i can pull a vacuum if i push it hard at all

 

[Wheaties]

Originally posted by Ramboy

Wheaties,

It was in the low 20's at night when I was experiencing this problem. The lows have warmed up to around 40 and I don't see the problem anymore. It seems that either the LP or the sender is temp. sensitive but I still don't know which one. I think I will get a mechanical gauge and try that.

Phil

I'd think that would be cold enough. Do they sell winter fuel in NM? If you got a batch that wasn't, it could have an effect.



I'd suggest that the heater grid cycling and the lift pump being pulsed to reduce pressure are two separate things. The lift pump is pulsed at startup by the ECM to prevent an over pressure condition that can prevent the injector pump from operating properly. I believe this is because the injector pump isn't drawing much fuel at startup and 'overpressure' is anything above 20 psi. This has been documented as a 'Hard Start Contition'. The heater grid will draw the voltage down to 12V when it cycles, and this may have some effect on the lift pump, but not enough to cause pressures as low as we are experiencing. At most this should cause a 15% drop in pressure, say from a normal of 12 psi down to 10.



I'm experiencing a drop from 12 to say about 2 on these cold start days.