Today was the first cold day here in this part of Texas and I noticed that my fuel pressure aint as high as it used to be when warm outside (idle, cruise, or wot). I usually idle around 18 and can't drop it down below 15 at wot w/ the Holley black. But today, I couldn't get'er above 15 at idle and wot was at 10. Any ideas? Come to think of it, I haven't replaced my fuel filter in about 10K miles, so that might make a difference. After the truck warms up after 15 mins of driving, my fuel pressure slowly climbed back up, but not as high as it usually is. But I'm wondering if any of you guys experience anything similar to this.

P.S. When I first started up the truck, the needle on my fp gauge bounced back furiously between 12 and 22 psi. Any ideas w/ this also?

Any responses welcome (expcept from BigBlue)

 

This is my first winter with the guages and I've noticed lower pressure.
Used to idle at a rock steady 15, now about 14.5.
Cruising was around 12-13, now around 11-12.

I'm due for a fuel filter change as well, planning on tackling this weekend.

Just figured it was normal, or would go back up after I change my fuel filter.

Wasn't going to ask till after I did the filter.


phox

 

Over the last few years I've noticed my pressure drop due to the grid heater current causing the alt to pull harder. After the grid heater kicks off my pressure goes back to normal. Cold weather also can cause the filter to not flow as good , I guess sort of like the way materials expand when warmed.

 

Ya, I no that the grid heater causes fluctuations in fp readings, but this violent bouncing seems a tad extreme for it to be just the grid heater.

 

When the temperature drops the viscosity of diesel gets thicker, it does not flow as good, even blended is thicker a colder temps.

Every winter and every spring mine does the rapid flucuation in pressure but settles down as soon as the outside temps stabilize, be it cold or warm. No explenation on that one.

 

dodgediesel4x4,
My gauges have only been installed since it's been cold out here. Did'nt have 'em on yet in the summer, but I don't notice the fp moving around too much at idle....just a little when the grid heater cycles.
Do you have stock fuel lines ? I wonder if bigger (3/8") lines would help give a smoother reading when cold? Do you have any pictures of how your Holley is plumbed in? I have a Holley Blue that I need to install soon. I'm seeing 10-11 @ idle, 7-8 @ cruise, and have to be really careful about going below 5psi., and that's all with the TST on Level 1. My fuel filter only has about 4k on it right now, so I don't think that's the culprit.

 

It's from the grid heaters kicking on and off. Mine does it to. My PE pump did it. When I had the black on my truck it did it to.

 

At start up the fuel pressure will be low, as the heater grid cycles the pressure begins to increase with each cycle until it reaches normal operation and pressures.

The irratic pulsing some are referring to is not heater grid cycling, there is some other factor involved that is not known. Like I said mine will do this when the outside temperature takes a dramatic turn, summer to winter and then winter to summer. I have seen the irratic fluctuation even when the truck is totally warmed up and driving down the road, the heater grid is not cycling. Then for no reason it stops fluctuating and all is fine until the weather changes again.

over the last two years I thought it was the lift pump going bad, biodiesel cleaning things out, contactor in the power distribution panel, evil spirits, etc. etc. but the only thing that has been constant is the weather changes.

Sorry I couldn't help with more positive information on why the fuel pressure does the extreme fluctuation thing but with electronics as engine controlers it could be as simple as a corroded wire or a glitch in the ECM program on some trucks.

 

Keep in mind....
You live in TX. They're not going to put the same amount (if any) fuel additives down there as they are up here in CO. We need the anti-gel additives to keep our trucks running up here, but odds are you won't see the 3 degree weather we had here last night.

Another thought- I run Biodiesel in my truck, and I know that when the temp dropped (and they hadn't been adding additives in the fuel) I was showing ridiculiously low FP's- 12PSI idle, 8psi WOT. This was at 35 degrees. Since they've been adding them- i'm seeing my regular 15PSI idle, 10psi WOT.

 

Mine has gone from 15 to as low as 12. Once the truck warms up it gets back to 14. I figured it was cold fuel. My pressure guage is before my stock fuel filter. I have both the FASS system and the stock system on my truck. I have an isolator on the mechanical and it uses anti-freeze to supply pressure readings. Maybe I need a better mix of anti-freeze. Looks like -30 this weekend.

 

You worry to much dd4x4, you know that.

 

exactly. and the fact that the grid heaters are cycling. normal for my truck as well in the cold.

Pat