Truck in sig in question. IP/LP about 2.5 years old. Have a fuel pressure gauge, usually reads 14-15 at idle and 12-13 cruising down the road. Replaced the belt tensioner, lower radiator hose, belt the other day. Anyway, the batteries were disconnected for about 2 days. When I test drove it last night, no problems, this morning on the way to work, fuel pressure (according to gauge) fluctuated between 8-15 down the road, finally dropped to nothing. Truck runs fine. I've had an issue once or twice with the pressure gauge reading low, if I shut the truck off and turned it back on, pressure gauge read fine. I'm expecting to start with a fuel filter, but was wondering if there was anything electrical that could be affecting my situation. Let me know. Thanks.

 

All could be the problem with out testing .
Low pressure can kill the main pump so make sure to use an other gauge to confirm the reading from the other gauge , have both hooked up at same time so if the read different , you can find a bad gauge or not , possible electrical with gauge .
Look for electrical connection issues with gauge and lift pump .

 

How many miles? May still be under warranty.

 

The LP/IP have about 50k miles on them since install. I just checked the codes, none showed up. Started the truck and the fuel pressure gauge is showing 14-15 like usual. I'll start by changing the fuel filter and checking the wires on the pressure gauge. I've been thinking I may have an electrical issue due to the way it sounds when it starts lately, maybe this is part of it.

 

Youre leaving out an important part of the equation - what kind of FP gauge do you have (mechanical w/ isolator or w/o isolator or electric), and how is it installed?

Sounds like the LP to me.

 

The pressure gauge is a mechanical ISSPRO. I had it installed while they were replacing the LP so I don't know for sure about the isolator. I would guess it probably doesn't have one.

 

ok...

Being an Isspro I would assume that its a mechanical guage - theres no need to check the wires since they only supply lighting to the guage.

If you follow the fuel line where it goes through the firewall it should be pretty obvious if you have an isolator or not. If you do have an isolator, temporarily bypassing it and running the fuel to the guage will help you see if the problem is with the isolator or not.

if you havent changed the fuel filter lately, thats probably a good place to start.

 

I missed this....do you mean that theres a unusual sound from the lift pump when you bump the starter?

 

The sound isn't out of the ordinary. The last couple of weeks the truck seems to crank a little slower. After I read your question about the fp gauge I realized my ignorance there. Of course if it's a mechanical gauge, there won't be electrical issues. I'm going to try the fuel filter first and see what happens. I'm just not looking forward to the cost/inconvenience of another LP or IP replacement, if that's what it is. The fuel filter is due anyway, so I'll start there.

 

Good Luck.

FYI, the stock LP isnt worth the money. Yes, the aftermarket pumps are more money but they are worth the extra $. There are some very good deals on the Air Dog pumps right now.