Engine/Transmission (1998.5 - 2002) Fuel pressure question

[Luke Warmwater]

Greetings,

New to the forum and have a question regarding fuel pressure. I have recently installed mods listed in my profile. I have been seeing 10-11 psi at idle and up to 11-15 psi while driving(3x5). I can pull it down to 6 psi or so WOT on 5x5. This morning I went out and started the truck. Went back in for a couple mins to grab some stuff and when I came out and climbed in I notice my fuel pressure was bouncing around at 2 psi. Rev it up and it would drop 1 psi. Well I'm like damn guess I won't drive this today so I pulled it back in the garage. Shut it off and after a few seconds I fired it up again. Pressure was right back up to 10-11 psi at idle. Let it run a few mins and it stayed up there fine. Question is what is going on? Never seen it do this before. Could the gauge be acting up or is my lift pump showing signs? What regulates fuel pressure? Disregarding the problem this morning of ultra low pressure, why does it seem to show lower at idle(10) verses normal driving in 3x5 of 11-13? Thanks!

 

[plongson]

Don't know if it would apply to you now, because warm weather is upon us (I don't know where you live) but when the grid heater cycles, it will momentarly cause the fuel pressure to drop. It has to do with the amperage the heater draws. It also makes your lights dim. Either condition should not last more than a few seconds, at least in my case.

 

[Luke Warmwater]

No help on this? For people who have suffered lift pump failure, what were the symptoms leading up to it? Anyone notice their pressure acting strangely as I described above? Thanks

 

[Casey Ray]

Had the same problem a few times, First time it was the Lift pump, second time it was sending unit, last time it was caused by a bad ground. I'd start with the electrical first, check you sending unit and check your ground connection.



cul,



Casey

 

[JPLB22]

I have a mechanical gauge with diesel all the way to the back ( no isolater ). But I am on my second LP. I replaced my 1st pump at 30,400 miles. I would be driving along on the freeway at 70 mph, at about 11. 5 psi, and then with no throttle change or load change on the engine, the fuel pressure would drop to 8. 5 psi. It would just stick there for a few minutes and then back up to 11. 5. I personaly don't like to see anything below 10 psi for regular freeway driving. So I replaced the LP.



This second pump looks like it is a terd right out of the box. I'm starting to get the same symptoms already at 9,000 miles on the LP. I'm convinced that if I hadn't installed a Wildcat Max Flow system at the same time as the LP, the LP wouldn't have even made it the 9,000 it has. I am going to try one more Carter LP down by the tank, if that one fails as quickly as these first two, it will be time for a FASS.



Not affiliated with Wildcat Diesel, just a satisfied customer.



Jeff

 

[Billy Diesel]

Originally posted by JPLB22

I I replaced my 1st pump at 30,400 miles. I would be driving along on the freeway at 70 mph, at about 11. 5 psi, and then with no throttle change or load change on the engine, the fuel pressure would drop to 8. 5 psi. It would just stick there for a few minutes and then back up to 11. 5.



This second pump looks like it is a terd right out of the box. I'm starting to get the same symptoms already at 9,000 miles on the LP.

Jeff

My first pump went slowly, just losing pressure over time, but this second one is doing what Jeff described. I will have 14psi at idle, be cruising at 11psi, then have it drop to 2-3psi, then hang out around 8psi, and then bounce up or down. #3 is going in next Monday. Thank goodness for good dealers!

 

[Ryan]

Another thing to check is the fuel system relay. I had a friends truck running a Blue start to act funny. Pressure dropping of and not being concistent. swapped out another blue and no change. He went to back out of the drive way to call it a night and the truck died. I was standing next to him when he tried to restart the truck and the Blue never cycled. Pulled the relay out and tapped it lightly a few times and put it back in and the pump worked fine. Replaced the relay the next day and havent had a problem with the pump running since. We did discover that he had a bad sending unit on his gauge in the process though.

 

[Luke Warmwater]

Thanks guys for the ideas!

 

[Shelby Griggs]

My guess is early sign of weak LP. My #3 started acting up recently too. Hot ambient temperatures (over 95° F) seem to cause the LP to stall. My #2 did this last fall prior to replacement. On Tuesday it wasn't heat, but for some reason mine started going very low and even went to a suction situation. I was WAY off road in 4 low coming downhill. Before I got back to pavement about 2 miles it started working again and has been fine since?? Anyway, all of my LP's failed gradually and one of the the first signs was intermittent low pressures.



SHG

 

[Tcolesanti]

My first lift pump went at around 38,000 miles and I put another on, great pressure for about 3 months (about 7,000 miles) and this one started to get intermittent. It would be fine 11-12 psi and then all of a sudden drop to 6psi. I just bought the fass setup and installed it today. The wiring harness they gave me left something to be desired.

 

[Beast2B]

Tcolesanti- What was your issue with the wiring harness? Looking at this upgrade, any other pros or cons?

Thanks

 

[SpicyJam]

Mine did the same thing, L/P replaced. Now I have what seems to be to much pressure... ... ... . 22, 23 at idle, have seen as much as 29 while driving at highway speeds. Can pull it down to 12 at WOT. Dump the pump, and all should be better.

 

[Tcolesanti]

I think the product was awesome. The billet aluminum fuel blocks and the pump are A-1, but the instructions in my mind were horrible and the wiring harness had a relay on it, that was never mentioned in the instructions along with the wires falling out of the back of the relay. I'm not an electrician by trade but I can hold my own. All I'm saying is that if I spend $550 on this setup the wiring harness should be bolt on, not hokey dokey like it was.