low fuel pressure
 

95 dodge all stock. I've had problems with this truck running rough and blowing white smoke when starting up cold. Put a new LP on awhile back and no change. I've pressurized the tank several times and looked for leaks...nothing.

Got a fuel pressure gauge put on today and pressure seems to be low. Holding 13 psi at idle. 20 at 2500rpm. On the highway it drops to 10 when I put my foot down.

Could something be restricting flow? (F
(Filter is new)

timing issue .. :s:

^ What he said. A 1995, all stock, chances are extremely good that the pump timing has never been messed with and has probably slipped. It will do that, and it doesn't take two decades... so I bet you're probably 3-4 degrees low at this point. It can eventually slip so low that it'll barely run. It only takes a few minutes for someone who knows how to do it to check it and see if it's where it belongs. Not that it hurts to check the flow culprits yourself: how old is the fuel filter? The pre-filter screen in the fuel heater can also get pretty full of crap if it isn't popped out every now and then.

Seems pretty low fuel pressure wise. Overflow valve ok?

Sent from my SCH-I605 using Tapatalk 2

I was kinda thinking the overflow valve too, especially if its the original.



Sent from my iPhone using Tapatalk

ofv all the way.

Yea I pinched the return line this morning and my pressure jumped to 30. It has a tork tech adjustable valve on it. The plug seemed extremely loose. I could turn it with my fingers.

I turned it down a little bit now getting 20 psi at idle. Only 25 at 2500rpm. Didn't seem to help the cutting out and white smoke. I'm going to order a new valve and if I can find someone to check my timing.

Any recommendations on the ofv I should get? Brand? Adjustable?

Truck still have a fuel heater?
I'd crank the fuel pressure on up and leave that ofv in place.
Sent from my SCH-I605 using Tapatalk 2

[QUOTE=burnhedge;1058386]
I'm going to order a new valve and if I can find someone to check my timing.
QUOTE]

i will be in KS in about a month. you got tools? LOL

Don't crank the ofv to much ... You will damage the IP if the flow isn't enough to cool he pump ...

As for the fuel heater I pulled out the plastic element back when I put the LP in. I didn't delete the housing just put the top and bottom back together. Pretty sure I put the screen back in.

I'm going to play around with the ofv adjustment more when I have time.

You might put additional strain on the lift pump but the injection pump won't be hurt until over 60psi according to quite a few big name pump shops. We've got a couple floating around at 35-40 with no issue. I see where your coming from but don't think you'll overheat the pump. After all the pump if oil lubricated and cooled.

Sent from my SCH-I605 using Tapatalk 2

---AutoMerged DoublePost---

Stay in the 35-45 range and you'll be fine. If the problem continues you'll most likely be looking a timing issue.

Sent from my SCH-I605 using Tapatalk 2

Good to know ... didnt have any numbers top go with the thought ..... just know its not real good to over do it ... :c:

I've heard they run really well at 60psi. Of course, it's pointless without significant mods to just about everything else, but still.

ahhh ... good to know :tu:

The bottom half is lubed by oil the plungers and barrels are lubed by fuel. Pinching off the overflow is alright as long as some fuel does return to the tank. For most street trucks 35 -40 psi of pressure is all you need.

If you really crank down on it the LP will make over 80. (Don't ask me how I know lol) I've never measured how much is returned but it seems like a good bit would still be returned at 35-50. Years ago I had a discussion with the guys up at enterprise and he mentioned that anything over 50 there was a chance of actually locking the rack up. I've never heard of or seen that happen but I'd rather not take that chance. The real benefit I'm guessing is fill time is reduced so all trucks benefit, big power trucks benefit more.

Sent from my SCH-I605 using Tapatalk 2

Very big power trucks.

Like 700+.
Still can definitely tell a difference in a stock truck or a 400hp truck but no insane power gains until big numbers.

Sent from my SCH-I605 using Tapatalk 2

Yes. Very big. My point (and I'm pulling this statistic straight out of my ass here) is that probably 90% of the 12V's on the road, running 60psi is as silly as a triple disc TC on a stock tranny.

I'd say more than that! Closer to 99.9% lol
But 30-40 is awesome.

Sent from my SCH-I605 using Tapatalk 2

Wait... so you're saying... all these guys that I meet like, almost every day, who are pushing 1000HP with stock head studs and twins, chewing up ZR1 Corvettes and spitting them out on the highway are... lying?

:nshock:


I'm glad we're on the same page here.

As for locking the rack (again, really whinging it on this) isn't that more or less likely to happen based on the model year p-pump in question? I'm not super clear on the differences, but I thought there was more to it than DV's.

Oh you have those guys too!?!?!? Are they the same ones who tow 25k at 700rwhp too? Lol
His explanation was they had a pump on a puller that was running a very high fuel pressure with no return (80-100psi). Mid track the pump ran away. They then benched the pump and found the rack "hydrostaticaly" (sp?) Locked. I'm not sure how you would determine that, What it is or how high fuel pressure would relate to that.

Sent from my SCH-I605 using Tapatalk 2

It depends on how the pump is set up for how much pressure needs to be run. For the locking the rack up with more pressure I personally have never seen this happen but at a high enough pressure I can see where it may happen.

You are correct on the fill time comment making power at higher rpm will require more fuel pressure to a point. Like it has been stated in this thread most trucks will be fine with 30-40 psi of pressure .

---AutoMerged DoublePost---

That is why the rack stuck. fuel must always return to the tank, that is how the plungers and barrels stay cool and lubed.

I've scaled 25K with a lot less than 700HP, but that said, over 7K of it was the truck.

Regardless, my best guess of what they were trying to say is- (since hydrostatics is essentially the science of liquid pressure at rest) that they somehow determined that more fuel was crammed into the pump than the rack had travel to move out the other side.
That isn't the way I'd have put it, but I'm sure they know more about it than I do...

That comment I made has a back story. A diesel mechanics group on Facebook has a number of members who feel their trucks are just as reliable at 500+ plus as factory trucks and towing has no effect on reliability while towing at those power levels. On guys goal is actually to build a 12v truck to pull 25k at 700rwhp. Not saying it can't be done but it can't be reliably done.

Sent from my SCH-I605 using Tapatalk 2

Well, I know mine has nowhere near 500, never mind 700. Hell, I'd be shocked if the average working power was half that. I do think it's a whole lot more reliable towing as it sits than it ever was from the factory, but most of that's the tranny. It just so happens that a tranny like this on a factory 12V is, well... sort of stupid.
Regardless, towing is a whole other ball of wax than running down the drag strip for sure, even if your venue means running down the drag strip with a sled behind you. It seems like anyone who knows their stuff should be able to make something hold together for under a minute of abuse, whereas pulling twice your weight across the state is a little more demanding on the reliability scale than it is on the dyno.

That all being said, most of the newer trucks in our fleet claim more power right off the showroom floor than mine optimistically has turned up as it is, but they all go out to work every day, and mine has proven to be far more reliable than these "factory supertrucks", out-performing them in every way but brakes, and cheaper to fix when it hits the fan. I certainly wouldn't say they are more reliable, modded or otherwise, and mine works circles around them to boot. But I may be missing your point.

I'm saying that a truck built with 300rwhp made to make 700rwhp regardless of modification isn't going to be as all out reliable as a truck with 300rwhp. They wear quicker. Design limits if you will. If the truck was factory built with that power and torque in mind absolutely. I'm not claiming that the trucks are not reliable, just saying added power reduces reliability, pulling more weight reduces it further. Any of the older trucks are far more reliable in my opinion than the newer ones. But taking a 12v to 700rwhp and maintaining egts, driveability, and keeping it in one piece is not as easy as some will have you think.

Sent from my SCH-I605 using Tapatalk 2

I couldnt agree more with all of ya ....


The more HP.. the shorter the lifespan .. no matter what the case is ... gas or diesel :s: