I installed my lift pump relo and big line kit a couple weeks ago, and a new fuel filter cartridge. My pressure was running about 14 at idle, dropping to about 12 under heavy acceleration/towing. Now the gauge is pretty slow to react, and likes to stay around 12.5 at idle and 10ish under power. Any ideas on what might cause this, and is it normal?

Another cause for concern. When I had the gauges installed about a month ago, I had pretty low fuel pressure. About 8 at idle, 4.5-5 at normal driving, and could suck it down to 0 at times. Replaced and relocated lp, etc. Worried that the vp could have been starving for quite a long time, and might have shortened it's life span. Haven't seen any symptoms yet, but I hate having something to worry about all the time.

 

Not much to add on this one, but are you taking into consideration how full the fuel tank is? Might have a slight effect on pressure, I've never checked it my self.

 

I don't see a comp in your sig, if you were pulling the lp to 0 with stock fueling......the lp is done, there is only sooooo much a big line kit can do for you. the fact that you had low fp readings, and now have fluctuating #'s all but confirm it.

 

I forgot to add that I replaced the lp with a new oem pump when I relocated it. I'll just watch and see what happens, it is running at 11 psi on the highway now, empty. Gonna go pull my bobcat with it in a minute and see how it does.

 

You got the isolator set up with your gauges, right?

I would check everything up there before I blamed it on the new LP. (not that it would be the first one to die quickly)

Where'd you get your LP from? Warranty?

 

You might be right PJ. I'm suspecting something with the gauge/isolator now. My fuel pressure this evening towing the bobcat remained on 10 psi, no matter what, even under stout and prolonged accelleration. Needle moves very very slowly, took it about 6 miles of driving to move off of 8 psi, climbed up to 10 and stayed there. When I first started the truck, it was at 5 psi, then slowly climbed to 10. I turned it off, came back a few minutes later and started truck again, this time went to 8. Then I drove it, slowly climbed to 10 like I said...

I guess I could check the fuel pressure with a mechanical gauge at the port where the gauge line runs into the connector on top of the fuel filter housing. How would I be able to diagnose a bad gauge (doubt it) or a bad isolator? Is there a way to remove the isolator from the system, and would I have to buy any more parts to do so? Not too worried about fuel in the cab, just want the gauge to work.

Could there possibly be an air bubble in the gauge line? I did have to bleed the injectors after I installed the big line kit, but the gauge seemed to work fine for a week or so after that. Did not mess with the gauge line, other than reconnect it to the new vulcan adapter.

 

You can drop the isolator, no problem there. I have the same tubing that is used with a boost gauge. I think it is oil resistant air brake line. Anyway, some new compression fittings, a needle valve and soem 1/4" fuel line from NAPA to "sheath" the tubing in and you'll be good to go.
You have a braided SS line to the isolator? You could just switch over to tubing there also. If you don't already have a valve inline, that'll be a must have with the fuel in the cab and all.
I don't imagine a litle air in the line would cause your issue. Is the line from the isolator to the gauge filled with antifreeze?

 

No idea about the antifreeze. The line to the isolator is braided stainless. Maybe if I just take the truck to napa and explain the problem, tell them "compression fittings, needle valve, and inline valve" they'll give me the right stuff. Is it pretty straight forward to unhook the isolator and install the other fittings? I'll have to do it tomorrow.

Dumb question, what is a compression fitting? Just where you would be connecting the two lines and the valve together?

 

The line from your isolator to the gauge should have been filled with anitfreeze (I think)

I would do a quick search, the needle valve is a weatherhead part, I have the number written down here somewhere, it's basically a 1/8" NPT 90* brass needle valve (looks alot like the saddle valve that would connect an icemaker to a fridge.)

MoparMan1973 has a nice pic in his gallery, I have a picture of tiny ball valve I used.
The compression fittings are what came with your boost and F/P gauge, they are made up of the outer (nut) and a ferrel that slides over the tubing to compress it when the nut is tightened. If you look on the back of your boost gauge, you'll see what I mean.
Careful, you don't have to man handle these small fittings, tighten them too much and you can damage them or crimp off the tube all together.

 

Thanks PJ. I'm gonna try to round up the parts today and remove the isolator. I think that is most likely the problem. I hope so anyway. Gonna get the GM brake cylinders while I'm in there too.

 

The guy at napa was worried that if I connected the braided ss line from the filter directly to the line going to the gauge that the pressure would be too much. I don't know. Basically, I'm just hooking the two lines on either side of the isolator directly together right?

 

Depends on whether 15psi is "too much", no worries.


phox

 

Yeah, too much is a relative term. If you had a 5 psi gauge I would agree, but for our purposes I think he's wrong.
In his defense, he may be thinking that since you told him you were a diesel application he's thinking of the 14,000 pis (or whatever it is) on the injector side of the IP.

Yes, essentially you are just taking the isolator out of the equation. Now then, if you still have the same readings, I would (if it were me and I already owned an isolator) just hook it right back up and move on to the LP as the cause.

I have heard many stories about failing isolators though.

 

I'm gonna check the pressure at the fuel filter first, removing the isolator from the system is gonna be a giant PIA. Sort of. I'd have to take the gauge out of the pod, hook the new line to it, route it through the firewall and hook it up. This sucks, the isolator and the whole gauge system are only a month old.