atc250r

I installed the FP gauge today and used a needle valve just barely cracked open to dampen the fluctuations from the pump in order to avoid damage to the gauge. I've got the truck idling and the pressure is a little low (15psi) but the gauge still has a little (1/2 psi) fluctuation from the pump. If I turn the needle valve any further closed then the gauge is very slow to respond to the changes in fuel pressure when the engine is revved. Is that very little fluctuation OK or do I have to close the valve a little and live with the slow response in order to prevent damage to the gauge?

Thanks.

John

John_P

John:

I was looking at your signature to see what kind of gauge you had??

To start off, IMO,.....15lbs @ idle is too low for that P-7100 Fuel Pump. You should have 25-30lbs @ idle and I don't feel that the pressure should ever get below about 20-22lbs. I would run a check of that pressure with a true mechanical gauge right off the pump, or close to it, to make sure you have good fuel pressure.

I ran the electrical type F.P. Gauges (Autometer and Isspro) on my 1996 and had ALOT of trouble with them. I used a "snubber" also and had the same problems you describe with the "fluctuations" as the engine ran. I had to have my "snubber" closed down pretty good but left it to where I was still reading "accurate" F.P. if that makes sense to you. I based my settings on what a true mechanical gauge read. Even with all that, NONE of the sending units on either of my two electric F.P. gauges lasted longer than about one year! It was frustrating, so I finally went to a "DiPricol" Mechanical F.P. Gauge but with the Isolator! My son had run one on his 2004 Dodge CTD CR and liked it very much and recommended it to me. It is the best thing I ever did! This gauge reads super accurate, there is no more of the constant
"fluctuation" as with the electrical gauges I had and they are pretty easy to install.

Hope this helps you some. Good luck buddy!

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John_P

infidel

For comparison my needle valves are cranked down enough that it takes maybe ten seconds for the gauge to come up to idle pressure when the engine is started. The needle is rock steady though.
FP on a 12 valve is just the mean of averages anyway since the lift pump pulses so much on each stroke.
Sounds like you need to replace your OF valve but think you already knew that. 18 psi is lowest I'd go at idle.

Geico266

What you are watching a guage for is trends in the readings over the long haul. Tighten down the needle valve so the guage moves slowly. Fluctuations or "bouncing" are the kiss of death for the delicate innerds of a guage.

TxDiesel007

As stated by John P and Infidel

I was having the same problem you are having, BUT i was gettin 10 psi at idle, Not good. Anyways be sure and you check the fuel return line and feed line for leaks. You might also want to check out the prefilter, and the fuel filter and get some new ones for your truck. If you have to ask what a pre filter is, then well, im sure it aint been done yet.. But anyways check for leaks and replace the filters, that would be a good enough start. What you are possibly looking at is a dead LP as well but there is a simple way to test for a bad OFV and a bad LP by doing this..

Go ahead and pinch the fuel return line (the one behind the fuel filter) or if you look from the driver side to where the lines are to the pump, the rear line, think of it this way, Front fuel, rear return, and with some small vice grips pinch the line. If your FP skyrockets to 60 psi or so right away you know your LP is good and your OFV is possibly bad, Pinch it three or four times in various locations to see what effects you get. If you get the same results you know ur LP is good and OFV is bad.. Try a replacement and see what it does for you... IF the FP dont go up then you know ur LP is shot for sure, and chances are that your LP and OFV are shot at the same time, If your truck has over 75K miles on it, chances are its shot for sure..

anyways before removing it, please make sure and grind the area around where you can pull off the OFV to facilitate its removal. TRUST ME youll thank me for this later... and replace it with a new one, no big deal a two 3/4 wrench and 5 minute job.

atc250r

Thanks everyone. Bill knows a little bit more than everyone else since I've been PM'ing with him about my set up as of late. I've got an Autometer Industrial 60psi mechanical gauge on there. I'm totally aware that the pressure is a bit low but I was just basing that on the factory spec of 17psi at idle and 25psi at 2500rpm, I'm about 2-4psi short on both of them depending on how long she's been running. I've got an OFV and LP sitting here waiting to go on but I wanted to get the gauge in first so I could get a before and after comparison. The pressure drops to about 10psi by the top of 4th so now I've got some real numbers to compare when I install my new OFV tomorrow. The LP will go in when it warms up a little, we're not supposed to get out of the 20's for the next few days and I've gotta work tomorrow which is supposed to be the warmest day for a while. I'll tighten that valve down a little tomorrow and put it back to the position it was in when the gauge moved slowly since it seems that's the way to keep it alive.

Thanks Again!

John

atc250r

007,

I read your posts about having fits with the fuel pressure in your rig and I even printed out the "How-To" you made about doing the LP. I'm going to do the lines with marine hose as soon as time, weather, and money permit but I will do them at the same time I do the fuel gauge sending unit. I should have put a little more info out there since I should've know that you all would be asking the questions that you have put out there. Yes, I have a new Fleetguard fuel filter in it (just did it last week), I'm going to do the prefilter when I do the LP, and I got a lift pump and OFV from Marty at Precision just the other day so I should be good to go after this. Hopefully this'll wake her up since it should be putting down more power than it is with the mods on it. BTW it only has 76,000 on it but 11 years has taken its toll.

John