Engine/Transmission (1994 - 1998) fuel pressure readings?

[Moparsean]

Ok,I installed a pressure gauge after my fuel filter on my 12 valve,and I did look up the spec. I have over 25 at rated rpm,but it swings a bit from 21-29 when i matt it to the floor in the driveway. Is this aceptable? Also when i pull a hill and my foot is threw the floor,i go down to 8-10 psi... is this normal? It goes right back up after i back off some. Never had a gauge before so just wondering what you guys see on yours. Could the swinging needle be a air leak on the suction side? i still need to by-pass my fuel heater,i have heard they suck air some-times. I did look over the suction hoses for colapsing issues,they look ok. Ideas on those numbers? Seems to run ok other than a quiver at one rpm... . but i have heard that is common.

 

[Moparsean]

Soooo... . anyone have any opinions? My gauge only goes to 30,i have a new one on order that will go to 60. From what i read in the past forums,most of you are up in the 40 range or so. I have more shims for my overflow valve,so i'll adjust it up more that direction when i get my new gauge. Also should i bypass the fuel heater /screen entirely and go straight into the transfer pump? I do have a pre-filter in line even before the heater/screen on the block (checked it,its ok). I'm just concerned with the 8 psi when i'm really into the throttle for a long time. Its like 20 -22 down the road at 68 mph on a flat. 28 -30 at idle... . about 25 or so at rated rpm in the driveway,with a slight fluctuation,but i think it could be the gauge as its a mechanical.



anyone have the screen in the tank block up and cause something like my 8 psi reading? ok am i worrying about nothin?



the lift pump has about 20k on it,i know that doesn't mean its good... . just seems that the volume isn't there when i matt it for a while... seems to run ok though...

 

[DBraunig]

I don't think your pressure should be falling to 8-10 loaded like that. The first two things that come to mind are the fuel filter itself (change it), if that doesn't help, remove and clean the prefilter screen. I have seen the tank module restricted with debris, but it's not the 1st place i'd start. If you get that far the tank module screen can be cleaned also.



Dave

 

[Moparsean]

fuel filter is brandy new,i'm going to look at that pre-filter on the block

 

[Joe G.]

Email me at -- email address removed -- for my write up on the 12 valve fuel supply system, how it works and how to fix it. It has how to deal with the fuel heater with pictures.

 

[JDiepstra]

Just a thought... with the fuel plate mod and injectors maybe it is normal to see that low pressure, as you did say it is only when you are "really into the throttle for a long time". But I have no idea.

 

[Joe G.]

Mine always has fuel pressure above 30 PSI regardless of throttle and I have 270 injectors and a 0 plate. The FP is mechanical. The faster the engine turns the more it pumps.

 

[hsmith]

Could it be a weak over flow valve?

 

[Joe G.]

It might be, but the good pressure some times symptom is not quite right for a weak overflow valve. A weak OF valve usually causes low pressure that stays that way. When my OF valve failed the pressure got worse and worse regardless of how I was driving.

 

[Moparsean]

I tweaked the overflow valve (its only a year old) already with some shims from another valve i had. I didn't go crazy,cuz my gauge pegs at 30 till my new one comes in. Thanks joe,i will e-mail you on that fuel system info. When i first got the truck about 25k ago,there was mud... and i mean mud in the filter,it wouldn't go over 15mph. So i drained the tank by siiphoning it from the neck,change the filter and all was good,but i did have to change the lift pump at that time too,it was factory with over 400k. I had to change filter every month for about 3 months then the crap finnaly worked its way out of the tank and i could go 8-9 months on a filter. i have never had the block pre filter off since i had the truck for 2 years now. its a place to start. I gotta fix the fuel float anyways... been broke for 2 years,so maybe pulling the tank is an idea as well to check for stuff on the screen on the module. thanks to everyone for there ideas,i plan on diving in again saturday night,so stay tuned.

 

[Joe G.]

The info is on the way. You may want to dose the fuel with a biocide. That sounds like algae in the fuel. When I bought a fish boat quite a few years ago it was infected bad from sitting for over a year with the tanks almost full. 1000 gallons of diesel with algae is no fun. The biocide killed it just fine. Then we had a LOT of dead algae (think dark snot) in the fuel. It took a lot of filters to get rid of that. Some of them had to be changed in rough sea conditions.

 

[hsmith]

Know about the gauge problem. My 30# would peg easily then started leaking around the bezel. Replaced with a 60# and after a few weeks, it did the same thing. Both mech Isspro units. Running without one now. May go electric.

 

[Joe G.]

I use a Westach electric fuel pressure gauge. It is at least eight years old and has always worked fine. When my OF valve failed that was somewhat of an acuracy test. I have marine alarm sensors on my fuel and oil pressures. It alarms at 10 PSI and turns on a light. When my fuel pressure as indicated by the gauge dropped below 10 PSI the light came on so the gauge and alarm agree.

 

[JHenry]

You didn't say whether your gauge is electric or mechanical. I bought Pricol gauges for my '98 12v, including an electric fuel pressure gauge. They assured me the electric gauge was as good as the mechanical gauge. I have had wide ranges of readings ever since installing, from 2# to 30+#. I have called the tech support several times and all I get is that it must be a bad ground or inconsistent voltage or that this is just how it works. No problems with the trans. temp. gauge or the pyrometer gauge.
I have learned to ignore it, since the pressure in the 12v is not as critical as in the 24v.

 

[Joe G.]

The fifth word in my post above is electric.

 

[JHenry]

wrong post

The fifth word in my post above is electric.

Sorry. I wasn't responding to your post. I was responding to MoparSean, the guy who originated the post. I don't think he said whether his gauge was electric or mech. :-laf

 

[Moparsean]

ok guys,looks like its the freakin gauge at this point. Its a e-bay iso-pro mechanical unit. Found it leaking antifreeze on the carpet today. The readings were steadly gettin worse since my last post. I'll talk to joe or who-ever thinks they have a good electric set up. Is there a kit,been lookin on the net,no luck yet. I can use the tapped fitting i already have right?

 

[JHenry]

I would stick with the mechanical type. I wish I had bought a mechanical one instead of electric. If you really want one I'll sell you my Pricol electric 0-60psi complete for $90. Paid around $170.

 

[Joe G.]

Email on the way.

 

[DBraunig]

Joe,



I'd like to read your write up on the fuel system as well. I sent you an email.



Thanks, Dave