Hi Guy's

Have just installed a few gauges in my 12v 1995 truck, I now can see ET, Boost and Fuel Pressure, However i'm a little concerned with the fuel pressure.
I pull a 10K trailer all the time. So i was keen to see what my truck was doing.
She has 105k on the clock, and has just been serviced along with a new fuel filter. When I start the truck I get 18~20 PSI, which is good, however when pulling up hill the pressure will drop to 5~7 PSI with Boost around 12PSI, the pressure will clime to 15PSI when the RPM climes to around 2.5k, once back on a flat the pressure will shoot to 25PSI and then fall to 15PSI, and that is where she sits when on a flat road, When slowing down the PSI will clime to 25, and then fall to 15PSI, once at a stop 18PSI.

Is this normal ? of is my bypass valve on its way out ?


Cheers

 

First service your prefilter.
Instructions> http://dodgeram.org/tech/dsl/filter/pre-filt_clean.htm

If your pressure doesn't improve after cleaning then with the engine idling pinch the rubber return hose that passes behind the fuel filter closed with pliers.
Gauge pressure should shoot up to at least 60 psi.
If it doesn't the lift pump is bad.
If it does the overflow valve is bad.
Best deal by far for an OEM overflow valve is on ebay.

 

The PreFilter was cleaned last week along with the new fuel filter. So I will try the pinching of the return line. Cheers for the advise, so I can take it that the fuel pressure is pretty low for a 12V towing ?

Cheers

 

You should see 25-27 at idle, 32-35 at WOT

 

Hi PatDaly,

Thank you for the PSI info, so its the same with no load (no trailer) as it is with load ( trailer 12k) behind you. So it does sound like my lift pump can't keep up with the demand. Are the lifters from Ebay any good?
http://cgi.ebay.com/ebaymotors/Dodge...item2c55c85ac7

 

Larry B is a top notch guy, I'm sure his lift pump is too.
I don't see the pump on his website but I bet if you call you might be able to get it cheaper than ebay.
http://www.fostertruck.com/dodge/default.htm

 

nutty, could be lift pump, could be your overflow valve. The only way to tell for sure is to pinch the return line. Normally I would agree with your diagnosis since the fuel pressure is dropping with load, but I have learned not to assume with these things.

And yep, LarryB is top notch, I ended up getting my starter contacts thru his Ebay store, same price as his website.

 

Hi Guy's

many thanks for all your help, I'm going to replace both, just to be sure i pinched the return line and the pressure went up but only to around 25~27 PSI.

I spoke to Larry B, and he has both in stock for under $100, with free shipping. very easy guy to work with.

The Truck only has 105k, but you can't be to sure....

Will let you know the outcome on Monday.

 

Hi Guy's

OK so i have replaced my Overflow valve and my lift pump alone with my fuel filter ( again) and I'm still getting around 7~10 PSI under load ( towing 10K up hill, my exhaust temp is around 1100, and Boost is around 12 pounds.... Any idea what could cause the low pressure ?


The truck runs OK, but has no real power when towing, go's like a bat out of hell when not towing?

 

Possible air leak on the draw side of the tank, I don't remember, did you change the lines out? A dumb move I pulled with one was to add extra hose to make it easier to put the tank up, well it kinked the rubber slightly and made for a low fuel pressure situation.

Your low boost might just be a low fuel situation, I would fix the low fuel pressure before I worried about the boost.

I take it she does not blow black under WOT right now?

 

Hi PatDaly.
To be hoist its hard to blow black smoke just when pulling away from a stop, will get a little white smoke on WOT.

However I think you may have something with regards the sucking air from the tank, being I have done nothing to the fuel line inside the tank i.e. pickup. I may just drop the tank and replace the pickup line, if that is cracked it will suck air and give low pressure, Cheers

 

OK, let me see if I got this straight. I get between 22-26 psi at an idle and 32 -36 psi at 2500 rpm. The needle on the gauge is fluctuating between these values. I then pinch the return line and get 60+ psi. Also the pressure when shut off drops to 0 within 5 seconds. Does this mean the overflow valve is bad?

 

Overflow sounds good to me.

 

The only thing that will keep the gauge from dropping to zero instantly on shutdown is an almost shut needle valve or gauge snubber.
They will also slow the gauge's climb on startup.

What's most important is your gauge only drops below 18-20 psi for very short periods under the highest load conditions you can throw at it.

 

OK, I'm trying to chase down a loss of power. I wanted to find out about the overflow valve without spending the money to replace it and it not be the problem. As well as the pressure tests, I have replaced the fuel filter, and air filter. Cleaned the IAT. And pressure tested the intake from the turbo to the intake manifold. I don't think the timing has slipped but that might be the next thing to check. I'm not sure what else to do.