1985 5.0 EFI Fuel pump - Before I go buy a bunch of crap

So I've been chasing down a strange problem:  About 75% of the time, when the truck is dead cold, I'll start it up and it will sputter and immediately die.  I turn the key again and it starts and continues to run fine for the rest of the day.

I've replaced the fuel filter, IAC and the MAP sensors.  The engine runs better and now idles great but the original problem still remains.  I have a sneaky feeling that it's fuel related.  Unfortunately, since my truck is a 1985 it doesn't have a Schrader valve to check fuel pressure.  I fixed this by installing and adjusting an Accufab regulator that I had laying around for my Mustang.  Its a direct replacement for the factory regulator and has a fuel pressure port and am using that to read fuel pressure.

Here is what I'm seeing:  

Scenario 1.  With the REAR tank active, I am getting only 10psi of pressure with the key on engine off, and that's with cycling the key several times.  Once I start it, it goes to 40psi and stays there.

Scenario 2.  With the FRONT tank active, I am getting 35psi with the key on engine off.  Once I start the engine, it goes up to 40psi and stays there.

My preliminary conclusion:  To me it looks like the rear tank pump is dead.  The one thing that bothers me is shouldn't the fuel pressure in Scenario 1. above be higher if the in-line fuel pump is active?  Another concern is that the engine does this cold start dying thing no matter what tank I have it set on.

Thanks for any advice.

-Shannon

One item peculiar to the 1985 and 1986 EFI trucks, the reservoir, switching valve (canister on the frame behind the pump) has a filter in it that should be now have been replaced. The actual switching valve system can fail also.

It appears to switch from tank to tank just fine.  Except for this irregularity at startup, the truck runs ok on either tank.  I have replaced the filter that you spoke of.  It was full of black filthy ilk.  I was "told" by the PO that the fuel tanks were cleaned out, but who knows.

Just for kicks I'll check the filter again to see how dirty it is since I've changed it.  That should give me some indication of the cleanliness of the tanks.

-Shannon

while you are checking and changing parts. you might install a new fuel pump relay just to cover the bases.

Do you know where the relay is on an 85?  I've looked for it (not that hard admittedly) but can't find it.

Thanks!

-Shannon

sorry for the delay but i believe the fpr is between the brake booster and the driver fender on a plastic bracket mounted to the firewall. it usually holds two relays that mount up from underneath, so they are protected from water.

Thanks Mat,

I have a relay on order.  Thanks for the info!

Just an update.  I have verified that that the rear tank pump was indeed trashed.  I pulled the rear tank today... not something that that recommending doing unless you need to.  The inside of the tank was badly corroded with lots of silt and sand-type stuff in it.   The pump filter was clogged and torn so I'm assuming that's what killed the pump.  

I went ahead and ordered a new tank.  it's a $100 delivered from amazon and made in Canada.  I'm installing a new pump/sending unit so at the end of the day everything will be new at least from that tank.  

I'm about 75% convinced to drop the mid-tank to see how dirty it is.  I was told by the PO that they had cleaned out both tanks before sale... I guess that was a bunch of BS.

I should have everything to re-install the tank by Tuesday.  So hopefully I can provide an update by the weekend.

-Shannon

I think you are money ahead to do as you are doing and replace the tanks - assuming of course that the mid-ship is like the rear tank.  

Shannon - Gary's right.  Smart to replace the tanks.  I also bought the same $100 tank from amazon and the fit is perfect, not to mention the relief knowing it's clean inside.
Good luck and keep us posted on how it goes.

peace of mind comes with doing both tanks. it is not that expensive when you really think about it. fussing with bad tanks can cost much more over time. the rear is by far the harder of the two. are you doing the fill hoses too? again, its cheap insurance and new hoses are much easier to install.

Thanks for the advice guys.  This is a bit of a father/son project (this is my son's truck), so I want the truck as reliable as possible.

I went ahead and ordered the second tank and pump/sender assembly.  I also picked up the filler hoses for each tank.  I also got new mounting hardware for the tanks.. of the 4 bolts for the rear tank, 3 were different.  For some reason, that really gets my goat.  

Mat, good to know the mid-tank is a bit easier to drop than the rear.  

-Shannon

when doing the mid tank, a transmission jack is a great help. without one, a ratchet strap can be very handy

Mat,

Great idea!  I have a transmission jack and never thought to use it.  

New tanks came in today (gotta love Amazon).  Just waiting for the fill hoses and I'm ready to button everything up.

BTW.  Just a trick I fabbed up for quickly removing the gas from a tank:  I used an old fuel pump with 5/16" hose and a 10 micron fuel filter so that I can reuse the old gas.  I removed 15 gallons of gas from the rear tank that way.  Works like a charm as long as you have a place to put it.

-Shannon

 i  have done that too. no fun dropping a loaded tank. a full tank is just heavy and wearing spilled fuel makes me nuts (angry). but a half tank keeps moving around and changing where the weight is. by all means, empty the tank if you can.

I got the mid-tank installed today.  Mat was right, much easier than the rear.  Odd thing: The fuel pump mounting tabs on the Spectra tank were reversed from the OEM tank, causing the fuel line outlets to be reversed and pointed in the wrong direction.  I had to add the tabs in the "right" place on the tank in order to fix that.

Still waiting on a replacement fuel pump wiring connector (that I broke) for the rear tank.  The supply line also cracked so I am waiting on the parts to fix that.  Never a dull moment, but starting to see the light at the end of the tunnel.

-Shannon

I think you may have the later tank.  When I bought 90's tanks for Big Blue I found that the slots were in the wrong place for the Bullnose sending units.  So I went with later sending units, actually called fuel delivery modules as they have the pump, sending unit, and check valve in one.

But if you cut the slots then you should be good.  The only issue might be rusting where you cut, but the rest of the galvanizing should prevent it.