A couple fuel related questions

[ryan.johnson]

I've recently been working on my fuel system; changed the selector solenoid for dual tanks, replacing fuel lines, installed an inline filter, and pulled the brass filters from my 80670 holley carb.

Well that instigated several other problems:

My right tank (sat unused for 5 years) still wont flow, my guess is the sock is clogged.

Truck died about 2 miles into a trip yesterday from fuel starvation, kept dying until i parked it at the house. My guess is I've aggravated the fuel pump.

The truck runs super rich when it does run and dies when its hot out, but I think thats a carb/distrib issue.

So here are the questions:

What is a reputable fuel sender brand? I've done some searching and the best I've come up with is you get what you pay for. I hear spectre likes to make the needle bounce and I'd prefer something better.

Every mechanical fuel pump I've come across outputs at around 9 psi and my carb doesnt like anything over 7 psi. I don't have room for a inline regulator unless I get a double output, which i'm not opposed to if i can find one with a gauge port. Are there pumps that max under 7 psi or do I need a regulator?

I'm also thinking about changing the carb for an edlbrock 650, I've been told it will help my efficiency.

thanks for any help in advance.

 

[RetroC10Sport]

How about using two thick gaskets on the pump? That will move the arm a little further away from the cam lobe and cut the fuel pressure down.

 

[HotRodPC]

Don't go blaming the fuel pump right off the bat. I've had an issue before with the switch. After I went back to the other tank, and then back again, it worked. I too thought it was fuel pump.

Do you know how to work this switch? Or should I ask first, Have you had one of these trucks before and do you know how to operate the switch? It's not just a flip switch like it appears.

 

[chengny]

changed the selector solenoid for dual tanks

This kind of goes with what Mr. HRPC means when he asks whether you are familiar with how to switch over fuel tanks. Unless someone has installed an older style system (i.e. one with a solenoid operated select valve), you have a 5 wire system which incorporates a bi-directional motorized valve.

Unlike a single wire/solenoid driven valve operator, which switches over almost instantaneously to the auxiliary tank and stays there as long as voltage is supplied (and defaults to the production tank by spring pressure when voltage is removed), the Pollak Valve used in your truck has a small motor that changes direction by reversing the polarity of the current as supplied by the switch on the dash.

The biggest difference between the two types of operators is that with the 5 wire motorized valve setup, the switch on the dash is meant to be held in the position of the desired tank for a sufficient interval to give the valve motor time to completely switch tank suctions. The manufaturer claims full stroke takes " a fraction of a second" (but I believe the GMC owners manual says at least 2 seconds).

The switch is of the DPDT rocker momentary type - i.e it only supplies power when depressed in either of the outer 2 positions. Brings up another key point, if the switch is allowed to spring back to the center (i.e. off) position and cuts the suppled power before the valve has completed its rotation, the valve will not allow a full flow of fuel. If it is stopped halfway between tank ports...it is not as if - you will get an equal draw from each tank. And that the 2 combined flows will equal one full flow from a single tank. NO - you will get a severly restricted flow.

The switch must be pressed in and held there for at least 2 seconds when changing tanks.

,My right tank (sat unused for 5 years) still wont flow, my guess is the sock is clogged.

There may be someone who knows better than I, but AFAIK there is no type of in-tank fuel filter on trucks equipped with carbureted engines.

Every mechanical fuel pump I've come across outputs at around 9 psi and my carb doesnt like anything over 7 psi. I don't have room for a inline regulator unless I get a double output, which i'm not opposed to if i can find one with a gauge port. Are there pumps that max under 7 psi or do I need a regulator?

A stock AC-Delco fuel pump for this engine has a pressure range of 4.0 - 6.5 psi.


Truck died about 2 miles into a trip yesterday from fuel starvation, kept dying until i parked it at the house. My guess is I've aggravated the fuel pump.

Never heard of an aggravated fuel pump before. These little positive displacement , diaphragm pumps are extremely dependable. And they are easy-going types, they could not care less whether they are pumping air or gasoline - makes no difference to them. If there is air in the line they pump that until it is gone and then they pump the gas.

Trust me, if you really are starved for fuel - it's a safe bet the reason is not the gas pump. And rest easy, you didn't harm your gas pump sucking some air or pumping against a vacuum.

Read your first words from above:

I've recently been working on my fuel system; changed the selector solenoid for dual tanks, replacing fuel lines, installed an inline filter, and pulled the brass filters from my 80670 holley carb.

Well that instigated several other problems:


I think the answer to your current situation most likely lies within those two sentences.


Seriously, check your work and do a fuel flow test at the carb inlet. Disco the inlet line, attach a rubber hose to the end of it, then while someone cranks the engine, direct the flow of fuel into a suitable container. You should be able to fill a 16 ounce beer can in about 15 seconds.

If you can move that much fuel you are not starved for flow - look at the carburetor.

If you cannot come close to 16 oz in 15 seconds, check your new lines for kinks and pinch points. Double check your wiring connection s for the Pollak valve. BTW here is the spec sheet and the wiring diagram:

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The rest of this post is about me - you can skip it if you don't like sea stories. But my point is - think about what you did last before this truck started acting up.


When I would get called down to the engine room (and the lights were going out so there wasn't alot of time for long conversations) I always asked the engineer on watch one question - "What was the last thing you were doing right before the generator tripped, (or lost the fires in the boilers, or lifted the safties, etc).

The kid would look at me like I was crazy - but would generally tell me the truth. And then usually, armed with that bit of seemingly unrelated bit of intellegnce, I would usually be able to piece together what the chain of events were and come up with a fix.

 

[ryan.johnson]

I checked all the lines but havent done a flow test yet, I appreciate the info on the selector valve and I make sure to hold the switch down until the gauge changes over. I dont believe it is an issue with the switch because I drove several days without issue When I got my new wheels.

If it wont flow out of just my right tank what could the issue be? Havent checked my hardlines but I dont have kinks in all the rubber.

 

[GTME94]

That right tank probably looks like this: http://www.gmsquarebody.com/forum/showthread.php?t=6146&highlight=tank
see post #6

 

[Boone83K10]

Yes, you're tank probably looked like mine.

 

[chengny]

Use compressed air to blow the contents of the line back into the tank. Then try to pulll gas out of it. If it suddenly flows normally but then tapers off again... the tank is probably contaminated and will need to be flushed.

 

[ryan.johnson]

I hope not. When I changed the selector I was able to drain about 8 gallons before I ran out of gas cans... it came out pretty clean just smelled really old. Last time the right was used was in 09.

So I either pulled in trash from the right into my main or its my pump? I dont have any problems with a cold start, just when its warmed up it starts dying, which is why I thought it was the pump.

Any recommendations on fuel senders? Tax refunds coming in, if like my gauge to read right and im pulling the right tank anyway.

Thanks in advance.

 

[bucket]

I thought it was the same company that supplies the same sending units to about everyone? The name escapes me at the moment.

It's not just a flip switch like it appears.

The older ones are, but that ended in '83 or '84 or somewhere around there.

 

[HotRodPC]

I thought it was the same company that supplies the same sending units to about everyone? The name escapes me at the moment.



The older ones are, but that ended in '83 or '84 or somewhere around there.

True, I just wanted to make sure he's operating the switch correctly and not spending money changing parts that don't need it. Some aren't aware you need to hold the switch for a couple seconds and wait for everything to take place.

 

[Boone83K10]

I hope not. When I changed the selector I was able to drain about 8 gallons before I ran out of gas cans... it came out pretty clean just smelled really old. Last time the right was used was in 09.

When I drained mine, it came out clean but stunk to high heaven. Then I pulled the sender and the pic shows what I saw. Never assume, one other thing to consider is if you suddenly are pulling vacuum within the fuel system after your repairs. Take the gas caps off and see if it runs better. Had this happen on a Plymouth Scamp.

 

[ryan.johnson]

Tried the gas caps, no dice. That would eliminate a vacuum issue right? And im pretty sure im using the switch correctly.

 

[ryan.johnson]

Just a little update: been running the truck a few times this week, works fine until it warms up ( on the left tank). I ordered a carter pump that puts out at 6.5 psi max. Now I'm looking for a sending unit for the right side. Who makes a good quality sending unit that will read correctly? I've heard some complaints on spectra senders not reading fuel levels very well.

 

[Boone83K10]

Mine is a spectra. Reads great, no complaints from me.

Did you check fuel line routing? Does it get too close to exhaust, engine, intake etc. You could be boiling the fuel in the line once you reach operating temperature.