Newbie trying to install gas tank

[84GMCK2500]

Howdy, I bought a clean 84 GMC K2500 with a 350 to work on and learn. It's great but the fuel filter keeps clogging with rust and gunk, so I'm going to try a gas tank install. It's a single drivers side tank. I've picked out the Spectra GM1B 20 gal, but not sure which sending unit is compatible. Any knowledge on this out there? Hope to lean on the community to keep my GMC running strong. Thanks.

 

[84GMCK2500]

Spectra has units with 2 outlets and 3 outlets (FG05H andFG05F). Anyone know which one?

 

[MrMarty51]

That depends on if the tank You are removing has a return hose, look at the fuel pump, if there are three hoses attached, You then will need the three holer.
If You order the three hose sending unit, the one port can always be capped, if Yours is the single with a vent.
Welcome to the forum.

 

[84GMCK2500]

From what I can see there are 2 hoses and 1 outlet line.

 

[HotRodPC]

From what I can see there are 2 hoses and 1 outlet line.

That sounds right. 1 of those if vented to the charcoal canister purge device in the driver side fender well. And I think no matter the lines, I think both sending units fits all the tanks. Not positive, so someone feel free to set me straight if not.

 

[Tyger13us]

That sounds right. 1 of those if vented to the charcoal canister purge device in the driver side fender well. And I think no matter the lines, I think both sending units fits all the tanks. Not positive, so someone feel free to set me straight if not.

there is a left and right sending unit.....

 

[HotRodPC]

there is a left and right sending unit.....

That is true, but the sizes of what fits the tank for mounting in the tank are all the same I do believe. Even the in tank fuel pump for TBI is still the same as the non pump pick up sock style. So long he's got the one for the left tank he SHOULD BE good to go with it. Having the 2 or 3 lines on the pick up are dependent upon the emissions of the vehicle IIRC. Models with Canister Purge will be 3 line pick ups to the tank.

 

[chengny]

Just a couple of ideas:

1. Rather than tear out an otherwise good tank (also source, pay for and install a new one) - maybe consider temporarily installing a large capacity fuel filter. I assume the filter you are currently changing is the one in the carburetor? Insert the pre-filter into the gas line in an accessible spot so it can be changed easily and frequently:

You must be registered for see images attach

The rust is probably coming from the dome (top level of the tank) and is usually the result of never fully filling the tank. Try keeping the tank completely full for awhile. Normal driving should dislodge any rust from the inner walls of the dome. Change the filter when there is an apparent drop in fuel flow (hesitation/surging at WOT). After a couple of filter changes the residual rust should be gone from the tank

Most -nearly all - fuel tank corrosion is from the outside. Any internal oxidation is mild and is either due to years of the tank not being filled or the truck sitting idle for an extended time.

2. If you do decide to install a new tank, there is no reason to buy a new sender - use the OEM. Yours will drop right in and work fine. The sender is the same for both the 20 gallon and 16 gallon (tank height/width is identical only length differs). 25 gallon tanks require a differently calibrated sender because they are wider.

Any knowledge on this out there? Hope to lean on the community to keep my GMC running strong.

Here is a tip from someone (me) who has learned the hard way - by making a lot of expensive mistakes:

Always try to keep your OEM components whenever possible.



BTW - the 3 connections to the tank at the sender are:

1. Fuel pump suction
2. Fuel return line
3. Vapor connection to the EFE system

 

[Tyger13us]

That is true, but the sizes of what fits the tank for mounting in the tank are all the same I do believe. Even the in tank fuel pump for TBI is still the same as the non pump pick up sock style. So long he's got the one for the left tank he SHOULD BE good to go with it. Having the 2 or 3 lines on the pick up are dependent upon the emissions of the vehicle IIRC. Models with Canister Purge will be 3 line pick ups to the tank.

yup,,

also? the only time ive ever seen a 3 line one was for a diesel,, now im not saying there not for gas also?

all my gas trucks have 2 lines and all the diesels have 3......74-86

 

[HotRodPC]

yup,,

also? the only time ive ever seen a 3 line one was for a diesel,, now im not saying there not for gas also?

all my gas trucks have 2 lines and all the diesels have 3......74-86

OK, then I'm possibly getting confused with dual tank models. Try to recall from picture memory, seems like I always see 3 lines going to the right, and that very well could be for the switch valve plumbing.

 

[MrMarty51]

The right side tank on My 79 { it is currently off the truck} has two lines for fuel, one 3/8ths for to feed the fuel pump, one 1/4 inch for a return and the center one, 5/16ths, is for emissions.
My pickup has no emissions installed as it is the heavy duty version and so, the center, emissions port has a breather on it.
The biggest forseable problem with the original sending unit is, the sock on the suction pipe, has probably got holes wore in it and or, possibly even split wide open, Mine are.
I got new ones from Summit Racing, item number "K405 sending unit filter screen-3/8ths", the problem with the new sock is, how do You keep it from falling off of the pickup tube ???
I cut all the old sock, right flush with the crimp, I used a tapered hole reamer to slightly enlarge the new socks attaching device. I thought, what the heck, they are crimped on, and so, I stuck a tack weld to it, to the original socks flange. Well, the new ones are glued, the heat softened the glue and so, I held it in its original position, until the glue reset, turned it over and tacked the other side, repeat the holding. I now have a new screen on the pickup tube of the right side fuel tank. I`ll do the other side affer I get it pulled apart.

And, Chengny is absolutely right on keeping as much of the original OEM equipment as possible, it fits, it is calibrated and there is probably not a thing the matter with it.

 

[84GMCK2500]

Ok, I'm having a heck of a time trying to quote, but I'm trying to digest this information. The fact that Tyger13us says that he's only seen 3 outlet units on diesels is interesting, because my single tank 350 says "diesel only" on the gas cap. The current unit does indeed have 3 outlets.
That aside, I really like chengny's suggestion of a large capacity pre filter. Any idea where I can get one? It doesn't come up on a search. Also, my gauge pegs past full when full and at 1/2 tank when empty. Could the sending unit be choked with gunk? Thanks to all!

 

[84GMCK2500]

I'm looking at a Fram G3 filter. Appropriate? Also, any issues with putting a filter before the pump?

 

[chengny]

That filter shown in the image above could very well be a Fram G3. It doesn't really matter. The most critical spec is the OD of the inlet and outlet. The nipples have to be able to slide into the rubber hose.

When (and if) you finally commit to inserting an in-line filter, snip out a 2" section with a pair of dikes. That much will have to be removed anyway to make room for the filter. Take the cropped out section with you when you go to get the filter. Open the package and make sure the hose will fit (snuggly) on to the inlet/outlet nipples.

Those clear Fram gas filters usually come with a couple of tiny hose clamps to seal the hose connections. If not, buy 2 good ones.

As far as locating the filter upstream from the fuel pump; you really have no other option.

Don't ever be tempted to mess with that section of shaped steel tubing that connects the fuel pump outlet to the carburetor inlet. It is a wicked hassle to make up to the carb if it gets distorted or it's length is modified. That is the reason so many Q-jets have F'd up inlet bosses.

 

[84GMCK2500]

Thanks Chengny, you've probably saved me a couple hundred here, not to mention holding on to OEM parts. Really nice solution!