87 tbi sending unit with walbro 450 e85 pump in Blazer tank.

[Operatorfailure]

I got my 87 Blazer tank in today and put the walbro 450 pump in the 87 Blazer sending unit. Everything went in great, just was curious about all of the connections on the sending unit. Two of the lines are obvious, feed and return. But there are two other lines. One small and one large. One is a vent and one is EVAP I assume. Can I just block off the EVAP?

The large line, is it the EVAP or the vent?

[ls1nova71]

The large one is the vent for the fuel filler tube so it's easier to fill, the smaller one is the vent for the tank and originally went to the charcoal canister. I would run it to a vent of some sort rather than capping it.

[Operatorfailure]

Perfect. Thanks!

[PAPABEAR]

that is the same tank setup am going with in my blazer and had the same questions on the sending unit, if you can elaborate on how is the best way to vent that last line would help alot maybe some pics? Thanks

[jamesjones]

Originally Posted by PAPABEAR

that is the same tank setup am going with in my blazer and had the same questions on the sending unit, if you can elaborate on how is the best way to vent that last line would help alot maybe some pics? Thanks

I was planning on just running some rubber hose off of it to the side.

[Operatorfailure]

Originally Posted by PAPABEAR

that is the same tank setup am going with in my blazer and had the same questions on the sending unit, if you can elaborate on how is the best way to vent that last line would help alot maybe some pics? Thanks

I plan on capping the small vent line and running the big vent to the filler neck and running a vented cap.

As far as fitment I haven't put the tank in the truck yet, waiting on some more line to connect to my old setup. I know I will have to remove the rear crossmember, but I am planning on making a new crossmember/receiver hitch after I put the tank in anyway.

For wiring it is pretty simple. Cut off the plug for the 87 tbi fuel pump.


solder in the power and ground wires for the pump.


Sit back and have a beer with your helper.


There are only two things that aren't perfect about this setup.

The first is when you go to put the assembly back in the tank you have to take the float off, put the assembly in the tank then plug the float back into the sender. Annoying, but totally doable.

Next, is if you are using an f-body or newer truck gauge cluster, like I am you have to cut the ground off the sending unit and run it out of the tank to use as your 5v reference wire. If you are using the stock 67-72 fuel gauge the 87 tbi sending unit should work perfect.

[jamesjones]

Thanks for the info.

[68c10airstream]

Hi operatorfailure, I think in time the 2 standard worm clamps will slowly cut the short rubber line between fuel pump and the sending unit. This is caused by the high pressure swelling the rubber, and the edges of the clamps cutting it. You need to get efi specific clamps at an auto store, not that expensive. Also the short rubber hose is a special hose, and is designed to be constantly immersed in gasoline. If it came with the pump you should be ok, if not i would suggest replacement. I believe it's 10$ a foot, but you only need a short piece. I'm not nit picking, just trying to help. Fixed a few low pressure drivability efi vehicles, thinking it was a worn out pump, only to discover it was a recent replacement and the rubber hose was swollen and/or cut from incorrect clamps. Good luck, Brian Fuller

[Operatorfailure]

Originally Posted by 68c10airstream

Hi operatorfailure, I think in time the 2 standard worm clamps will slowly cut the short rubber line between fuel pump and the sending unit. This is caused by the high pressure swelling the rubber, and the edges of the clamps cutting it. You need to get efi specific clamps at an auto store, not that expensive. Also the short rubber hose is a special hose, and is designed to be constantly immersed in gasoline. If it came with the pump you should be ok, if not i would suggest replacement. I believe it's 10$ a foot, but you only need a short piece. I'm not nit picking, just trying to help. Fixed a few low pressure drivability efi vehicles, thinking it was a worn out pump, only to discover it was a recent replacement and the rubber hose was swollen and/or cut from incorrect clamps. Good luck, Brian Fuller

Thanks for the reply. The hose is what came with the pump and also so are the worm clamps. I didn't think about it but what you are saying does make sense. I will swap them out before I put the tank in the truck.

[jamesjones]

Originally Posted by Operatorfailure

I got my 87 Blazer tank in today and put the walbro 450 pump in the 87 Blazer sending unit. Everything went in great, just was curious about all of the connections on the sending unit. Two of the lines are obvious, feed and return. But there are two other lines. One small and one large. One is a vent and one is EVAP I assume. Can I just block off the EVAP?

The large line, is it the EVAP or the vent?

Could you expand on any wiring or fitment issues you had?

I'm going with that tank/sending unit setup in my Blazer and was planning on using a Walbro 400.

[PAPABEAR]

Thanks for the info guys! I wonder if a atv gas cap check valve would work on that last line, so no dirt or bugs can get in? There a couple bucks at the motorcycle shop.

[terrylgreenjr]

Will the factory TBI pump put enough pressure/volume for the LS swap?

[PAPABEAR]

No not enough pressure, you have use something like a acdelco ep381 or other aftermarket pump but it drops right into the factory tbi sending unit.

[terrylgreenjr]

Not to hijack but do you think this will work?

http://m.summitracing.com/parts/VPN-GCA758-2

[Operatorfailure]

Originally Posted by terrylgreenjr

Not to hijack but do you think this will work?

http://m.summitracing.com/parts/VPN-GCA758-2

That pump will work but you can get pumps on ebay cheaper. I paid $133 shipped and mine should handle 600+ whp.

[Jonboy]

Which colors on your sender are fuel level and pump power?

[68c10airstream]

Hi jonboy, typical gm is easy, of all the wires at the sender plugin outside the tank, the largest diameter wire (probably purple) is 12+, black is pump/sender ground and gray is the variable sender signal for the gas gauge. Good luck, Brian Fuller

[Operatorfailure]

Honestly I questioned that also. I figure I will test it before I install the tank.

[Jonboy]

Thanks Brian! All of the diagrams I liked at were showing pink and brown (I think). The sender I bought ("87 R10 LH tank) had purple and grey wires. That is how I thought they were wired, just wanted to make sure.

[PAPABEAR]

Hey operatorfailure did your tank come painted black? Mine came in today and it is a spectra just wax coated steel.

[Operatorfailure]

Yeah, mine came in black. I was pleasantly surprised.

[Operatorfailure]

This is the tank I bought.
http://m.ebay.com/itm/130969404868?txnId=921480825003

[Slowguy]

Can anyone tell me the size of fittings for the supply and return lines? I think I’ll make my own braided hose/-an fittings