What's this J-Tube mod?

[Doward]

I'm thinking of getting a MkIV fuel pump to replace my old one... I'm hearing things about a J-Tube mod, and a search yielded very little.

SupraForums.com is down. Big suprise. :3d_frown:

Can anyone point me to a link, or detail what and why the J-Tube mod is done?

[GrimJack]

Heh... this is pretty simple.

The Engineers at Toyota wanted to make sure you could have enough fuel pressure to make it to a shop even if your pressure reg failed. So, they put a restriction in the return line - it's called the J-tube, and it's a J shaped tube bolted to the intake side of the block next to the motor mount.

When we go for more fuel delivery, this restriction can cause problems - so people bypass it or drill it out. Just make sure you have a good pump and fuel pressure regulator first. :)

[lagged]

the jtube is a fail safe incase the stock FPR blows up. when you install an AFPR along with a high flow fuel pump such as a 255lph unit you bypass the jtube. sefl explanitory.

you can then either leave it there, by a block off plate, or remove yours and grind down the tube, polish up whats left over and have a jtube "block off plate" for free :)

edit: grimjack beat me to it!

[bcg04]

and if you are going to go through the trouble of installing a new fuel pump, you may want to consider a Walbro instead.

[bcg04]

Oh and PS - just had a discussion on J-tube block off plates and stuff... few pics in there so you can see it's not a difficult "mod".

http://www.supramania.com/forums/showthread.php?t=10845

[boost fiend]

so what fittings need to be blocked off?

[shaeff]

so what fittings need to be blocked off?

none, it's either bypassed completely, or you simply drill out the end of it. here's a pic of the part that needs to be drilled, if you decide to actually drill it. see that little pinhole in the end of it? yep, drill that out! :)

the other option is to get some regular gas line and just compeletly bypass it, going from the fuel pressure regulator's return side, directly to the return line under the car. :)

on to the pic:

-shaeff

[supra90turbo]

shaeff, the resident J-Tube expert, so it seems. lol
Nice pic btw. :bigthumb:

[shaeff]

shaeff, the resident J-Tube expert, so it seems. lol
Nice pic btw. :bigthumb:

haha. that's one of the most commonly asked questions, so if there's a plethora of information about it, surely when the next person uses the search function, it'll pop up, thus saving us from reposts in the future. :)

aside from that, i'm starting to work on som FAQ's, of which include the J-tube mod. :)

-shaeff