Topic: TBI fuel tank swap

[que89yj]

My 89 YJ is a TBI I have a poly tank setup from a 92 YJ MPI. Can I put the poly tank and fuel pump into my 89? I know the pressure is different but shouldn't the fuel regulator limit pressure at the TBI? If the pressure is an issue can I put the TBI fuel pump in the poly tank and replace the MPI pump? 

[que89yj]

I bought a fuel tank including the skid plate and pump off of Craigslist several months ago planning on upgrading my fuel tank to the poly tank from a 92YJ. In the mean time I have been playing with all the upgrades and tweaks like header, electric fan, alternator, etc. 3 weeks of work and I finally got everything back together. After 1 day of driving my original fuel pump died! I started the prep to swap the tanks. I looked at the specs for the pumps and I found out the TBI fuel pump is rated at 40PSI regulated to 14 and the MPI fuel pump is rated at 100 regulated to 40. There was no way I could trust the regulator to hold against that high of pressure so I decided to pull the tank I bought on Craigslist apart and swap the pump to the lower pressure. I am glad I did but very very pissed off too. When I pulled off the tank assembly I found every bit of rubber inside on the fuel pump assembly dissolved and laying in a melted goo at the bottom of the tank making the fuel sending unit totally useless.  The guy I bought it from must have been using Ethanol and caused it to desentigrate. I am now in a dilema. I am not going to spend 160.00 for a fuel sending unit and pump only to throw the pump away because the units only come with the high pressure pump  I looked and I couldn't find anyone who had either used the high pressure pump in the TBI setup or swapped the lower pressure TBI pump into the later model poly tanks. I am ready to trash the whole mod at this point.
Any input at this point is appreciated.

[sharpxmen]

first: i am not familiar with the TBI so take all this with caution.

a pump pressure rating is the max pressure that pump could deliver before no flow of fuel or if you want at 0 flow. if the pump has a higher rating than yours the problem is not the pressure but the flow - in other words it would flow more fuel at a lower pressure. Think of it this way, if you look at household pumps they will tell you the flow at a certain height (500 gallons per hour at 10 feet elevation for example) - the higher you go the lower the flow - that elevation is actually pressure given by the weight of the column of water in the line/hose/pipe and the pump needs to overcome that with it's turbine. same for fuel pumps, the lower the pressure the higher the flow. the fuel pump you bought off a 92 YJ can function no problem at 14 psi, but you have to make sure your pressure regulator and return line can cope with the return fuel flow - you will have much more than with the stock pump - so that being said you could have a look if the return valve has a calibrated outlet or it is same as the mpfi one. Also, look at your return line, what is the diameter of your line and is your pump located in the gastank same as the one on the 92YJ tank. if your return can accomodate the extra flow you should be fine in my opinion, again not familiar with TBI so take this with caution. You could run the pump w/o starting the engine and see what the pressure is - just give it a bit of voltage (for a second or 2) and if you see the pressure jumping skyhigh then is not looking good.

EDIT: forgot to mention that i had a fuel injection pump that was off an mpfi bmw engine installed on a carburetted engine (mind you it had 4 horizontal carbs) and it was fine

[que89yj]

My concern is the Throttle body Injection system pressure regulator diaphram wouldn't deal with all the extra pressure. I know it would work as far as bolting right up. I was hoping that someone would have hooked up the poly tank and fuel pump to one of the Throttle Bodies so I could know for certain.

[sharpxmen]

where is your regulator? do you have a pic?

[que89yj]

Because of the problems I had with the sending unit that was on the poly tank I bought I am going to backself this mod for a later day if I can find a deal on a sending unit for the later model YJ. I cant beleive how the Ethanol literaly disolved the rubber in the sending unit and the fuel pump isolators. I appreciate the help but this one is going to have to wait. I ned to get a working YJ first then look at doing the poly at another time.

[chardrc]

i was just reading throw some fsm stuff and found that the fuel pressure regulator is adjustable with a torqs head under its bowl... you just need a way to measure the pressure post pressure regulator.. found the info here http://jeepgarage.free.fr/OWN/fuel%20injection%20system%20tbi.pdf

[que89yj]

Wow, that is a great summary sheet. Thanks. I wasn't worried about controlling the output of the regulator so much as the MPI pump rating is about 100% more than the TBI pump rating. The design for most system is a tolerance of about 15% so I was afraid the diaphram from the pressure regulator wouldn't last against that much more input pressure.  After looking at it again last night. I went to work and I think I saved the sending unit from the donor tank and I am going to go ahead and try putting on the lower pressure pump. I found a fuel pump kit at NAPA that has all the rubber bushings for the pump included to replace all the ones the Ethanol ate up. 

[que89yj]

Cannot just swap the fuel pump in the tanks. The TBI pump is much bigger then the MPI pump. The TBI pump I bought will not mount into the MPI pump bracket. Looks like I will stay with the metal tank for a while.

[chardrc]

im bringing this thread back to life as it answered my main question i was going to ask. but i have more to add.
i found a write up on jeep forum that swapped to the mpfi plastic tank with the mpfi pump adn it worked minus having the return too long at first.. but the remaining problem is that the tbi pump has a check valve but the mpfi one doesn't (according to link).. keep in mind at this time the person has only run this set up for a few weeks.

http://www.jeepforum.com/forum/f12/metal-plastic-fuel-tank-swap-1088945/

also found this

http://www.jeepforum.com/forum/f12/tbi-vs-mpi-fuel-pump-compability-1080029/

hopefully this will be good for future reference for others

[sharpxmen]

im bringing this thread back to life as it answered my main question i was going to ask. but i have more to add.
i found a write up on jeep forum that swapped to the mpfi plastic tank with the mpfi pump adn it worked minus having the return too long at first.. but the remaining problem is that the tbi pump has a check valve but the mpfi one doesn't (according to link).. keep in mind at this time the person has only run this set up for a few weeks.

http://www.jeepforum.com/forum/f12/metal-plastic-fuel-tank-swap-1088945/

also found this

http://www.jeepforum.com/forum/f12/tbi-vs-mpi-fuel-pump-compability-1080029/

hopefully this will be good for future reference for others

it will work as it will push fuel - just measure the fuel pressure to make sure is not too much (the regulator should take care of it but the return might increase the pressure if it has not enough flow capacity). there is a check valve, could be on the assembly (mount) and not the pump (i always thought is on the pump but don't know for sure) so if you swap the whole tank with sender and pump you should be fine.