1989 Fuel Pump replacement

[Jeepers8606]

1989 MJ has been a bit sluggish, can't get of the way of itself, backfiring, originally didn't want to idle. 

 

Initial OBD codes were 27, 14, 51, 27, cleared 27 & 14, 51 (heated O2 sensor input indicates lean air/fuel ratio during engine operation, adaptive memory at rich limit) & 27 (injector output driver does not respond properly to SBEC (PCM) control signal) remain

Cleaned up 1996 transplant XJ 4.0 mill (& automatic drivetrain) throttle body (60mm), replaced fuel filter, IAC, MAP, fuel regulator. Ran better (much better in reverse), getting up to 45 mph with fuel regulator vacuum line disconnected, still a dog with it connected.

Next step replace fuel pump, although I did not test jumpered fuel pump relay, initial prime pressure is a consistent 22-23psi, as I have (safely) removed most of the 18 gallons that were in the tank.

I see others have ordered and installed MTX Company JPSU-6P4.0 with the EFPK-3204 fuel pump, for the (original?) 18 gallon fuel tank with side mount fuel pump. I ordered this set up today.

Has anyone had any experience with this set up, experienced any pit-falls, additional modifications required? (Jeremy/ MTX suggested this pump has a much higher pressure), or could it actually be a like-for like replacement and I can get back on the road?

 

 

[Jeepers8606]

Sorry, typo, MTS Company

[Eagle_SX4]

That set up works fine in my truck but it is running the original engine and fuel system (Renix). If you do have a 96 and obd you will probably have a return-less fuel system and some mods will need to be made to accommodate that. I am not sure how to do this and have not looked in to it.

[89 MJ]

@ghetdjc320seems very knowledgeable when it comes to the fuel system on HOs. 

[Jeepers8606]

The motor/ drivetrain swap was accomplished years ago, prior to myself and most recent p/o. it appears to be utilizing original equipment modified to the modern set up.

 

Again, any suggestions appreciated

[89 MJ]

To me, it sounds like you should probably upgrade the pump to one with the pressure and flow rate of an HO one and then swap to the return style fuel rail found on the HOs. 

[Jeepers8606]

Dually noted sir, thank you

[89 MJ]

Don’t take that as gospel though, I have only worked on Renix Jeeps. I’ve only pulled parts off of HOs, never actually worked on one. 

[Eagle_SX4]

Fuel pumps were the same from 87-93 then jeep swapped to the new style rotary-vein pump for 94-95 with the same pressure. In 96 they changed to a return-less system with the pressure regulator inside the tank.

[gogmorgo]

The ‘96+ returnless system should be easy enough to identify. You’d only have one fuel line going to the rail. 
If you’ve had a ‘91+ cluster installed you probably have a ‘91+ sending unit installed to go with. I don’t remember the actual result of mixing Renix and HO fuel gauge and sending unit, just know they’re not compatible. I’ve never confirmed either if MTS is making the ‘91+ sending unit, I’ve seen people say definitely yes and definitely no. 
 

To me your fuel pressure seems on the low side, but low fuel pressure doesn’t tend to throw all the codes you got, you just get symptoms of running really lean. You also don’t necessarily get a good pressure reading after a few seconds of priming, especially if you’re sucking air with a mostly drained fuel tank.

I’d be suspicious of a wiring concern connecting all the sensors. There’s a ground at the back of the head/manifold (I don’t remember exactly where) with a few wires going to it.

Of course you’d also get a bunch of codes if you’ve been unplugging stuff, creating vacuum leaks, etc. 
And just confirming you’ve got two instances of code 27? Looks like you said you cleared it and it both did and didn’t come back. 

[Jeepers8606]

To clarify, I had a full tank when testing prime pressure, i knew I had to drain tank to replace the pump/ float assembly, and working with no trained flashlight holder, limited daylight and low (rural NY) daytime temperatures, I focused on draining the tank. I should have tested pressure while jumping the pump relay as well, while draining tank.

Continuing to accept recommendations/ advice/ even trash talk.

I will update thread when pump has been replaced, due in Monday 12/23.

[Gojira94]

The MTS unit uses a pump that "Replaces Airtex # E7006". Airtex E7006 is a roller-vane style pump and the one in the MTS unit appears also to be a roller-vane pump. If MTS' pump is comparable to the Airtex E7006, it can be expected to be about 45GPH (170lph) free flow. 170lph is at the upper end of requirements for an early 4.0 running 29-39psi from idle to WOT, but should be able to deliver enough fuel when restricted/ regulated up to 49psi. The MTS unit has a return provision, but that can certainly be left capped for a returnless setup, if that's indeed what you have. You can always upgrade to a turbine style pump later, with a small bit of modification to fitment of the pump to the sending unit. And to gogmorgo's point, the MTS unit's sender is made for 87-90 gauges, and sends from about 2 ohms (empty) to about 115 ohms (full). I don't know if HO 91-96 is just backwards on the wires at the gauge, uses a different set of resistance values, or both.