Topic: Am I on the right track to converting to MPI?

[Mr_Random]

I just picked up a 2002 Intake, fuel rail, and injectors. Because of the lack of fuel return line, I'm looking for TJ fuel pumps (pretty sure the pump has a workaround to the absent return line).

I'll be getting an exhaust manny (hopefully) tomorrow for $25 or less.

I'm looking to get all the sensors, ECU, and Harness locally, I know I'll have to do something about the P/S pump bracket, I need a new pump anyways...

The local engine is a 93 or 95 (can't remember), so I'll be running the matching ECU, OBDI appeals to me more anyways...

Lastly, I'll pick up a 4.0 TB...

Does this sound good?? I MAY be able to reuse my EVAP can, but if I can't I'll just plug the lines and run like that for a while.

I hope the existing body harness can stay, if not I'm a superb electrician!

[Jeffy]

Why are you mixing and matching?

Some things that might come up.  The cam on the +'97 is different then the pre-'97's.  Injectors are also higher PSI then the older engines.  Since you want to run an older ECM, I think you'll run a bit rich.

The MAP on the +'97's is on the TB while the pre-'97's is tapped into the side of the intake which could throw things off.
 
Then the harness will probably be wired for two O2 sensors. The ECM is designed to read online the pre-cat sensor.

Honestly, if you're not good at electrical, I would highly recommend sticking with the setup that closely resembles teh stock setup.  Mixing OBDI with OBDII is just making things more complicated then it needs to be.

[Mr_Random]

Well you have me a little mistaken, if you reread the last line it says I'm a SUPERB electrician, I'm only seventeen (almost eighteen) and have been studying all levels of electronics/electricity for six years. If someone gave me JUST the connectors to each sensor and the ECU, I could wire myself a system within a week (I've done much more complicated before).

Also, the injectors aren't higher PSI, they're higher Flow Rate. The whole system is higher PSI, so you are essentially correct, but that mistake can make other things unclear.

More PSI and higher flow rate means shorter required pulse width, meaning more overall control of the fuel system.

AH... I came across wrong... Think of it this way; my fuel rail, injectors, and fuel pump are the ONLY things that aren't gonna be from an OBDI system. I plan to strip the WHOLE engine harness (the sensors too) from a 93, and the ECU, and use that to control it all...

OBDI's are supposedly alot more forgiving to adjustments, plenty of people have put new cams, injectors, and bored TB's (as you know) on the older system and had it live up well!

The combination of the 4.0 TB and better fuel delivery should get more ponies and throttle response, while evening out the A/F ratio. I don't really have to worry about higher flowing exhaust; the PO removed the CAT (if I get scared about it I'll gut a busted one and put it on, or just go for a high flow in the future).

Sorry for the long post, just trying to clarify to possibly find more help... thanks though!

[Jeffy]

By higher PSI, I did mean PSI/hr which is the flow rate.  Stock TJ's are 23.2psi/hr while the stock YJ's are 17.4psi/hr.

Yes, the computer should be able to control the pulse timing but only down to a certain point.  The MAP controls the air/fuel ratio and has a limited range, which is why people install adjustable piggy-back unit to the MAP.   You will want a wideband O2 sensor to make sure you're not going too rich.

More flow is good to a point. You really start changing the torque bad when doing CIA and high flow exhausts.  Too much flow and you'll give up low end torque for higher end HP.  Some minor tweaking does make a big difference.

Still that doesn't answer the question, why cobble a TJ harness, fuel and intake with a YJ system?

[Mr_Random]

No TJ harness, only YJ... EVERYTHING electronic/controlling will be from a 93 YJ. Essentially, the ONLY TJ parts would be the fuel pump, fuel rail, and injectors.

I would understand a piggyback controller if I was doing some kind of forced induction, but with just the little higher air flow (from the larger TB) I'll be getting, shouldn't I only have to install a potentiometer or "adjustable MAP" between the MAP and ECU? Widebands aren't cheap, but again, I've only seen their applications on high flowing/forced induction rigs.

If I get the right amount of resistance on the MAP, I don't think I'll have to fool the ECU any further, like using a WB O2.

In no way do I want to wing this, I'm glad you are making me think more about it too, but if it comes down to it; I'll just DO IT and have a backup in place in case it doesn't work out as well as I'd like.

The harder it is, the more fun it will be, and the better I'll feel when I'm done with it. I'm not past the PNR yet, but I kind of had to jump in and start or I'd never actually get to it.

I could probably go on forever with the details (not even exact ones yet, haven't quite gotten there) of this plan, so I'll ask you one question; do you think I'm crazy for making it this more complicated than normal?

Oh yeah, and I have an XJ... haha, It'll deliver gas like a TJ, think it's a YJ, but BE an XJ... sounds just unique enough for me!

[Mr_Random]

Is there no way to edit my posts now? Did you remove it the capability entirely?

After all that, I didn't answer your last question;

I got a great deal on the Intake, Fuel rail, and Injectors from a 2002 TJ, but know that the YJ systems made slightly more power because they were not as restricted by emission requirements. I know it's somewhat trivial, but I'm slightly insane and just kinda went "Why not?"

I remember reading somewhere that the TJ Fuel Rail got away with not having a return line because of the pump being different in itself.

SO that means; use what I already have, pick up a newer XJ 4.0 F/P (same PSI I believe as the TJ, but I need to look into that more), and use YJ stuff for everything else!

I'm either a genius or an idiot; I'll find out for sure in the future.