A few comments on fuel control:

• Fuel pressure at the fuel rail is all that matters. I'm reasonably certain that any specification on fuel pressure will be at the rail. Its this way because the fuel injector pulsewidth calculations have to be based on the pressure at the rail.
• The higher flow rate injectors may or may not be compensating for your fuel pressure issue. It depends on how the ECU handles high load (open loop) fuel control conditions. Some ECUs will factor the long term fuel trim (LTFT) into the open loop fuel control calculation. In this case, the larger injectors are canceled out by the LTFT correction which will be affected by the larger injectors. However, if the open loop fuel calculation does not included an LTFT correction, then the larger injectors are helping.
• A larger diameter TB makes no difference in the fuel calculation. This is true for both MAF and MAP-based (XJ) fuel calculations.

I very much recommend installing a new fuel pump. Unfortunately, the available options seem suboptimal. The typical approach is to replace the entire fuel pump assembly which includes the pump, carrier, fuel level assembly, and regulator which is also the fuel filter. The Delphi assembly seems to be the best available, but it has plenty of poor reviews.

As a side note, an interesting question here is whether the fuel pump is toast or whether the fuel pressure regulator/filter has become clogged.

 

Nice score on the transfer case!

 

Dang man - you absolutely stole that transfer case. I paid $1400 for mine about two years ago and thought that was a good deal then. Some people are selling them in used condition for >$2K.

Mine swapped over to the ax15 with ease. The trans tunnel needed to be massaged and the clearance in there is TIGHT but it works. The stock speedo works for me but is about 10mph off. I also kept the stock rear yoke and had a custom driveshaft made up to work with it rather than swapping yokes. The shifter was a pain - ended up with a Novak cable shifter that works.

4:1 is awesome but it runs out of gears in low range quick. I've been thinking of going back to 4.11s vs 4.56s because of it. Crawling though is just incredible.

 

Don't regear! That's an excuse to go to bigger tires.

 

Your post indicating low fuel pressure at high engine load inspired me to check my own fuel system. I rented/borrowed a fuel pressure diagnostic kit from Autozone. First thing I realized is that the pressure gauge connector to the rail was not readily depressing the schrader valve to allow it to see fuel pressure. I had to wrench it on to the fuel rail connection pretty tightly, and then I verified that the schrader valve was open by depressing the gauge pressure relief button which allowed lots of fuel to flow through the pressure relief line when the engine is running.

Then I took it out for a drive. I just had new diff gears installed a few days ago, and the shop told me not to wail on the throttle for 500 miles, so I only took the engine to about 50% load as indicated by the OBDII output. This was about 50% throttle and about 3300 rpm. At idle, fuel pressure was right on 49.5 psi, and at 50% load, fuel pressure dropped to 49 psi. Its not nearly as much load as you put on your motor, but it covers 98-99% of how hard I'd push my XJ motor.

Anyhow, hopefully this is useful information for you as well.

 

I really cannot believe I came home with that case. Talk about getting a Facebook marketplace rush! I briefly considered flipping it for a profit, but I'll never find another one for $500. I guess running out of gear quick is a good problem to have lol.

I have a friend who runs one in an XJ with it clocked up flat. Doesn't look like too much work needs to be done to get it to fit. I'll likely do the same. The shifter is a problem for another day right now.




I haven't been able to find a straight answer on whether or not the PCM adjusts the open loop fuel map based on long term trim values. The FSM states "During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming." which makes it sounds like it doesn't, but I'm not sure.

I ordered a Delphi pump module. Fingers crossed. I'm also a bit suspect that the root cause problem is the regulator/filter is partially clogged, but its all gotta come out anyway.


That is helpful! Thank you for doing that and posting it. I'm glad that I inspired some testing. Is that the OEM pump?

 

Good luck with the Delphi assembly.

As far as I know, my XJ has the OE fuel pump assembly. But it also only has 122k miles on it.

 

Since my last post, I went on my honeymoon, then had a few weeks to prepare for an annual offroad event called the Pilgrimage which happens in Vermont each year. Also, my truck had been in the shop for weeks, so I was dailying the Jeep on the 32" street tires, despite it feeling a bit down on power.

I've still been dealing with a vibration/noise when the front driveshaft is installed. I tried 3 different driveshafts with the same result. My pinion angle should be good enough, but its not perfect. Probably about 2 degrees off. I believe the JK axle's pinion offset is about 3/4" offset compared to the Dana 30's, so I'm ending up with a small amount of lateral misalignment that is contributing to my pinion angle imperfection. I would like to try to make it perfect before assuming its something in the front diff, but I am still suspect its something in the front diff based on the weirdness I felt in the spider gears when installing the axle.





Regardless, its not that bad, so I was just driving it anyway.


In preparation for the Pilgrimage, I got both of my lockers operational. For the front, I bought the connector harness and haphazardly wired it up, leaving a switch zip tied to the dash. For the rear, I wired my compressor to my existing subwoofer wiring, and rigged up a 1 gallon air tank with a pressure switch and manifold to run the ARB. The compressor is controlled with the subwoofer switch, and I just loosely ran 2 wires up to the front of the cab with a switch for the rear locker.

Its a real eyesore of a setup, but this was my "I want to go wheeling right now" solution.







Then, as fate would have it, I started having problems about a week before the Pilgrimage. My "down on power" situation turn into being downright undrivable. I couldn't maintain 40 mph on flat ground.

I assumed my fuel pump finally gave up or got more clogged. I already had everything I needed, so I tore right into it and got the pump replaced.

Went well enough, other than my fuel tank skid has seen better days. It took some convincing to get this back on.









After replacement, I measured 54 psi of pressure. A bit on the high side, but within the +/- 5 psi factory spec. I was happy to see the pressure hold steady even at full load. Problem solved.







However, while that did resolve my fuel issues, that did not resolve my running issue. I didn't know where to start diagnosing. I began chasing the thought that it was dropping spark, or I was getting odd readings from a sensor. Eventually, I pulled the front O2 sensor and test drove with the hole open. What do you know, problem went away. I put a pressure gauge in the port and saw the gauge pegged out at 20+ psi of back pressure in the exhaust. Something had plugged up my exhaust.

I hacked off my muffler and immediately found the issue. My catalytic converter had puked its guts into the muffler and plugged it.










I got a pretty good laugh from this. No surprise the cat broke up. It had some good dents in it from getting abused on rocks.

I proceeded to cut the bottom of the cat off, take all the honeycomb out, shake all the stuff out of the muffler, and weld everything back together.








Good as new! Thing is running better now than it has in a long time. I shaved 4 seconds off my 0-60 time LOL.






THEN, it was time to go wheeling! More to come...

 

I had heard that cats can get plugged up, but I wasn't sure how that could happen. I suppose an oil burner could spit enough oil into the cat to clog it, but otherwise, not obvious to me how a cat could get plugged. Your situation was a bit different. Fascinating to see huge chunks wedged into the muffler. I guess you fished those out?

BTW, I hope you are planning to replace the cat. I can't stand the smell of driving behind a catless vehicle. I'm nowhere near you, but I'll speak for all the other people who also hate it. Rather ironically, I drove a catless vehicle for many years. I now understand why so many people felt compelled to pass me even when I was driving 5+ mph over the speed limit. :-)

 

go away Karen

 

I figured there was a good chance that someone would say something.

There's no drawback to running a cat. The performance penalty is like 5% and only at high engine loads. If you like a loud exhaust, can still have it with a cat. The only thing it really changes is the exhaust smell (and of course the added pollution).

 

So you made the comment knowing you would stir crap up?

how much pollution is the jeep adding to the atmosphere? More than cow farts? More than your favorite celebrity jet setting around the world?

Find something else to complain about.

 

Play nice.


I wouldn’t mind putting a cat back in it. Truthfully, it doesn’t smell nearly as bad as I thought it would. Even being out wheeling behind my vehicle with someone else driving. With that said, when I was removing it I was doing it with intentions of replacing it, mostly so I don’t get a CEL. Funny enough, I’ve now driven it ~500 miles with the rear O2 sensor zip tied to the floor (not in the exhaust) and haven’t gotten a code for it yet.

It definitely made my vehicle louder, which I’m not thrilled about. My exhaust needs rework (again), so if I ever redo it, I’ll strongly consider putting one back in.

 

During my weekend of wheeling Vermont's class 4 roads, I found myself thinking "huh, I made my Jeep too capable". It did very very well. Fully locked is like cheat mode. The suspension articulates happily. It went everywhere I asked it to.






















https://www.youtube.com/watch?v=uMNx...ature=youtu.be



I definitely need to do a bit more massaging to clear 37's. I messed my front fenders up pretty good, and my rear axle could go back another inch to stop from rubbing on the tube fenders. Also, my steering is severely underpowered. I'm definitely thinking about hydro-assist. All minor stuff though. It went great!

 

Cool pictures!