Timberwolf24

Hey guy, i have some questions that hopefully someone can help me with. I'm pretty new to the forum I've only posted a couple times. my apologies if i'm posting in the wrong place or defying any other "forum protocol ..

Any way, I have a 99 Jeep xj 4.0 I6, Automatic, sitting on 4.5in lift and 33's (4.10 gearing).
I seem to have a real Loss of power high mid and low range and im getting about 11-12 mpg. I know some people say that's all i can get with this butl ive gotten 18 out of it before the loss of power. she runs smooth other than the occasional l hard misfire up hills almost like a transmission slip.any help would be seriously appreciated im at a loss. Also there are no codes.

So here is what ive replaced, some to "fix" the problem some were just upgrade mods--

New TPS
New crank sensor
New map sensor
New IAT sensor
New accel performance cap rotor Copper core plugs (.035) New Wires
New oem Coil
Bosch 02 sensor was put in about a year ago (to be replaced with OEM soon)
rebuilt 4 hole injectors from a F350
Deep Cleaned throttle body/IAC
K&N Cold Air intake
Magnaflow High flow cat
AFE cat back
Synthetic everything, Gears, trans, engine, TC
Bakes are not sticking
Fuel pressure is a solid 48 psi through the ranges

I don't think i forgot any but we'll see

Things i know i haven't replaced--

ECT (engine coolant temp) Cause it seems to be reading right.
Ignition pickup sensor ( also known as cam sensor)

Anyone that can help please do im getting really burnt out haha

Thanks, Joe

Fred/N0AZZ

Not know the injector numbers or brand and only going on from a "F-350" it makes me think they are too large for your 4.0. As all F-350's used larger V-8's in them with higher HP numbers, but I could be wrong on that.

I run 33" tires on a 4 1/2" lift also but with the proper gear a 4.56's and my mpg runs 15-18 highway depending on load.

When you were trouble shooting you did do one thing at a time then test it again to see if it took care of the original problem didn't you? That is rule 101 never do more than one thing at once.

BTW welcome to the Forum

XJmember

Maybe check each cylinders compression? 120 psi to 150 psi, variation between cylinders is 30 psi.

Timberwolf24

Thanks guys.
Sorry i didn't clarify what injectors I'm running, I was rushing out the door when doing this right up.. the injectors are Bosch 0280-155-917 XL2E-C5A. 200cc/min 19lb/hr @43.5 psi
correct me if I'm wrong but that would mean im running on the lean side. i believe stock injectors are above 230cc and are 22.5lb/hr @49 psi.
I didn't really know anything about injectors when i upgraded those for $60
I welcome any input or advise in what to do with my injectors.

All that being said my injectors were done a long time before my problems. probably about a year and a half. so i don't think they're causing the problem

Every part was replaced one at a time and driven to test for improvement.

As far as the compression test, i know i need to do it, I just keep putting it off haha.
Also the speedo gear is matched (as close as it can be)

Photojared

Compression and leak down tests are going to narrow down actual engine issues rather than sensor issues.

Timberwolf24

^ Agreed, I'm checking the compression next. I'm just trying to get all the possibilities and suggestions I can because I honestly don't believe it's the compression it's only about 165,000 miles and no other real signs of a worn engine. I am going to check it though, it'd be dumb of me not to. also I don't have internet at my shop so I can't just check it then update my post.

salad

That's a pretty extensive list... so lemme ask you:

Of all that stuff replaced, has any of it actually been TESTED? Using all OE Mopar stuff is EXPENSIVE, so I'm assuming most/all of the sensors are aftermarket. Is the MAP correct? TPS? IAT? You noted the ECT is correct but that's it. Also you can replace sensors all day long, but it won't make a differenceif their grounds are ****ty and the PCM doesn't get an accurate signal.

Do you have access to an OBD-II scanner? Not a code reader.

Timberwolf24

Yes, all have been tested and replaced along the way, do to either being shot completely or not reading accurately enough only A couple have been replaced recently, I just wanted to put out in depth as to not waste time with the things that have already been tackled. Some of the important ones like the map and crank are Mopar I wasn't gonna mess around with buying aftermarket to save a couple bucks with important ones. As far as scan tool Yes but it's a scantech. I think it was like $120

salad

Okay cool. Does it give live output? We're looking for STFT and LTFT

Timberwolf24

Yeah, Checked a couple days ago STFT was Bouncing around 0 to 5 pretty consistent but occasionally going as low as -3
Long term I think was showing 0 at idle. And around 10 when I was driving, Though I don't really know how "fuel trim" works to be honest.
Also my upstream o2 sensor was reading rich I believe, around .700-.840 aviation ally dropping real low but then bouncing right back up. I checked it cold idling up to temp idling and out on the road it always stayed real high. Again I don't know much about reading live data I'm a carpenter by trade an mechanic by hobby :P so reading the data is new to me.

Unforgiven

Typically, I only watch LTFT. If it is 10 off idle, I would be concerned about that. I don't like long term to vary more than 3 either positive or negative but prefer it to be negative. 5 at the most. The injectors bother me. On mostly stock vehicles of any brand I've always seen problems with different sized injectors whether they are larger or smaller. Notice I said mostly stock, meaning engine-wise i.e. no significant changes to camshaft, cylinder head flow, or displacement. I would be tempted to try a set of good, stock injectors.

salad

Yeah that's messed up. I'd change to more reliable NTK sensors before chasing that venue further.

Were these injectors tested prior to install?

Timberwolf24

Yeah I have a NTK on the way. And yes I rebuilt the injectors and tested them. But that doesn't mean they haven't failed. They do hold pressure tho. Im probably going to put 784s in eventually because the ones I have aren't really the best option. Can you tell me what the fuel trims should look like?

Timberwolf24

Sorry didn't see unforgiven's post. The 0280155784s are close to stock specs with better atomization. I've never heard anyone stand by the stock injectors. But Like I said previously I don't know a ton about injectors

salad

I don't know if the fuel trims are expressed in a specific unit, but the gist of the fuel trim variables is how much fuel the PCM needs to either add or remove from the pre-calculated injection amount to meet the target Air-to-Fuel Ratio. LTFT of +10 means essentially that long term the PCM thinks it's running very very lean. Something like this usually indicates a failed O2 sensor, exhaust leak, or an actual lean condition. STFT normally bounces around quite a bit but you can spot a trend faster than the PCM updates LTFT.