I bought some remanufactored Bosch 4-hole injectors from Ebay for a really good price, $45 for all 6, and the guy said they're for 96, 97 (my year's), and 98 Cherokee XJs. The part numbers were all 0280155923. This is the ebay listing: https://www.ebay.com/itm/96-97-98-Je...53.m1438.l2649

I installed them yesterday following this guide: https://thexjguys.wordpress.com/2012...injector-swap/

After checking for any fuel leaks, I turned on the motor and as expected the idle was very rough/choppy. Also the Check Engine Light came on, it was off before.

So I went through their procedure to reset the ECU's Adaptive Memory tables (touch the positive battery terminal to ground for 30+ seconds, turn the ignition to ON, turn the headlights ON, turn the headlights OFF, then turn the ignition to OFF).

I then started the engine, but the idle was still extremely rough. Choppy is a very good way to describe it. I actually then repeated the Adaptive Memory reset procedure just to make sure it worked. Started the engine and it was no different. Oh, and the CEL was still on.

Drove it to work this morning and there is definitely a major loss of power and throttle response, most noticeably at lower RPMs.

So, is this normal?

It says it needs 50 warm up cycles to re-populate the Adaptive Memory tables. Does this mean it will slowly get better over the course of the next few weeks?

Or maybe one of the injectors is bad or not getting voltage? Should I test by pulling the wires off each injector while its running and see note the changes to idle and see if there is an injector that when unplugged doesn't change the idle? Can I assume that that is a bad one?

Thanks!

One last thing: I labeled the wires before disconnecting them from the old injectors so I could reinstall them in the same order, so I don't think that's the problem. I can recheck though to make sure.


(astute observers will notice that I broke the rear breather valve thingy why trying to get the vacuum line out of the way of the fuel rail. I temporarily fixed it with electrical tape so I don't think a vacuum leak is the problem I'm experience..)

 

On that rear plastic valve cover elbow, its not the plastic piece being broken that will cause the vacuum leak, it is the tubing that you pulled off it. Has that tubing been repaired or temporarily sealed up?

Additionally, I think anyone who is going to make any modification that can effect air/fuel ratio should have an OBD2 scanner available so that they can see what the fuel trims and O2 voltage levels are doing before/after the job. You can get these scanners for $20 these days and use your android or iphone to connect and view their data. You can get standalone ones for a little more.

Getting a set of injectors that cheap is of course a bit of a gamble. Like you said, it is very possible that one or more of them is having a problem. At that price, I doubt anybody spent any significant time testing, cleaning, and flow matching them. They are probably just cleaning them up with some plastic conditioner and creating sets by throwing them together. I could be wrong of course, but that is a really low price.

The PCM reset stuff is overrated. The PCM will being adjusting fuel flow immediately once the O2 sensors are providing readings (about 1-2 minutes of running after a cold startup). They only take a few moments to adjust, the short term fuel trim will change within seconds, and the long term fuel trim will adjust over a period of minutes. These do not depend on 50 drive cycles. They happen all the time.

The stuff about memory and drive cycles has a little more to do with what fuel/air strategy the PCM will use when the vehicle is first starting. Since it is starting from nothing. It will take the engine coolant temperature sensor data, and prior fuel trim averages, as well as intake air temperature and crank/cam data and make a decision on what is the best initial fuel strategy is for an engine start. Once it is started and O2 heaters are up to temp, the air/fuel ratio will be trimmed in real-time based on the upstream O2 sensor voltage levels.

 

What did it run like before?

 

I would toss the old ones back in, see if still acts the same way. Might be the cheap injectors from fleabay.

 

At that price those are probably Chinese knock off crap and not really rebuilt injectors.

They say rebuilt instead of new so people think they are rebuilt and genuine but they are not.

 

SOLVED!!

Once I knew that this was not normal behavior, I started diagnosing. First thing I did was tap on them with a screw driver: no bueno. Next, I grabbed my IR thermometer gun and pointed it at each header tube to see if one or two was colder then the others. This was much easier and faster then pulling plugs.

Sure enough, #2 was only 100 degrees while the others were around 300 degrees.

I pulled the #2 injector plug, while it was running, and nothing changed in the idle. I then unplugged the adapter that came with this set of injectors (so they'll fit the Cherokee 4.0, that's probably why they're so cheap), plugged it back onto the injector and then plugged the connector back onto that - boom! Idle evened out and the vehicle stopped shaking.

I drove it to work just now and it's much better then it was this morning, though I can't say it's a huge improvement over the way it was before the swap. Maybe the ECU is still "learning" though.

The tube was fine, not cracked, actually it looked new like maybe it was replaced not long ago.

That's also a good point about getting a OBD2 scanner, though I think the $20 claim is a bit exaggerated. Do you know of something that cheap that will work with an iPhone? I've had my eye on the ScanGaugeII and ScanGauge^e for a little while now, so I can monitor my real time MPG. They're $150 and $100, respectively.

I also suspected that the ECM/PCM (whatever, idk) "Adaptive Memory" stuff was a little bit of a wive's tail but who am I to know. I figured it could only help, especially since most people report that doing this helped them a lot.

It ran great. Gas millage is in the pits though, like 12 or 13mpg city and 17mpg highway (65mph).



$45 is pretty hard to beat and its running now at least as well as it did before the swap. After burning through this tank of gas, I'll record the next tank of gas and mileage (multiplying my mileage by 1.102 because I have 31" tires) to get a new MPG reading. Then we'll see who has egg on their face

 

I wouldn't expect a noticeable improvement in MPG unless it was running like crap before the injector swap.

 

Holy **** yes!! Buying one right ****ing now

 

The scanners I've been getting for my Jeep are BAFX OBD2 bluetooth scanners. They are for Android. The last 3 I have purchases have been less then $25 via Amazon. They are so cheap I give them as gifts to my friends during holidays.

I popped one open and wired it permanently into my Jeep, added to that a $49 tablet from walmart, and I have a full time digital dash with OBD2 data all for less than $80. (that includes the $5 I paid for the full version of Torque app for the tablet).

 

Brilliant. Where do you mount the tablet? How big is the display?

 

Depending on how one drives that isn't at all out of the ordinary.
Those that claim 20+ mpg reflect full well the fact the US ranks in the bottom third of math scores worldwide.

 

I think it was a run-of-the-mill 7" screen (sound about right?). They had an endcap of these, there must have been 100 boxes of them. $49 each. So I crossed my fingers that they would have what it takes. It performed fine. Keep in mind that battery life is not all that important because it is permantently pluggged in anytime the vehicle is running.

The only drawback is that on a really cheap tablet like that you probably won't get GPS or compass sensors. So I can't use it as a moving map in addition to being my digital dashboard. (spend a few dollars more, and you can, but I already have my phone if I need a map).

Here is how I mounted it. I have a 96, so your options might be just slightly different. I took one of those ball-and-socket suction cup mounts that comes on small GPS units like the Garmin Nuvi. The mounts can be bought standalone on amazone for a few bucks. I happen to have a couple of unused ones in the garage from old cheap gps that have since been tossed. I simply took the part of the mount that would normally attach to the gps, trimmed it a bit, and glued it to the back of the tablet. Its a $49 tablet, what do I care. Then I suctioned the mount just to the right of my dashboard where the 96 has a blank spot between the gauges and stereo/heater controls. So I can pop the tablet off the mount and throw under a seat or something if I want to. But most the time it just stays up. The suction cup needs to be re-suctioned every few months (depending on the weather).

Then I just run torque pro with a custom dash layout showing my favorite data points (coolant, speed, rpm, intake temp, load %, long and short term fuel trims, open/close loop status, etc...you get the picture).