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Thread: 99 Jeep XJ

  1. #1
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    99 Jeep XJ

    First off, I think it's awesome that HP Tuners has added support for the 4.0 Jeeps. There are a ton of them out there, and stroker kitted 4.0's are becoming pretty common these days.

    So, I reflashed my 99 XJ last night and there a couple of issues that I found. Since reflashing, I get a CEL (MIL) for P0700, TCM request for MIL Light. When I scan the TCM, there are no codes present and the trans shifts perfectly, converter lockup and all. Next is, even after I disable the rear O2 sensor in HPT Editor, A CEL will continue to pop up for low voltage on the post-cat O2 sensor. Neither of these are big issues since I can still make fuel and spark changes and the vehicle still runs and drives fine. Just the annoying CEL light.

    Right now, I have it forced into continuous open loop and have been playing with my CO meter to make changes to the fuel delivery. I know it's old-school and not precise, but I'm waiting for a wide band so I can do some data logging.

    That brings me up to the next issue with the scanner...
    The beta scanner is still a little buggy and will stop functioning if you start opening up too many applications on your computer while logging (using a Dell M6600 with Windows 10 Pro, 32G RAM, and Nvidia Quadro K4000M graphics card). The scanner seems to confirm the issues with the mystery codes. The HPT scanner indicates that the MIL light is "ON", but doesn't display any codes and if you try the "clear codes" button nothing happens. Now... After the reflash, I did get a code for CAN Bus failure and I was able to clear the code with the HPT scanner. The other 'phantom codes' I can only clear out with my Matco scan tool. But the TCM and rear O2 sensor codes pop up again after a few minutes of driving.

    Other that these issues, I'm pretty happy. Nice job HP Tuners!

  2. #2
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    So... I've made a few changes without the benefit of a wideband, but I do have a portable 5-gas analyzer. Doin' a little old-school tuning.

    The changes I've made so far are:
    Disable both O2 sensors and raise the temp for closed loop enable to 370F (forcing constant open loop operation).
    Add 10 of timing at idle bringing the total to 20.
    Add a global timing increase of 3
    Set the minimum idle timing to 17
    Richen the "EGR OFF" fuel table between 500 and 900 RPM and 12 to 39 KPa by 20%.
    Pull 5% out of the remaining fuel table.
    Reduced the 'air enrichment' (fuel/general/fuel correction/air enrichment) by 10%.

    The net results are the idle and off-idle transition are much smoother. The idle MAP has dropped from 4.5 PSI to about 3 PSI. The idle is now at 2.5% CO (it was at 0.3%) There's a no noticeable difference in performance. CO at cruise (1700 RPM at about 60KPa manifold pressure is a steady 0.5 to 0.8%) indicates a mixture slightly under 14.7. About the same as closed loop operation. Testing was done with fuel containing around 6% ethanol. The reduction of the 'air enrichment' function should help with the deterioration of cold weather fuel economy. Before doing the tune, my fuel mileage was 19-20 mpg in mixed driving. Wintertime (ambient temps below 45F) would usually drop fuel mileage to 17-18 MPG. Will run a few tanks of fuel through to see in there's any difference. I also have a wideband on the way to refine this tune. Once I have some confidence in the tune, I'll post in the repository.

    Have had some issues with a random P0700 code showing up after reflashing. I'll post details later.
    Last edited by grimmechanic; 4 Weeks Ago at 10:51 PM.

  3. #3
    Advanced Tuner axekick's Avatar
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    Nice work! Good start on the Jeep tuning!

  4. #4
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    I've reflased my ECM 3 times and have had a few issues.

    A bit of history on the vehicle: A very stock 1999 Jeep XJ Cherokee with 4.0 engine and AW4 trans. 257,000 miles on the original engine. Timing chain replaced at 180K, otherwise original engine. The stock exhaust manifold was replaced with a modified 2000+ dual outlet manifold. The down pipe to to cat was replaced with a 2000-2001 49 state (no pre-cats) dual pipe. Cat removed and the remaining exhaust is 2.5" with a Flowmaster muffler. The rear O2 sensor was modified with a R-C network (similar to what's sold as a "mil-eliminator" for 96-04 Mustangs) to keep the P0164 code from showing up. It's worked for 5 years. Then, a few weeks ago, the P0164 code showed up. Looks like my capacitor in my R-C network went out of spec and I get a wonky waveform triggering a P0137 code.

    The first reflash I disabled the rear O2 sensor in VCM Editor (beta). After the reflash, I had two new codes pop up. A P0700 code indicating a request for a MIL sent by the TCM to the ECM and a Bus failure code. Codes would not clear using the VCM Scanner (beta). Used my Matco scan tool and checked for TCM codes and there were none saved or pending. Cleared the P0700 and bus codes in the ECM with the Matco Scan tool. As soon as I started driving the vehicle, the MIL light came on again. P0700 again and P0137. Hmmmm......

    Made some adjustments to fuel and spark and reflashed again. The 2nd reflash resulted in the TCM and rear O2 codes popping up again, but no bus error. Drove it for a day and everything functioned fine with the trans, but after clearing both the codes, they would immediately reappear.

    Made a few more changes to fuel and timing and reflashed the ECM. Same P0700 code reappeared again, but this time, even though there were no stored codes in the TCM, I cleared all TCM data (with the Matco scan tool) before clearing the P0700 in the ECM. The P0700 phantom code seems to have been resolved, AND the rear O2 sensor was finally disabled (not showing any output on my Matco scan tool).

    So, I have two observations here:
    1. The reflash on this vehicle somehow triggers a phantom P0700 code that shows no errors in the TCM. Despite this, clearing stored data in the TCM prior to clearing codes in the ECM might resolve this issue, BUT NOT WITH THE VCM SCANNER (BETA) version.
    2. Even when O2 sensors are disabled, it may leave some code vestiges that prohibit the disabling from taking hold the first time 'round.

    Despite these two problems, I have a MIL light free vehicle at the moment.... I'll know if it stays this way tomorrow.
    Last edited by grimmechanic; 4 Weeks Ago at 09:18 PM.

  5. #5
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    Drive to work this morning and the P0137 code popped back up. Even with both O2 sensors disabled. Funny thing is, the front O2 sensor still shows voltage in the Matco scanner, just no mixture switching. But the rear O2 sensor shows zero voltage.

    So, after work, I pulled the R-C adapter off the rear O2 sensor and now it shows voltage matching the front sensor on the Matco scan tool, but not in the VCM Scanner (beta). After returning the wiring to stock on the rear O2 sensor, no more P137 code. Even with the cat removed.

    The lesson learned here is that even though the O2 sensors are disabled and the ECM forced into constant open loop operation, both have to be present and functioning, but they will not trigger codes.

    Still haven't figured out why the P0700 code comes up after reflashing the ECU. But the last time I reflashed the ECU, I managed to get it to clear in the VCM Scanner (beta). But there were no codes visible in the VCM Scanner. I could only see the P0700 code with my Matco scan tool.

  6. #6
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    P0700 is coming up due to lost communication with tcm/cluster during flashing. Mine is doing the same thing, after 2 key cycles it?s been going away.

  7. #7
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    Did any of y'all run into a definitions failed to load? My 97 extracted and saved but won't bring up the info. Their isn't anything special you got to do with the beta is their?

  8. #8
    Advanced Tuner axekick's Avatar
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    The last Beta I downloaded was 4.5.864 and it all worked normally. I never had that problem. Try downloading the Beta again from your device page and pulling the tune again. I will point out that I have to have internet anytime i'm flashing mine.
    2006 Tahoe
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  9. #9
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    I had the definition failed to load; had to put a case in. Your probably the 1st person with that particular file and it needs to be released by hptuners.

  10. #10
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    Quote Originally Posted by Dustinjv View Post
    I had the definition failed to load; had to put a case in. Your probably the 1st person with that particular file and it needs to be released by hptuners.
    I figured as fresh as this is. How long did it take for them to send an update?

  11. #11
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    24 hours or so, they are super helpful with anything you need.

  12. #12
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    Yup just got my update. Didn't take long at all thanx guys. Got excited then freaked out now back to excitement lol