Jump to content

Shift points for XJ auto? Too low rpm


Recommended Posts

My 87 MJ with 4.0 Renix shifts way too low for my liking, keeping it under 2,000 rpm.  I don't care too much about mpg, as this isn't a daily driver.  Is there anything that can be done to adjust the shift points?

 

I am still looking for a 89-90 428 ECU to swap in, which I hope helps the acceleration a bit (and perhaps fixes this issue).  It just seems so slow after shifting out of first gear.

Link to post
Share on other sites
2 hours ago, rynoshark said:

My 87 MJ with 4.0 Renix shifts way too low for my liking, keeping it under 2,000 rpm.  I don't care too much about mpg, as this isn't a daily driver.  Is there anything that can be done to adjust the shift points?

 

I am still looking for a 89-90 428 ECU to swap in, which I hope helps the acceleration a bit (and perhaps fixes this issue).  It just seems so slow after shifting out of first gear.

Have you done any of the tips on my website?

 

Adjust the throttle valve cable as Don suggested also. 

Link to post
Share on other sites
10 hours ago, omega_rugal said:

is the comfort mode on?

Good question!!

 

BYPASSING THE POWER/COMFORT SWITCH

Remove and unplug the switch. In the harness are 3 wires.  One has a stripe, one is tan, and the other wire is black.

Make a 4″ jumper wire with a male spade at each end.Jumper wire

Plug one end of the jumper wire in the cavity for the tan wire and the other in the cavity for the striped wire of the harness and you’ll be in permanent Power mode.

Stuff the harness back in and reinstall the switch for looks if you want.

Make sure the 7.5 amp “Trans” fuse in the fusebox is good.

If you happen to have a 91 or 92 XJ/MJ and it has the Power/Comfort switch, just jumper the Tan and Blue wires in the harness plug.

NEVER include the black wire when jumpering!!!

 

Also consider doing this:

 

RENIX GROUND REFRESHING

 

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.

All the components listed below ground at the dipstick tube stud:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the Oxygen sensor, Knock Sensor, Cruise Control and Transmission Sync signal. All extremely important stuff.

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

  • Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. If the whole stud turns, you can use a 7/32″ six point socket or wrench to hold it so the nut can be removed. Worst case, cut the wires and remove the stud and nut. Install new terminal eyelets on the wires when going back together.  Scrape any and all paint from the stud’s mounting surface where the wires will attach. Surfaces must be clean, shiny and free of any oil, grease, or paint.
  • Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Apply a liberal coating of OxGard, which is available at Lowe’s and other stores. Reinstall all the wires to the stud and tighten thdipstick stude nut down securely.

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, apply OxGard, and reattach securely.

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for its intended use and subject to corrosion and poor connections at each end.

  • Remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Apply OxGard. Reattach securely.
  • Remove the other end of the cable from the rear of the head using a 3’4″ socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely with a liberal coating of OxGard.

2 STRONG suggestions regarding the ground system:

I prefer to add a #4 gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18″ long with a 3/8″ lug on each end works great and you can get one at any parts store already made up. NAPA has them as part number 781116.

A further improvement to the grounding system can be made using a #4 cable, about 10″ long with 3/8″ terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. NAPA part number 781115.

For those of us with Comanches, it’s very important to remove the driver’s side tail lamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal.  Add a 10 gauge wire, with an eyelet on each end, from that grounding point to a bolt on the frame. Better yet, on both Cherokees and Comanches, complete Tip 29 for the best fuel pump grounding. Be sure to scrape all mounting points to bare metal and apply OxGard also.Fuel Pump Ground Comanche

If you want to upgrade your ground and battery cables with custom made parts, contact Neal at www.meanlemons.com 

Neal's cables

Revised 02/04/2017

 

Link to post
Share on other sites
  • 3 weeks later...

So Eagle, if the TCU is separate for 1987, how can the shift points be modified?  Is there a replacement TCU that can be used?  The TCU in my 1987 is the 8953003433 with a date code stamp of "86J" (built October 1986).

 

I have the 428 ECU from a 1990 Renix already installed.

 

Thanks Cruiser for the AWESOME tips, I have been working through them.  Replaced 428 ECU, Volvo injectors, comfort mode bypass with jumper cable.  However, for some reason the light for the comfort mode switch no longer lights up, despite the jumper between the tan cable and striped cable.  It could have just been I looked during the day and need to check again at night.  I would have thought the light would be on if the jumper was working?

 

Will work on the grounds as well.

Link to post
Share on other sites

ok i have a question, when the comfort/power button was removed, did they just hardwired the mode (grouding the pins in the harness) or was the ECU modified to remove the comfort mode? in theory you could undo the hardwiring  and reinstall the switch...

Link to post
Share on other sites
6 minutes ago, omega_rugal said:

ok i have a question, when the comfort/power button was removed, did they just hardwired the mode (grouding the pins in the harness) or was the ECU modified to remove the comfort mode? in theory you could undo the hardwiring  and reinstall the switch...

 

The Power/Comfort switch turns a 12V signal on/off at pin C11 of the TCU. It has no direct connection to the ECU.

Link to post
Share on other sites

87 TCU was different from the 88 to 90 and had early shifting issues.

 

But, the TCU grounds at the engine dipstick tube stud as does it's "logic" circuit. Hint hint!

 

Tip 10 makes sure there isn't too much resistance in the connectors from the TPS to TCU and solenoid activation. Another hint.....

 

Have you done the TV cable adjustment Hornbrod suggested?

 

Get all this^^ done and we'll revisit this. 

Link to post
Share on other sites

I couldn't find this documented anywhere, so here is what I've pieced together so far on TCM/TCU modules with light gray connectors for the AW4:

 

8953003433 = green (TCM 3433), 1987 TCM from 4.0 4x4 AW4 (one year only, poor shift points)

8953005305 = red (TCM 5305), 1988-1990 TCM (revision A example dated coded 90D)

 

The later ones which I believe don't work with the Renix Comanches (they have the green connector) received a new model numbering scheme:

 

56026769 = yellow, 1992-1996 Cherokee XJ, 4.0, possibly for 4wd only (example date coded 91M, 93G)

56041016 = green, Cherokee XJ 1992-96 (example date coded 96B)

56027951 = magenta, ?-1997 Cherokee XJ  (example date coded 96L)

 

After the model number appears a white box with a stamped revision identifier inside (blank=original version, A=revision 1, B=revision 2, etc). I suspect it would be impossible to figure out what is different in the revisions.

 

Link to post
Share on other sites

I ran 31's with stock 3.55 ratio. It was a bit doggy.  This is on a '98 XJ. I did regear 4.10s beginning this year. Much better. I am running about 2200 RPMs at 70 mph. I'd say 3.73 ratio for your 30s.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...