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RPM sticks in 4th gear


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I have a 88 4.0 with the AW4. Whenever I’m driving and hit 45 mph, the transmission shifts into overdrive and RPMs drop to 1500. However if I push on the gas pedal after, I don’t really get any response. It will slightly increase RPMs. The only way it will pick up the throttle is if I fully floor it and it will “unstick” and it will hit 2000-3000 depending on how long I hold it. I haven’t had this problem until after I cleaned the c101 connector on the firewall. It doesn’t really affect me, but I don’t really want to have to floor it to try and get a quick acceleration past 45 mph.

 

 

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Sounds like you need to adjust your kickdown cable to me.

Tried that and it just locks in after I push the button. Even if I push the throttle down in the truck, it won’t move. I manually pulled it out to see if there was any change and it still acted the same.


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Just now, Dammerung said:


Tried that and it just locks in after I push the button. Even if I push the throttle down in the truck, it won’t move. I manually pulled it out to see if there was any change and it still acted the same.
 

 

Button? There is no button associated with the kickdown cable. It's in the engine compartment, attached to the throttle body.

 

Your problem is not "RPMs sticking," your problem is that your transmission is in overdrive and it's not downshifting to third when it should. The first thing to look at for that problem is the kickdown cable adjustment.

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336007470c2bbdd897ec844e34f273c1.jpg
So you’re telling me this is NOT the kick down cable? I’m just trying to adapt what I’ve found out on newer Cherokees. This was the most similar thing to the kick down cable they were talking about. You’re supposed to press that button, push the yellow thing all the way in, push the throttle pedal inside the truck, and it should self adjust. At least from what others have said. If there’s a different or better way of doing it, please inform me.

Also, “RPMs sticking” was the best way for me to describe the symptom. I don’t know a whole lot about cars and trucks.


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instead of pushing the yellow thing grab and pill the cable from the back side. once tight then open the throttle from the bell crank or the throttle body, lots of play between the pedal and the throttle body.

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Actually, it's NOT a kickdown cable. but, it needs to be adjusted properly.

It's a Throttle Valve cable AKA TV cable. 

 

What position is your Power/Comfort switch set at?  

BYPASSING THE POWER/COMFORT SWITCH

Even though the indicator lights up in your Power/Comfort switch, that does not mean the switch is working and putting the Transmission Control Unit into Power mode.

The switches had a high failure rate.

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!!!

Have you performed tip 5 and Tip 10?

RENIX SENSOR GROUND TEST

 

The sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the ignition is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.Backprobe 2

Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud.

Refreshing of the dipstick tube connection is covered in Renix Ground Refreshing, and the sensor ground upgrade is covered in Tip #6 – Sensor Ground Upgrade.

On 87 and 88 models, you could have a poor connection at the C101 connector as well. See Tip #2 – C101 Refreshing and Tip #27 – C101 Elimination.

 

TRANSMISSION CONNECTOR REFRESHING

 

trans plugs

Over near the transmission dipstick tube are 2 rather large connectors. One is black and goes to the NSS and the gray connector goes to the transmission itselfTCU fuseTCU location



. These 2 connectors carry all the info between TPS, TCU, NSS, speed sensor, and transmission solenoids.

Unplug each one, visually inspect for corrosion or bent pins, spray them out with electrical contact cleaner and plug them back in.

Additionally, if your Jeep is an ’87 to ’90 Renix, it’s always a good idea to reach up under the glovebox area and unplug the connector to the TCU and spray it out along with the receptacle of the TCU. While you’re there, find the fuse right in that area for the TCU. Remove it and spray out it’s receptacle and clean any corrosion from the fuse.

 

The TPS is the signal for kicking down to a lower gear.

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