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Shifting issue and no power!!!!

itsa svx

NAXJA Forum User
Hello - Having a weird issue with my jeep that I could use some help figuring out.

If I put it in Drive it has no power when starting off like it is starting in 4th gear. I can start off in 1-2 then manually shift up and it is fine power wise but occasionally after a short ride it will just feel like it has no power and won't go over about 35mph. If I pull over and turn it off for a minute then start it back up it will run good for a while then repeat the issue. I was thinking the TCU was bad so I swapped in another but no change. I verfied all fuses are good - even the positive in-line to the TCU and it has power at the harness into the TCU. No Check Engine light on...

Thinking of maybe a bad TPS but not sure it could cause this much of an issue.

Any suggestions would be greatly appreciated.
 
What year, engine, transmission, modifications, or other info, to help solve your problem ?

TPS has a direct effect on shifting.

Test the TPS.

You may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

You should have 5 volts going into the Throttle Position Sensor (TPS). It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The other wire will be the ground and should show no voltage.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
 
Ok - Checked the TPS and it was reading good. Threw a new one in just to be safe but didn't fix the problem of it wanting to start off in 4th.

Any other ideas of what I should be checking for?

Anyone around Fredericksburg, VA that would be willing to take a look and offer an opinion?
 
Google for the AW-4 Service and Diagnostics Manual. Follow the troubleshooting charts and perform the tests. Consider the Transmission Control Unit is faulty. After AW-4 diagnostics and testing you may want to find a good used one.
 
I have seen some connections in the harness give similar problems. Over near the trans dipstick tube are 2 kinda large squarish connectors. All the signals between the TCU, TPS, solenoids, vehicle speed sensor travel through them. Try disconnecting them and spraying them out with electronics cleaner and giving them a good visual inspection.
 
Hello - Having a weird issue with my jeep that I could use some help figuring out.

If I put it in Drive it has no power when starting off like it is starting in 4th gear. I can start off in 1-2 then manually shift up and it is fine power wise but occasionally after a short ride it will just feel like it has no power and won't go over about 35mph. If I pull over and turn it off for a minute then start it back up it will run good for a while then repeat the issue. I was thinking the TCU was bad so I swapped in another but no change. I verfied all fuses are good - even the positive in-line to the TCU and it has power at the harness into the TCU. No Check Engine light on...

Thinking of maybe a bad TPS but not sure it could cause this much of an issue.

Any suggestions would be greatly appreciated.

When my XJ did that same thing, it turned out to be two of the three solonoids in the AW4 were bad. A simple OHM test with one test lead on the wire and the other other to ground would give an indication of the health of the solonoids. This could be done at the connector on the TCU or the connector in the engine room passenger side. There was one or more threads in recent days out lining how to do the test and the results/resistance of the solonoids.

I drove my XJ several hundred miles in South Florida with the TCU disconnected and shifting it manually. Fuel consumption was higher because there was no torque converter lockup.
 
I had this issue crop up for a few reasons over the years, as everyone else said, check the TCU, also check the TCU fuse, usually it's right under the passenger side dash board (when you see it you will say "what's that fuse for") like I did, when I pulled the fuse and then had trans issues. Another thing to check is the vacuum lines to the kick down, I don't think this is your problem, it's most likely TCU related, but checking your vacuum bottle, and vac lines couldn't hurt anyways. Checking the electrical harness is a lot easier than digging through solenoid tests.
 
Ok - checked and cleaned all of the connections under the hood with electronic spray and all are good but no changes. Swapped in another TCU an no difference at all. It's weird but it acts the same whether the TCU is connected or not - I can shift manually but it won't shift at all on its own. Still no check engine light and no codes stored - I know the light is good because it came on when I changed the TPS but cleared after I drove it a bit. Guess I will move on to checking the shift solenoids.
 
No vacuum involvement in the AW4, throttle valve cable is a mechanical one (it might need adjusting but wouldn't cause this issue.)

I would bet on a solenoid or electrical failure but it might be an actual hydraulic/geartrain issue, hopefully not. The fault detection electronics on the 96 and earlier transmission control system are nearly nonexistent, I have completely blown two AW4s in my 96 and neither one ever set off a CEL.

Something to check, though it probably isn't it - there is a self tapper screw on the inner fender, driver side, between the ECU, air filter housing, and brake master cyl. If that is loose you will get an intermittent ground to the transmission control system, 4x4 indicator lamps, HVAC blower, and a few other things.

Without the TCU, does it drive fine aside from having to shift manually, with no torque converter lockup and no second gear? If so, you have ruled out a mechanical/hydraulic failure and it's down to the electronics being faulty somehow.
 
Yep - with the TCU unplugged it shifts good manually. There is still the issue where every so often it just feels like it has no power while driving but it is intermittent and honestly I can't remember if it happened to me with the TCU unplugged or not. When it happens if i pull over and shut the jeep off for a minute and start off again it is fine for a bit then the trouble will repeat. I don't drive it much since it is so unpredictable. I haven't had a chance to check the solenoids yet but plan to tonight.
 
Yep - with the TCU unplugged it shifts good manually. There is still the issue where every so often it just feels like it has no power while driving but it is intermittent and honestly I can't remember if it happened to me with the TCU unplugged or not. When it happens if i pull over and shut the jeep off for a minute and start off again it is fine for a bit then the trouble will repeat. I don't drive it much since it is so unpredictable. I haven't had a chance to check the solenoids yet but plan to tonight.

It does appear you have more than one issue. If you select the proper gear manually, the 4.0L should have plenty of get up and go. You said if you shut the engine off for a few minutes it run fine after that lead me to believe there is a fuel delivery problem. Check the fuel filter/s.

One poster here hinted there may not be power going to the TCU. Did you verify that? If every thing checks out fine then the problem may well be the solonoids.

By the way, the weeks I drove my XJ with the TCU disconnected and manually shifting it, it had no problem getting up to speed on the highway through Miami. The only problem being the high RPM due to there being no over drive and the associated decrease in MPG.
 
You went down a list of the usual suspects, TPS and wires, TCU wires and fuse, checked/cleaned some wire plugs. Next step is to test the solenoids and to perform some of the other simple diagnostic tests in
the AW-4 Service and Diagnostics Manual (easily found on the interwebz).


Shutting off the engine and getting a re-set, points more toward sensors and computers than to fuel pressure.
 
Yep - found both shift solenoids were bad but the lock up was good. Went ahead and changed all three out and now it is shifting good. Haven't had a chance for a far enough trip to see if it will still have the loss of power issue but think it was tranny fluid getting overheated that was causing it. I plan on taking it to a friends shop tomorrow that it didn't make it to without having to pull over a couple times last week.
 
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