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AW4 slipping, overheating. Pump/Torque Converter troubleshooting


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So I've been meaning to post in general for a while about a couple particular problems, but generally I end up figuring them out. But this most recent has me a bit nervous. After driving about 140 miles, on my home stretch, coming up a hill, I completely lost power. So much so that when trying to crest this hill, I was rolling backwards. I popped the hood and nothing was obvious, I'd fixed the MAP sensor vacuum line the week before but it was fine. I bring this up because it seems a lot of loss of power questions end up being the MAP sensor. After a few minutes I just tried again and it got me further up the hill but it happened again. Sit, trying again and thankfully I got to the flat. Interestingly the engine sounded fine until the point of power loss, then high whiny revving. Specs...

 

'88 Renix 4.0L 4x4

 

 

-- Morgan

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You gave a little info there, but not much.  Sounds like a fuel delivery issue to me, as you didn't mention any issues with cranking, and didn't mention anything electrical like no lights, no voltage on your voltmeter, etc.  Are you low on gas, or out of gas? 

 

Can you check the fuel pressure at the fuel rail just to see if there is enough fuel in the fuel rail?  Unscrew the cap, cover with a rag, and use your key to push the pin in.  If gas sprays out, you have pressure at the rail.  If it drips out, or none comes out, you don't.  Pic for reference:

 

fuel-rail.jpg

 

If you have low or no fuel pressure at your fuel rail, sometimes just waiting a few minutes and trying to restart works.  The fuel pump might respond by sending more fuel into the rail.  Usually enough to fill the rail and no more.  If this is your condition, you have a potential wiring issue (like the fuel pump ground in the taillight being bad), and/or need a new fuel pump relay, ballast resistor, and/or fuel pump.  The ballast resistor can be bypassed to rule that out, and the fuel pump relay can be switched with a known working relay to rule that out.  If the fuel pump is bad, you have very little time before it ceases working altogether. 

 

Further on fuel delivery issues, do you hear your fuel pump prime when you put your key in the ignition and turn your key before starting the vehicle?  On fuel injected vehicles you are supposed to turn the key, wait until you hear the fuel pump prime, then start the vehicle.  Do you hear it prime?  Always? Sometimes?  Never?

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I just re-read the OP and the 'high whining revving' does not sound like a fuel issue.  Missed that.

 

Can you define what power loss means to you?  Did you lose RPMs, or just the ability to move forward?  Did you have your foot to the floor and the engine at high RPMs without the vehicle moving?

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If there was a loss of RPM, it wasn't super significant. But I wasn't moving, in fact, I rolled backwards at the worse point.

 

Things I've checked, the good.

* Yes I heard the pump prime

* Yes, there is fuel pressure

* Yes there is transmission fluid

 

Things I checked, the bad

I am out of radiator fluid and just now realized when I check underneath, there significant amount of some liquid around the underside of the engine and in my tired state, I think looked at the windshield fluid instead of the radiator. Could overheating cause loss of power like this? If so guess my dash lights need going over....

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No electrical issues stated, no loss of fuel pressure, no RPM loss.  It doesn't sound like you lost power at the engine - it sounds like you lost the ability to move forward, meaning you lost power at the wheels.  This sounds to me like the torque converter in that automatic transmission may be going out.  I think the issue is with the transmission or behind it, so some other members will have to post in here to help.  I have almost no experience with automatics, and I could be wrong in my assessment.  Good luck.  Hoping others chime in.

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fwiw, the whining  wasn't super loud and it sounded more like it was coming from the engine, though I could have just been focusing on that... Additionally, if the pump had been totally dead would I have felt that once driving on the flats? I ask because once I let it sit for 5min or so it drove fine.

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any shiney bits?

I would drain and refill, (yes low trans fluid could cause a overheat issue as the trans cooler is in the radiator). i would also flush the lines. its worth a shot, when draining look to see if there is any metal flakes in the fluid or chunks. as stated before just drain and fill, the dipstick tube is a huge pain.

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I'd agree that based on your description I think your transmission is slipping, rather than any issue with the engine. I would agree with the others and say that that transmission fluid looks terrible, but I've seen worse in AW4s that still work just fine. As a general rule, these transmissions are very durable, so don't count it out just yet. You might get lucky and have it work fine once you fill it back up with fluid.

 

I would start with a fluid+filter change, as well as topping up every other fluid in the truck. If the transmission is shot, it's not the end of the world. You shouldn't have too much trouble finding a good used replacement. Don't spend the money having it rebuilt.

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TROUBLESHOOT THE ISSUE FIRST!!

As mentioned it's likely transmission related but don't start tearing it apart yet and don't just fire the parts cannon at it.

 

First unplug your TCU and try to drive it starting in 1st gear and shifting manually to 3rd then D.  This will determine if it's an electrical or mechanical issue.  

 

If it does still has power loss with the TCU unplugged, you will know it's a mechanical issue.  Assuming it's mechanical, you would then move to a fluid drain and replace and test again.  

 

Post up your results of the TCU test and results of the fluid change if it's a mechanical issue.  We can then help from there.

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Keep in mind that draining the transmission pan -- whether you pull the plug or drop the pan -- doesn't drain the torque converter. Because iof the dip stick issue, I would start by just pulling the tranny drain plug. Drain, refill, drive it a bit (even if all you do is jack the rear wheels off the ground and run it in the air, then do another drain and refill to purge as much of the old, nasty fluid as possible.

 

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15 minutes ago, Eagle said:

Keep in mind that draining the transmission pan -- whether you pull the plug or drop the pan -- doesn't drain the torque converter. Because iof the dip stick issue, I would start by just pulling the tranny drain plug. Drain, refill, drive it a bit (even if all you do is jack the rear wheels off the ground and run it in the air, then do another drain and refill to purge as much of the old, nasty fluid as possible.

 

^^^this is a good point.  You will want to do the fluid change multiple times to get all the old fluid out.  If at all possible you should drive it to circulate the fluid over running on jackstands but that will work in a pinch, just be sure to chock the front wheels and point it in a safe direction in case it falls.  Also make sure you are in it to hit the brakes if that happens.

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Update from work yesterday.

Dumped just under 3 quarts of ATF that smelled of burnt roadkill and replaced with 4qt.

Not having enough to do another complete dump figured it would be good to drive into town to recirculate, get more, flush again.

I took the hill route, so if it were to slip, it would leaving the house instead of getting stuck coming home. Seemed to handle it no problem,

as with the next couple small hills. But on the return trip it noticeably slipped, with the engine revving up twice, then complete lack of power

on the same hills on the prior trip.

 

I'm going to check out the TCU/computer today and see if that turns anything up and wanted to add a couple more details I've noticed/might be relevant.

* The truck has a broken Power/Comfort swtich, I don't' know what position its in, the rocker is cracked and just moved freely.

* Last night when I had to pull over, shifting into 3 or 2-1 did nothing but then coming back to D drove like it was fine, for a minute or two at least. Same with turning the car off/on.

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19 minutes ago, driveslowsnackoften said:

he truck has a broken Power/Comfort swtich, I don't' know what position its in, the rocker is cracked and just moved freely.

cruiser has a mod to make it power all the time/ see link in signature

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28 minutes ago, driveslowsnackoften said:

Last night when I had to pull over, shifting into 3 or 2-1 did nothing but then coming back to D drove like it was fine, for a minute or two at least. Same with turning the car off/on.

Turning the car off/on did nothing or it caused it to drive fine for a bit afterwards? 

 

If it seems to be fine after shifting/power cycling that would point more to an electrical/sensor issue.

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  • driveslowsnackoften changed the title to AW4 slipping, overheating. Pump/Torque Converter troubleshooting

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