UPDATED: '00 3.4L automatic trans overdrive noise

So when the automatic trans shifts into overdrive, I hear a low rumbling sound and steady, low vibration. Turn the O/D button off and drop back into 3rd and everything is normal. Turn the button back on and it kicks into 4th (overdrive) and sound/vibration comes back. A guy at a local shop suggested it might be one of the "switches", that it might be "worn out", but he wanted to charge me a diagnostic fee to find out.

Anyone have this problem before?

 

When your truck shifts into 4th gear and the torque converter locks up directly to your engine, all it would take is a partially missing spark plug and your truck would feel like a big wheel tractor from 1931 travelling down the road .
With this said when was your last tune up ?
How long has it been happening ?
Are your universaljoints good ?
Mileage on the truck ?
There is some info here you can read regarding your transmission but if I had to guess ,your issue sounds more engine related .
http://www.tacomaworld.com/forum/te...warner-340-series-transmissions-write-up.html

 

Ok well I did have a fragmented spark plug I found today, the truck was misfiring and running rough randomly. So I replaced the plug and it runs normal now, but I just ordered a fresh set of six NGK DP twin-prongs and NGK wires. Still... it runs smooth for the time being, but the overdrive issue is still there. Why wouldn't this happen in 1st - 3rd, and instead just in 4th?

 

If your problem is a missfire , it will still be there in 1/2/3 but very easy to feel in overdrive 4th gear . Your torque converter comes on in 4th gear to save you fuel .
When the torque converter comes on in 4th , it locks the engine directly to the transmission .

You can verify this by driving the truck in 4th gear . When the truck starts to make the noise or rumbling sound ,very gently tap your brake pedal with your left foot while your right foot remains on the gas pedal . Manipulating the break switch will turn the torque converter off and the rumbling will go away for a breif second or two .This is by far the most common issue

 

That makes a lot of sense, thanks After I replace the plugs and wires I'll report back in, but later tonight when I get home I'll give your brake trick a try. I bet that's what's going on!

 

Ok so changed out old Denso plugs and OEM wires for some NGK Laser DP (w/ dual prongs) and NGK wires.

Problem is still there. And in overdrive... it rumbles while you supply pedal pressure, but stops when you back off and coast in overdrive.... apply gas pedal and the low rumble comes back. Turn off overdrive (with button) and it drops you back into 3rd and rumble goes away.

While in overdrive with low rumble, still drives normal, no gear slip. Shifts between gears normally.

Any ideas? A shop I spoke with suggested it was some sort of failing switch or solenid on or in the trans.

?????

 

From your explanation ,it sounds like the transmission is working properly but you still feel the rumbling when the torque converter is applied .
You could try cleaning the throttle body / idle air control motor and mass air flow sensor
Did you try tapping the brake pedal when you feel the rumbling ?
Have you ever scanned the truck for codes ?

When was your last transmission service

 

Transmission was serviced less than 5K ago. Brake pedal tap doesn't help.

 

Oh and no codes, I have a couple different OBD2 scanners and once I replaced the plugs and wires the misfire codes seem to have stopped. Like I said it runs smoothly motor-wise, and shifts up and down properly and without delays when you modulate the gas pedal. I'm really concerned about this noise though.

 

All I can think of at this point is to drop by a transmission shop and have one of the guys take your truck for a free road test .Sounds are difficult to diagnose over a keyboard .I am positive that a free test drive will help you figure out whats going on .

 

Sounds crazy, but I had the precise same symptoms, it was a bad injector... only happened in OD, hit the OD OFF button and the rpms would kick up and it it went away, and keeping the POWER button pressed made it better b/c it kept the rpms higher. I was searching every transmission article to no avail.

I got the OBD2 bluetooth and torque pro app... turned out my AFR (air fuel ratio) was out of whack, But it only manifested itself when the engine was really loaded (shifting into OD). BTW, even running at 17.8:1 it never thew a code or lit the CEL.

#4 spark plug was wrecked due to running lean.

Good luck.

 

I have Torque Pro, what are you using on it to diagnose that?

 

Using the AFR (measured) gauge. The AFR should be in the 14 or 15 to 1 ratio.

I like to use the half-dial (meter) gauge because in addition to the meter sweep, it updates and displays the min and max at the bottom of the gauge. In my case the rumbling noise correlated with running too lean b/c the max would jump to 17.8 to 1 at the bottom of the gauge.

Hope this function works as well in a '00 as it does in my '04

Good luck

 

How did you determine which injector?