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William B
William B, Auto Service Technician
Category: Car
Satisfied Customers: 393
Experience:  Associate Degree Automotive Technology, Master ASE, Master BMW, Master Mazda, 30+ years experience
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95 mazda 626 4 cyl. automatic trans. intermittent bucking/chugging.

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'95 mazda 626 4 cyl. automatic trans.    intermittent bucking/chugging. High revs no power for a few seconds, then a few seconds of normal engine speed, then repeats. Problem sually appears after engine warms up (4-5 minutes). Always settles down after 20-30 minutes and seems normal. More pronounced on (even very slight) uphill grades. Cool/hot/dry/wet weather makes no difference. idles & revs normal in N. Problem less severe in 2nd gear. Always accompanied by flashing 'overdrive' light on dash- (the light that comes on when the side button on tghe shift lever is engaged). It's going to the shop next week but I'd rather have some idea of the problem in advance. Any ideas? Thanks so much.
Submitted: 8 years ago.
Category: Car
Expert:  William B replied 8 years ago.
Hey davidproducer thanks for the question,

Any time the "O/D" light flashes then there might be a concern with the automatic transmission itself. The fact that the engine runs and idles normal and revs like normal in neutral and I assume drive, means that there maybe an internal failure inside the transmission itself.

The intermitten chugging and the bucking you describe along with the high revs no power for a few seconds you describe leads me to believe that the transmission itself is slipping and might be near failure. This will cause a O/D light to flash and sets a code for a speed failure, (trans slips and engine is running correctly, so car speed is not correct) that can be downloaded with a scan tool to see if the fault is set by engine or transmission problem.

The fact that it happens under any conditions and usually only in first gear means that the problem might be with the first gear in the automatic transmission, and naturally the first low gear is the most used everytime the car is started and ran down the road, so for the low or first gear to fail or normally wear out is not uncommom.

I would make sure the fluid level in the transmission is full to the proper level, hopefully that has already been checked, but if the fluid is full and has a slight burnt odor or is dark in color then more than likely there is a problem internally inside the transmission. Automatic transmissions will not last forever and especially if there are high miles on the vehicle then it might be time for a transmission replacement or rebuild.

Hope this helps, click "accept" for payment. Let me know if you have any questions. All bonuses and feedback appreciated!
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Customer: replied 8 years ago.
I think you mis-read the part about first gear. The symptom happens in drive, happens less frequently and less severely when I engage 2nd gear, and happens in first gear about the same as 2nd, although I don't usually downshift to first because it raises the engine speed.
On uphill grades the sympton gets worse, then settles back on flat road. Could it be a computer-related problem? Behaves kind of like a cold-solder joint .
I sure hope it's not a transmission problem, but if you're right, I'll pay you the higher pay option.
Expert:  William B replied 8 years ago.
Well what I meant was everytime you put it in "drive" and you are sitting still at idle the automatic transmission will be in "first" or low gear, depending on how you want to call it.

And like I said, everytime you come to a stop sign or to a stop for whatever reason the automatic will naturally downshift to low or first gear and then upshift to second and so on, so again the 1 to 2 shift is the most common in any automatic transmission.

Many times this "hunting" for the correct gear, first (low) or second is due to a slippage of the internals of the transmission, so in effect the transmission control unit is trying to do it's job, it takes off in low gear, tries to shift to second gear, but because it slips or does not engage like it is suppose to, then the car speed slows down some and the control unit says, "hey wait a minute we are going to slow for second gear, so it downshifts back to low" and then tries to do the upshifting all over again.

Obviously it could be a control unit problem, but the most common failure would be the normal wear and tear of this or any automatic transmission, especially if the transmission has some miles on it. Cold solder joint? Computer problems? Wiring problems? Well of couse anything is possible, especially if the car has been in a serious wreck or had fire damage or something odd, but again internals of the automatic would be the most likely place to look for problem.

Most any professional repair shop or Mazda dealership should be able use a scan tool to download the code for the flashing OD light so it maybe time to have the codes checked and start there for any obvious cause first.
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