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Vehicle surging/bucking--Engine problems or Transmission problems?

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Old 12-30-2011, 03:13 PM
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Vehicle surging/bucking--Engine problems or Transmission problems?

I have a 2000 Expedition 5.4L 4x4 with a 4R100 143,000 miles.

The vehicle is bucking and shuddering when going up hills or heavy acceleration. Feels like the transmission is slipping ?? The confusing part is it will also buck and shudder when driving on flat level roads under no load at all, which makes me wonder if the engine is missing and causing the bucking feeling. There is NO CEL, and I have not ever seen it flash momentarily indicating a temporary problem.

How do you tell the difference between an engine that's missing and a transmission/torque converter problem? Engine idles fine and revs up fine while in neutral.

Thanks!

Kevin
 
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Old 12-30-2011, 04:09 PM
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You will need a good scanner that can display the TCC slip, TCC apply, and also able to read non continuous data to check on engine misses that haven't turned the CEL on.

I would have it checked by someone that understands transmissions and you trust or at least a test drive by someone who has been there done that. This condition is easily miss diagnosed, I have had other general repair shops send me the transmission work only to find that it is a engine miss.
 
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Old 12-30-2011, 06:51 PM
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I've diagnosed a lot of these. I haven't found any that were the transmission, especially in trucks with the modular engine. Your problem is very likely to be one or more weak ignition coils. While you're there you'll want to replace the spark plugs, too.
 
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Old 12-30-2011, 07:06 PM
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JK080-- Thank you, I'll get the truck into a shop to have them diagnose the transmission, etc.

Mark--Thank you as well. Question for you though, the check engine light is not on and I also pulled codes to see if there where any pending codes and there were none. If the engine was missing due to faulty COP's would it run that bad (while driving) and not throw a code? The engine idles fine and revs fine. Problem is only evident when actually driving down the road.

I have not changed the spark plugs. We bought the vehicle about four years ago with 120,000 miles on it. It ran great for about a year, only issue was a bad thermostat that wouldn't let the engine reach full operating temp. Didn't realize it till the next winter when the heater didn't work worth beans .


I'll change the plugs and see if that helps.

Thanks again for the replies!

-Kevin
 
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Old 12-30-2011, 08:33 PM
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Just changing the plugs probably won't fix your problem. Go back and read my previous post.
 
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Old 12-30-2011, 08:51 PM
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Mark- If I check the coils with an ohm meter will this tell me if they are good, or is it possible for them to check out ok and still have issues. The COP's are $50-$90 apiece and I do not have the money to just replace them all if they are not what is causing the problem.

Is there another way of isolating which coil(s) are weak or not functioning?

Can the engine have a miss that would cause this severe of an issue and NOT throw a CEL?

Thanks again for the help.

-Kevin
 
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