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Old 03-09-2006, 06:09 PM   #1
SydX
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undercarriage scrape causing vibrations & check engine?

Riddle me this. The undercarriage of my 2001 Mercury Grand Marquis was scraped on a badly maintained driveway incline which apparently does this to every car there. I'm having trouble finding the impact point, but I believe it was pretty far up from the rear--the drivetrain maybe. I drove 30 miles okay after that (or possibly without noticing). Then the car sat for about a week, and now on its first drive I noticed a strange shaking vibration coming from the same area in the undercarriage. It's somewhat subtle, but when I got on the highway the check engine light came on, but immediately shut off when I decelerated. The vibration occurs on most acceleration and deceleration, and is worse to constant if driving above 40-50mph. If you try to glide (tap accelerator, coast, repeat) under 38mph it can be avoided.

Anyone have a suggestion? Maybe take the vehicle, drive it up the incline, and park it at high speed in the crap motel lobby the parking lot belongs to?
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Old 03-09-2006, 06:18 PM   #2
Cliffy
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Quote:
Originally Posted by SydX
Riddle me this. The undercarriage of my 2001 Mercury Grand Marquis was scraped on a badly maintained driveway incline which apparently does this to every car there. I'm having trouble finding the impact point, but I believe it was pretty far up from the rear--the drivetrain maybe. I drove 30 miles okay after that (or possibly without noticing). Then the car sat for about a week, and now on its first drive I noticed a strange shaking vibration coming from the same area in the undercarriage. It's somewhat subtle, but when I got on the highway the check engine light came on, but immediately shut off when I decelerated. The vibration occurs on most acceleration and deceleration, and is worse to constant if driving above 40-50mph. If you try to glide (tap accelerator, coast, repeat) under 38mph it can be avoided.

Anyone have a suggestion? Maybe take the vehicle, drive it up the incline, and park it at high speed in the crap motel lobby the parking lot belongs to?
It's a stab in the dark here....but seeing as how you say the check engine light illuminates (I assume it's the little amber/yellow lamp with a picture of an engine on it?....an engine management light?). I recon you've maybe knocked the wires off your lamda sensor...It would explain the management light atleast...?
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Old 03-09-2006, 06:46 PM   #3
SydX
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Thanks for the reply.

Maybe the check engine light is an orange herring, but it did come on when the vibration was worse, ramping up speed on the highway. And I've never had problems with the light coming on before. I'm more concerned with the vibration. It's not just something minor and annoying. It actually feels pretty scary.
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Old 03-09-2006, 07:59 PM   #4
glagon1979
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Quote:
Originally Posted by SydX
Thanks for the reply.

Maybe the check engine light is an orange herring, but it did come on when the vibration was worse, ramping up speed on the highway. And I've never had problems with the light coming on before. I'm more concerned with the vibration. It's not just something minor and annoying. It actually feels pretty scary.

you could have bent the drive shaft when you scraped.
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Old 03-11-2006, 12:23 AM   #5
SydX
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Thanks. I didn't know a bent driveshaft would cause vibration, but it looks like that's what it is.
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