Bounce at stop or low speed

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Aug 20, 2009 | 09:48 PM

beerguy5812

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Bounce at stop or low speed

1997 Explorer 4x4 V6 SOHC has a peculiar "bumping" or shudded at noticeable at stop or low speed. Doesn't seem to be linked strongly to idle that I can tell (cleaned MAF, didn't help). Best I can describe is a slight, intermittance bouncing sensation...any ideas?

Thanks

Jeff

Aug 20, 2009 | 11:14 PM

aquanaut20

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From: BC Canada

you have to be more specific.

Is the "BUMP" related to movement (SLOW)?, or does it happen at stop (0mph).

Is it related to engine or truck(Chassis/drive train)

Aug 21, 2009 | 07:46 AM

beerguy5812

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Does not have to be moving, can feel it at a stop (i.e. waiting for a light to change). My wife says it's noticeable at low speeds. Feels almost like it would if the engine was missing, but more borne from the chassis or undercarraige than front end. I observed the engine for a while and it seemed reasonably smooth and consistent. Basically a single, isloated vibration every 10-15 seconds or so.....sorry, it's hard to try to describe, but thanks for your help.

Jeff

Aug 21, 2009 | 12:58 PM

shorod

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From: Cedar Rapids, IA

That really sounds like a random misfire. See if you can find a scan tool that is able to monitor the component parameters. That should show you if there are misfire counts on individual cylinders, even if the counts are not yet high enough to trigger a diagnostic code and the CEL. Also examine the vacuum lines under the hood. There is an elbow that is pretty common to fail, a quick search of the forum should yield more details.

-Rod

Aug 21, 2009 | 09:56 PM

beerguy5812

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I took a closer look at the engine and there does appear to be a more pronounced shudder at time that about coincides with the vibration, so I am beginning to think you are correct on the intermittent misfire. I couldn't see where any of the vacuum lines were breached...is there a conclusive way to diagnose a vacuum leak that is difficult to see or detect (I can't hear a pronouced sucking sound). thanks for your help.

Aug 22, 2009 | 09:18 AM

shorod

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From: Cedar Rapids, IA

There are easy ways for the DIY'er to check for vacuum leaks, but the one that comes to mind involves flammable liquids so I tend to not suggest that one. Other than that, the DIY'er will need to resort to visual inspections with good lighting and listening closely, as you've done.

When is the last time a tune up was performed? You might be due for spark plug wires and spark plugs, fuel filter, air filter, and making sure the intake air tubing is securely connected.

It's also possible that you have a faulty coil pack or possible early signs of a failing crankshaft position sensor. Connecting a scan tool and checking the component parameters can speed up the diagnostic process greatly....

-Rod

Aug 22, 2009 | 01:37 PM

beerguy5812

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Thank you Rod.

Plug wires, air filter, fuel filter all new within range of last year 10-15K miles. Plugs are about 55K old, so I will plan to slam some new ones in today and see what happens or if any of them are fouled. I cleaned the MAF sensor the other night.

Thanks again for your help.

Jeff