Engine Vibration 2500-3500 rpm

[sc012v]

My 98 4.0L OHV X (130k miles) has a vibration that I can not figure out. It does it whether driving or in neutral/park. The idle is smooth. I've changed the plugs, wires, injectors, coil pack, oxygen sensors, dampner, IAC... still the same issue. Checked for vacuum leaks- no problems found. No CEL. Motor mounts are fine.

I'm baffled. The only items left I can think of is the flexplate or crank imbalance left.

I'm open to any ideas... please help!

 

[sevenservices]

OMG, Im having this same problem.

I have a 1999 Ranger XLT 4x4 V6 5 Speed, runs great except a weird vibration at the engine which starts at 2500 RPMs. Almost like having a helecopter hovering right above me...

Where you ever able to find a fix for it? I noticed it is with the engine. As in nuetral with the clutch in or out it still vibrates. My mechanic found a vacuum line that came off and that was fixed but it still shakes like described. We also found a reading that said cylinder #1 is running a little lean. My first thought was to change plugs... Sure as heck seems like the engine is out of balance from something??? Anyone think maybe the catalitic convertor could be clogged up?

ANY thoughts are welcomed on this one. Thanks a million!

 

[swetrid]

Flexplates are known to crack

 

[sevenservices]

hmm... I will have to check that out. It seems so much like a crankshaft based vibration to. Very low end shake when reved up to 2500.

Im also fighting a second issue of some serious drag on the truck. I think something broke back in the brakes, my wife said it banged like she backed into something then the truck has been fighting just to go down the road. This was about three weeks now since the original shake started happening.

Wife says thanks! we can pull it open and check it out. Im wondering if I can check it through the clutch inspection hole or if I need to break the bellhousing open?

 

[sevenservices]

Engine vibration at 2500 RPM FIXED 4/9/2011

Changed plugs and it changed to 1800 RPM. This one was a bugger… The engine shook and vibrated like a helicopter hovering above it. It would drive but had hardly any power and shook like crazy. First we replaced the sparkplugs. Second, the coil pack and the wires. Symptoms were still the same after this… Now remember, an engine needs three things to run right. Compression, Fuel and Spark. It had plenty of compression, now we had to narrow down the spark/fuel issue. With it running I put a glove on and pulled each spark plug wire off the coil pack one at a time until I found the one that made absolutely no difference in the way the engine ran. Turned out to be the middle cylinder on the passenger side. Pulled the spark plug and it was dry as a bone. Placed it on top of the engine and cranked it over, plenty of spark. So, I have a bum cylinder… that one is not firing and it HAS compression and it HAS spark so what does that leave? Fuel. I took the fuel rail off (be careful it will spray slightly when it pops off the top of the injectors if you do not relieve the pressure first.) and pulled out the middle fuel injector. It was soaked at the top into the fuel rail and like the spark plug, it was dry as a bone at the bottom. I cleaned it well and worked the needle in and out. Put it back together and… no difference. So, I pulled it back out again and replaced it ($56.00) and guess what? ITS FIXED! No more horrible engine shake! OMG my wife is so happy to have her truck back. Mind you, we took this to two other mechanics who could not figure it out. They tested vacuum, sensors, etc… Don’t ever forget the basics of what a cylinder needs (Compression, spark and fuel). If it’s not running right, somewhere its lacking one of those three things.