Help me pin point this rought idle...!

[tomj76]

Use straight pins.

Also, the source of that misfire may not be electrical. For example, it may be a mixture issue from a vacuum leak or from an injector.

The MIL doesn't activate until certain misfire conditions are met. A "one off" misfire may be logged but it won't set the MIL. I believe some scan tools actually report the number of misfires detected. I beleive Ford has an OBDII document that explains this.

[aussie_bob]

Unless my timing gun is at fault, I believe I am close to root cause on this.
The timing mark on the crank pulley is stable and jumps forward about an inch at random ... at the same time the engine appears to misses / vibrates.

Now, I assume that with the inertia of the crank and all the moving parts the crank rotation can't change instantaneously so assume the rotational speed is roughly constant ( at idle ), the only way for the timing mark to "jump" is that the ignition triggered the timing gun early or late .

I have examined the coil pack wiring and it goes to the PCM behind the glove box. So, I am thinking the PCM is acting up or the crank or cam position sensor signals are bad. I'm thinking the cam position sensor possibly.

But just moving the wires around in the area of the coil pack appears to change things since after examining where the coil pack primary and +12V wires were going ( looking for a ICM ), the vibration was much less and today it was gone ... what it that ... ?

[12Ounce]

I'm guessing a high-voltage leak thru the cables or off the pack itself.

[olopezm]

Have you checked the coil pack itself?

These tend to crack at the back and the spark arcs to ground.

Oscar.

[Searles Lewis]

Originally Posted by aussie_bob

Hi Guys I'm back.

My engine vibration has gone away 9 times and come back 10 times. I can't explain what causes it to come and go but once I parked in the street and it had the vibration and the next morning starting cold it was gone.

I spent some time replacing plugs and spark plug leads ... no change.

I have also had a problem with coolant loss and the cylinder 4 missfire very randomly maybe once a month. Various people have looked at my 96 3.8L Windstar and said vacuum leak was causing the vibration / rough idle ... normally I can track down a leak but was not able to . Radiator stop leak helped stop the coolant loss ... but I finally pulled the plenum and lower intake manifold to see if there was a problem there with coolant or vacuum. Both gaskets showed evidence that coolant was leaking across to cylinders 1 and 4 ..

I replaces those gaskets, cleaned out the clogged EGR ports and replaced the 12 isolator bolts with green ones. Plus I soaked the inbectors and replaced O-rings + plastic washer + plastic cap.

No change regarding the vibration ... but I expect the coolant loss issue to be resolved.

Here is why I don't think I have a vacuum leak .... because with open throttle at 2000 or 3000 rpm, I still feel some vibration and some loss of power. With a vacuum leak, I would expect at open throttle it would be a non issue since the vacuum is much less and a leak would be swamped by the open throttle ( correct ? )

Also I isolated the EGR exhaust source incase that was the issue with a stuck EGR valve / clogged EGR ports but that had no effect.

1) So I will inestigate the "harmnic balancer".
2) I swapped the 3 injectors for cylinders 1-2-3 with cylinders 4-5-6 to have access to them as I thought removing the wires from #1 injector hade no change in idle rpm.
3) My only other thought was that the coil pack has 3 coils ... if one coil is going bad could it cause a vibration due to poor spark on 2 cylinders ?

4) a clogged catalitic converter ?

If I could describe the vibration better, someone may nail this ... it is a mechanical vibration... the whole car shakes and at 1000 rpm, it resonates ... and at 2000 or 3000 rpm I can feel a background vibration via the steering wheel. BUT, when it decides to go away, the Windstar runs so smooth and I believe has about 20% more power.

I am determined to fix this and want to use the "scientific method".

Thanks in advance ... Bob.

Exhaust hangers? I had them go, noise reduced after replacement, it was even swinging the car.

On the plymouth, I thot the tranny was gone-it rocked the car, messed with gas mileage, and made an awful roaring sound. I cut thru and replaced both, and it immediately stopped.