Topic: Is this engine "missing"?

[noel]

Auto: 1990 V6 3.0L Ford Taurus with 125K miles.

At speeds ~45 - 65 MPH, when under load (acceleration or maintaining steady speed especially uphill) I get a vibration. If I let off the accelerator, or go am going downhill, it goes away. Two engine mounts were replaced ~ a year ago. (That had produced a similar symptom, but I could see the engine really jerk when I hit the gas and that is not happening; there is only a small amount of movement.) Gas mileage is routinely 20 MPG, sometimes as good as 22 MPG, which seems normal. It does not seem like water in the gas, which would be more sporadic and noticeable at idle and other speeds. I think the last major service was at 90K miles.  

At the last oil change, I asked them about this, so they took it for a brief spin around the block, looked under the hood while I started and gunned the engine; they told me they did not see anything and asked me if it was missing. Well, it is not backfiring or stalling. (The regular mechanic was not in, so I do not have full confidence in what I was told.)

Does what I describe sound to you as if it is "missing", or doing something else that might be related to timing, spark plugs, etc. (i.e., needs a tuneup)?

[weebl]

Did you check under the hood to see if it's still there? - Just kidding, I couldn't resist.

My old Civic did that, but I never had any serious tries to get the problem fixed (I knew I'd be getting rid of the old sucker soon anyway).  I think my mechanic suspected engine mounts, so it's possible there is something wrong with the replacements.  Other than that, I'm not familiar with what else to check for this problem.

[exserviceguy]

Merry Christmas, (sorry couldn't resist Noel besides you've never heard that before)
An engine 'miss' caused by an ignition fault, (poor plug or wire) or failing injector can cause the vibration you describe.  Also a transaxle 'out of mount adjustment'can be responsible as well.  If a recently installed engine/transmission mount has shifted slightly on its slotted mount holes then the entire affair can cause a vibration on accel or decel.  Ford's posted cure was to loosen off all of the bolts for the 3 mounts and then start the engine and with the brake on, run the gear shift lever through the gears and back to park. Then with the engine off, retighten all the bolts and 'voila' everything should be hunky dory.  (Has anyone ever rowed a hunky dory?)
But I'd start with getting the ignition system checked first.

[ericthejet]

Are your wheels out of balance?  Tire wear uneven?  If it's coming from the engine I might suggest fresh plugs and a good inspection of the rest of the ign. system. (wires, cap/rotor & ign pack if equipped)  Fuel filter changed recently as your getting close to milage interval if I remember correctly. If under load then mounts would also be under load not allowing them to move too much.  How is the throttle body? Clean'd as of late?  Do you use fuel injector cleaner ever now and then?
These are the things that come to mind.  Start with the basics first and the items you can handle yourself.  Make a small list as you go to avoid duplicity.
Good luck.

[blue_oval_fan]

Okay, you may not like this advice..but I'd take the car in to a Ford dealer and have them do a diagnostic on it to find the problem. In the GTA/Niagara area, be prepared to pay around $ 83 for the check.

[barrie1]

Noel how old is the spark plugs in this car and I would also assume the wires may be the originals as well. Defintely the place to start looking.

[articsteve]

OK, put one foot on the brake and in drive raise the rpm to 3000.  I assume there is no tach so just raise the revs until you can feel some serious tension.  If it is firing on 5 cylinders you will know.

Or with an insulated pair of pliers pull one plug wire off at a time.  One off and then back on, then the next, etc. Back up against solid object, place in reverse and put parking brake on and slightly raise rpm to say 1000 rpm to do this.  If you see a difference in engine operation on each plug wire when pulled out then you can rule ignition out.

I'm leaning towards something more in the drivetrain like a drive axel and such.

[duck]

Metallic grinding vibration?   Something out of alignment.  Don't waste your money. Drive the car until it dies.

[maritime_storm]

Sounds more like a miss then a drivetrain issue. Like it was mentioned, she's probably due for a complete tune-up{wires, plugs, cap & rotor and fuel filter}. Before doing so run a can or 2 of fuel injector cleaner through it and be a bit harder on her then usual, it may be something as simple as being carboned up and the PCM retarding the spark timing due to spark knock while accelerating or climbing a hill. If it persists after this, then have it checked for fault code.

[noel]

Thanks to all of you for so many replies so soon! In response to various points raised: tires/balance/alignment are new within 1K miles or so and I have no sense at all that that is the problem, there  are no metallic grinding noises, the original plugs were "platinum" and I assume that the replacements by Ford Dealer were too, the Fault Codes are generated but not remembered in this vintage Taurus. I am also getting a rubbing sound when taking right corners at 35+ MPH, but this does not occur when driving straight ahead; this might be a wheel bearing which was previously replaced and did not last 20K miles; interestingly, I replaced a right front wheel bearing at the same time as the new tires and it started making noises when I drove away from the shop! I kept driving right back to their front door and it was replaced as "defective"; maybe they switched them, and squirted some grease into the old one! (Though these components are all sealed units now, I'd bet that the pros know how to "grease" them.)

As for encounters with dealers on complex engine control issues, we've already been through it with this car: they tend to clean the throttle body and replace parts which fix the problem for a little while, until it reoccurs exactly as before. You go back and they replace another part with similar results. Eventually, they have replaced everything with new parts and the problem still reoccurs. Finally, they replace the engine control module or something that costs an arm and a leg, which was probably defective from the start but is no longer under warranty after all this delay. Whether it is malicious intent or stupidity and incompetence is tough to figure out. There is ample evidence in favor of incompetence and too much evidence of, and more significantly, tolerance of, incompetence to rule out just plain old fraud.

Therefore, before paying a dealer too much to do too little to cheat me out of too much, I will try out the suggestion by ArcticSteve. Chances are good it is a bit overdue for a tuneup, and despite the fact that I have never noticed any changes in performance after prior tuneups (well, maybe they didn't really do anything!?), who knows that this time it won't work some magic?

[maritime_storm]

"the original plugs were "platinum" and I assume that the replacements by Ford Dealer were too"

They may not be, check your receipt.

[blue_oval_fan]

1990 Taurus and platinum plugs? I don't think so. My 1992 Taurus didn't have them.

[noel]

Here is the final answer to the mystery:

The front sway bar links were worn; that was not the problem, but caused a clunking noised when going over bumps at lower speeds.

The transmission mount (there is one, on the left) was bad; that was not the problem, but it probably did not help and needed to be replaced. (The two engine mounts, on the other end, were replaced about a year ago.)

There was no noticeable problem when the car was put up on a lift and "driven", but the mechanic found some play in the  right front axle shaft by pulling on it.  This part was replaced and the problem is gone!

[noel]

By the way, one suggestion I got was that there might be a problem with the torque converter lockup ... that it was malfunctioning and not being successful getting from 3rd to OD; I tested this by taking the car out of Overdrive and bringing it up to speed; there was no difference, so that was ruled out.

[Roadrunner]

There you go! That was going to be My suggestion. Pull on the right front axle shaft and look for play! (Kidding)