Car Jerks at highway speeds

I have a 1993 Ford Ranger 3.0L V6, Automatic Transmission. The truck has 217,000 miles on it. Recently I have noticed that at high speeds, normally around 50-60 MPH, the car jerks violently as if it is misfiring. Also, while this is happening, the tachometer jumps in a range of around 500 RPMs. This only happens as described at high speeds or while under heavy load (up a giant hill, trying to pass someone). When driving around the city, it runs pretty well, except for a little rough at idle. I have also noticed that even at idle the tachometer bounces a bit, but not nearly as pronounced as it does at high speeds. I have already change the fuel filter and had only small improvements, if any. I get a check engine light from time to time, but it disappears after a few minutes, only to return again a while later. What could be the problem?

When was the last time the spark plugs and wires were changed? Cap and rotor (if equipped)?

The plugs have not been changed in a few years, but they will be tomorrow :). The distributor, along with the cap, was changed in January. I will let you know how the plugs help. Thanks

I don’t understand why you would change the distributor before you would change the spark plugs. Was it because the camshaft position sensor is in the distributor? Then, it may be the wiring that is at fault, now.
You can do the electrical checks on the distributor following these instructions:

I changed the distributor for a different issue before this started

Another thing to think about are fuel and air filters. It would also be good to check the fuel pressure.

It would help you a lot to figure out what code is being set when the check engine light comes on. A '93 will be OBD I rather than II so the auto parts stores won’t be able to read them. But on some cars you can pull the codes without a reader. I’d do some internet searching - unless you have a repair manual - to find out the easiest way for you to pull the codes.

Although spark/fuel/air come first, another thing to think about is the torque converter clutch - the conditions and symptoms (including the RPM jump) are consistent with a TCC that is not locking/unlocking properly. What is the transmission service history?

You might also have the catalytic converter checked out if it’s still the original one. I’d suspect replacing a 15 year old cat might do this truck a world of good regardless.

when was the last time you had your transmission serviced? I had a van with a similar problem, and it turned out to be the transmission. It was something about the torque convertor hanging. Mine would also get really bad at highway speed, probably because the lock up torque convertor was trying to engage

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I had this exact same problem on my 1997 Nissan Quest. It turned out to be the retaining bolt on my distributor rotor had come loose. The rotor was just sitting on the shaft loosely with friction. At higher RPMs the speed overcame the friction and the rotor would spin randomly, causing violent engine knocking. This is because the rotor has to spin in sync with the engine RPMs in order to generate more sparks.

After a few days the rotor got stuck in a dysynchronized state and then the car wouldnt start at all. I tested the startup by spraying some starting fluid in the intake, and that didnt work so I knew it wasn’t fuel. So I traced back the spark system until I took apart the distributor. The retaining bolt was just lying there under the cap. The rotor spun freely with my finger. After screwing it back in (with more torque this time) the car worked fine.

I guess what I learned from this is:

  1. Dont panic. Its usually something small. I could have fixed this in the parking lot I broke down in with nothing more than a screwdriver.
  2. Keep a can of starting fluid in your car, so you can diagnose on the road.
  3. Put a nice head mounted light in your car. Its much easier to work on a car without a flashlight in your mouth.

When I had a slight miss under load on my Riviera, it turned out to be the crank sensor going south. Cost me a lot trying to find the problem but then broke in two on the road so the problem was obvious.

the car, or the sensor ? :wink: