My daily drive has been acting very poorly lately with lots of stumbling and misfires. This problem started occurring after I had the car completely die due to a failed ignition rotor. I tried various other ignition parts, crank sensor and ignition module because when I tested the rotor with an ohm meter it showed connectivity from the center to the point. Once I finally replaced the rotor, the car started right up so my no-start issue did turn out to be the ignition rotor.. But on the first test drive this problem with the stumbles & misfires started occurring after 5 - 8 minutes of driving from cold. The only ignition part I have not swapped out is the coil.

As I said initially the problem seemed worse after the car had warmed up after about 5 - 8 minutes of driving but it seems like the past day or two it has gotten worse with the misfires and stumbles happening much sooner from cold. Or it could be that because the outside temps have risen here in the past few days perhaps the engine is not cooling off to the same point.

At this point I am uncertain if it is the ignition system or the fuel system causing the problem. My plan is to check the fuel system pressure tomorrow by hooking a gauge up to it in such a way that I will be able to see the gauge while driving. I am also going to pull a spark plug or two to see what the color of the plugs might be like to see if they look to indicate a lean or overly rich condition.

Any suggestions would be greatly appreciated. I will post back with the results of the fuel system pressure test.

 

Could be time to clean out your air intake. The maf sensor could be dirty, the vent tube from the cam cover will tend to get nasty slime in it which will then migrate to your throttle sensor and cause it to fill up and lose accuracy. How is your air filter?

 

Hi Steve,

Have you checked the VCM for any stored diagnostic trouble codes?

Did you purchase fuel somewhere different than usual? Could you have water in the tank?

Take a close look at the distributor shaft. Check for any sideward play and for any signs of spark arcing down the shaft.

A clogged catalytic converter could be another cause.

Don

 

Try tightening the top six nuts and screws on the intake manifold to cylinder head. They loosen over time and may leak.
Checking them on mine is a regular maintenance item. It may be time for a complete maintenance and parts repair-go through each system, clean replace as necessary. I performed same on my '90 Majestic with 125K+ miles. My car runs like it's new, a real pleasure to drive. My neighbors tell me that they can't believe how quiet and smooth it runs.

 

In this case I would always start with the parts you worked on. The rest won't change that much all of a sudden, is my assumption.

you pulled the distributor cap, to replace the rotor.

- do you have the right rotor
- Is the distributor cap put back correctly
- did you half-unplug a spark plug wire while replacing the rotor? push all spark plug wires firmly back. Botch on the spark plugs, as well as on distributor cap. Including the one goin to the coil, on both ends.
- dit a spark plug wire got loose a bit, and is now rubbing somewhere?

 

I had a similar problem in a 1994 3.2 XJ40.
It started after I had cleaned the engine down.
Turned out I had water in the plug holes.
Ran OK until the water got hot and steam condensed on the plug and leads.
Worth checking

 

Coolant temp sensor can cause symptoms like this. Cheap to replace and easy to fit.

Larry