My 99 4.0 OHV has been intermittently bucking/missing for about 2 weeks. It is always when maintaining a constant speed, but some days it happens 4 times and some days it doesn't happen at all. Shortly after this started it also started intermittently squeaking from the rear of the engine, same thing, some days really loud and some days just a chirp once in a while. I did some research and found that the chirp could be the cam position sensor which I just replaced tonight. It is too early to tell whether the chirping is gone but during my 1 mile test drive it bucked/missed twice. The missfire is not throwing a code, which is frustrating to say the least. The missing varies in itself from just a light buck to a major jolt. I am stumped without a code and am hoping it will eventually throw me a bone, but until then any ideas?

 

Crank sensor can cause timing issues as well.


Check your plugs first.

 

I changed my plug wires and it got rid of the bucking. The DPFE sensor on the egr system could go bad causing this problem or the egr valve can get stuck but that will usually throw a code.