I have been dealing with this problem for a few months now. I received a lot of useful advices on other forums, i tried most of them, but i am still dealing with the same issue. I did replace a lot of parts and i did a lot of testing. I feel really stuck!! I've sunk a lot of money into this old truck buying new/used parts, swapping one part for another and i still have the same problem with very little improvement. Here is the latest.... i would appreciate any feedback, advices, tips, etc. I have a 1994 Mazda B4000 truck which is essentially a Ford Ranger with 4.0L V6 and 5-speed M/T, 2WD. Truck has 101k miles. California edition (emission) Here is the problem: My truck feels as if it’s misfiring/hesitating and shaking/vibrating during acceleration and it feels underpowered. Almost as if I am in the wrong gear at a low speed. Also, quite often, while I am accelerating and I press on the gas harder, I can hear/feel some sort of loud “detonations” (for lack of better word) happening somewhere under the hood, in addition to feeling the lack of power. It sounds like “knocks” inside the engine or inside the exhaust. It's hard to describe but it is very obvious inside the truck and i am sure people outside can also hear it. If i am gentle with the acceleration - the detonations/knocks are not happening. The problem seems to be more obvious when the truck is warm. Only sometimes, even though for only a short time, it just starts to run fine without any issues and then all of a sudden the misfires and lack of power are back. Feels like something is making a bad contact and as soon as it makes a good connection – the truck is back to normal. ** Currently, the OBD scanner shows NO error codes in the system. I used to have code 216 for a long time but I just fixed it a week ago with a new Camshaft sensor. ** Here is what I have done/checked and replaced so far with no results: - New spark plugs (autolite) -2nd set because one plug was cracked from the new set I installed 3 months ago. - New generic brand spark plug cables (2-mo old) - New coil pack (2-mo old). I tried with a used one before from a junk yard – got same behavior. - New crankshaft sensor (I was getting “CID error“ code – OBD 216 for a looong time but truck drove fine) - New camshaft sensor (this fixed the OBD 216 code finally but it did not fix the misfire/detonations/lack of power) - Newer fuel filter (2-3k miles old) - Newer air filter - Cleaned MAF sensor with MAF sensor cleaner twice – made no difference at all - Ran SeaFoam cleaner thru intake – lots of smoke out of exhaust but made no difference - New injectors – installed 6 rebuilt OEM injectors and new intake manifold gaskets – made no difference at all - New CAT converters installed a month ago – made no difference - I measured the fuel pressure using a pressure gauge and it showed pretty much everything in spec. A bit border line low, but within spec. - I tested for spark at each plug, using a $10 spark plug tester and I got spark on all 6-cyl @ idle. - Truck starts easily - every time. No need for excessive cranking. - My idle seems to be very stable and healthy at all times. If i rev the engine RPM in "neutral", there are no issues or hesitation!! - ** The misfire/hesitation starts to happen once I start accelerating, especially between 2nd to 3rd and 3rd to 4th gear, etc. Sometimes i even hear the detonations/shaking leaving from a stop light. ** - After driving the truck for awhile, when I stop at a light, I can feel the engine idling fine but vibrating/shaking more than it used to. Occasionally - it will become smooth and then start shaking again. Feels like a cylinder may be off...on...off. - Something interesting: last week, after I replaced the Camshaft sensor (it required removing of the intake, fuel rail, etc to get to it) I took the truck for a test drive and for the first 5-7 minutes of driving it drove 95% fine!!! There was very little engine vibration under acceleration but I did not feel any misfiring, any detonations or lack of power. The truck was much smoothers and quicker. Took it on the freeway, accelerated to 75-80mph with almost no issue (slight vibration under load)…drove for 1-2 minutes in 5th gear fine, …. I Stepped on the gas to take it to 85mph and I started to feel the hesitation again. I felt and heard a few very obvious “detonations” under the hood too when pressing the gas. The truck went back to the old behavior. My hope that the new Camshaft sensor fixed everything disappeared. The problem must be somewhere else and I don’t know where to look. Something did fix it for a few minutes. Not sure what. Like i said - i am really stuck!!! Not sure where to look next. Sorry for making this so long. If you can give me any pointers or ideas, I will be very thankful.