I cannot figure out what the problem is on my '97 2.3L. I threw a p0340 code last week and the truck started misfiring while idling and driving (especially 2500 rpm and beyond). I have 93,000 miles on the truck and decided it was time to replace the timing belt while I replaced the camshaft positioning sensor. A local shop checked the signal from the CPS and it was good as well as the wiring. The alternator is not throwing any A/C current either (the CPS is magnetic). Does anyone know more about this problem? I have read about every thread about this. Should I replace my PCM?

 

Are you saying that this misfiring started after replacing the timing belt and after replacing the CPS?
How old are the spark plugs and wires?
Did you check the vacuum lines? They are thin and brittle at that age.

That is all I can think of now. If these pointers are fruitless you may go to fordforum.com or "the ranger station" since this Mazda is a re-badged Ranger 2.3.

Good luck.

 

Thanks for the reply. These issues arose before the timing belt change. I have put new plugs in the vehicle since as well as a new battery (mine died). As far as I can tell the vacuum lines are fine. I am about to try a reman PCM. Is it possible the ICM and the crankshaft sensor are not telling the plugs to fire causing a misfire? Can the PCM screw up the codes?

 

Did you test the alternator for output, does it need replacing!
The PCM does help control voltage.
Low voltage while starting is not a good thing, it might not start and misfire. Could also be a bad ignition coil, wire

 

Yep. I tested the alternator and it is giving the correct voltage output. I'm going to check the coils and ICM before I put in a new PCM.

It does not have a misfire upon starting. The PCM somehow looses the signal from the camshaft positioning sensor, especially past 2500 rpm.

 

Gonna give you my favorite Misfire List:

Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: Red Line Synthetic Oil - Gasoline Fuel Additives - SI-1 Complete Fuel System Cleaner
Inspect wires. Re-set ECU after doing above.

I had a misfire on 1 specific cylinder with only 30,000 km. After changing the ignition coil, spark plugs (all), fuel injector for that cylinder, they changed the fuel tank and the fuel pump. (all under warranty) Still got a misfire! They changed the pre-cat on 1 side.
It was the **** poor exhaust design! Poor exhaust flow. I immediately changed the exhaust design after the pre-cats. Not under warranty: I changed the main cat and the pipes coming out of the pre-cats. No more issues!
For more in depth, read: https://www.mazdaforum.com/forum/maz...-design-28940/

 

This is really a great list to work from. Go from cheap fixes to the more expensive one. Test, test , test, clean and re-use. Do not throw parts at it.

 

Oh yeah, my misfire only happened at hi revs at around 5000 rpm while i was flooring it, getting on the highway in 2nd or 3rd gear!
Good luck.