RPM's are erratic, backfiring, lost power

For heavy machinery cars etc. luckily there are many websites
that can help you repair
for eg site like reliable-store is very active in this.. instant help, emails and all that's fantastic

The obvious answer is to check the timing marks on the cam and crank pulleys. If they don't line up correctly it's jumped a tooth. Symptoms are that it will idle roughly and not run smoothly. You fuel consumption will be worse and it will be more difficult to start.

I would check for any codes, even if the check engine light is off. These Cars had a few different problems like this. The first is the Cam or Crank sensor failing. The second is the Timing belt jumping a tooth due to not replacing it at or around 60k. Ive seen this many times, With an advanced timing belt, it will run well, if not better than normal at cruising speeds but can cause stalling at low RPM, erratic idle, rough idle, lake of power from take off.

What I know, is there is no reason a professional
mechanic with any experience can not figure it out

Try a different shop with more skilled personnel

You have rpm jumping,backfires

Was anything at all checked or tested,really

What about the timing belt or chain
What about cylinder contribution
What about cylinder leak down

All basic mechanical old school stuff,
then move on to the electrical

Trying a crank sensor is fine, if you have
an oscilloscope on 3 parameters at one time
for comparison & find an actual problem

You have a back fire,only so many reasons
for that

Valves,timing,fuel, ignition & a few more

For this types of problem,there are few help inks to troubleshoot the problem.Click the link below to go through the troubleshooting procedure to resolve the issues :----Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html-----------van idles rough? http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html
--------------runs lean and idles rough? http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html
-----------Car still runs Rough after tune up? http://howtobyme.blogspot.com/2011/12/car-still-runs-rough-after-tune-up.html
------------Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed? http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html
----------High rpm in neutral? Inconsistant high RPM in neutral? http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html
------------Engine Backfires? http://technoanswers.blogspot.in/2012/02/jeep-backfires.html----------- Nissan stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

-----------
Nissan Pathfinder Backfires? http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-backfires.html
---------How to adjust rpm? http://schematicsdiagram.blogspot.com/2011/12/how-to-adjust-rpm-on-2009-dodge-charger.html
------------Engine cuts out at 3000 RPM? http://schematicsdiagram.blogspot.com/2011/12/engine-cuts-out-at-3000-rpm.html
----------This will help.Thanks.

Well this is a good possibility.If your has lost power,backfires and runs really bad or does not run at all it is good possibility that it has jumped a notch or two. You can verify by checking the timing with a timing light or by removing the covers around the timing chain or belt and checking the alignment grooves on the head and block to the ones on the pulleys.

Vacuum leaks. Check all hoses and intake bolts. Leaking EGR or plugged PCV valve. Air filter plugged. Leaking head gasket. Worn timing chain. Camshaft lobes worn. Valves burned or leaking. Fuel idle control system or sensor. Good luck!

sounds like you have jumped a tooth on the timing if not timing out

Your timing belt could be broken. You want to have this checked as soon as possible to prevent any further engine problems.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_62314e5b2470e8b5