I am experiencing engine hesitation on my 2000 Mercury Cougar 2.5L. I've since changed Coil park, wires, plugs, O2 sensors, Transimission speed sensor, changed Trans Oil, Fuel pump, EGR valve, air flow sensor, air filter, cleaned injectors. Today, another mechanic thinks cylinder 2 & 3 are not firing. What is your opinion?

The following fixya link tells how to change and where to find the vss How to replace the speed sensor on 2000 mercury villager

You need to run the OBD2 Diagnostics. You will need to have someone hook up a scanner to the vehicle and retrieve the codes. This is the best place to start.

A P0301 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #1.

Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present

A code P0301 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

Possible Solutions:
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Hope helps.

maf sensor

Try new plugs, wires, fuel filter, air filter, pcv valve, and if its still not too
good,, do the 02 sensors..

Have a good day !

I had the same kind of problem and I ended up solving it by actually checking for recalls for the 2000 Cougar and when you do, you'll see that there is a fuel pump recall. I dont' know if you've already done this but I figured i'd post this and try and help out!

Much luck

First, disconnect neg battery cable 10 minutes and reattach to clear codes.
Lean condition means it is not getting same fuel as other side of engine.
Since you had it scanned before, try Autozone to see if new results.
You might try a TPS switch which regulates spark and fuel feed. At lower speeds EGR starts to open-you should have code for a problem there.

a multiple misfire code can relate to a fuel problem check filter pump pressure let me know alan wrench

I just got done replacing the O2 sensors in my 99 Cougar due to throwing a P0135 malfunction code. There's 3. Facing the engine there's one in the front coming off of the front header, which is easy to get to. Another more tricky one if between the engine and the fire wall on the rear header pipe. The third is under the vehicle behind the transmission pan on top of the exhaust. In order to replace the O2 sensor near the fire wall you will need to remove the 4 retaining bolts for the ECM module and move it out of the way. Additionally you will need to remove the 2 retaining nuts for a wiring harness that is seated below the ECM module. Pay close attention to the connectors because the front and under vehicle O2 sensors have round connectors the one near the firewall has a squared connector. I was able to replace all 3 by myself in approximately 35 minutes. If your throwing a O2 heater malfunction code it is most likely going to be the sensor near the firewall. make sure that you know someone with a code reader so the code can be cleared. If you're do for an emmissions inspection be sure to put at least 40 miles on the new O2 sensor with different types of driving (e.g. highway, coasting, decellerated turns and rapid acceleration). Gotta love project cars for your kids!!

You will have to get to it probably from under the car it will be located just to the right of the driver's side axle