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AC squeals because fan belt is loose or failing, unrelated to engine issue.
After engine is warmed up, if possible.
Shut off the engine
Turn the key on
Press the gas pedal to the floor and hold it down all the way
Now turn the key to START
Engine should NOT start, it should just crank and not fire at all.
Key on, engine off, gas pedal to the floor = Clear Flooded Engine routine
In Clear Flooded Engine routine the computer shuts off all fuel injectors but leaves spark on.
So the engine should not start.........unless...........fuel is leaking in.
If you had a fuel injector that was leaking fuel then MPG would be bad and engine would barely run at lower RPMs because it would be flooding out.
If engine starts, then you can see if it is a leaking injector with same test.
Do the same test BUT.........unplug the coil's 4 wire connector, so no spark.
Crank the engine a few times, now pull out each spark plug, and look at each one, you are looking for a WET spark plug, wet with fuel, which it shouldn't be since you were in the Clear Flooded Engine routine.
If you find a wet spark plug then that cylinders injector is the one with the leak
Next possible problem, EGR system.
Exhaust gas recirculation(EGR) is used to cool the cylinders when engine is under a load.
Hot cylinder makes lots of NOx, a bad pollutant, adding exhaust gases slows the burning of the air/fuel mix so keeps cylinder temps lower, less NOx.
If the EGR valve is opening when it shouldn't then MPG would be down and low RPM would be choked with unburnable gases.
With engine idling remove the vacuum hose from the EGR Valve.
There should be NO vacuum on that hose, EGR is only used when engine is under load, accelerating, driving at above 50mph, going uphill, ect......but not while idling.
If there is no vacuum the system is OK but EGR valve may be bad, gotta remove it to have a look.
If there is a vacuum then EGR modulator is most likely bad, and when you unplug the hose engine should start idling better, plug the hose, it is OK to drive without EGR system but listen for pinging, pinging is very bad for the engine, so drive it less aggressively unlit you get it fixed.
intake manifold=====(Vacuum hose)========EGR Modulator==============EGR Valve
Intake is of course the source of the vacuum
EGR modulator is a 12volt solenoid valve, computer pulses 12volts to this device to open it a little or alot to match the load on the engine.
EGR Valve is a vacuum operated valve that lets exhaust flow into the intake manifold when vacuum is applied.
Another part of EGR system is the DPFE sensor, this tells computer it EGR valve is opening by pressure differences in the exhaust manifold/EGR tube.
These do fail but you almost always get a CEL and code
Last edited by RonD; 06-16-2016 at 08:58 PM.