1993 Ford Explorer Spark plugs carbon fouling

Hi allenhudson91,

Thank you for the donation.

If the plugs are fouling due to excessive sooting, it most probably is caused by vacumn leakages.

Other possibility could be a compression problem. Get the compression tested if no vacumn leakages are found.

I could not find the specific compresion presure and this is the general guidline as specified in my database.

ENGINE COMPRESSION
Check engine compression with engine at normal operating temperature, all spark plugs removed (on
dual plugs, remove exhaust side only), and throttle wide open. Ensure crankcase is full and oil is of
correct viscosity. With compression gauge installed, use remote starter to crank engine.
Crank engine at least 5 revolutions, and record highest reading. Repeat procedure for all cylinders,
using approximately same number of revolutions. Lowest compression reading should not be less
than 75 percent of highest compression reading. No cylinder compression reading should be less
than 100 psi (7 kg/cm 2 ).

If the engine is not firing correctly, it would foul up very fast.

Possible causes are :

1. Fuel pressure and injectors. Bad injectors would cause excessive fuel to be supplied. Check if there are any clogging of the fuel return between both banks which would cause a higher fuel pressure between the banks.

2. Spark plugs and related parts. Ignition coils etc.

3. Bad cylinder head gasket, this would cause low compression which you have ruled out with the test carried out.

4. Clogged exhaust system.

You would have to concentrate on the above for the bank that is giving problem.

You would need a fuel pressure gauge and appropriate attachments to install the gauge onto the Schrader valve located on the fuel rail.

Before installation, release the fuel pressure and after installation, turn the ignition on and use diagnostics equipment to command the PCM to run the fuel pump. If you do not have diagnostics equipment, try cranking the engine a few times to see if the pressure builds up.

Was the problem there before replacement of the head gaskets?
Are the valve timing correctly set?

The ignition timing is non adjustable for the 4.0 L engine but the timing chain installation would affect the valve timing, which is the one I am referring to.

Was anything done or did anything happened prior to the problem occurring?

Sorry for confusing you.

What I meant was, when did the initial problem occurred and was any repairs carried out prior to it happening?