Ford Enthusiast

[BroncoJoe19]

Normally a spark jumps a gap in the plug which ignites a fuel air mixture that is under pressure six times per revolution of your engine. It happens once in each cylinder per revolution. If by chance one cylinder fails to fire that is a missfire. IF multiple cyls missfire then you have multiple missfires.

What causes a miss? Not enough air, too much air (vacuum leak). No fuel,(bad/clogged injector, empty tank, low fuel pressure - dirty fuel filter,weak connection to pump , weak pump) no spark, weak spark, lack of compression, valve timing, burnt valve, spark/ignition timing.

When you replaced the camshaft position sensor, did you remove the synchronizer too? Or just the sensor? The synchronizer can be installed improperly.

In the 60's and 70's one could run an engine with a dead miss all day, but not so with the newer engines. I'm not sure about the 3.8, but with my 4.6, if I have a dead miss, the engine REALLY pukes. The PCM senses the dead miss, and to protect the CATs from overheating cuts off half of the fuel injectors. It goes into limp mode, and you can't get over 30 mph. When you have a dead miss, the fuel that should have been burned gets dumped into the exhaust and gets burned in the CAT causing it to overheat.

Did you reconnect your O2 sensors?

I just re-read this post, and realized that you never answered me when I asked if you looked for vacuum leaks.
Two things I suggest at this point is:
1. Look for a vacuum leak
2. Check and clean your grounds. (even the little ones to the fenders, radiator support etc.)
3. is your battery up to 12 volts or more?

Checking for vacuum leaks.
Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.
Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard ford-forums... Don't forget to remind folks to check the PCV valve, hose and grommet !

Courtesy Ramnasal ford-forums... Clamp off the hose that runs to the vacuum booster (brake booster) or pull it and plug it. It is possible that the diaphram on the inside of the booster may go bad and cause a vacuum leak.