I have done all this and still have the 303 code flashing light when you step on gas. P0303 is cylinder #3 misfire detected. Start by changing the spark plug. If that doesn't clear it then try changing the plug wire. If that doesn't clear it, then you might need to look at the injector.
After you make a repair you need to clear the computer codes. Try taking the pos cable off the battery for 5 or 10 minutes, then put it back on, DO NOT let the pos. cable touch anything on the car, wrap a thick rag around it.
SOURCE: Check engine light on. I
Chek that the car computer is working properly .Seek for a professional electrical-mechanic that can check an diagnose your car computer. Sammyc47
SOURCE: HAD TRAILBLAZER PUT ON COMPUTER. SAID #3 CYLINDER
What money?
Who is working on it,a repair shop?
Plugs don't fix a misfire
A bad coil would,if you got the correct one.
There are no computers used for any automotive
diagnostic work what so ever,unless you run scan
tool software on your notebook
Need to continue to look at all data related to
whatever problem you now have,since changing
plugs & coil
No check lights on dash, doesn't mean they aren't
stored in data
You could have worn out O2 Sensors,Bad TPS Sensor,
Vacuum Leaks & Evap Issues,& any number of things
Look at fuel trim,timing,smoke test intake & evap
Cylinder 3 Misfire Detected
Possible Causes:
Air leak in the intake manifold, or in the EGR or PCV system.Base engine mechanical fault that affects only one cylinder.Fuel delivery component fault that affects only one cylinder (i.e., a contaminated, dirty or sticking fuel injector).Ignition system problem (coil or plug) that affects one cylinder.TSB 00-06-04-024 contains a repair procedure for this code.Here's what is listed for this code.303 means it's cylinder 3 that has a problem.To check injector,may be dirty,is to trade it out with another cylinder and see if the problem has left cylinder number 3 and it's at where the injector went.Was the spark that you replaced oily or clean.Could be a mechanical problem,bad piston ring,usually a oily plug in this case.Check for leaks by number 3.
2004 Marauder and 2003-2004 Mustang vehicles built before 12/19/2004 equipped with 4.6L 4V/5.4 4V engine may exhibit a runs rough, lacks power, and engine misfire, prompted by a MIL light and DTC codes P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, and P0316.
ACTION
Diagnose engine for engine misfire concern. If diagnostics determine an engine misfire which is characterized by leakage through exhaust valve(s), only replace the affected cylinder head(s).
SERVICE PROCEDURE FOR VEHICLES WITH RUNS ROUGH/MISFIRE CONDITION:
1. Perform relative compression check on all cylinders. If abnormal, check cylinder leakage and actual compression for "low" cylinders refer to Workshop Manual (WSM), Section 303-00.
2. If leakage/compression check indicates a valve train concern, per valve train diagnostics in WSM, Section 303-00, replace cylinder head and cam assembly, pipe plugs and timing chain tensioner, per procedure outlined in WSM, Section 303-01.
3. If cylinder leakage and compression tests are inconclusive, perform misfire diagnostic, per TSB 05-22-8.
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