- This topic has 16 replies, 6 voices, and was last updated 10 years, 4 months ago by
.
-
Topic
-
4.6L V-8,200K miles. Started running poorly this morning, poor acceleration, rough idle, no check engine light until this afternoon. Checked code and got 304 misfire on cylinder four. Mass Air Flow Sensor hums from time to tme. Thinking clean Mass Air Flow Sensor, then maybe replace coil and injector? I prolly should buy the manual for this car too. Been just an awesome car.
-
Replies
-
That code is pointing you to cylinder number 4. It sounds like a secondary ignition misfire based on symptoms described. It could, however be something else. Before throwing parts at it, try some simple diagnostic tests. Here is some great info from Eric regarding where you might start…
Ford’s on plug coils are notorious pattern failure parts. Just the same, it’s always more fun and economical to prove the part that’s actually failing. Why replace the coil AND the injector when only one of them might be causing the problem. Some easy and free diagnostics are to simply swap the coil with another nearby cylinder and then swap the spark plug with yet another cylinder. Then drive the car for a bit and look to see if you’ve gained a new misfire code. Lets say you swap coils between three and four and then swap plugs between two and four. If you gain a P0303, that coil is junk. If you gain P0302, your plug is fouled somehow. If your misfire code stays at cylinder four, then you can swap an injector the same way you swapped the coils. If the problem still stays at number four, you’ve still got more diagnosing to do, but you’ve saved yourself at least a fifty dollar bill on parts you didn’t need to replace.
The thing about cylinder four on those 4.6’s in that car is that so many parts rub on other parts in that spot. Your heater core hoses and your evap purge solenoid are in that area and the number four coil and injector connectors can get broken wires right where they exit their connectors. They tend to rub through from contact with those other parts. Do a good visual inspection while you’re looking at and swapping around parts. You might have the car diagnosed before you even turn a screw out.
Good luck.
On a 4.6 Ford cylinder #4 is a common cylinder to misfire. The heater hose connection leaks and fills the spark plug tube with coolant and shorts the spark to ground. Could also be a bad spark plug or coil, broken PCV valve fitting at the rear of the intake manifold, bad injector or low compression. I could keep going but you get the idea.
The noise you’re hearing is not the MAF sensor but a bad IAC valve. Another common failure.
Sounds like you’ve got some great suggestions to start with. I’ll just add this as it applies to any performance issues.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted on your progress.
Remove ignition pack off # 4 and swap it out with any other easy access cylinder. If code moved with swap to that cylinder, say, you now have P036, it’s ignition pack. That easy to diagnose.
Thanks for all the replies folks! Much obliged! Just an FYI—cleared the code, swapped COP with next cylinder, noted no appearence of coolant hose leaks above #4. check engine light briefly came on, then went out on the 25 mile drive home but definetly noticed a difference. The misfire defintely feels like it’s on a different cylinder.
Wondering if the short check engine light duration left a code to read and will check again tomorrow.
I find this all very interesting as I never really looked at this 4.6L engine, as it ran great and now I am seeing how different an engine this is than I am used too. Old school cap, rotor and plug wire guy. Kinda like the ease of the COP idea and the location of the injectors.
Noticing all this always leads to more questions-
– what to watch out for when removing the fuel rail
– what kinda project is the timing belt scenario—and how many miles they last.
Lastly, I will buy the repair manual tomorrow–along with the COP.
Great unbiased information is to be found here and am glad to have found Eric’s web sight! Awesome!The fuel rail shouldn’t have any surprises, just clean your o-rings and lightly oil them when you’re reinstalling them. If you can blow off the entire intake before hand with compressed air, you win. I really doubt you’re going to get that far though. It’s odd to hear the light went on and then went off. You can look for pending codes when you’re ready. They can be stored in the PCM but wont throw the CEL on. You don’t have a timing belt. You’re running chains and they should easily last the life of the car. 03+ engines had some tensioner problems that caused a knock at startup. Your 2000 model shouldn’t give you that problem.
Bear with me and again–great unbiased interst in this! Code 304 came back this morning after about 35 miles–going for the spark plugs next–prolly shudda started there first. But hey–never used a code reader to diagnose engine issues and am enjoying the process of learning. Just can’t say enough about how everyone here just puts it out there! Like the man says “stay dirty”! I almost want to keep this website a secret! great info on the timing chains, engine knock at start-up, fuel rail and injectors!
Threw in a set of NGK spark plugs, gaps checked and cured the problem. Running great! Not used to plugs going bad that are not fouled. Thanks Folks!
Spark plugs can fail in a few ways besides fouling. Sometimes the resistor within the porcelain goes bad and sometimes the porcelain cracks internally and the spark goes to ground before it reaches the gap. Most commonly on a 4.6 ford the spark jumps down the outside of the porcelain to ground. It usually leaves a black line down the side of the plug.
Electricity follows the path of the least resistance so if the plug is worn out it will find an easier path to ground that causes a misfire.
- You must be logged in to reply to this topic.