Here's the deal. I am still getting code P0305 which is a misfire on #5. I have changed coil pack, plugs and wires one at a time to isolate the problem. I even took off the TB, IAC and MAF and cleaned them real good. Replaced fuel filter and air filter as I do every year. Took it out for a ride and it was running great then it started the same old thing of shuttering/shaking (misfire) and CEL came back on. It will stay on and blink on and off. Can not find a vacuum leak, not saying that there might still be one but can't find one. One more thing, sometimes, but not all the time, when at a complete stop and slowly take off, it runs rough for a few seconds, then smooths out until I cruise at steady speed and I get the misfire. Any ideas guys would be greatly appriciated. Going crazy here.

1998 F-150, 4.2, V-6, auto, 4X2.

 

Try looking at the plug area and the wire at night to see a possible leakage point.
With all the parts replaced and still #5, something else has to be happening.
Remove the plug for a look at it's tip and insulator.
Are the wires placed as they were stock so cross fire is not a problem?
The flashing CEL means a loss of cylinder ignition allowing unburnt gas to pass theough the cylinder into the cats where it could burn and melt the cats.
Good luck.

 

Check the compression.

 

OK guys....thanks....I'll get back to you as soon as I recheck and do what you all have ask me to do/check. Thanks

 

OK....I rechecked everything and everything is where it is suppose to be. Check #5 plug and it is firing. Changed around plug wire with one of same size and still having misfire. Had my compression checked and its good. So, coil pack, wires, plugs, fuel filter, O2 sensors all changed. TB, IAC and MAF all cleaned. Good ground on coil pack....all this done and still getting code PO305 misfire on #5. What else can it be??? Any ideas out there?

 

As you found, Maf, IAC, Tb, Ox sensor, fuel filter, fuel injector none of which will cause one cylinder to missfire "and flash" the CEL.
A 305 is very specific to that cylinder.
All you have is the coil pak, the plug wire and the plug with it's boot to that cylinder and the PCM switch that fires that cylinder.
The flashing CEL is the loss of spark very specificaly and not be a compression issue, or valve action issue or an intake air or fuel issue..
At this point, I would uses a good clamp-on timing light around that plug wire to see if there is any spark at any time that will trigger the light then goes missing.
If yes, the next check is to monitor the ground coming from the PCM for that cylinder's coil for missing while the motor is at idle.
You have to go to these lengths now to get a handle on what the root cause is.
And be sure you have the plug wires on the coils correctly.
Good luck.

 

Bluegrass.....OK, I did what you said to do as yes I can see where the timing light goes out and then back on. I also checked the other wire just for grins and the other the light stays on with no miss. So now for the dumb question for the next step. How do I check/monitor the ground from the PCM for #5 cyclinder? I think the PCM is located behind the kickboard on passenger side? Thanks for your help.

 

All the coils have 12 volts standing on one lead.
The other lead goes back to the PCM through the harness so the PCM can ground switch the coil.
Use an analogue meter to see if the PCM is switching the ground reliably.
From here back it could be the harness has a break in the insulation or the PCM switch could be faulty.
Normally if you look back at the PCM switch with an ohmmeter set to see 10,000 ohms somewhere on it's scale, you should see that resistance+/-.
If you see an open it could be the harness or the switch.
If you see low resistance it could be either a ground or the switch is shorted.
Put the light back on the coil leads and move the harenss around to see if there is an issue close by.
Good luck.

 

Bluegrass....thanks for the info. I have not completed this last task cause of work. All I have done so far is look at the wires that plug into the coil pack coming from the harness. I noticed that there are only 4 wires at the plug. I traced the wires into a bigger harness that is behind the motor and from there it goes into the PCM. The harness is tied off behind the motor so I couldn't at this time open it to see if there is a break on one of the 4 wires. Will have to do it when I'm off this coming wed and thur. Do you think I should use a T-pin to check the wires or just poke the wires with my probe?

 

You can, but you need to seal locations once finished or they WILL corrode. Use a dielectric or silicone sealant, unless your test pin covers it's own tracks. I use a large brass alligator type (test pin) myself.

 

Bluegrass and jbrew...OK guys....sorry it took so long to get back on this but I finally got the ball rolling again. Did everything Bluegrass asked me to do and all checks to specs. I did a smoke test to make sure I didn't have a vaccum leak and still didn't find any. Now, as I was going over all my notes, I found something I neglected to mention in my first post. Not only did I get a misfire code for #5, I also got codes PO171 and 174 (lean) on bank 1 and 2. So, I did alot of research on 171 and 174 and found metioned many times about a isolator bolt going bad. I talked with a Ford tech and he told me that my truck does not have any isolator bolts. Now I am lost as I read my chilton book and it shows that it does have them. Can anyone please help me out on this before I start to tear the engine apart. Thanks guys!!!

 

Look at where they are used on a V6 and see.
V8 does not use them.
Good luck.

 

It's a V6 Essex. 4.2L. Try the v6 forum. Here you go a 98 like yours ,

https://www.f150online.com/forums/v6...171-p0174.html

 

Hey guys....thanks for the input. I'll keep you posted as to my progress

 

jbrews post is spot on but, that may be 1/2 the solution for you.
I have the exact same truck as yours and I had issues with the elbow rotted, cracked, collapsed as shown in the link jbrew provided.
It cured my leak for about six months and the CEL lit up again with the 174 code.

What I found is theres another elbow that needs replacing. Feel under your intake plenum right behind the throttle body; you'll discover the second elbow there. CAREFULLY pull it down and off the plenum...you can shine a light on it and check the condition....my bet is it's toast too.
Now here's where you have to really be careful: the elbow is attached to a plastic tube that runs under the plenum and terminates back at the PCV......don't pull on the tube or you'll have issues reconnecting. Instead, using two hands, hold it steady and CAREFULLY pull off the elbow.....

I used Dorman PCV Elbow purchased at Autozone...part number 46022...under the Help! line of parts.

Carefully re-install on the tube and slide back on the nipple on the underside of the plenum.....

Clear your code and Drive!!! Mine ran like new..............hope this helps......

If you pull the tube out completely, let me know and I'll walk you through it..........