Nox

I am new to this forum and enjoying it so far. A few days ago my 98 F150 4.6L suddenly started running VERY poorly. It felt like I lost three cylinders. The Engine light came on with a code that indicated a misfire on cylinder #3. So I started the process of troubleshooting. I know others of you have been through this as I have read through some of the threads, so I'm hoping I can get some advice.
Here is what I have done:
-Checked the obvious...found nothing like vacuum hose break, broken wire, etc. I tried the starting fluid trick(around the vaccum hoses), but found no signs of a leak. Also put in some ejector cleaner.

-I pulled #3 spark plug. It was oily on and around the boot. My assumption was a valve cover leak. Cleaned up the plug. same problem. Put in new Motocraft plug....same problem.

-Tried to isolate the problem by pulling select plug wires off...but nothing obvious. #3 plug wire resistance similar to others

-Swapped coil packs. This engine has two. Thought I could see if the problem goes from #3 to another cylinder indicating a problem in one of the coil packs.....I even cleaned up the ground connections. Results: same problem. Now the "check engine" light is off so I cannot get a code. lol
One thing to note. After each step I took trying to find the problem, the truck would go about 1/4 mile with no problem occuring (or at least I could not feel it). Then suddenly, wham, like I'm running without 3 cylinders. Since I cannot get a code I dont know if the problem has moved to another cylinder, but given that when I drive the first 1/4 with no major problem, its looking like it may not be electrical?

So here is my question: What is the next most logical place to search for this problem? Any thoughts would be greatly appriciated.

ONELOWF

How old is the fuel filter? How many miles on the truck?

proudfordowner

I wonder if it has something to do with your vacuum advance. Check your Air Mass Sensor. Or it could be a bad oxygen sensor too.
just my 2 cents
stephen

hcbph

Sounds like my 97, check out your plug wires. Had this happen twice, both times it was a bad plug wire.

Nox

Thanks for the input so far.
The truck has 154K on it. The current plugs and wires have ~40K on them. Wires LOOK ok...and the resistance on a few that I checked was in spec.

Nox

Also, In response to OnelowF, I have bought a fuel filter...I thought I would try that next because I cannot remember ever changing it. Bought truck with ~60K onit, so my guess is that it has never been changed. Also have been reading up on Injectors (how to check,clean, etc)....but so far no codes on them, but thought PCM may interprete as misfire.

ONELOWF

I always mention the fuel filter as everybody seems to ignore them, and in your case the truck starts off OK for a short distance.
I read very little about bad injectors but lots about vac leaks, and particularly the the pcv elbow at the rear of the throttle body....but you have checked all that.
Make sure you disconnect the battery occasionally when retesting to clear the memory.

Nox

Quick update:
- I put Noid light on each of the injector plugs. so I know they are getting a signal.
-I listened to each injector with stethescope.....All seemed to be energizing as I could here each of them clicking. Of course, one or more could be clogged, but dont want to go there yet
-Fuel delivery: I put on fuel pressure guage. Key on, Engine off was 36psi with spec range 30-45. Tested bleedback...ok(1psi). Fuel pressure regulator seems to be working correctly. Idle pressure about 35psi...funny, my manual list keyon,engine off spec, but could not find running spec. Anywho, my son and I decided not to change gas filter yet, as it did not seem to be the problem (at least according to our gauges.

Am I there yet?
Well believe it or not....I still really do not know if the EGR is working correctly.....do not have a vaccum pump, but think Im gona rig one up. problem is I see no performace difference with EGR connected or disconnnected. Could be the problem, ye?....Well I tested the same way on my For van and saw no difference there. Guess Im old school here, as I recall just pullin off the vacuum hose and seeing if the engine dies or accelerates poorly.
Any advice here would be appriciated(how to really test EGR...or at least see if it is causing my very rough running engine.

- Someone mentioned plug wires....and I have to admit I have not pulled each one off. but perhaps I should.....This is almost like "is it plugged in?"...a no brainer to check thoroughly
-MAF was mentioned....havent gone there yet....but I have to admit, It does seems like one component causing multiple cyliders not to fire.....as opposed to just cylider#3 not firing as the code read. Or even if it is multiple cylinders.....would the plugs or wires go bad suddenly?....I dont think so, but it could have just "crossed the line I guess"
Anyway, I really appriciate the insights, and stay "tuned" as I defeat this little grimlin

ONELOWF

This started as an ignition problem and has become global, I guess. lol
Clean the maf, very simple. Replace the fuel filter anyway, unless you can test the fuel pressure under load....particularly if you can't remember the last change.
Remove the throttle body elbow and clean the egr ports, simple but annoying. Soak the egr bolts over night with PB blaster or equiv first.
My egr ports were 80% clogged at 55k miles.
How many miles on yours?

Nox

OneLowf,
Thanks for input/advice.....I'll let you know results soon from Round IV with the truck.