1998 F-150, 2WD, 4.2 L (V-6), Automatic trans, 208K miles...

The truck has been running a little rough lately, but not terrible. The miss is mostly noticeable at 1200-1600 rpm, but she smooths out if I rev it up... At 2000+ rpm, even under load, everything seems normal (for whatever that's worth).

I got the codes read at Autozone, and it said misfire on #2 and #3 cylinder.

They recommended plugs and wires, but I went ahead and got a new coil pack too.

(Six years ago, I replaced the plugs/wires/coils... I did the plugs and wires first, but that didn't solve it. The coil pack is what solved it... So, when this started happening, I checked the receipts to see if the coil pack was still under warranty. The coil pack was only warranted for 3 years, so that's why I grabbed a coil pack too)

Yesterday I started by removing and inspecting the #2 and #3 plugs. They weren't as bad as I expected. They were a little bit wet at the base, but the spark gap was clean and the gap was still perfect (.054-.055).

...so I figured I'd go straight for the jugular and just replace the coil pack first. I knew I was breaking the cardinal rule "test before replacing", but time was short and it's such a quick job. Four or five miles later, the CEL started flashing again. Ugh, $100 wasted...

So, today, I did the plugs and wires. The miss still seems to be there, but I didn't drive anywhere yet. I only tested/listened while in park. The miss might be a little better, but I think I'm just being optimistic.

The battery is disconnected right now (to reset the light), and I'll leave it like that for at least four-five hours, but I expect the CEL to come on again once I get on the road.

I don't know what to check next, any suggestions? Thanks in advance!

 

You don't need to leave the power off for more than a few minutes.
Get a Scanner hooked up that has a trap feature and see what cylinder is causing the loss of ignition.
That's what causes the flashing CEL.
Flashing tells you the cats are in danger from lack of ignition. Raw gas can burn in the cats melting them if gone on long enough.
You dealing with an issue beyond your ability unless you do it right and understand.
Good luck.

 

I always appreciate your input Bluegrass, but that one doesn't help me at all.

I don't have any access to a scanner that has that trap feature, and I doubt the old truck is worth paying a mechanic to fix it. I already looked up the blue book value, and mine has some rust on the roof that's getting kinda serious. Also could use some front end parts, and various little odds and ends around the edges...

So I gotta figure this out, or else sell it for parts.

I'm not a mechanic by trade, but it's been a real long time since anyone else wrenched on a vehicle I owned. If I know what to test/replace, I can almost always get it done.

And yeah, I know the cats are at risk... They've been abused for a few weeks now, and they were abused heavily about six years ago too.. Could that have anything to do with it? (It's an aftermarket exhaust system, at least ten years old)

Compression on cyl #2 was kinda low last time I checked it (about 18 months ago), could that have anything to do with it?

But really, those questions don't matter.

The only question that matters is; what can I check for next?

 

Low compression on #2?

Oh yeah, that’s your misfire right there. One of them, at least. Probably #3 as well, but don’t confuse your cause and effect. Misfires roast cat converters, not the other way around.

So, odds are you need an engine. Probably makes your decision regarding the truck easier now. What’s left to check is repair or sell.

Not really sure what else Bluegrass could do for you. If you don’t have the tools to diagnose, you’re firing the proverbial parts cannon at this and spending more money than a shop visit to whip out a compression tester would have cost you.

 

what the scanner would tell you is the fuel trim numbers.. You might have a MISS FIRE due to the plug / wire / coil .......... or maybe you don't have enough gas ? Fouled injector ? ...... Bluegrass is trying to tell you there are OTHER possible causes of your problem.

And we assume when you change the coil / plugs/ wires, that you get all the electrical connectors CLEAN and installed TIGHT.

 

Thanks you guys, I appreciate all the advice around here

Bluegrass, I hope I didn't come off like a ***** in my comment to you. It's just that I was frustrated, and I don't like to be told to take it to a mechanic. The reason I come here is to find understanding so I can fix it myself.. Thanks for all the advice/understanding you gave me in the past, and I apologize if my comment came off wrong.

Johnny, you're probably right about the engine being on it's way out. I can borrow a compression tester, so maybe I'll check it again to see if it got much worse since last time I checked it. But she still pulls a smoky burnout with both tires, so maybe I'll just have to do that every once in a while to blow out the cats

And Steve, thank you too. I don't fully understand how all the sensors work, but I assume it has something to do with unburned fuel at one of the O2 sensors. But I don't understand how the computer would be able know exactly which cylinder...

I'm absolutely confident that the new plugs/wires/coils are installed correctly. The whole job went very smooth, and I used dielectric grease on all the connections, and Anti-sieze on all the plugs... Just like every other time I ever did this...

I only posted here in the hope that there would be some other simple thing that I could do or check.

PS, Steve, I don't understand how it could be a fouled injector. I can smell unburned fuel when she's idling.. But then again, I don't understand how low compression in #2 cylinder would cause a misfire code either.

At idle, she's not quite as smooth as should be (but not too bad).
At about 1400-1800 rpm (in park) the steering wheel vibrates.
But, on the road, under heavy acceleration, it's all pretty smooth (even in the 1400-1800 range).
hmmm, maybe it is an injector. ?

In any event, I gotta get a little more time out of this baby. Even if I have to drive 'er into the ground.

I don't mind a little lack of performance, I just want to get that damn light to stop flashing.

Thanks again to all you you guys!

 

To help you understand why low cylinder compression can result in a misfire code.
Simple..... the only way the computer has to know of a misfire is to time the crank rotation time every time a cylinder is sparked (fired).
The Crank sensor does all the timing functions and reports to the PCM over it's two wire pair.
If the rotation time become slower than the average of all the cylinders >>>for any reason<<< it is called a (logical) misfire in the program, and a code can be set if it keeps repeating beyond the program min, limit for a hard fault..
Intermittent misfires are also stored in another part of the program.
The only way to see them in this stored area is with a Scanner. Mode 6, test 53 location.
The reason these don't set code is because they come and go such that the program cancels the code request, but still keeps a record that can be viewed with a Scanner by request 'only'. An additional way to see intermittents is with a Scanner that has Trapping capability to freeze data when it happens. This record area does not have the ability to set code or turn the CEL on.
There comes a time in everyone's life when they need to ask for help when things get beyond their ability, same as going to a Doctor.
You came and asked, I made the effort to explain. It would be up to you to carry out and use the help in some way. The answer is there to be found.
I write the above also to help others who have the same issues and the why and how to handle it. Then they decide what to do.
Good luck.

 

Once again, many thanks Bluegrass!

I only read your reply 3 times so far, so I'm still trying to wrap my brain around it.... You have a very concise way of describing things, so I'm still trying to add it all up in my mind.

This part here, is something I didn't know...

Now that you describe it, it makes sense. I'm still adding it up, but it seems to describe what's happening.

The CEL tends to start flashing when I'm just tooling along, but hitting the gas seems to help stop the flashing. I can see how that would be related to the low compression on #2...

I'll have to read your post a few more times to see what else I can glean from it, but thanks again man!

 

The CEL is flashed by program design.
It is to get your attention that "Ignition' was lost on a cylinder.
Reason;this endanger the CAT converters because raw fuel may burn in the CATS that can melt them.

 

One of the things I've done for this same topic/issue is to use an oil additive.
it reduced the number of misfire faults tremendously.
Anyone else reading along use an oil additive or recommend a specific oil beyond the original recommendations?

 

Have you checked for clogged EGR ports? I know the low compression is a concern but whats the actual reading? Anyhoo, these 4.2s are bad for the EGR ports getting clogged with carbon except one or two. This forces all the EGR gas into whatever cylinder has a open port and causes it to misfire. A quick and easy check is unplug the EGR valve and see if it still misfires. Or you can apply vacuum to the valve at idle and see if the engine starts skipping or stalls. If it skips then you know the ports are clogged.

 

If it is seeing misfires it will store a code. If it can pick out misfires on a particular cylinder or cylinders it will store codes for those too. It should be P0301 through P0306 on yours. A cheap OBD2 reader will tell what these codes are. If they are all over, then it could be a few things, one of which I haven't seen mentioned here: fuel pressure. How is the fuel pressure on this? At idle and while driving and while having the issue?

I totally get that the newer computer-controlled engines are a bit of a mystery to those of us who learned on old-school cars, but they're not impossible to learn at the conceptual level . . . and once you've crossed into reading stored codes you'll find it can really help with diagnosis.

 

Assuming two things as discribed;
A. Flashing CEL.
B. On an intermittent basis.
This suggest intermittent spark to a cylinder. (CEL flashing)
1. Is it vibration sensitive? Intermittent..
2. A connector seating issue. "
3. A coil issue. "

 

I'll have to look into that EGR thing.
Thanks for that.
I had just kind of accepted the low compression as the only cause.

Also to follow up on my circumstance, I noticed the blinking only when first starting up.
I had assumed that would be before the oil fully circulated and lubed up the cylinder walls.

 

Thank you sir!

I have a vacuum, so I just did the test...

Removing the vacuum line at idle didn't change anything. But when I gave it a little vacuum, the idle dropped immediately.

I guess I have a thing to go after now, many thanks!

~Jim