99 5.0 Misfires when warmed up

[Sedare]

Ive been digging thru forums and google for 2 weeks now trying to figure out what the hell is going on.
I have a 5.0 Eddie Bauer with almost 303k miles.(I have owned it since 240k) I deal with small issues like the subwoofer works once every 6 months for 5 minutes, or the temp gauge on the ceiling has a short and only gives a read out when you hit the side of it then fades out again, or the back wiper didnt make contact with the glass so I took it off, or the fact that my car has been the victim of 4 ****ing parking lot hit and run tags in the last year and no one saw anything.

This car was a steal at 2200, and I my wife and I consider this car to be the best car either of us have ever owned. So we decided, we will maintain it no matter the miles as long as nothing catastrophic happens.

Now, recently I had noticed a very subtle shake during idle. my friend told me I was experiencing a cylinder miss. It didnt feel bad, so I put it off. 4 weeks ago I ticked over 300k, decided to spoil the car with a bit of over due maintenance. I did the plugs first. I started the car, and I drove for 5 minutes and got to running temperature (keep this point in mind. Its a running theme) and the plug in cylinder fouled, or failed or something. I pulled the shroud off behind the wheel, and I could hear a tick/click and the plug was arcing to the engine from the wire. I googled this, and I realized that the plug was likely bad. (autolite double plat - Would have gone Bosch if they had 8 on hand) took it back to autozone and they exchanged it for me, and I put the new plug in in the parking lot. I spent like 90 minutes swapping this and dealing with the manager.(10pm, in a 3 piece suit, using an old rusty horrible freight tool kit in my trunk, and in the rain. The delay helped the engine cool down.). I drove for 10 minutes (back to running temp), and right before I got home, it started to miss again. I didn't pull the codes again, I was mad, went to bed, and had to work 3 days straight roofing. It was not 100% missing like it was with the one fouled plug, but now it was a scattered inconsistent misfire I decided I could live with that for now. So I went forward with more maintenance, bought a new IAC, new plug wires.

Then something got WAY worse after I swapped the IAC(EDIT - to clarify, I think something was already getting worse, and I didnt notice it until after I swapped it and found the misfire was still there), and before I did the wires. I nearly stalled once or twice a day at a stop when I was fully warmed up, if the car is warm, and I park for a few minutes, and start it up again, it nearly stalls right after I turn it over, so I pulled the codes again.
Now I am misfiring on 2, 5 and 6, and Fuel too lean (car is at my wifes work, I cant remember codes, but that was the readout from the parts store)
Now, I work early. I roof, and now its really cooling down in the mornings in Spokane. In the last week, I realized that the car has ZERO misfires when the engine is cold. It takes at LEAST 10 minutes of freeway driving for the misfires to show up.

Here is my reasoning points, and where I need some guru's to bounce this off of.
Disclaimer 1: Ive been very sick for the last 4 days, and have still not changed the wires. My plan is tomorrow for this.

I have ruled out wire shorts as the misfire is not present when the car is cooled down.
I have reasoned that it cant be the coil packs, because Wire 2, is on one coil pack, but 5 and 6 wires are on the 2nd coil pack. The likelihood of them BOTH failing within a day of each other... VERY low odds. Im looking elsewhere.
My gas mileage is down to 11/12 mpg, but I tend to drive it hard ( sue me I love this car ) but when we were doing long drives in north dakota, we were getting 18-22mpg routinely. So something is definitely affecting the fuel. I reason that this is not 2 separate problems creating a larger single issue.

So what gives the coil pack its signal? is there a single source that does this? Because I dont think that could be it, because this power would feed all 8 cylinders, and could cause random misfires across all wires if the signal source was the issue. Instead I am locked on 2, 5 and 6, CONSISTENTLY WHEN WARM.

If I am missing something here, point it out or I can test it. Keep in mind, these 3 cylinders do not miss 100% of the time either. It is VERY random, sometimes you have all 3 miss in one revolution and it nearly stalls, sometimes it goes 3-4 seconds between and nothing misfires. This inconsistency is maddening.

Andrew


**EDIT - 11/2/2017**
Resolved due to apparent user error. Plug in cylinder 6 was cracked upon install. I replaced it, and the problem is fixed 100%. Likely I tightened to much, and never checked it after I installed them originally. Oh well. Got some basic things replaced that I will just consider 300k maintenance!

 

[Turdle]

Fuel pressure? I'd measure this.
When was the last fuel filter?

 

[Sedare]

I can test this soon, but would not explain why only 3 of the 8 cylinders are missing, and there is ZERO issue under cold temperature.

 

[Turdle]

If those 3 injectors are partially clogged and fuel pressure went low it sure could combined with the p0172-p0174 ( fuel too lean) code.

Misfiring due to ignition problem would trigger a too rich code if anything.

Just trying to help. Your post reads like you are panicked.

Edit.
The ECT ( engine coolant temp) 2 wire sensor is known to create issues when cold or warm if it fails.

 

[Sedare]

Seeing that it only happens when it is warmed up, (when liquids usually flow better compared to when it is cold)
and that it gets progressively worse the warmer the engine is, it appears easy to rule out.
http://www.explorerforum.com/forums/index.php?threads/multiple-misfire-failed-coil-pack-test.343616/
I read this, and even if it is referencing the V6, it clearly shows the same conceptual issue, and was related to the coil packs. The only difference between mine and his issue, is mine is temperature dependent. He never stated if his was, and its not the same motor.

Either way, his post explains why the fuel too lean shows up when cylinders are misfiring when it has nothing to do with the fuel pressure.

I am however going to add fuel filter to my maintanence list.

 

[Sedare]

Ill look that ECT up. I didnt see that edit.

 

[Mbrooks420]

Liquid might flow better at higher temps (although that's not true of all liquids) electronics that pump, measure, meter, spray and such do not. Many electrical roblens worsen, or 'appear' with heat. I'd change your plug wires and see if it changes anything. It could be they've been damaged by repeated removal and being way overdue.

 

[Sedare]

Ok, I will get outside here in a couple hours and swap those. Ill update then.

 

[J_C]

I'd look around for vac leaks, something static might cause misfires and lean code once the engine gets warm and tries to optimize the mix ratio.

 

[Sedare]

Outside doing the wires. These clips are obnoxious. Lol

 

[Sedare]

If I ever meet the person who decided on the route for the 4th plug wire...

There will be words. Many.

 

[Sedare]

It appears I am not alone on that 4th plug wire. The last time the wires were changed(previous owner), the 4th wire was not, and the other 7 were. So this time, I did the same. I left it there, and the 3 cylinder misfire problem went away. (well after I realized I had 7 and 8 swapped. Seriously thought I made it worse again)

I am going to find a program for my laptop that I can install to clear the codes myself, as I have an OBD2-USB cable but have not used it 5 years.

I digress, because now I am back to the original misfire that caused me to swap the plugs a while back. The very soft one during idle at a stop sign, that has no effect on acceleration, or casual driving. It only misfires at a stop while holding the brake. This was the original reason for me doing my plugs. However, this misfire happens at all temps cold and hot.

 

[Mbrooks420]

Replace the last wire. Clear the codes by pulling the negative terminal for several minutes.

 

[Sedare]

Replace the last wire. Clear the codes by pulling the negative terminal for several minutes.

Do you know if a technique? I couldn't find a way to reach around the back side of the engine bay... I know I'm missing something, but I never back down from hard work. I had no choice today... My wife works and I need to watch my kids and I live in an apartment... Lol ill get to it Monday at my dad's garage.

I'm super happy that the wires actually were responsible for the misfire. Would you mind explaining in a bit more detail why a bad wire would create an inconsistent fire? I have worked on computers for 20 years, and with that experience, temperature never changed a wire short. Im very interested to understand why.

 

[Mbrooks420]

With heat resistance goes up, typically. Rubber softens, and might contribute to an arcing condition. Plus, the computer changes many things when the motor is up to temperature.

 

[J_C]

Do you know if a technique? I couldn't find a way to reach around the back side of the engine bay.

It may be easier to access it by going in through the wheel well with the well liner off.

 

[CDW6212R]

With heat resistance goes up, typically. Rubber softens, and might contribute to an arcing condition. Plus, the computer changes many things when the motor is up to temperature.

Yes exactly, heat reduces the current that passes through the plug wires. Also, the plug wire current doesn't simply go through a main conductor with insulation around it. Plug wires are a combination of a core(not wire), and windings around that, which are what transmit the current along. A simple wire would create tons of interference. That's why a simple resistance test does not always locate a bad plug wire, that only checks the inner core path resistance.

Plug wires are very fragile, especially with years of age. Old wires are almost likely to fail/break from the removal process. It is very smart to replace plug wires at regular intervals, say every five years. Cheaper(lifetime warranted) plug wires go bad sooner and easier. Buy OEM or something similar in price.

 

[Sedare]

It may be easier to access it by going in through the wheel well with the well liner off.

I did all of these buy removing the shroud from the wheel wells. I had no issues getting the cables into place like they need to be. I did end up breaking 4 of the wire clips in the process, but I did remember that this car was in north dakota for 13 years, and the cold/heat contract it was exposed to wreaks havok on plastic. So I zip tied them in place near the same locations to avoid the exhaust manifold, and the steering shaft. I dont see this being an issue. Having the access from the wheel well was the only way I was able to swap the plugs last month. Trying to reach down there was maddening, (then I googled it) found a forum post saying to remove the shroud.... it led to me swapping the plugs successfully, but I think I may have damaged a couple of the wires due to their old age when I put the wires back onto the new plugs, and that spawned the triple cylinder misfire issue. That had been worsened by a single cylinder misfire when I swapped just the plugs, and one of the plugs had fouled out so bad it was eating away at the threads. I had no idea plugs could do that. I regret waiting this long, but it is what it is. I dont care if the car is at 302k miles. I hope to get this thing to 400k, and I am willing to do what it takes to get it there.

Now, to figure out the reason for the passive misfire....

 

[Mbrooks420]

It's probably the plug wire that is two changes old.

 

[Sedare]

It's probably the plug wire that is two changes old.

See im torn on that. That very subtle misfire has been there for 2 years with ZERO degradation. No change at all. At first the only major issue I had been experiencing a blatent cut in power when the air temp is over 95F. I traced that to the Idle Air Control Valve, and I swapped that. But it has not gotten hot enough to make sure that fixed the issue yet. See, in all honesty, I was a honda guy till I was in north dakota, and needed a decent rig to commute 70 miles a day in winter. So we got this, and we loved it to death. Best rig either of us have ever owned.

I didnt know what to expect, but the durability of the 5.0 on this explorer has impressed me so much, that I want to keep it running. A long time.

I replaced the bearings in the alternator at 260k, I replaced the water pump (in january when it was -4F, with my brother in law put a screwdriver thru the radiator and made that repair much more costly) and thermostat around 250, Serp belt at the same time.

I am losing oil somewhere, but I have not been motivated enough to trace it. But for now, the only major issue I want to fix is this... almost secondary misfire. I hope the wire change fixes that. I will update as things change.