As of this morning my 2001 5.4 is running on 7 cylinders. It's damp and warm for February here in KS so I figure one of the COPs is not firing because of the moisture.

I drove to work and back today (about 20 miles total) and it hasn't thrown a code yet. Will the computer eventually light up the Check Engine Light or am I going to have to feel for the cold port on the exhaust manifold?

 

Well , let us know if that works

To force a CEL, you can try pushing the engine when it begins to miss. You won't get a CEL with a low grade miss, you'll get a blinking CEL. It will blink 3-6 times then shut off. It should do this as you push the engine. Don't worry, your not hurting the motor when pushing. What's hurting is continuing to run it this way.

You may have a DTC in memory currently. Have you checked ? The CEL doesn't have to be illuminated to have one stored.

 

Well feeling with my hand may be a bit of stretch but shouldn't an infrared non-contact thermometer be able to see the temperature difference in the exhaust port on the manifold with the misfire? That sure has worked well for me in the past on 4 cylinder motorcycles with similar issues.

Either way, I'll head down to Auto-Zone in the morning to borrow their reader. Thanks for letting me know that I don't need a CEL showing to know there might be a code in there already.

 

Background is you are dealing with a horse of a different type.
It's not a motor cycle engne.
If you have no CEL, a coil is likely faulty with low output voltage and not outright failure. Measuring coil resistance is no help for a shorted turns condition.
The pcm sees the fault but the system cannot decide because it's not a 'hard' fault.
The miss occurrs at lean fuel/air ratios when coil voltage is marginal to fire the lean mix.
How the pcm detects it is by measureing the crank rotation time when that cylinder fires. It will be slower than the others by compairson to a table that holds the average times for all good cylinders.
Unless the PCM has accumulated data to support which cylinder it is, you need a coil stress test to find the faulty coil.
Swapping coil positions still would not tell you what cylinder it is.
A good 'scanner' is needed to look at the data and you have to know what and how to interpet what you see. Most auto parts stores are not proficient to do this.
If you are caught out and the miss goes solid, do not force drive the truck any distance because the injector is still dumping gas into that cylinder and being pumped out the exhaust into the cat..
This raw gas will ignite in the cat on that bank, overheat it and can melt the rare metals coating on the substrate and permantly damage the cat for more expense. When that happens you get a 420/430 code depending on what bank the fault is at..
Good luck.

 

If it's a complete failure, and not an intermittent miss you can just start working your way around the motor disconnecting one coil at a time. Each coil disconnected will make the idle worse. Yes, it will be noticeable. The disconnected coil that makes no change in idle quality is the bad one. I've uses this technique twice now with perfect results.

 

Well, yesterday it was a complete failure but this morning in my test drive it has gone back to intermittent. With the complete failure I had hoped I would be able to diagnose it in the driveway.

I borrowed the store's code reader, but nothing came up. I drove about 20 minutes after that, alternating between it firing on all 8 and it missing. No CEL.

I guess I'll wait a few more days and see if the CEL pops up. Other than that, it's back to replacing all 8. I've done this twice before when the intermittent miss has appeared.

Thank for the help guys.

 

Yea, it's impossible to have Primary failure and not have a DTC. Primary failure, - -the CEL will be blinding yuh. So , your not even close to Primary or secondary failure. Like Bluegrass mentioned, a good scanner w/mode 6 data for cylinder history would indicate which one it is, -but you would have to take it in for that.

Try increasing the misfire rate within the drivecycle. Find the load and hold it there to increase the count. These misfires are counted over a continuous 200 and 1000 revolution period. At the end of each period, the misfire rate for each cylinder is computed and compared to a engine/load threshold table in ROM. If the misfire rate exceeds this threshold on the 200 revolutions period and the PCM computes a risk of immediate damage to the washcoat in the Catalyst, this is a Type A misfire. The CEL will flash while the misfire is occurring and that's when a DTC is stored.

That's really the best you can do with a low grade misfire. Find that spot (load) and try to keep it there for as long as possible. Watch for the CEL to blink.

 

I know it's an older thread, but I just had my second coil go bad in 2 months and after 2 days of driving, the CEL never came on. So I got an extra coil and just started swapping them out. First I put the new one in the #8 spot cause that was the one I just replaced 2 months ago. Figured maybe the new one went bad already. I tested it by power braking the truck (foot on brake to keep it from moving and revving it to 1500). It still missed, so I took the one I took out of the #8 and put it in the #7 spot. Tested it again. That didn't work so I took the one I took out of the #7 and put in the #5 spot (I did the pass side first cause it's easy to get to). I did this until it didn't miss when tested. Wouldn't you know it was the #6 cylinder which was the 8th one I did of course.

Anyway if other folks have this problem and don't want to wait for the CEL to come on to tell you which one is bad, this worked for me. I'm pulling my boat this weekend and didn't want to do it with an engine that was missing. This whole process took me about an hour to do. May take longer if you haven't replaced the coils before and have to figure out how to do it. Loosening the screws that hold the fuel rail on but not taking them out helps give some play in the fuel rail to access the screws that hold the coils a little easier. Be careful not pull the rails off the injectors otherwise you may have to replace some o-rings and re-seat the fuel rail, which really isn't a big deal, it just makes a mess when the gas pours out.

Good luck.

 

Atta boy.
Sometime ya gota take the 'cat' by the horns!
Good luck.

 

I'm running into a similar problem with my expedition. Its been raining a lot lately and the truck has started acting up on occasion. CEL came on the other day and it was a #3 cyl misfire and a 171 lean code. Stopped raining and the next day truck ran fine. CEL went away by itself and it doesn't seem to be having a problem right now. Something I need to look further into? Or should I just drive it?

 

I just changed all my coils and spark plugs in my 2001 5.4 supercrew, because there was a misfire, i just couldnt figure out which one, but as i got down to the process of elimination it turned out to be number 4, which is on the passenger side all the way in the back, water had in gotten in the plug well, and just completely destroyed the coil, it was really bad, i've heard that the engine holds water it you get rain water to drip down in there, i still havent found out if thats the case for me, but water in the plug well is bad no matter where it comes. just my 2 cents, since lightning expo said that it's number 3, its still in that range where water sits and can drip down and get under the coil grommet. check that out lightning, just pull the coil and see if there is moisture.

 

so you if have a gotts mod done, could that cause a lean mixture, i havent got a CEL or anything, im just curious.

 

To Optimus, the gotts mod on these year trucks 97 to 2003 usually would not cause a lean mixture. There is no way for this to happen by doing any mod ahead of the mass air meter on a stock motor.
Your not in 'possesion' of all the facts my statement is based on.
The reference to 'lean' is to a specific set of driving conditions not to general operation.
It's the operation of the EGR system that generates the very lean conditions where a coils within their 'rated voltage outputs' have enough reserve voltage to fire the lean mixtures.
If just one coil's voltage falls below the min. a missfire results for that cylinder 'during the specific set of conditions' otherwise is not present at other times unless the coil really falls to a very low output.
A fault like this is not a 'hard' fault {open or shorted} and most often does not result in a code or CEL but you still feel the effects as a skip, hesitation, studder etc.
I don't often go beyond this point but this coil condition 'can' reflect an interference signal back to the PCM and actually stop the PCM from processing any data for a very short time, then 'recover' and go on as if nothing had happened.
When this happens, the motor acts as if the ignition key were turned off then on quickly under power causing a very hard jerk by feel.
.As an example: I have experienced this effect on my truck and elswhere.
I was present once on the floor with a very large computer system on the top floor of a 5 story building completely stop when a lightning stroke flashed across the sky over the building.
Machine stopped dead then began again. Absolutely eriey to experience.
The stroke inducted 'trash' on the busses from the high electric discharge field and stopped processing for a few seconds then recovered and went on as if nothing had ever happened.
The master control console lit, up all operating noise stopped then resumed.
Good luck.

 

Yea eerie. - Like something you'll never forget. I've witness that as well, - seen some crazy things happen after a lightning strike.

 

Thanks bluegrass for clearing that up, because before my coil problem got worse, it would be intermittent. I was just trying to eliminate any other cause in case it comes back again. thank you.