Miss-fire on Cylinder 5

[l008com]

I think I've reached the limit of the diagnosing I can do with my limited skillset on automotive stuff. I couldn't get an appointment to have a mechanic look at my truck for 1 to 2 weeks but turns out my mom has an appointment for some minor stuff on her car so she's giving me her appointment at the mechanic she uses so hopefully they can fix it Monday.

Once this starting issue is fixed, then I'll get back to what this post was originally about. Including pics of the spark plugs.

 

[l008com]

Ok the no-start issue is fixed. Turns out it was in fact just a bad starter. And it really did just happen to fail at the exact moment I popped the hood and removed two spark plugs, something I've never done before.

So $820 later and I'm good to go. I'm assuming thats really high but I couldn't do it myself and I couldn't wait 2 weeks to have my regular shop look at it so it is what it is.

At least now I can (A) drive to work when needed and (B) get back to this misfire thing. . .

 

[l008com]

BACK to the misfire. Attached are some pics of my plugs and wires. All pics are of the same two plugs and wires. This is what I meant very early on when I said I don't know what bad plugs look like. Are these plugs perfectly fine or totally worn out? I really don't know.

Also I didn't see any corrosion on the wires, at least on the 2 I checked. Everything looked fine.

Despite that, I'm thinking that unless the consensus is that those plugs are 100% fine, and given the AC Delco plug sale, I should probably just replace all plugs and wires.

What would make this a lot easier to diagnose is, is there a way to add some kind of realtime or almost-realtime misfire "gauge" using OBDFusion? Ideally something that can show it split up among all 8 cylinders. But even just a simple total count. Something I can use to compare my numbers to "typical" number, and so I can see if replacing plugs and wires has any effect, or if more is needed (replacing coils).

AC Delco Irigiums are only about $3 each right now after rebate. And a set of 8 wires is another $40. All very reasonable and I hope I can do THAT repair myself.

However the ignition coils are more like $30 each. And I have 8 of them. So Ideally I would like to definitively confirm how bad the problem is, and then if new plugs fix it, before I start buying all these coils. Especially since the stupid starter wiped me out :/

 

[christo829]

Those plugs don't look terrible, but if you have a spark plug gauge, check the gap. Over time, erosion of the electrode can change the gap a bit, though iridium plugs are generally less prone to this. I may have missed it as I re-read the thread, but how many miles on those plugs, coils and wires?

Also, in your first picture, I can't tell if it's a lighting issue and there's dielectric grease, or if there's corrosion in those connectors. If there's any corrosion, that can definitely cause a problem.

As far as the coils, you might be able to take a meter to them and see if any differ noticeably as far as internal resistance. They should all be about the same. That's not a definitive test, as coils can fail under load but appear fine otherwise, but it's a low cost check you can do.

Check for any rubs or abrasions on the wires. Anything that changes the overall insulation on a high voltage wire can allow for leakage. Such things can cause voltage leaks in high moisture conditions as well, and doesn't actually need to be that bad a wear spot.

I'm not sure about OBDFusion as far as real time misfires. I know it can be done in Torque Pro, so most likely there *is* a way to see it in OBDFusion, I just don't have that loaded anywhere.

Cheers-

Chris

 

[Mooseman]

They look worn to me. The center electrode is usually longer and the gap looks pretty large. They might be original.

 

[TollKeeper]

Im glad I was able to get the brakes pumped before we went to far down that starter rabbit hole!

Those wires look nasty. If the wires are like that, you might as well replace the spark plugs.

Caution.. Spark plug hole #1, #4, #6, and #7 can be a pain to replace. #8 is easy to replace if you go thru the wheel well (tire off, lift flap up, easy access). I also go thru the wheel well for #4 and #6 if I can.

 

[Redbeard]

Just as a note, do not try to gap Irridium plugs. In days of old all plugs needed to be set even when new. Do not do this with irridium plugs. And stick with the A/C plugs only. Be carefull not to purchase what seems "to cheap to be true" on these plugs because in recent years there have been many fake irridium plugs from places like Amazon and ebay, so be careful what you purchase.
just my 2¢

 

[TollKeeper]

I agree with what @Redbeard about the plugs.. I was a victim of the Amazon ACDelco Plug scam.

 

[l008com]

Update: No change!

That is, everything has been running great. We have had very low humidity in the last week or so. But no misfire engine light, zero misfires shown on my app. It's been running great.

So my question is, should I replace the plugs and wires anyway?

To put it another way, what other benefits are there to replacing the plugs BESIDES fixing a misfire problem? Could it potentially make the engine more responsive? A little more peppy?

 

[christo829]

What was the gap on those old plugs? Note that I'm not suggesting adjusting, just checking. If those are out of spec, you can expect the others to be as well. In that case, you're not getting the hottest spark from the plugs, so even if they're not misfiring, they can be performing worse and eventually might *start* misfiring.

And any wire wear or chafe can cause voltage leakage. On my old Toronado, one night just for the heck of it I turned off all the lights in the garage while it was running, and there were small sparks and coronas in a number of places...with wires that weren't that old and *appeared* fairly good. Not going to comment on the overall quality of those wires, mind you. I was in high school, and got what my budget could afford...

Anything that saps power from the spark means you're not getting the best ignition of the fuel/air mixture, so it can not only rob power, but also start clogging up your cat if it's not burning off the fuel well enough.

Cheers-

Chris

 

[Mooseman]

To be absolutely sure, try misting some water from a spray bottle onto the ignition system while it's running. Try the coils first, then the wires and plugs.

 

[RiverGuy]

Update: No change!

That is, everything has been running great. We have had very low humidity in the last week or so. But no misfire engine light, zero misfires shown on my app. It's been running great.

So my question is, should I replace the plugs and wires anyway?

To put it another way, what other benefits are there to replacing the plugs BESIDES fixing a misfire problem? Could it potentially make the engine more responsive? A little more peppy?

So...after having nearly identical problems to yours in the last 5 years with three low-mileage oldsters (2008 Pontiac G6 GT, 2003 Olds Aurora and my 2004 Olds Bravada) -- in all three cases it was changing the PLUG WIRES that finally fixed it! In all three cases, the original plug wires became problematic at around 12 years of age, even though the mileages on all three vehicles were very low. My theory is that the plasticizer compounds in the rubber/silicone insulation dry out or 'outgas' over time, and the dried-out wires can then soak up moisture out of the air...then the 'wet' plug wires begin to dissipate voltage along their length. This is similar to the losses you can hear as a 'sizzling' sound on high-tension power lines on very humid days.
-==-
In the case of the Pontiac (my most recent example) it was the one plug wire that was running right up against a very hot alternator that caused only ONE cylinder to miss intermittently -- and YES, it did seem it was weather/humidity related!
-==-
Nowadays, I >>start<< by changing plug wires. Old wires are far more likely to cause a problem than plugs that look ok and are gapped right.

 

[l008com]

This problem has not come back. We've had plenty of muggy and rainy days, but the engine has always run fine. I've used the ODB sensor to try to quantify the misfires but it always records 0 across the board. Not sure if that really means zero, or if the app isn't actually configured properly. It's so hard to tell with that thing.

But anyway, despite that, I just ordered new plugs and wires anyway. They're not that cheap and AC Delco has a lot of rebates. Maybe I'll see some improvement, and that will be nice. And if not, at least I won't have to do them again any time soon.

 

[Chickenhawk]

This problem has not come back. We've had plenty of muggy and rainy days, but the engine has always run fine. I've used the ODB sensor to try to quantify the misfires but it always records 0 across the board. Not sure if that really means zero, or if the app isn't actually configured properly. It's so hard to tell with that thing.

But anyway, despite that, I just ordered new plugs and wires anyway. They're not that cheap and AC Delco has a lot of rebates. Maybe I'll see some improvement, and that will be nice. And if not, at least I won't have to do them again any time soon.

Before you change the wires, I would suggest you follow Mooseman's advice and get a spray bottle with water. Do this with all the interior lights off in a VERY dark garage or the darkest location you can find. Spray each wire and coil area. It is shocking how many misfires will suddenly appear.

 

[l008com]

I did mist the engine with the hose at one point to see if it would misfire and I didn't hear any misfires, and my app didn't show any misfires. Although it's possible they were just subtle and the app isn't actually counting them :-/ I don't have a garage though so I can't really do it in the dark to see what happens there.

 

[l008com]

Mission Accomplished.
It took me all day and I'm pretty sure I'm sunburned, but I got all 8 done. I have no garage nor any trees that cast shade on my driveway. It was hot as balls out today and was overall pretty brutal. But one by one I got them all done.

First, the results:
I can definitely feel a difference. Its seems to rev up from idle faster. And when I'm hard on the gas, it seems to apply power more sharply, without any lag. But most noticeably, when you're in a high load situation, like driving up a steep hill without giving it much gas, a situation that might bog down the engine, it muscles up without any hesitation. I'm very interested to see how it feels after I drive it some more. At first I wondered if it was just all in my head that it was driving better. But after the hill climb, I'm pretty sure it's legit.
Also my engine light went out. That could entirely be a coincidence, it does go off periodically then come back on. But could plug issues be cause my P1174 engine code for something about air fuel mix I think it was? Seems plausible, and that would be a nice bonus. Also I imagine the fuel economy must be getting some kind of a small boost if I'm combusting more efficiently? Nothing I'll see until I stop mashing on the gas at every green light. Eventually that gets old, even with a 5.3

Next, the old stuff:
I took some pics of the old stuff before I tossed it. The wires look... like wires.


The plugs on the other hand, were more interesting. The gap is WAYYYY off on one of the 8 plugs. It's so bad, I thought no way I was driving with that, I must have dropped it while removing and that bent the top of the plug. So I did a test drop of another old one and it didn't move at all. This was definitely like this. And there was no impact indications on the top of the plug, like the piston or something had smacked it. Of course if that had happened, I assume that would also mean the engine was dead. But it wasn't, it was running perfectly fine, just without the throttle response of a brand new engine.



Pretty strange, what do you make of this? I do NOT think this plug came from #5, where I had the misfire and misfire code earlier this summer. It is not in contact, there is a gap there. Just not much of one.

 

[l008com]

Engine light came back on, so the new plugs didn't fix that problem after all. Wishfull thinking I guess. Still its driving great. I didn't realize how much hesitation and un-smooth-ness the engine had until it went away. I went with double platinum plugs which should easily last for the rest of the life of this truck.

 

[christo829]

Ah, that's too bad! I'm assuming it's the same code?

 

[l008com]

Yup same code. I don't remember it offhand and I can't look it up right now. But I think it was something air/fuel related.

Edit: I have a separate post about that issue: https://gmtnation.com/forums/threads/from-o2-sensor-code-right-to-a-new-code-p1174.23421/

Also I towed my 1900 LB boat today, in city traffic, with my new plugs. Accelerations are so smooooooooooooth. I'm basically re-falling in love with my V8.

 

[l008com]

Hey yall. Its been about a year and a half. The truck ran great for a long time, but its starting to feel weak and underpowered again. It snot underpowered if I gun it. Far from it. But its underpowered during normal, light throttle driving.

Anyway, I'm reviving this thread because its the same question over again.

How long do plugs last? How long to plug wires last? Plugs are pretty cheap so I'm thinking I'll replace them all again next month when its warmer out and see if that makes a big difference. But this time I'm thinking one year old wires are probably good enough to keep.

It looks like the plugs I installed in September 2023 were AC Delco Double Platinum, supposed to last "3x as long".

Also note, there are no misfire codes currently, or any misfiring I can feel. But it felt underpowered like this for a long time before it actually started misfiring before. I'd rather spend $40 and get my power back even if they only last a year.

 

[Mooseman]

Unless the plugs are actually worn or fouled and there is no misfiring, I would look elsewhere. Spark is spark. If there is no misfiring, it's firing.

You have to remember the four cycles of the engine: suck, squeeze, bang, blow

Suck: The engine's ability to suck in air and fuel. Restriction or lack of from either will affect performance

Squeeze: Its ability to compress the air/fuel mix. If compression is low, so will be power

Bang: Its ability to ignite the mixture. No spark, no bang

Blow: Its ability to push out the exhaust gasses. If there is a restriction, it will use some of that power to push exhaust

Since spark is good, I'd first look at compression, which would give a chance to check the spark plugs at the same time Then look towards the intake. Check/clean the MAF and MAP sensors and the air filter. Then look for an exhaust restriction. A back pressure test would be in order.

Speaking about spark plugs, on the 4.2L, we all know that it's very sensitive to the plugs that are used and we use only ACDelco Iridium 41-103. LS engines are not as sensitive however it's never a bad bet to just use Iridium 41-162 plugs. ACDelco warranties them for 7 years. Just be sure they are genuine as even I got caught with fakes.