Miss-fire on Cylinder 5

[l008com]

This just happened today for the first time. I started up my truck and while I was getting my phone settled, it started running rough. Then the engine light started flashing, but never stayed on. You could feel something was wrong. I opened up the code reader app and there was a misfire on cylinder 5.

It has been raining heavily all day but I haven't gone out at all, so it's not like water got up into anything. Except maybe just humidity. Or it could be unrelated. Suddenly bad spark plug(s)?

To be honest, this kind of engine centric diagnosing and repair is way behind anything I've done. But now that I'm poor, I have to at least give it a try myself. Plus my mechanic is on vacation until next month!

 

[Blckshdw]

Few things you can do. Pull the plug, and it's neighbor and compare how they look. Does #5 look fouled or sooty? If it looks fine, swap the plugs, clear the code and then run the engine. See if the misfire comes back on 5, or moves and follows where you put that plug. If it does move, then bad plug to replace. If the misfire stays, maybe bad plug wire? A swap of the wires could confirm if the misfire moves along with that.

 

[l008com]

Ok some followup info.....

As mentioned, its been pouring all day and it is SUPER humid out. I made this post after starting it up and driving about 1.5 miles. It was idling rough, driving rough, and when I got out, the exhaust did smell unusually bad. I didn't hear any unusual ticks or anything. Just the same old valve noise I've always had.

BUT THEN after making that post, I drove home the long way. And once everything warmed up, the problem went away. It seemed to idle just fine after that. I cleared the codes and it never came back. I got some gas, mailed a package, went the long way home and everything was great.

Maybe it was just the moisture? If so, does that still indicate some kind of problem that needs to be fixed? You should be able to drive a car on humid days after all!

Another thing I noticed when the misfire was happening is that when I'd hit the gas from a stop, it would hesitate a bit before it went. I've felt this before! Sometimes it would act like that and I've always felt it feels kind of like a loose motor mount, where you get a little bit of go, the motor shifts, then you get the normal amount of go. But it never happened a lot and it was never bad enough for me to look in to. NOW I'm thinking that was the same problem as this, which is my engine not running great when it's wet or very humid out.

Note: The humidity is 95% right now and my arms are more or less stuck to my desk as I type this message.

I'm feeling pretty good right now though because after starting this thread, I read some other similar misfire posts and they were all talking about major repairs due to stuck lifters etc.

 

[l008com]

Also regarding fouled plugs, do you have some sample images of good, so-so, and bad spark plugs? I ask because I've been "checking the plugs" on small engines for decades and they always look the same to me! I usually just end up replacing them every few years because they are cheap and easy to do. One plug per small engine. Except my boat which as 3. But I really don't know what a fouled vs good plug looks like. Just one time, I did replace a plug and it did fix a motor that was running rough. I forget which motor it was though. Not a car, a small engine in some power tool or toy.

 

[Blckshdw]

If plugs are something you check regularly, then I think you'd notice if you saw a bad one. Since the issue went away after the engine got up to temp, I'd say it's likely that water got somewhere it shouldn't, and evaporated off.

I know with the I6s, we have the issue of sometimes the hood seal leaking above the engine and water dripping on the coil pack, sometimes getting into the cylinder and causing some misfires. Not sure if something similar can happen with the V8s, but it may be something to look into, cuz you're right, a heavy rain and/or humidity shouldn't cause you problems.

 

[Mooseman]

I'd be suspecting either a bad wire or coil with moisture affecting it. Move the #5 coil to 3 and the wire to 7 and see if it happens again and which cylinder. Also check that the wires are all tight on the coils and plugs. I had one loose on the plug once causing an occasional misfire.

 

[TollKeeper]

Since this happened while it was raining... Maybe some "heat" fuel additive in the gas tank. Also check your gas cap seal.

 

[TJBaker57]

Then the engine light started flashing, but never stayed on

Since no one else mentioned this,,,, and it is a good thing to know,,,, a flashing check engine light is a worse condition than a solid check engine light.

 

[l008com]

I'd be suspecting either a bad wire or coil with moisture affecting it. Move the #5 coil to 3 and the wire to 7 and see if it happens again and which cylinder. Also check that the wires are all tight on the coils and plugs. I had one loose on the plug once causing an occasional misfire.

The prooooblem with doing this, is that it has gone away. And it's not like it's something that happens every time it rains. I think it may have happened before but I'm not sure. And i certainly don't remember it every flashing my engine light before.

 

[Mooseman]

You can still do it and make a note of which part went to which cylinder so next time it happens, you will know which part is failing. You could also mist some water onto the engine while it's running and see if it happens.

 

[l008com]

Another update:

I did some errands today and there were no missfires you could feel, no rough idle, no misfire engine codes. The other P1174 engine code did happen to come back though.

But a new symptom, my truck seems to be REALLY underpowered. With the AC on, it was struggling to move up hills. I had to put it into 3rd gear to get on the highway.

This from the V8 that used to have so much power, I would pass cars in the left lane going up steep hills on the interstate, WITH my boat in tow.

So I'm wondering if all or at least most of my problems might be a simple matter of bad plugs? I've had this truck for about 40,000 miles now and I don't think I've ever had the plugs replaced. And who knows when the previous owners did.

Could that explain all of this? Or at least all of is sans the P1174 engine code.

 

[Chickenhawk]

I would put money on a plugged cat, especially if that misfire went undetected for a while.

 

[l008com]

How would you diagnose a plugged cat?

Also I did mist my engine while idling today, nothing happened.

I would expect a plugged cat to affect revving but not so much idle, since minimal air is trying to pass through at idle? Based on zero experience with the matter, just me sitting here thinking about it.

 

[Mooseman]

Remove the two upstream O2 sensors and see if the power improves.

 

[6716]

The prooooblem with doing this, is that it has gone away. And it's not like it's something that happens every time it rains. I think it may have happened before but I'm not sure. And i certainly don't remember it every flashing my engine light before.

The root of the problem is likely ignition. I had a VW Jetta that exhibited similar initial behavior, when it rained it ran like shit on startup until it warmed up. Once warm or on a clear day it ran great. That vehicle had one central coil unit that sent power down the plug wires. The coil unit was cracked, and the wire connection at the coil to the #1 chamber was heavily corroded. That vehicle had 50,000 miles on it at the time. It took me a minute to figure it out because it was intermittent.

I've also replaced coils on my Trailblazer, coils are not forever parts. You might also have more things wrong, but I bet there's a pretty good chance that you could stand new plugs and coils, and maybe the new cat. The cat gets wonky as a result of poor ignition.

At the very least, something tells me you will learn something if you dig in and pull a couple of coils and plugs and look at them, especially #5, especially since the maintenance history here is unknown.

 

[budwich]

look at your fuel trims at idle and at constant medium throttle. That may suggest things happening in the fueling / air controls. Go from there.

 

[l008com]

look at your fuel trims

I don't know what this means, or how to do this

 

[budwich]

I don't know what this means, or how to do this

how are you getting your misfire information / counts?

 

[Mooseman]

Do you have a scanner capable of live data, beyond a basic code scanner? Without this, you're basically just taking pot shots in the air.

 

[budwich]

Since no one else mentioned this,,,, and it is a good thing to know,,,, a flashing check engine light is a worse condition than a solid check engine light.

Actually, now that the OP has asked the question about "how to get fuel trims"... this comment about the "flashing light" is very appropriate. I suspect that the OP does not actually know how bad the misfires are and where. I suspect he is just getting the code for a misfire for a specific cylinder. BUT this code is set when a significant number of misfires happens in a window of time. IF you don't get that limit, then no code is set BUT you can still have misfires (less than the limit). Further, the "flashing check light" ALSO has a similar "filter" for when to "flash"... IF that limit is not reached, the flashing does not happen but again, that does not mean there is no misfires. Further, the "flashing check light" may not have set any code for the OP to read on by just a code reader. Thus, it is possible that the problem is "bigger".... as tjbaker57 suggests.

 

[l008com]

I've been getting codes via the ODBFusion app and the bluetooth plugin dongle.
There's a million different things you can look up but things aren't organized or categorized very well in that app so its kind of a pain setting up new scanners unless you're very specific.

Also the misfire thing kind of makes sense since I do feel like there is a bit of hesitation from idle sometimes. Its very subtle though, I only realized it after the not subtle misfire incident the other day.

As of right now, my plan is to pull out a few easy to access plugs when I get a chance and see what they look like. And maybe check out the wires too. Plugs and wires are pretty cheap if thats the whole problem. AC Delco plugs are currently on sale too.

If you know what the specific displays are called in odbfusion for fuel trims, I can set that up and report back whatever it finds.

Unfortunately I have to drive a long trip Wednseday for work so I'm going to cross my fingers and hope for the best because theres no way ill have time to even pull plugs before I go.

 

[Chickenhawk]

Actually, now that the OP has asked the question about "how to get fuel trims"... this comment about the "flashing light" is very appropriate. I suspect that the OP does not actually know how bad the misfires are and where. I suspect he is just getting the code for a misfire for a specific cylinder. BUT this code is set when a significant number of misfires happens in a window of time. IF you don't get that limit, then no code is set BUT you can still have misfires (less than the limit). Further, the "flashing check light" ALSO has a similar "filter" for when to "flash"... IF that limit is not reached, the flashing does not happen but again, that does not mean there is no misfires. Further, the "flashing check light" may not have set any code for the OP to read on by just a code reader. Thus, it is possible that the problem is "bigger".... as tjbaker57 suggests.

This is 100% correct. Catalytic converters run on very narrow stoichiometric ratios, and slight misfires not yet reaching the threshold of a flashing check engine light can still plug a cat within a few months. Misfires that set off a flashing engine light can plug a cat within MINUTES.

The very first symptom of a plugged cat is loss of engine power at highway speeds, especially when accelerating or climbing hills.

Step one is solve the misfires. Plugs, wires and coils do not last forever.

Step two is test the cat. My guess is that step three in this case is to then replace the cat.

 

[l008com]

Ok I just took two easy to access plugs out to check their condition. cyl 3 and 5 I believe. I took pics of everything and then I put it back together.

Now when I turn the key, nothing happens. It doesn't try to start, no clicking or anything. Just nada.

All I did was pop two cables, to plugs, then put everything back together. Any thoughts on this?

 

[Mooseman]

Check the fuses. One that supplies the coils also supplies the PCM.

 

[l008com]

I checked every fuse in the panel, they all looked good. I'll recheck again tomorrow. I had to abandon my truck at my "other house" for the night.

Kind of an odd coincidence that the PCM fuse would blow right when I was taking out the plugs to check them, no?

Am I right in assuming that even if i messed up the plug reinstall, like even if the plugs weren't in at all, the engine should still crank, wildly unsuccessfully, shouldn't it? But I did put them in right so beats me.

Heres a pic of everything back together with arrows pointing to the two plugs I removed. All I did was pop em out and pop em back in after taking pics of them (which i'll post once I get the vehicle starting again).

 

[Mooseman]

IIRC, that's the main harness that goes to the PCM. Check it out. See if you can communicate with the PCM and check for codes.

 

[l008com]

No codes. Well, old codes but no new codes, no codes related to the no start.
Also there there are a lot of wires in that picture, which are you suggesting I check?

Also I tried starting in neutral today, no luck. And I swapped the PCM fuse, still no luck.

Friday I'm going to get into it a little more.

 

[Mooseman]

The arrow on the left. I suggest you basically do the normal checks for a no crank condition. Maybe just a coincidence that the ignition switch decided to quit? Would be worth it to check its output.

No Crank, Like Attempting To Start In Drive

 

[TollKeeper]

Lets back up a bit here..

Come on guys, basic diagnostics.

Lets verify that its not just a coincidence. Maybe the starter just happened to fail.

First start by jumping the starter relay.

If it doesnt turn over, I would have you jump the starter at the starter... But on the V8 models, thats a big of a problem. But you need to verify that the start signal is making it to the starter.

 

[Mooseman]

We should put together a flowchart for these or pull the one from the manual.

 

[l008com]

Flowchart would be excellent, although a newb like me would still probably have lots of questions for each step.

Moving on, i DID jump the starter relay and what I got was NO cranking, but a definite subtle click each time. It's possible it was doing the click when I turned the key and I just can't hear it from inside the cabin. It's a lot quieter than the normal CLICK CLICK CLICK you get from starting on a too-weak battery.

Another friend at this point suggested making sure the main power wire is not rotted or loose. And I could jump the starter itself. But all that leads to one very important question. Where is my starter?

 

[TollKeeper]

The starters on these are quite a pain in the ass to replace..

If you have a 2wd.,.

@Mooseman will be jealous.. a rust free GMT360!

 

[Mooseman]

Check your battery connections and the battery... just in case.

 

[l008com]

Check your battery connections and the battery... just in case.

I did, everything looks good. I removed them and reattached them anyway. Still nothing.

 

[Mooseman]

What about the main battery to block cable? And the battery to starter cable? Eliminate the obvious before condemning the starter. It is a bitch to get it out but it can be done. I have on the Saab. Lots of twisting and turning. Also try hitting the starter with a hammer or a long screwdriver and hammer while someone is trying to crank it. It might make it work a couple of more times but plan to replace it ASAP.

 

[TollKeeper]

Now when I turn the key, nothing happens. It doesn't try to start, no clicking or anything. Just nada.

So lets back this up a bit further, and it ties into what @Mooseman said

When you say no start, no clicking, nada.. Explain exactly what you mean..

No dash lights?
No power windows?
No power door locks?
No windshield wipers? Front and rear?
No Gear Shift Indicator?
No HVAC actuation?
No Power Seats?

Or

Everything works just fine, just no starter engagement?

 

[budwich]

dead battery

 

[Mooseman]

I did, everything looks good. I removed them and reattached them anyway. Still nothing.

And the battery?

 

[l008com]

Battery is new and fully charged. This condition started after hours of problem free driving. Everything electrical works. But when you turn the key to crank, all the dash lights turn off, but no cranking happens. No dead battery clicking either.

 

[Mooseman]

Then go to the thread I linked in post #28 and follow the recommendations there. Lots of troubleshooting steps in it including a video on what signals to look for.