misfire question and torque app driving me crazy

[Stayathomedad]

I have an 05 ext. with a misfire I keep chasing and am not sure if I should just let it go. Started with a misfire on #2, light would come on then off shortly after on it's own. Changed new and correct plugs, it was fine for a file then same thing. Light would come on then off, no flashing and would come on normally when sitting at ideal. Then it changed to random misfires. Moved plug and coil, still random then #2. Tighten intact bolts, which were not tight and I've read is a common problem. Cleaned throttle body, wasn't bad but still did, added fuel inject cleaner. I'm still getting a code set but the light isn't coming on all the time. Could this be something more internal be going on? Is it time to say good by? All other maintence is up to day it has 110k. Should I not check until the light comes on and not worry about it or what?
I have the full version of the torque, which is what I'm using to read and clear codes. Does anyone know if there is a way to see cylinder firing info?
any ideas would be great, really starting to mess with my mind

 

[The_Roadie]

I'd check the other threads we have about random misfires. You might consider slapping in a new CPAS on speculation, then a Seafoam treatment if you believe in that (I do, but it's not universal), and then check cylinder compression for reassurance you don't have sticky valves.

 

[Stayathomedad]

cpas replaced about a year or so ago. I hate to just throw parts at it without confirming the problem. A compression test was what I was thinking but I'm afraid of the possible results.

 

[The_Roadie]

I hate colonoscopies, too. Necessary evil.

 

[AtlWrk]

To answer the other part of your question: Not sure how familiar you are with Torque but it does have current and historical misfire count PIDs for each cylinder. I set up a seperate page with a small digital display for each of the 12 PIDs (6 current misfire counts + 6 historical misfire counts):
View attachment 32828

It's a little tedious setting up twelve displays but you only have to do it once and now you can monitor for misfires in real time

 

[Stayathomedad]

That's awesome, can you please walk me through or give me directions on how and where to set this up. I just got torque 2 weeks ago and am still trying to find everything it can do.
Thanks

 

[AtlWrk]

It's not really anything more involved than setting up a new display in the "Realtime Information" section of Torque.
I'm not trying to be dismissive but Google and YouTube searches for using Torque will probably be more fruitful than anything I could type out for you here.

You may have to load the GM extended PID list (again, Google is your friend) to get the misfire PIDs (but you should load these anyway if you haven't already...lots of goodies)

 

[IllogicTC]

What do you mean tightening "intact" bolts? Are some missing? I'd say it's necessary to have every single bold on there tightened to the proper torque. If you have to remove some bad ones or replace missing ones, it's going to cost you for a set of bolts but it'd give peace of mind.

 

[Stayathomedad]

Stupid spell check, intake bolts. They are all there they just work themselves loose causing extra air in resulting in a random misfire code. It's a common 4.2 problem.
Thanks so much for the torque app info. I have it set up, now just drive with it. This is really a cool app that does alot of things that a normal scanner can't do

 

[IllogicTC]

Stupid spell check, intake bolts. They are all there they just work themselves loose causing extra air in resulting in a random misfire code. It's a common 4.2 problem.
Thanks so much for the torque app info. I have it set up, now just drive with it. This is really a cool app that does alot of things that a normal scanner can't do

Oh, you can get a scanner that'll do that stuff. For at least 10x the price, minimum.

Well at least all the bolts are there after all. I'm not sure if any sort of application is done to the threads, like threadlocker or anti-seize. I can try looking it up, if such a thing existed it may be worth doing a fresh application.

 

[AtlWrk]

I have it set up, now just drive with it.

Remember: eyes on the road

Fortunately the intake bolts are captive in the manifold. I had several that were loose and 2 that backed out comepletely. Unfortunately that also means it may be difficult to get any sort of thread locker on the threads without removing the entire manifold. I didn't realize a leaking intake would cause misfires though?

 

[Stayathomedad]

Misfire update.
After driving it around watching the misfire monitors, I found that #2 only misfires at idle, not while driving. It never turns the light on. Now I'm leaning towards some kind of vaccum leak. any ideas

 

[IllogicTC]

Misfire update.
After driving it around watching the misfire monitors, I found that #2 only misfires at idle, not while driving. It never turns the light on. Now I'm leaning towards some kind of vaccum leak. any ideas

I can't think of any off-hand, unless somehow the resonator vacuum is loose but I wouldn't think that'd get quite so specific with a particular cylinder. As long as it's tight, the one into the intake manifold's tight, and the nipple on the front top of the intake manifold is intact, vacuum should be okay.

I would question:
1.) Coil wiring. There may be some sort of intermittent fail condition, though it should be expected to fail at all RPM ranges, not just at idle.
2.) Fuel Injector. The injector may be going bad in some fashion.
3.) Fuel rail contamination. 2005-2009 have a non-serviceable fuel filter located in the fuel tank. Funny enough, there's also a TSB out on just these years about how thanks to the non-return fuel system setup (and I suspect the different filter, too) sediment can accrue over time in the fuel rail. This is most easily identified by misfires on cylinder #6 during quick acceleration and #1 during quick stops, as that would shift the sediment toward one end of the rail or the other.

 

[Hypnotoad]

Typically, if it's a bad plug, injector or coil it's going to misfire all the time. Not just at idle.

Sounds like carbon build up possibly. A leaky valve maybe.

 

[IllogicTC]

Typically, if it's a bad plug, injector or coil it's going to misfire all the time. Not just at idle.

Sounds like carbon build up possibly. A leaky valve maybe.

There's a TSB on this issue (misfire/rough idle) for 2005-2009 that suggests doing a leakdown or compression test. Can't remember which one. Mentions a sticky intake valve as one potential issue, specifically. Carbon buildup can of course be another issue just like you said.

I find it funny that it gives intake valve as a potential problem, there's another TSB about sediment in the fuel rail in 05-09, and 05 was the first year they removed the inline fuel filter and made the "non-serviceable" one in the tank instead. Sounds like they really messed up on that one.

 

[Stayathomedad]

Update
Bad news, cylinder2 compression 37 psi below others. I guess I have to start looking for another truck. sad.
Thanks for all of the advice and help.

 

[nodogs027]

I had similar problem a few years ago. Turned out one of the spark plug rings (or something like that ) had rusted and caused it to miss and eventually quit running. If I remember right, it was some sort of defect from manufacture that lets water seep down where it shouldn't. I'll try to find paper work of repair & let you know exactly what it was. Just a thought.

 

[hooverrwh]

Hey guys, I'v got a 2003 Gmc Envoy with random misfires and it not throwing any codes at all. Lately it started slight vibration in park. Sounds like a slight change in the sound of the engine when excellerating. Acts and feels like old days vac leak. wanted to replace intake gaskets but have no idea on how to get to them. Any ideas on it?? I've changed plugs, fuel filter, checked fuel pressure(at 54 psi) cleaned TB. So....how in the world do you get to the intake bolts......lol. Thanks, ray

 

[joeredspecial]

I'll bump this thread because it's recent and I'm having the exact same problem on my 02 SWB

Friday night I got a blinking CEL, rough idle, and a bad exhaust sound (an obvious misfire). When I go to my destination (I did drive with it blinking for ~5 miles) I used my OBDII bluetooth reader and Torque app to read the code, P0300. On the way home the CEL turned solid right away and the problem went away by the time I got to my house. I pulled the code and it changed to a misfire on cylinder 2. Cleared it, and put Techron in on Saturday. No problems at all, everything was back to normal until tonight. Started it up and I had a rough idle but no code so I let it run and got a misfire on #2.

I'll be swapping plugs/coils tomorrow to try and isolate the cause, I might even be able to use a Tech II. I really am hoping it's only a bad plug/injector/coil.

 

[The_Roadie]

So....how in the world do you get to the intake bolts......lol. Thanks, ray

Sorry I missed your post for a while. I removed my inner fender liner a while ago for offroading, and just go in through the wheel well. Straight shot from there. Otherwise you need a collection of extensions, a manual that gives you a hint where they are, and a little mirror might help to locate them.

 

[joeredspecial]

Well I've pinpointed my problem, it's ignition coil #2. Ordered a new one, should be able to replace it by the weekend.

How will I tell if I've damaged my cat? Will I get codes from the O2 sensors and such?

 

[BRomanJr]

Well I've pinpointed my problem, it's ignition coil #2. Ordered a new one, should be able to replace it by the weekend.

How will I tell if I've damaged my cat? Will I get codes from the O2 sensors and such?

O2 sensors usually won't code until they are dead, they can cause driveabilty and economy issues long before that. Most upstream sensors should be changed (use OEM or NGK only) every 100k. Downstream sensors last much longer, usually can wait until these set a code.

Damaged cats will either be restricted (loss of power), plugged (almost no power) or ineffective but still flow (Should set a code).

 

[joeredspecial]

O2 sensors usually won't code until they are dead, they can cause driveabilty and economy issues long before that. Most upstream sensors should be changed (use OEM or NGK only) every 100k. Downstream sensors last much longer, usually can wait until these set a code.

Damaged cats will either be restricted (loss of power), plugged (almost no power) or ineffective but still flow (Should set a code).

Ok thanks, I figured I'd sense the loss of power before anything. I doubt I did any damage, but I'll see after I change that coil.