4.2 misfires , no codes...

KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
engine started stumbling about 3 weeks ago and has gotten worse, I has a whining pulley so I thought it was the belt slipping. I changed the idler pully , and it was better for a few days then started again , my compressor bearing is going also now that I can hear it with the idler replaced , but its definitely a misfire with the stumbling.

I have no codes at all , my tb was cleaned a few months ago to help with the engine stalling with the a/c on , I put in a 16 oz can of seafoam through the brake booster line , let it sit a half hour and started it up it smoked for about 10 minutes. all was good till yesterday when it was 12 degrees here in nyc , now its back worse than ever

I have a 2nd can of seafoam , I was gonna drop it in the tank when I filled up , but am I wasting time using it on cleaning the manifold again ?

this truck is more headache then reliable to me at this point , after I fix one thing two more seem to pop up. maintenance I get I feel like im rebuilding the truck one part at a time here.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I don't know if it would cause a stumble but low power and increased fuel consumption could be the cat getting plugged, which may have been caused by gunk getting sent into it by the Seafoam.

When you say "stumble", do you mean an off-idle stumble? Like when you just touch the gas after it has been idling for a while, it has a slight stumble? My '02 had that and was never able to figure it out.

I'd try and figure out the noise. If it's creating a drag on the engine at idle, it might be compensating in some way and creating this stumble. Take the belt off and run the engine a little to ensure it is something driven by the belt. See if it still has this stumble.
 

KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
stumble as in misfire... either at idle in park or under acceleration it was doing it before the seafoam, after the treatment it was gone 100% , now just yesterday came back.
the noise is the a/c pulley bearing. it goes away when the compressor turns on , seemed completely odd to me but there was a few posts I found on trailvoy and a fix , just need time to get under the truck there are different bearing sizes apparently.

if the cat is clogged im done with the truck , I need a caifornia emssions one and no one makes it aftermarket. I don't know what the difference between a cali cat system is and a regular cat that I can let anywhere online.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
You would need a backpressure test to confirm a clogged cat.

If it was an actual misfire, it would throw a code or at least register them as historical. Do you have access to an OBD scanner that can give live data? Might be worth it.to check.actual.misfire data.
 

mrrsm

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Oct 22, 2015
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The intermittent nature of the Misfires coupled with the serious drop in Ambient Temperature makes me think that the Fasteners holding the Intake Manifold to the Engine Head are either Loose...or the (3) Figure 8 "O" Rings sealing the Flange Line have flattened out over time if your Engine has High Mileage in evidence. The material contractions caused by Colder Temperatures will break their solid seal along the Flange. As the engine runs and vibrates... with the weight of the Throttle Body on One Side of the IM Runners...and the opposing weight of the PCM ...the IM can rock enough back and forth to allow the intermittent ingestion of air into the different cylinders.

Please remember that if you have to snug them up NOT to exceed 87 INCH Pounds. The One Fastener near the Center of the Intake Manifold on the Top ...is obscured and hidden behind the Short Black Rubber Elbow Hose connecting between the IM and the Engine Head that is also difficult to get off without damaging it.

In order for the PCM to trigger any expected P03XX Codes... there have to be at least 30 Events that pass the threshold of its programmed tolerance level within a certain Time Frame before you get one to show up as a Code. At the very least, try to tighten up any of them that are the easiest to access. There have been some historical Threads in which the OPS have complained "They were SO LOOSE... I could move them with my Fingers!". So it might be worth the time and effort to investigate this idea.

You should be aware that the last Fastener on the IM Flange closest to the Firewall is OHPITA (One HUGE Pain In The....) to access and will require a combination of a 3/8" Wobble Extension, a 3/8" "U"Joint Adapter and a Socket...with the need to put some Clear Plastic Tape at their connection points to ensure that they do not separate and fall down into the lower regions of the Vehicle while you tighten down that last Trapped Fastener.
 
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KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
ill have to see about where I can do a test

I thought it would throw a code also , but nothing.. google searches say others have had the same issues with no stored code which perplexes me.

I have an innova 3160g and it doesn't give detailed data on everything , basically coolant temp , and o2 sensors , I think map sensor unless im doing something wrong... my old auto xray did , I could monitor each cylinder , throttle position , etc
 

mrrsm

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Oct 22, 2015
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...See what I mean...? ;>)
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
It won't throw a code for misfires unless you reach a particular threshold. I had been dealing with an actual slight misfire issue at idle only and would only trigger a code/CEL after a certain number has been reached.

I would recommend a cheap Bluetooth OBD adapter and the Torque app for Android for reading live data. If there are actual misfires, you'll see them even if they don't trigger a code.
 
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KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
P0302 popped up this morning finally. I checked the manifold and all seems in order , I sprayed starter fluid and there doesn't seem to be any leak.

now that I have a code it isn't missing as bad , ambient temp also went up a lot today to around 30 so I don't know if it was the bitter cold and a vacuum leak or what

ill be changing all the coils and plugs , I doubt they've ever been changed and a set of coils for $80 on amazon with 200+ 4 star reviews ill take the chance

imm gonna play with this scanner more... @ $300 it better do what my old did and show everything , otherwise its going back
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Which scanner are you trying?
 

KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
no heres a kicker that baffles me..... code on yesterday , still knocking of course , I was below a 1/4 tank so I stopped and put 20 gallons in and the seafoam , drove another 30-40 minutes home ( less than 10 miles , welcome to nyc rush hour ) , my daughter to the truck to run to the store and home , this morning its around 45-50 degrees out , I remote start the car , I get in and the light is off !!

I know the light will go off when the computer sees the problem is gone , but I still have a slight misfire , only feel 1-2 at most coming to a stop or taking off from a light.

I haven't pulled a plug yet , so oil and /or carbon contamination is not known , I ordered a new set of delco plugs being its just over 100k and don't know if they were ever done , but I am stumped on this one
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
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gmcman

Member
Dec 12, 2011
4,656
I would put a vacuum gauge on the hose going into the throttle body, is the needle rock steady? By steady, I mean not shaking but can wander slightly.

Get a can of BG44K and use it at your next fill up. Use it alone, no other chemicals.

Make sure the large black hose under the intake resonator is attached.

What is the alternator output at idle? Use a separate gauge.
 

KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
I don't have a vacuum gauge just yet unfortunately , the plugs were changed and 6 aftermarket coils installed. was good for a week or so and now had P0300 come back on this morning. the rpm needle surges up and down during each misfire , the harder the miss I feel the higher the jump
@gmcman

alt output is 13.4 volts
 

gmcman

Member
Dec 12, 2011
4,656
Not doubting you, but how did you verify alternator output...OBD, DMM?

I will need to verify, but I believe min VDC is 13.8.

With the engine idling, check voltage again then turn on low beams, then add high beams, then add rear defrost, then add seat heat if you have it. This will create a large load for the alternator and it should keep up.

Report findings please, also, did you use AC Delco 41-103 plugs?
 
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KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
87676 For some reason it wouldn’t let me upload a pic yesterday


And yes , 41-103 plugs and the gaps were checked

The temps have been up and down here , so I don’t know if that is playing a role , or my fuel level. I noticed the past 2-3 times it’s happened I was below 1/4 tank , it would still miss after filling up but a day or two of driving and it’s running smooth again
 

KEEBZ489

Original poster
Member
Jan 16, 2018
245
Howard Beach NY
SOLVED FINALLY It started missing bad and threw a code Coil #5 was bad , swapped it and still missing , pulled the plug and it looked good but swapped. #2 was also missing so I swapped everything out and it’s running smooth now


I posted in the other section asking about an app for iPhone users and no one answered , it took me a while , but dash command shows full PIDs if anyone is interested. It’s made by auto meter , so it’s a solid build. It’s $10 plus a $10 add on but well worth it. I learned I need two speed sensors now !
 

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