[Tonio]

So this infamous multiple misfire crap has me on the verge of getting rid of the car. Car has 167k miles on it, so still "has time" and what's weird is when I cruise, I get NO misfires. My mechanic connected his "expensive" OBD interface and saw too there are absolutely no misfires when cruising.

So yeah, I did everything below and STILL have the misfire, mostly while accelerating and at idle...

Made sure the replacements were all OEM parts too, smh.

Spark plugs
Coils
PCV valve
Intake hose (had a small crack)
MAF sensor
Idle Control Valve
EGR Valve
Timing belt change with water pump, tensioner, etc.
Valve adjustment
Fuel Injectors

Also,

Cleaned EGR ports and throttle body
Did seafoam through vacuum hose and gas (separately)

Mechanic checked the pressure of the fuel pump and he said it was fine.

Misfire for cylinders 1, 2, 4, 6 is what I normally get. Even though they are all new plugs and coils, still tried changing it around, same misfire codes.

I've legit searched through this whole forum, but no luck 😑

 

[dzionassi]

So there is CEL? or just scanner shows misfires on live data?

 

[Tonio]

Yup, check engine light states those cylinders are misfiring.

But as I was driving, my mechanic used his computer to check the live data, and those four cylinders are misfiring when idling and accelerating. Perfect / no misfires when on cruise control, on flat roads. So weird man. I cant figure it out.

So there is CEL? or just scanner shows misfires on live data?

 

[2011BlackUbmMDX]

So this infamous multiple misfire crap has me on the verge of getting rid of the car. Car has 167k miles on it, so still "has time" and what's weird is when I cruise, I get NO misfires. My mechanic connected his "expensive" OBD interface and saw too there are absolutely no misfires when cruising.

So yeah, I did everything below and STILL have the misfire, mostly while accelerating and at idle...

Made sure the replacements were all OEM parts too, smh.

Spark plugs
Coils
PCV valve
Intake hose (had a small crack)
MAF sensor
Idle Control Valve
EGR Valve
Timing belt change with water pump, tensioner, etc.
Valve adjustment
Fuel Injectors

Also,

Cleaned EGR ports and throttle body
Did seafoam through vacuum hose and gas (separately)

Mechanic checked the pressure of the fuel pump and he said it was fine.

Misfire for cylinders 1, 2, 4, 6 is what I normally get. Even though they are all new plugs and coils, still tried changing it around, same misfire codes.

I've legit searched through this whole forum, but no luck

Sounds like a valves leak or bad valve seals


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[2011BlackUbmMDX]

Sounds like a valves leak or bad valve seals


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Do a compression test or leak down test


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[qqzj]

Have you had chance to look at cleaning throttle body overall, and then adjust throttle position sensor? Since you have tried so many things, this is logically a weak link. You need a fancy scanner to reset it though.

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[Tonio]

When my mechanic did the valve adjustment, and he changed the seals...but you're right, it could be that. Thanks

Sounds like a valves leak or bad valve seals


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[Tonio]

Yeah, that was the first thing I did, hoping it would correct it.

Have you had chance to look at cleaning throttle body overall, and then adjust throttle position sensor? Since you have tried so many things, this is logically a weak link. You need a fancy scanner to reset it though.

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[Tonio]

He said the compressions look fine, not sure about the leak down test, I'll look into that too, thanks!

Do a compression test or leak down test


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[dzionassi]

Cats cats cats, check your cats, also fuel pressure. Most overlooked bad cat symptom is a misfire. O2 sensors not always trigger CEL

 

[2011BlackUbmMDX]

When my mechanic did the valve adjustment, and he changed the seals...but you're right, it could be that. Thanks

Did you double your timing belt is lining up EXACTLY?


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[Tonio]

The cats are operating fine, according to his "computer," had my mechanic check that too, after reading the blogs on here 😕

Cats cats cats, check your cats, also fuel pressure. Most overlooked bad cat symptom is a misfire. O2 sensors not always trigger CEL

 

[Tonio]

Yup, had another mechanic check to be sure. Problem is, before the timing belt was changed, the misfires were already happening 😔

Did you double your timing belt is lining up EXACTLY?


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[2011BlackUbmMDX]

Yup, had another mechanic check to be sure. Problem is, before the timing belt was changed, the misfires were already happening

Bend valves are possible or the valves aren’t seated probably or bad valve seals.
To check all of these the head has to be removed but it would be the resort because it’s a major tear down.


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[2011BlackUbmMDX]

Did you cleaned or replaced the EGR valve?
A partially open during idle or acceleration will cause the engine to shake or shouldered and then trigger random misfires.

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[dzionassi]

The cats are operating fine, according to his "computer," had my mechanic check that too, after reading the blogs on here 😕

Sorry but logging not always show full the story, gave to inspect it with camera...

 

[2011BlackUbmMDX]

Maybe you have simple problem with the wire being broken or shorted somewhere. Maybe you have rodents chewed up your wirings. Check all the wirings and connectors are associated with the emission


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[carpayment4life]

For reference, what year is it?

 

[Tonio]

Yup replaced it for a new one and cleaned the ports out

Did you cleaned or replaced the EGR valve?
A partially open during idle or acceleration will cause the engine to shake or shouldered and then trigger random misfires.

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[hcall]

You may try finding a shop that has a smoke machine. This guy is an awesome through mechanic and he figure it out on this ridgeline.