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2011 MDX, 60,000 miles. 2 weeks ago got a P0303 code (cylinder 3 misfire). Mechanic suggested replacing the coil -- code came back. Ran Seafoam through gas tank -- code came back. Replaced all the spark plugs with OEM plugs -- code came back. Opened up manifold and EGR ports looked fine but wiped it down and vacuumed it to be sure. Just put in more Seafoam and swapped the coil with another on the off-chance that the new coil is malfunctioning, but I expect the code to return. Running out of options - any suggestions before I take it in?

By the way about 2 weeks before this all started I was getting some engine knock even when I used top-tier premium so the dealership upgraded some software which made the knock go away -- could the misfire be related to this? Thanks for any and all help . . .
 

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Can you check fuel injectors?

Valve adjustment?
Thanks for the response. Seems like that is the next step, but I don't have the time/experience to do that, so I'll probably be taking it in for my mechanic to diagnose.
 

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This is where you should of took it to a dealership to let them properly diagnose it.
Misfires can be complicated to diagnose.

You spent too much time and money to let your "mechanic" throw guesses and parts at your car.

Where are you located?
What are your fuel trims at idle on Cyl#3?
What are your MAP readings at fully warmed up?
Cyl 3 misfire can you feel it missing or cant feel anything at all??
 

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Thanks for the response. Seems like that is the next step, but I don't have the time/experience to do that, so I'll probably be taking it in for my mechanic to diagnose.


1st, verify that you are getting sparks. There are many YouTube videos. I know you replaced wire and plug. But u need to see the plugs using your eyes or timing gun.

Next, like others said, look at long short fuel trim s. So you at least know it’s burning lean or rich.

Also check compression and fuel injector. You need air fuel compression spark all correct for it to fire properly.


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2011 MDX, 60,000 miles. 2 weeks ago got a P0303 code (cylinder 3 misfire). Mechanic suggested replacing the coil -- code came back. Ran Seafoam through gas tank -- code came back. Replaced all the spark plugs with OEM plugs -- code came back. Opened up manifold and EGR ports looked fine but wiped it down and vacuumed it to be sure. Just put in more Seafoam and swapped the coil with another on the off-chance that the new coil is malfunctioning, but I expect the code to return. Running out of options - any suggestions before I take it in?

By the way about 2 weeks before this all started I was getting some engine knock even when I used top-tier premium so the dealership upgraded some software which made the knock go away -- could the misfire be related to this? Thanks for any and all help . . .

1. You said the mechanic suggested replacing the coil. Did you or him actually replaced the coil?
2. You said the coil was swapped with another cylinder. Good, as long as you know exactly which numbers where swapped. It is part of the troubleshooting procedure. From here, if the misfire comes back at cyl #3, your problem is with the injector. If the problem follows the coil to the cylinder it was moved to, then the problem is the coil.


You are doing good so far. Just wait for the trouble code to come back and check what cylinder the misfire is on.
 

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1)Check for fuel at the injector
2)check map voltage at warm idle for valve lash indication
3)check compression using a leak down tester


I might move the leak down testing up the list from your reports of knock preceding this incident. They could very well be related.
 

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First thing that should have been done is a compression test.
Then you should start swapping parts with another cylinder to see if you can get it to move with that part.
 

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Thanks for all the replies. It was the fuel injector. Hope this helps someone in the future.
Please more details. What test did you do and why did you replaced the injector? Was it clogged or leaking?
 

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i think it was an electrical issue at the connector. a noid light or any testing light will show the problem, you could also listen for it firing with a mechanics stethoscope
 

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1)Check for fuel at the injector

2)check map voltage at warm idle for valve lash indication

3)check compression using a leak down tester





I might move the leak down testing up the list from your reports of knock preceding this incident. They could very well be related.


You don't use a Leak down tester to check compression.

Leak down test and compression test are two different procedures.
 

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You don't use a Leak down tester to check compression.

Leak down test and compression test are two different procedures.


I know they are different procedures...a leak down test will TEST where COMPRESSION is escaping the COMBUSTION CHAMBER. So it IS a compression test, and it’s also way more useful than a simple compression test. Because 99% of the time if your compression test comes out low on one cyl what are you doing next? A leak down....so skip the compression test go straight for leakdown. Especially in this case where valves could be the culprit.

This is all moot, op solved the issue, well done



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Discussion Starter #14
Please more details. What test did you do and why did you replaced the injector? Was it clogged or leaking?
Sorry for my late reply. My mechanic replaced the injector because the needle inside was no longer moving. It was not clogged or leaking, it was an electrical malfunction inside the injector unit itself. The pintle (aka needle) was not moving because the internal coil was not functioning. My mechanic said that Honda had changed the design of the injector body from mostly metal to mostly plastic. He said as a result, he has seen these new plastic-bodied injectors fail at a greater rate. He said that Toyota still makes metal-bodied injectors and he hardly ever has seen them fail like the Honda ones do.
 
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