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Discussion Starter #1
I've been perusing these boards since having misfires on a 2013 MDX 70K mile starting three weeks ago. Took it to my local mechanic who is diligent, but not an Acura, Honda specialist. I haven't done my 60K maintenance yet so I thought it may be why it started. I only use 93 octane fuel. I do use the paddles to drive more aggressively than the average driver, but not unreasonably. I passed inspection in December.

  • Changed injector coils, spark plugs (OEM spark plugs) - no help
  • Changed Crankshaft Position Sensor due to a code which mechanic saw in addition to above, but no longer showing after sensor changed - no help.
  • Cleaned EGR valve (was pretty clean) and passageways - no help.
  • Did a pressurization test - all cylinders had the same pressure which the mechanic felt was normal level.
  • Tried new fuel injectors - all injectors working well per mechanic (I spent the today with their best mechanic as we went after this).
    • At this point noticed that the misfires happen under acceleration and not at idle or low rpm.
    • The cylinder that was really misfiring was #2.
  • Mechanic then tested the two electric wires into the #2 fuel injector by removing the wires and terminal that plugs into the injector and attaching a gadget that lights up when current goes through the two wires.
    • The light flickers and he tells me the power to the #2 fuel injector is intermittent.
  • I stepped away to look at the electrical diagram with owner. When I got back to the mechanic, he was adamant that the issue was not the wiring either from the terminal to all the fuel injectors, nor the specific 2 to the fuel injector -- given there is current flowing but is intermittent under acceleration.
  • Thus this points to the ECU.
  • I bought the car at 28K miles from an elderly original owner and only have had one issue.
  • In the last year I have had the power steering whine which has gotten progressively worse. Don't think this would be related to this somehow, but now that I am looking at ECU don't want to rule out.
  • The other factor is I have been working from home a lot so I drive short trips every other day of ~ 5 miles, with a 60 mile round trip drive 1-2x a week.
  • Before I go any further if any one has ideas, would appreciate feedback. I have boned up on the above due to the issue, but not a DIY mechanic at this point.
 

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Fuel pressure ok?
 

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Discussion Starter #3
Good point. Owner didn't think so when I raised it, but they are just following a code decision tree and Snap-on likely culprits. I will circle back on that.

From my research on these boards:
  • Low fuel Pressure
    • bad fuel pump vs bad fuel filter very challenging.
      • How do you tell them apart? A clogged fuel filter will have high pressure on its input side and low pressure on its output side. They are both going to cause the same hesitation at high speed and difficulty starting. The only way to truly tell is to place a fuel pressure gauge on both sides of the line and get a reading from both.
The master mechanic does some work on Sundays. I'll see.
 

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Best thing is to connect air pressurized tank with some fuel set at 60psi or so and go for a drive ;) Not the safest, but it will help to eliminate fuel related problems.
At what rpm rage you getting misfires ?
 

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Discussion Starter #5
I'll ask the mechanic.

RPMs I'd guess normal acceleration in a city type driving. Went on a highway when first started but haven't since it kicked in.
 

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So you cant replicate misfires every time you drive?
 

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Discussion Starter #7
Yes I can. If you accelerate from a standing start or acceleration on the move it will misfire. Not if coasting.

But engine started to turn more and more for ignition to turn on and even very low acceleration, now running rough as well to my ear when driving to mechanic. Ignition has always been instant. All in last 3 weeks.
 

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Yes I can. If you accelerate from a standing start or acceleration on the move it will misfire. Not if coasting.

But engine started to turn more and more for ignition to turn on and even very low acceleration, now running rough as well to my ear when driving to mechanic. Ignition has always been instant. All in last 3 weeks.
Ok, look in to fuel delivery please.
 

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Find a better mechanic or give up and go to the dealers.

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Discussion Starter #11
The only thing strange about fuel pressure is why its showing up with two cylinders only per codes, or really cylinder 2 per mechanic.
 

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The only thing strange about fuel pressure is why its showing up with two cylinders only per codes, or really cylinder 2 per mechanic.
Misfire counters on the MDX is not accurate. The MDX can misfire on one specific cylinder, but prompt misfire codes on multiple cylinders. Looks like the Mechanic is guessing and throwing a parts canon on your MDX.

The #2 Fuel Injector could be clogged.... I would take Live Data from a scanner while running and look at the Short Term Fuel Trims on Bank#1 and Bank#2. Cylinder#2 is on Bank#1, so I would expect STFT on Bank#1 to be greater the +/- 10%...
 

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Discussion Starter #13
Misfire counters on the MDX is not accurate. The MDX can misfire on one specific cylinder, but prompt misfire codes on multiple cylinders. Looks like the Mechanic is guessing and throwing a parts canon on your MDX.

The #2 Fuel Injector could be clogged.... I would take Live Data from a scanner while running and look at the Short Term Fuel Trims on Bank#1 and Bank#2. Cylinder#2 is on Bank#1, so I would expect STFT on Bank#1 to be greater the +/- 10%...
Thanks. On the ECU front, I am researching right now if I can buy a cheap ECU and just do the check if it stops the misfiring since the mechanic is so adamant that current is intermittent, and switch back to my ECU if not -- see what that means for programming.

He switched in a fuel injector into cylynder # 2 and it did not stop the misfiring, he switched it back to my original, which is how he went to test the wires leading into the fuel injector for cylilnder #2. I stepped away to get food, but they tested the fuel injectors and ruled that out.
 

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Also, you indicated a compression test was performed, but did not reveal the results.... what are the compression numbers for all 6 cylinders?

Fuel injectors were replaced? Did the mechanic do a relative resistance test on all 6 Injectors prior to replacemen? How bout a pressure test on the Fuel Rails?
 

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Thanks. On the ECU front, I am researching right now if I can buy a cheap ECU and just do the check if it stops the misfiring since the mechanic is so adamant that current is intermittent, and switch back to my ECU if not -- see what that means for programming.

He switched in a fuel injector into cylynder # 2 and it did not stop the misfiring, he switched it back to my original, which is how he went to test the wires leading into the fuel injector for cylilnder #2. I stepped away to get food, but they tested the fuel injectors and ruled that out.
Please stop buying parts without proper diagnosis...Fuel Injectors are not supposed to have 12v.... should be pulsing 12v.....To elaborate, +12v is supplied to the injectorconstantly, however the ground is pulsing delivered by the ECM
 

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Discussion Starter #16
Also, you indicated a compression test was performed, but did not reveal the results.... what are the compression numbers for all 6 cylinders?

Fuel injectors were replaced? Did the mechanic do a relative resistance test on all 6 Injectors prior to replacemen? How bout a pressure test on the Fuel Rails?
Thanks.

  • I have to ask him what the exact pressure was, but I confirmed with all of us there that the pressure in all cylinders was the same. A pressure test is where we went before going to the fuel injectors.
  • He replaced the one into cylinder two so it wasn't function of the injector, but interesting point about the relative resistance. He should be arriving soon to the garage and I have OHM meter and will measure these myself.
  • He actually did do a pressure test on fuel rails I think - I went to get lunch for the mechanics working on this yesterday, so cam back as they were doing these tests, but it was at 50psi regularly when I rejoined them. They thought it had to be the fuel injectors and spent quite a bit of time testing fuel pressure. Going to ask him about it again.
 

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Discussion Starter #17
Please stop buying parts without proper diagnosis...Fuel Injectors are not supposed to have 12v.... should be pulsing 12v.....To elaborate, +12v is supplied to the injectorconstantly, however the ground is pulsing delivered by the ECM
Thanks. I am going to go over all of this on the injector again.
  • I will understand after reviewing with him how he is ruling out pressure issues and charge issues. I need to understand this better.
 

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Discussion Starter #18
Also, you indicated a compression test was performed, but did not reveal the results.... what are the compression numbers for all 6 cylinders?

Fuel injectors were replaced? Did the mechanic do a relative resistance test on all 6 Injectors prior to replacemen? How bout a pressure test on the Fuel Rails?
The compression test was 180 in each cylinder.

The senior mechanic that worked on it w me is very confident that the fuel pressure is fine as they worked on that for awhile yesterday.

I'm at the shop w a digital multimeter and willl measure the voltage to the fuel injectors.


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With a multi meter, run a resistance check on all injectors and compare values....This problem is not a ECM issue... if it was, that Misfire would also be triggered at idle...l. The fact that you are only getting misfires under load tells me it’s probably an injector occlusion or clog....
 

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Discussion Starter #20
Please stop buying parts without proper diagnosis...Fuel Injectors are not supposed to have 12v.... should be pulsing 12v.....To elaborate, +12v is supplied to the injectorconstantly, however the ground is pulsing delivered by the ECM
Hello. Thanks!

You are right that the fuel injector harness should be pulsing when working.

For cylinder 2, under idle the harness is pulsing (using a light indicator you plug into the harness like at 1:25 here
).

However, under decent acceleration, it stops pulsing and becomes constant light. The misfires happen under acceleration as well, though ignition is happening slowly now.

That is why he thinks it is a signal problem and nothing wrong with engine, fuel pressure, exhaust.


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