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It would be handy to know what the battery voltage is when the problem is happening - unlikely that it would be falling below "failure threshold" for those systems (ignition, VTM-4) under the conditions you describe, but stranger things have happened. You can guy an el cheapo voltage monitor that plugs into your cigarette lighter plug for just a few bucks (I have one that's also got an FM modulator and hands-free Bluetooth phone system, and it was still silly cheap).

Don't buy all new coil packs - they just don't fail, and the aftermarket ones aren't as good as the used Honda coil packs, even with 200,000 miles on them. They don't "wear out" so will be as good as the day they were built until they have an electronic failure.

There are quite a few things that can cause multiple misfires, including valve adjustment (and if your vehicle hasn't had this done, it's WAY overdue), PCV valve (dirt cheap and takes seconds to replace), as a start... other "more interesting" things can cause the misfires, including EGR system problems, fuel pressure, etc.
 

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Well, with the maint history, you’re also overdue for plugs so would change those.

If you know which cylinders are misfiring, as Habby suggested, it’s probably not the coils but you could switch coils with a good cylinder and see if the problem follows. Do one coil at a time and keep track.

Couple other things to try. Clean the throttle body with TB cleaner and spray the rag (away from paint). Wipe the mouth and the edges of the butterfly valve. Don’t spray the cleaner down the TB and keep the cleaner off the butterfly valve shafts bc you want to keep them lubed. Use a screwdriver handle and a rag or similar to hold the valve open to do the top edge. Be sure you don’t use a small tool or rag that can fall into the TB. I’m sure you can find a YouTube on it.

Change the air filter if not done in last 30K miles.

After that, you might need a valve adjustment - I would almost bet on it but do the easy, low cost stuff first and rule out some other potential causes.

Btw, the 105K service interval includes the valve adjust, plugs, trans fluid, VTM, oil/filter, air filter, cabin filter, tire rotation/balance.

Good luck!
 

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Current status: replaced EGR valve (had seen some post that this resolved their issue and mine looked “old” but didn’t seem too clogged or anything - thought maybe it had a failure). Also checked the coil packs and they all seemed to be firing fine. Still had same issue - CEL flashing and VTM-4 light on.

Also tried to follow your advice about cleaning with TB cleaner, but totally didn’t follow instructions. I just sprayed it right into the TB, all over the butterfly valve, etc. So I might cause an issue with the throttle, but it started and is running, for now...

So, when I started it after replacing the EGR valve and spraying the TB with cleaner, I noticed it was struggling to crank - almost like it was ‘skipping’ or something. But I remembered what the guy at Oreillys telling me about the battery could potentially cause the electrical system to act ‘weird’. So, I went over to Walmart and bought an Everstart battery, swapped it out in the parking lot, cranked it, and... Cranked right up, no CEL and no VTM-4 light. ?

I was thinking “you gotta be kidding me”, but then before I got to my next destination the CEL starts flashing again (doesn’t stay on, but flashed occasionally). And still no VTM-4 light.

So, I’m thinking I ‘helped’ the issue by replacing the battery, but still have a misfire.

thoughts?
 

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That's plausible (bad battery). If the battery had a shorted cell, it would serve to limit the "system voltage" to under 12 volts. This is a good example of fixing a problem by replacing something that needed to be replaced anyway. Now just get an OBD reader, or go by an Autozone and have them read the codes so you could have a better idea of any remaining problems.
 

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hi all, dunno if we have a P0300 and misfire megathread, but this is the biggest one that turned up on a search.
2005 MDX Touring, 160k miles. Just finished an 800-ish mile road trip this winter and it performed great. After a few days home, boom, out of nowhere:

P0300, P0301, P0303, P0306 popped up. CEL and VTM-4 are on. CEL starts flashing at idle, and it idles very, very rough. You can feel the car shaking. The misfires seem to actually get better, or at least are less noticeable at speed. After 10 minutes of driving, the misfires felt gone, at stoplights or parked. It got new plugs and timing belt 2 yrs ago. Don't think it's ever had an EGR cleaning or valve replacement. I don't really have any tools for diagnosis aside from an OBD2 scanner to get those 4 codes above. Do we have like a flowchart or procedure sequence for diagnosis?
 

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Hi @ghent96 @rss0213,
Any updates on your cylinder misfire issues? I am currently dealing with the same problem on my 05 MDX with 130k miles - CEL and occasionally VTM4 light, p0300, 0303, 0305, 0306, rough idle when starting either hot or cold. I only notice the misfires happening at startup; when driving it feels fine and even idles fine at a stoplight.

So far I have already replaced all 6 fuel injectors, spark plugs, and coils, and valves were inspected. Obviously this was not cheap, but the previous owner had installed a few random aftermarket injectors and coils, so it made sense to try going back to genuine Honda parts. This fixed the problem for about 3 weeks but now my misfire codes are back.

I have not yet looked at the EGR valve or throttle body - these seem like easy and cheap things to try. I mentioned this to my mechanic and he says it's possible but does not suspect that is the problem. Do you guys recommend trying these things first? Is there any significance of the location of the cylinders misfiring? For me it's cylinders 3, 5, 6 (codes p0303, 0305, 0306) - these are on the driver's side of the engine - EGR valve and air intake are also driver's side.

Thanks,
Matt
 

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Well, at least you ruled out the items replaced.

What does your mech say?

I would check 3 things:

1) Vacuum leak - check hoses for cracks. Pay attention to the one going from the front of the engine across to the radiator and down to the front motor mount. That hose or mount could be leaking. The mount works on vacuum. One way to check it is to pinch it off with pliers to see if the engine smooths out. Then it could be the hose or mount.

2) If your X is hard to start, check the fuel pressure - should be 57-64 psi. However, if the X starts right up, probably not be the fuel pump.
3) Check the radiator fluid for exhaust residue to check for a blown head gasket. You can get a loaner tool from OReillys or Autozone and the test fluid is about $10. Pretty simple, easy test. The blue test fluid will turn orange if there’s exhaust res in your coolant. Hopefully, it’s not this. Another way to check is if you have a borescope, you can remove the spark plug and look inside the cylinder for shiny surfaces and droplets. The surfaces on a normal cylinder will look dry. Might have carbon, but dry.

Good luck!
 

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2004 Acura MDX Touring w/ RES & NAV
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Any chance it was in a accident...drivers side?
 
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