[pkrface]

Hope it doesn't upset anyone too much posting about an MDX issue here. Posted on MDXERS, but there are far less people who get hands on with issues there. Still a J 6 cyl, so figure maybe one of the gurus here understands the motor well enough to point me in the right direction. Searching the forum both here and on MDXERS turned up nothing.

2007 MDX with 192K. Recent maintenance (last few weeks) done includes new spark plugs, PCV valve, and throttle body cleaned. The plugs had about 90K on them, so close to due, and I had no history on the PCV or throttle body, but both were definitely needed. I took the "make sure maintenance is up to date first" approach.

Problem has been ongoing for pushing nine months and gradually getting worse. Bad miss (seems like more than one cylinder) at cold start that does not occur when driven daily, but is mild if driven every other day and worse on day 3, even worse on day 4, then seems to pretty well level out at that point. If left to just idle will throw a CEL with P0300, but if you give it a little gas as soon as it starts it clears right up and you can drive away with no CEL running smooth. No miss, good power, runs great after that point and if driven daily the problem is non-existent. I‘ve tried giving it a few seconds after turning on the ignition in case it’s a fuel pressure bleed down and that changes nothing. My biggest suspicion now is a couple of poorly performing coils or injectors, but just cannot make logic of why sitting for 48 hours or longer produces the issue when it would seem sitting overnight should be a "cold start is a cold start" scenario.

 

[DIY Fan]

My guess is timing belt, tensioner, valve adjustment, or VCM if equiped. Issue seems to be related to expansion/cooling of metal.

 

[pkrface]

No VCM and 30K on timing belt. The valve adjustment crossed my mind, but why would it act differently the longer it sits cold? For the record this issue is consistent regardless of cold or warm temps. Same issue at 0F or 90F.

 

[DIY Fan]

Was Tensioner changed? EGR valve or passage?

 

[pkrface]

Was Tensioner changed?

Yep, entire kit. Again, if driven daily or if run up to 1,500 rpm right away at start up it drives out right with plenty of power. If it sits for 48 hours or more and is started without immediately bumping the rpm’s will sit there and miss then throw P0300 code which indicates multiple mis-fires and that is how it acts, like it’s running on 3 or 4 cylinders. There is no VCM the motor. Ongoing issue for the last 3K miles that is gradually getting worse, but car has been driven on numerous 100 or 200 mile trips and runs perfectly past the initial start up. No hint of a miss, all kinds of power, etc., the whole way. How it can be this consistent is baffling me as usually I can come up with a logical explanation of why something is happening.

 

[DIY Fan]

Switch the coils back to front. Costs nothing.

 

[pkrface]

I understand the idea if I had specific cylinder misfire codes, but without that I could move coils around and learn nothing. Same result on different cylinders. I’ve always made due with just getting the parts store to pull codes for me, but this may be the point where I break down and buy a reader so I can get real time info. Then I could let it sit a few days, get the specific misfire codes then swap coils and let it sit again and see if the misfire moves.

 

[DIY Fan]

Worn camshaft?

 

[pkrface]

Worn camshaft?

Again, why would that impact differently if it sits 48 hours vs 24 hours. Cold should be cold at that point. Thanks for continuing to throw out ideas, and I’m not ruling any of it out. Just looking to truly diagnose it rather than throw guesses at it. Whatever it is hopefully it will help someone else when I get it figured out.

 

[DIY Fan]

Dude, I am just guessing. I do all my own maintenance but am not a pro. Good Luck!

 

[pkrface]

Dude, I am just guessing. I do all my own maintenance but am not a pro. Good Luck!

Yep me too lol! I see your join date here of Feb 2022 which of course doesn’t mean you don’t have skills, but I’ve been here (MIA lately) since 2010 and there are a couple of truly genius guys I’m hoping will see this and put their 2 cents in. Like I said before, I’m not ruling out any of your suggestions. Just want to get to the why and if someone can explain the why for their idea it turns into a more educated guess which is what I’m looking for. And I really hope you’re wrong on the worn cam. The car is still nice, but not nice enough to justify that kind of work.

 

[DIY Fan]

Well I did a J35 timing belt recently and it did not blow up so I know a couple things on cars.

 

[pkrface]

Well I did a J35 timing belt recently and it did not blow up so I know a couple things on cars.

I’m a decent parts changer, but wish I was a good diag guy. Those guys are worth gold!

 

[thscott]

John Clark has been MIA here for the last year or so.
I miss his sage advice.

 

[pkrface]

John Clark has been MIA here for the last year or so.
I miss his sage advice.

Bummer! I’ve not been on much in that time period either, not that I can add much beyond what many others can.

 

[WiiMaster]

I think someone on the Accord forum had a misfire issue on one bank on cold starts and ended up just replacing that head which solved the issue.

 

[WiiMaster]

John Clark has been MIA here for the last year or so.
I miss his sage advice.

He was last seen Jan 1 of this year, so hasn't been too long yet.

 

[marvinstockman]

Sounds like oil leak-down to me. The Ody has mechanical lifters. What does the MDX have? On an older Mecedes, I had lifter clatter if the car sat for a few days, I changed to a heavier oil, and problem when away.

On an older BMW, it would develop a cold misfire which I solved by keeping the revs up for a few minutes. The previous owner had spent literally thousands chasing this misfire. My right foot cured it for nothing! My son wrecked the car before we actually found the 'problem'.

 

[pkrface]

Sounds like oil leak-down to me. The Ody has mechanical lifters. What does the MDX have? On an older Mecedes, I had lifter clatter if the car sat for a few days, I changed to a heavier oil, and problem when away.

On an older BMW, it would develop a cold misfire which I solved by keeping the revs up for a few minutes. The previous owner had spent literally thousands chasing this misfire. My right foot cured it for nothing! My son wrecked the car before we actually found the 'problem'.

The 3.7 is pretty much the same as the 3.5. Just tweaked a bit to run higher compression to turn out 300 hp when the Ody was at 244 hp. This is the kind of thinking I’m looking for though. The problem has been slightly improved since the PCV valve change and the throttle body cleaning. By my logic that may indicate a poor performing injector or two? Cleaning the throttle body should have improved the air flow, correct? So an injector not spraying a perfectly fine mist, but not too far off or spec, might cause the problem right at start up and clear up quickly because added throttle increases the air flow plus heat builds pretty quick. That’s my best working theory at the moment, but still having trouble rectifying the 24 hours cold vs 48+ hours cold. What if the injectors were leaking down very slowly and had no pressure at start up? The faulty injector when it leaks down would develop a small air pocket, so turning the key and waiting for pressure to build before turning over would be of no use because the air pocket can’t escape fast enough just because fuel pressure was applied, but the injector had yet to be fired? So if instead of P0300 multiple misfires I could determine which injectors were the culprit I could change just the offenders. Thoughts?

 

[bbrages]

Are you getting any black smoke when it starts cold?

I had a 1998 Maxima that would have hard starts when cold and would make a lot of black smoke when started. A bad injector was leaking fuel into the cylinder when it was cold and I suppose it also made the fuel pump have to re-prime the system. I had a mechanic do a fuel system clean, I guess they pumped something through the fuel rail, and that fixed it.

So bad injector is the only thing that really makes sense to me.