Odd Cold Start Issue

pkrface · Jun 30, 2022

bbrages said:
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.

Thanks for asking! Funny how you forget some things until the question is asked. There is a puff of white smoke when it first starts. Again, the longer it sits the more pronounced. Have not had to add coolant which is of course the first thing that comes to mind when white smoke is involved.

feels · Jun 30, 2022

My Odyssey encountered random misfire P0300 that took near to 1 month to diagnose. I bought a Honda HDS diagnostic tool to have full visibility at dealer level, and accumulated full understanding of everything about the ignition, fuel and PCM/ECU system that should helped you.

If you have a misfire after left the car not driven for few days, then the most possible cause is fuel injector slow leaking (early failure). There are 2 banks of fuel injector, each connects to 3 fuel injectors. All of them reside below the air intake/distribution box, so it is not directly accessible.

Due to above constrain, my suggestion to determine whether you have a slow leaking fuel injector if purposely leave the car not driven for 4 days (to accumulate more fuel inside the cylinders):
Option 1: Remove each spark plugs, roll a newspaper that is about 8" or longer and small enough that can fit into the spark plug hole. Push the small newspaper roll into the spark plug hole, and all the way to the bottom of it (touch the piston). Checks whether the newspaper is wet. If it did, then that fuel injector is leaking and needs to be replaced

Option 2: Pull out all 6 spark plugs. Rest 1 piece of newspaper on top front 3 rows of spark plugs, and another piece on rear 3 rows of spark plugs. If can leave it longer than 4 days is better, so there is more fuel accumulated. Crank the engine and makes all 6 cylinders move several times. Check the newspaper for fuel spray pattern. The hole with fuel will be the cylinder with a leaky fuel injector

If you don't have time to diagnose above, but would like to temporary prevent this from happening, you can disconnect the fuel hose at the firewall area, as it is easily reachable, as well as easily reconnects back. Upon power off, there is some fuel pressure, so recommend to put a can below it when loosen the bolt/cramp to catch the fuel.

A fuel injector cost < $100, but they are highly reliable. So I suspect only 1 is broken. On early failure, they will leak, but slowly degrading. Another diff failure scenario (not what you experiencing) is that the magnetic coil burned, and that will immediate fail, and won't operate (that means consistently not firing in 1 specific cylinder).

If your fuel injector is not original Honda, then you can replaced those with used Honda injector as it is troublesome to find a skillful mechanics to troubleshoot this kind of soft failure issue.

Hope this helped

bbrages · Jun 30, 2022

Hmm, sounds like something is leaking into the cylinder over several days and that's what's causing the misfire.

pkrface · Jun 30, 2022

feels said:
My Odyssey encountered random misfire P0300 that took near to 1 month to diagnose. I bought a Honda HDS diagnostic tool to have full visibility at dealer level, and accumulated full understanding of everything about the ignition, fuel and PCM/ECU system that should helped you.

If you have a misfire after left the car not driven for few days, then the most possible cause is fuel injector slow leaking (early failure). There are 2 banks of fuel injector, each connects to 3 fuel injectors. All of them reside below the air intake/distribution box, so it is not directly accessible.

Due to above constrain, my suggestion to determine whether you have a slow leaking fuel injector if purposely leave the car not driven for 4 days (to accumulate more fuel inside the cylinders):
Option 1: Remove each spark plugs, roll a newspaper that is about 8" or longer and small enough that can fit into the spark plug hole. Push the small newspaper roll into the spark plug hole, and all the way to the bottom of it (touch the piston). Checks whether the newspaper is wet. If it did, then that fuel injector is leaking and needs to be replaced

Option 2: Pull out all 6 spark plugs. Rest 1 piece of newspaper on top front 3 rows of spark plugs, and another piece on rear 3 rows of spark plugs. If can leave it longer than 4 days is better, so there is more fuel accumulated. Crank the engine and makes all 6 cylinders move several times. Check the newspaper for fuel spray pattern. The hole with fuel will be the cylinder with a leaky fuel injector

If you don't have time to diagnose above, but would like to temporary prevent this from happening, you can disconnect the fuel hose at the firewall area, as it is easily reachable, as well as easily reconnects back. Upon power off, there is some fuel pressure, so recommend to put a can below it when loosen the bolt/cramp to catch the fuel.

A fuel injector cost < $100, but they are highly reliable. So I suspect only 1 is broken. On early failure, they will leak, but slowly degrading. Another diff failure scenario (not what you experiencing) is that the magnetic coil burned, and that will immediate fail, and won't operate (that means consistently not firing in 1 specific cylinder).

If your fuel injector is not original Honda, then you can replaced those with used Honda injector as it is troublesome to find a skillful mechanics to troubleshoot this kind of soft failure issue.

Hope this helped

That helps a lot! From a diagnostic perspective it by far makes the most sense. Thanks!

geotek · Jun 30, 2022

pkrface said:
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.

I will give you my guess. Since the engine has an aluminum block and heads. The steel bore sleeves and the valve seats, valves, and valve hardware cool at a different rate. It may take 3 days for them to cool of and shrink slightly. Then when you run it for a little while everything expands. You are over due for the valve adjustment, so this may help.
when you clean an Ody throttle body there is a factory service manual to follow, you might check the Acura manual to see if it has one.

pkrface · Jun 30, 2022

bbrages said:
Hmm, sounds like something is leaking into the cylinder over several days and that's what's causing the misfire.

Fuel makes the most sense except for white smoke. Could be light blue, but it for sure isn’t black.

pkrface · Jun 30, 2022

geotek said:
I will give you my guess. Since the engine has an aluminum block and heads. The steel bore sleeves and the valve seats, valves, and valve hardware cool at a different rate. It may take 3 days for them to cool of and shrink slightly. Then when you run it for a little while everything expands. You are over due for the valve adjustment, so this may help.
when you clean an Ody throttle body there is a factory service manual to follow, you might check the Acura manual to see if it has one.

The issue existed before the throttle body cleaning. If anything between the new PCV valve and throttle body cleaning it became slightly less pronounced. In fact it had progressed to the point where it would do it mildly when driven daily and is back to a smooth start on daily start ups. I agree that it is overdue for a valve adjustment and should just bite the bullet, but my Ody has 257K on with no valve adjustment and runs fine. Both cars are at the point where replacement is imminent and my major motivation to figure out the MDX issue is to not pass it along to someone else with the issue. Most shops would chase their tail and rack up a big bill and may still not fix it. I’m tempted to do a proper fuel system cleaning where they hook up to the fuel rails and see if that does anything as I’m willing to try a few low cost things that are good maintenance anyway. I could do the valve adjust myself, so not terribly costly with just gaskets, but also not stoked about the job unless I’m reasonably sure that would fix it. Personally I could drive it for years like it is, but it would freak out most others to have it run rough and throw the CEL.

geotek · Jun 30, 2022

pkrface said:
The issue existed before the throttle body cleaning. If anything between the new PCV valve and throttle body cleaning it became slightly less pronounced. In fact it had progressed to the point where it would do it mildly when driven daily and is back to a smooth start on daily start ups. I agree that it is overdue for a valve adjustment and should just bite the bullet, but my Ody has 257K on with no valve adjustment and runs fine. Both cars are at the point where replacement is imminent and my major motivation to figure out the MDX issue is to not pass it along to someone else with the issue. Most shops would chase their tail and rack up a big bill and may still not fix it. I’m tempted to do a proper fuel system cleaning where they hook up to the fuel rails and see if that does anything as I’m willing to try a few low cost things that are good maintenance anyway. I could do the valve adjust myself, so not terribly costly with just gaskets, but also not stoked about the job unless I’m reasonably sure that would fix it. Personally I could drive it for years like it is, but it would freak out most others to have it run rough and throw the CEL.

Well, if my theory is correct, doing a valve adjustment could make it worse because you would be increasing spacing.

pkrface · Jun 30, 2022

geotek said:
Well, if my theory is correct, doing a valve adjustment could make it worse because you would be increasing spacing.

Lol definitely don’t want to do that! I’m not savvy enough to follow you on that. The studying I’ve done on the valve adjustment says the exhaust valves get tight and the intake valves get loose, so you’re saying proper adjustment would mean less air coming in so if there’s raw fuel laying there the issue would be magnified? I guess that makes sense, but at the same time I could see the fuel sitting there for a few days, but when it sits for a week wouldn’t it be gone having pushed past the rings and ending up in the crankcase? I’m not seeing evidence of fuel in the oil, granted we are likely talking about a very small amount of fuel per shut down.

feels · Jul 1, 2022

I am checking back to see whether OP (original poster) made any progress to eliminate slowly leaking FI that I suspected yesterday. I recalled that OP indicated see does see more white smoke on cold start, and more smoke if left for days, which I didn't comment.

FI slow leak will cause excessive white smoke on cold start (FI stays open, in yr case, slight open). Certainly it could be due to head gasket failure and coolant leak into the engine head, but you indicated the coolant is clean, and eliminated this possibility.

I checked in Internet to see what are other symptoms on leaky FI (internal leak, not external leak), and surprisingly read about following:
1. engine oil thinning - fuel leak through the cylinder piston ring, and get into the engine oil
2. hydrolocking - many fuel leak into top of piston, and flooded it with gasoline

In case you done some research, and worry about above 2 issues, let me share my experience from 1 month of testing when I done a head gasket job on Honda's 4 cylinder engine:

1. Piston ring is very well sealing when the piston is not moving (not firing), unless engine has existing problem (yr car doesn't has VCM, so let's remove potential piston ring damage due to VCM). I have testing to leave gasoline and acetone on top of the piston for 1 week to study these 2 thin liquid as well as to proof how valid this could applies to Honda engine produced in 1990's. I covered 2 of those piston with plastic bag to eliminate air evaporation, and pour some into a tin can as benchmark how much they evaporated. After 1 week, I don't see any evidence that the gasoline and acetone leak through the piston ring and get into the engine oil. So for a good engine (holding the pressure for 15 min, let's say), engine oil thinning is not applicable for car produced after 1990's

2. hydrolocking required the top of the piston flooded with fuel (or any liquid, such as in BMW, it is engine oil due to PCV valve failure). A little of fuel leak is not sufficient to fully flood the piston's combustion area. As your FI is slowly getting worse, so the gasoline flood won't happen immediately, but eventually could happen until it get worse. During my Honda engine head gasket replacement, which I have access to the valve, I done an experiment on how well Honda's valve seal vs leak on a good working engine. I used gasoline to clean the valve as well as study how leaking is the good valve. I was surprise to see that all 16 valve are able to leak gasoline, even the engine was able to hold pressure. As I am using gasoline to clean carbon deposit, gasoline leak is making my job messy, but it was a valuable knowledge to observe. What this mean is that if the piston is at top position, hydrolocking is not possible. If piston is at bottom position, hydrolocking is more possible even the intake valve is closed (gasoline will able to leak through intake valve). It is highly recommend to remove the spark plug to understand how serious the fuel injector leak week to week, and ensure the spark plug is not wet (covers with gasoline) and no gasoline smell (covers with gasoline vapor). If the leak is not serious, then you can delay the repair. If the leak become more serious few weeks later, then take temporary workaround by disconnecting the fuel line after turn off engine. If you not comfortable with fuel line, then remove the spark plugs will be an easier way to prevent hydrolock (gas will splash through the spark plug hole)

pkrface · Jul 1, 2022

feels said:
I am checking back to see whether OP (original poster) made any progress to eliminate slowly leaking FI that I suspected yesterday. I recalled that OP indicated see does see more white smoke on cold start, and more smoke if left for days, which I didn't comment.

FI slow leak will cause excessive white smoke on cold start (FI stays open, in yr case, slight open). Certainly it could be due to head gasket failure and coolant leak into the engine head, but you indicated the coolant is clean, and eliminated this possibility.

I checked in Internet to see what are other symptoms on leaky FI (internal leak, not external leak), and surprisingly read about following:
1. engine oil thinning - fuel leak through the cylinder piston ring, and get into the engine oil
2. hydrolocking - many fuel leak into top of piston, and flooded it with gasoline

In case you done some research, and worry about above 2 issues, let me share my experience from 1 month of testing when I done a head gasket job on Honda's 4 cylinder engine:

1. Piston ring is very well sealing when the piston is not moving (not firing), unless engine has existing problem (yr car doesn't has VCM, so let's remove potential piston ring damage due to VCM). I have testing to leave gasoline and acetone on top of the piston for 1 week to study these 2 thin liquid as well as to proof how valid this could applies to Honda engine produced in 1990's. I covered 2 of those piston with plastic bag to eliminate air evaporation, and pour some into a tin can as benchmark how much they evaporated. After 1 week, I don't see any evidence that the gasoline and acetone leak through the piston ring and get into the engine oil. So for a good engine (holding the pressure for 15 min, let's say), engine oil thinning is not applicable for car produced after 1990's

2. hydrolocking required the top of the piston flooded with fuel (or any liquid, such as in BMW, it is engine oil due to PCV valve failure). A little of fuel leak is not sufficient to fully flood the piston's combustion area. As your FI is slowly getting worse, so the gasoline flood won't happen immediately, but eventually could happen until it get worse. During my Honda engine head gasket replacement, which I have access to the valve, I done an experiment on how well Honda's valve seal vs leak on a good working engine. I used gasoline to clean the valve as well as study how leaking is the good valve. I was surprise to see that all 16 valve are able to leak gasoline, even the engine was able to hold pressure. As I am using gasoline to clean carbon deposit, gasoline leak is making my job messy, but it was a valuable knowledge to observe. What this mean is that if the piston is at top position, hydrolocking is not possible. If piston is at bottom position, hydrolocking is more possible even the intake valve is closed (gasoline will able to leak through intake valve). It is highly recommend to remove the spark plug to understand how serious the fuel injector leak week to week, and ensure the spark plug is not wet (covers with gasoline) and no gasoline smell (covers with gasoline vapor). If the leak is not serious, then you can delay the repair. If the leak become more serious few weeks later, then take temporary workaround by disconnecting the fuel line after turn off engine. If you not comfortable with fuel line, then remove the spark plugs will be an easier way to prevent hydrolock (gas will splash through the spark plug hole)

Thanks! More and more pointing to the issue being an injector or two that is leaking down. Next step is to see if I can catch the specific cylinder(s) so I just replace the bad one(s).

Dvp813 · Jul 6, 2022

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

Timing components wouldn't cause this and valve adjustment symptom would be constant upon starting regardless of how long the vehicle sat.
If you suspect fuel pressure leak down put a gauge on it and watch the pressure as it sits over a few days.
It's still a good idea to check the valve clearance if it hasn't been done recently.

Dvp813 · Jul 6, 2022

pkrface said:
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.

Timing components wouldn't cause this and valve adjustment symptom would be constant upon starting regardless of how long the vehicle sat.
If you suspect fuel pressure leak down put a gauge on it and watch the pressure as it sits over a few days.

pkrface · Jul 6, 2022

Dvp813 said:
Timing components wouldn't cause this and valve adjustment symptom would be constant upon starting regardless of how long the vehicle sat.
If you suspect fuel pressure leak down put a gauge on it and watch the pressure as it sits over a few days.

Thanks for that input! I‘m not super good at diag, but have a rudimentary mechanical understanding enough to feel like it really didn’t make sense to be a timing or valve adjustment issue. Also thanks fo4 the suggestion of a putting a gauge on the fuel pressure. I don’t currently have one, but would be a good investment as it won’t cost near as much as a shop diag charge.

gomst1 · Jul 6, 2022

Carbon buildup on the intake valves will cause cold start misfires. Since MDX is not direct injection, injected fuel passes through the intake valves. On initial cold start fuel injected is absorbed by carbon buildup on the intake valves causing temporary lean fuel air mixture therefore misfires. I recommend you find a shop that knows how to decarb the intake valves. Also, a fuel injector cleaning is a good recommendation.

pkrface · Jul 6, 2022

gomst1 said:
Carbon buildup on the intake valves will cause cold start misfires. Since MDX is not direct injection, injected fuel passes through the intake valves. On initial cold start fuel injected is absorbed by carbon buildup on the intake valves causing temporary lean fuel air mixture therefore misfires. I recommend you find a shop that knows how to decarb the intake valves. Also, a fuel injector cleaning is a good recommendation.

Thanks, both good suggestions.

Dvp813 · Jul 6, 2022

gomst1 said:
Carbon buildup on the intake valves will cause cold start misfires. Since MDX is not direct injection, injected fuel passes through the intake valves. On initial cold start fuel injected is absorbed by carbon buildup on the intake valves causing temporary lean fuel air mixture therefore misfires. I recommend you find a shop that knows how to decarb the intake valves. Also, a fuel injector cleaning is a good recommendation.

Direct injected engines tend to accumulate carbon on the intakes as there is no fuel passing over the intakes. This isn't usually the case of port injected engines especially if they use a decent quality fuel. Carbon related cold start issues seem to be common on direct injected engines. I've cleaned a bunch of GM 3.6 direct injected engines and some were really carboned up to almost the diameter of the valve face. I do agree with the fuel injector cleaning.

gomst1 · Jul 6, 2022

If he was not using cheap gas, fuel injector cleaning maybe good enough.

Dvp813 · Jul 6, 2022

gomst1 said:
If he was not using cheap gas, fuel injector cleaning maybe good enough.

Definitely the first step

DIY Fan · Jul 6, 2022

Borescope in spark plug holes. Cheap and easy.

Odd Cold Start Issue

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