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BF 225 Misfire found. It was not the easiest task.

N

Nasty Wendy

Regular Contributor
So I'm doing so long needed maintenance on my engines while I have the boat home because of non-engine work I had to do to it. All the typical stuff plus I pulled the injectors to have them cleaned. The starboard engine had definite miss at low rpm. I cleaned and changed all the filters and screens (yes ALL those hidden ones too). The one at the FPR wasn't dirty. It wasn't pristine but nothing to inhibit fuel flow was there. I changed the FPRs on both engines as well as new NGK plugs (I have a set of autolites that are listed as a direct replacement for the NGKs but I haven't had the courage or need to try them). The professional cleaning of the injectors, new plugs, and the new FPRs have my engine purring like a single kitten (port engine) and a sick kitten (starboard engine). I changed the FPRs because my fuel pressure was a wee bit low on my starboard engine (changing them both allows me to keep one to have as a test part should I need it) and my pumps are nearly new and pumping strong. New regulator did get me back in the specified range (I was at 37psi and now I'm at 45 psi). The starboard engine's misfire was still present and even easier to pinpoint with the other 5 cylinders dancing perfectly. So I popped on a new ignition module even though the original one tested good (I keep extra stuff for this type of thing) and it made no change. I moved sparkplugs around but the misfire remained on cylinder 6 (bottom cylinder on my left). I chased vacuum leaks even though there weren't any. I fixed the IAB to get it moving freely again and I know that needed to be done but it didn't fix the misfire. So I pulled the injector and checked it. I ohm'd it and it checked out 11.5Ω, perfect. I clicked it open with a 9v battery and sprayed brake parts cleaner through it and it worked. I put it back in puzzled. Fired up the engine and the misfire was still present. So now I'm talking to all my car buddies and they all are stumped. It has fuel, air, and spark but won't fire. Today I decide I'm going to move the fuel injector to a different cylinder and the freaking misfire moved with it. I'll have another injector here soon but I'm puzzled as to how a fuel injector can pass all the tests and still not be good. The misfire moved with this injector and the previous non firing cylinder is now firing. So after reading this book I wrote I'm asking ya'll to respond with theories, experience, knowledge, or guesses as to how an injector can pass every test but not pass fuel into the cylinder.
 
Here's a SWAG - bad or weak internal spring or compromised seal, not allowing the injector to seal completely when closed. Consequently, insufficient pressure to atomize fuel. However, that should have shown up as a bad burn on the spark plug coating. In an earlier post, I think you said it was chocolate brown like all the others.
 
It hasn't made sense to evaluate the spark plug in this cylinder because it was known to be misfiring. All the others were OK not great but OK. I can tell the engine is running better from the lack of effect the still misfiring cylinder is causing. Once I get the injector replaced I'll give it a run and check the plugs. For ships and giggles I did pull the vacuum line off of the FPR and plug it to see if it would idle smoother with a higher (non vacuum reduced) fuel pressure. It still stumbled but you could tell it was trying to fire. If I momentarily pinched the return line closed the idle smoothed out. The SWAG of not enough pressure to atomize the fuel is somewhere in the ballpark it seems. The "bad" injector is the only one of the 6 not doing so at the correct fuel pressure but with a raised fuel pressure it "works".

I have no reason to believe that the burn won't be perfect once the injector is replaced based on how much better the engine is running from the tune up stuff.
 
You said: "If I momentarily pinched the return line closed the idle smoothed out." Specifically, what return line are you talking about?
 
chawk_man said:
You said: "If I momentarily pinched the return line closed the idle smoothed out." Specifically, what return line are you talking about?
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I'm using car talk I guess. I'm talking about the line from the fuel pressure regulator back to the VST. It raises fuel pressure by dead heading the fuel system. Pressure just builds in the rail and all lines. I'm sure you can cause a failure somewhere by leaving it pinched for to long so I rarely advise it but it is a quick way to check if additional fuel pressure would fix your problem. I did diagnose the fuel pressure regulator by doing this and later used a gauge to see just how worn out the regulator was.
 
Got it. That sorta supports the theory that the injector may not have been sealing well due to a bad seal or weak spring.
 
What tests were done on the injector (s) and by whom?

You said you pulled them to have them cleaned. Did that involve taking/sending them to a "jobber" to have them cleaned and flow tested? If so, what did that cost and would you do that again?

Just curious.
 
I have similar symptons: Currently my fuel pressure is down to 31 psi, and its idling rough with an occasion misfire. But when the air line from FPR to the intake manifold is removed the engine idle is smooth. Honda tech consulted his Honda main service. They said, the fuel pump with over 1717 hours on it is the root cause of the pressure problem and needs to be replacement. Due to be replaced this Friday, hopefully this does it for me.

PS: I had already replaced every filter, screen, mesh, had fuel injectors professionally serviced, VST cleaned, remote fresh fuel tank used, spark wires checked out, etc. etc.
 
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jgmo said:
What tests were done on the injector (s) and by whom?

You said you pulled them to have them cleaned. Did that involve taking/sending them to a "jobber" to have them cleaned and flow tested? If so, what did that cost and would you do that again?

Just curious.
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i have a shop local to me that is outfitted with the proper equipment to clean them. They replace the screens as well. The service is $20 per injector and I'm not sure if they do a flow check. I'd want my injectors flow checked if I were replacing them all so I'll know that they were all within a tight range but I didn't ask for it due to it being an original set. It probably would have flow checked fine with the luck I'd been having with it. Yeah I'd pay to have that service done again. I don't think $120 every 15 years is a bad price to keep injectors in tip top shape. :)
 
Seachaser said:
I have similar symptons: Currently my fuel pressure is down to 31 psi, and its idling rough with an occasion misfire. But when the air line from FPR to the intake manifold is removed the engine idle is smooth. Honda tech consulted his Honda main service. They said, the fuel pump with over 1717 hours on it is the root cause of the pressure problem and needs to be replacement. Due to be replaced this Friday, hopefully this does it for me.

PS: I had already replaced every filter, screen, mesh, had fuel injectors professionally serviced, VST cleaned, remote fresh fuel tank used, spark wires checked out, etc. etc.
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I hope this fixes your problem but I won't be surprised if it doesn't. Tell them you want your old fuel pump because if this doesn't fix the issue then your old fuel pump is still good and you should hold onto that overpriced $54 Honda Odyssey fuel pump.

I did have a weak fuel pressure regulator on one of my engines but I'm not convinced that is a common problem.
 
For mine, I paid $18 per fuel injector, they did flow and spray test before and after, gave printout of test values. They replaced all o-rings and filters, they sent back the old ones. Not in the water yet, but will soon.

Add in extra cost for insurance.
 
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Nasty Wendy said:
I hope this fixes your problem but I won't be surprised if it doesn't. Tell them you want your old fuel pump because if this doesn't fix the issue then your old fuel pump is still good and you should hold onto that overpriced $54 Honda Odyssey fuel pump.

I did have a weak fuel pressure regulator on one of my engines but I'm not convinced that is a common problem.
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Yea, I was think the same thing. Not sure what honda tech is going to charge me on the pump? The Online boats parts I think their price is ~$205.

I would have done the swap myself but, I've been working on this engine off an on for the last two months. Need my time for other things.
 
Seachaser said:
For mine, I paid $18 per fuel injector, they did flow and spray test before and after, gave printout of test values. They replaced all o-rings and filters, they sent back the old ones. Not in the water yet, but will soon.

Add in extra cost for insurance.
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That is a good price. I know I could have done better on the price and gotten more service but all I wanted was to have them cleaned and with this place being a drop it off and pick it up the next day it allowed me to get them back in the engine quickly. The plan was to get it back together and go fishing but the persistence of the misfire stopped that plan. The injectors did pass the bench tests but I didn't ask for a flow check. I was told that they did look great as far as the spray pattern goes but again I didn't request any special documentation of it.
 
Well, the flow test and spray pattern IS something that I consider important.....especially if I were chasing a runability issue.

Thanks for sharing your experience.
 
jgmo said:
Well, the flow test and spray pattern IS something that I consider important.....especially if I were chasing a runability issue.

Thanks for sharing your experience.
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The cleaning was done as "maintenance". The chase of the problem didn't start until after the "tune up" and injector cleaning had been done. If I knew that I'd be trobleshooting an injector related issue then I absolutely would have it extensively tested. Yeah the engine had a miss but it was also overdue for plugs so I didn't figure on the miss being injector related. Hind sight is 20/20 and yeah now I wish I would have tested it but this type of thing can bite numerous asses a day. You know milk can spoil before the expiration date but we don't open the carton in the store to check. Some times things can catch you with your pants down.
 
Ah - the joy of owning a boat!!!!!

On the other hand, issues like this do keep the ole brain cells chugging along. Personally, I find solving mechanical problems interesting and rewarding.
 
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