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BF150 micro surging issue in mid RPM range

D

dcastillo

New member
Hoping for a little direction/help on my motor issue. Ill try to keep it quick.2004 honda BF150
~1000hrs
up until this summer she pretty much ran perfectly for her age. Over the summer I ended up with a thermostat cover leak which through horrible engineering design, gets water into the air intake. Unfortunately I drove it for a few days in the keys this summer without knowing this was going on.
Fast forward to now... leak is fixed, and Ive ran a bottle of seafoam through her as well as sprayed in the intake while running for a bit. Spark plugs were corroded (even though she still ran) so those were replaced. I inspected the throttle body (without disassembly) and it didnt look bad.
symptoms:
she fires right up with new plugs, jumps out of the hole just fine. around 4K rpm or so she sometimes does a surging thing where she momentarily loses power then comes right back (very quickly). It seems like theres no issue when I take her up to 5k RPM, she run great....


Sadly I am trying to sell her (season of life) and would like to get her running better before I do.


Any thoughts on what other issues could cause the micro surges in the mid rpm range?
thanks for any help
Danny
 
Hi,

Not the resident expert on these but I will pose a couple of questions. You seem to indicate that this symptom pretty much "popped up" in conjunction with your discovery of the Tstat cover water leak and spark plug "damage". Is that correct?

I will say it's interesting that the engine seems to function very well except for that specific rpm "band". That could make figuring this out difficult at best.

I am always suspicious of electrical connections on outboards especially in cases where harmonic vibrations set up at varying speeds and engine loads might come into play. To that end, I might tend to want to inspect and clean all connectors that I could easily access. Especially considering the water intrusion issue.

But one component that is very rpm specific here is the throttle position sensor (TPS). I can't instruct you on how to do it on your engine but you may want to look into performing a simple "sweep" test" to verify that the operation is smooth and there are no "glitches" at or about that 4k throttle setting.

Another component or it's connections that might cause this sort of complaint would be the load sensor. The manifold absolute pressure (MAP) sensor is vacuum activated so close inspection of the hose as well as the electrical connector is something to do. The hose can crack and leak, especially where it slips over the connection nipples at either end. Also make sure that the sensor's vent to atmosphere is unobstructed.

Beyond those "ideas", I see that the crankshaft position sensor is located near where the water was leaking so scrutinize that well too.


When was the last VST cleaning or fuel filter replacement? Just curious.because you never know.

Good luck.
 
Really appreciate the response and insight. In response to your comments (in order)

Yes, after the water leak was found, which was discovered as the alternator got saltwater on it and seized up and needed replaced, it was the next trip out that I noticed the surging issue.

I will double check the connectors that I can easily access when I get the boat this weekend and see if I notice anything

For the TPS, I think I found it on the motor and can try taking it out this weekend as well. From what I can tell its just a variable resistor that I can ohm out through the range right? It looks like I cant buy it directly, but I know a local salvage guy that has a completely torn down motor that likely has the part.

I may also grab the MAP sensor from hi,m as well

I definitely will double check all the hose connection around the top of the engine to see if any are loose or appear damaged, thats definitely possible with all the times I had to take her apart and move the hoses around.

As for the VST, I am really hoping thats not the issue. Im fairly handy and have done a lot, but when I looked up the vst earlier this year, it did not look like something I wanted to tackle.

Thanks again for your advice and hopefully I will find time around my sons base ball tournament this weekend to take another look.
-Danny
 
Last edited:
Hi,

Yes, you are correct, the TPS is a variable resistor that, in most cases, can be checked unpowered using an ohmmeter. As with most electronic sensors it has a "working range".

As I said, I'm no expert on these. My fuel iinjection experience is automotive based. But I believe these are very similar.

It would be best to have the specifications from the manual but, if not, I would expect the sensor to read approximately 0.5 to 0.9 ohms at no throttle and somewhere between 4 to 4.5 ohms at full throttle.

As you "sweep" the sensor from no throttle to full the resistance should change smoothly with no spikes or dropouts. Sweeping the sensor slowly and doing it several times is the best practice.

That test should suffice but many auto techs these days prefer to test TPS while it is powered and connected to an oscilloscpe or professional level scanner to reveal minor faults and electrical "noise" that can sometimes occur.

It's great that you may have another one to compare it with.

I hope others here with actual experience with your outboard will offer better advice.

I will say though that you saying the alternator was replaced is information that has me thinking...could this be related? Did you notice this symptom right after doing that? If so, you may want to disconnect the alternator and test drive to see if that makes a difference.

Good luck.
 
If you've had water through the engine it will have damaged the O2 sensor, this is the most common cause of the symptoms you describe
 
thank again guys.
I didnt have much time this weekend due to my kids travel ball but checked a few things.
-none of the hoses seemed damaged or loose
- I checked the TPS and it appeared to cleanly sweep from about 800 Ohms to 4.7KOhms no issue

I read online that a bad MAP sensor could lead to running lean which would cause surging and overheating, so 'hopefully' that is the culprit.

So the MAP new is 120 and the LAF (O2 sensor I believe) is over 300
they are on Ebay (not the ones shipped from china) for around 40 and 120ish...
would I be taking to much risk trying to save money?

thanks
Danny
 
There is a way to identify the problem and that is with the use of DrH, a scan tool where you can watch what each sensor is doing, that however takes experience. In the 20 years I've been working on these I have never replaced a map sensor causing this issue, they usually fail completely and log a fault. The O2 sensor on the other hand is a different story, over time they become "lazy" and still work but become slow to react resulting in surging in the midrange. So, no gauranteed answer, if you work without proper diagnostics you are risking buying parts unnecessarily as so many people have done in the past on this forum.
 
Just want to add to what Ian is telling you because what he is saying makes perfect sense in your case. AND...He IS one of the resident pros on this Honda forum IMO.

The possibility of the 02 sensor being "poisoned" by the suspected water ingestion is very logical. I didn't suggest that to you because my background is automotive and salt water ingress never happens there. I should have thought of that anyway though.

I also agree that MAP sensors rarely need replacement. More often than not a MAP sensor gets "skewed" because of a plugged vent or a cracked vacuum hose.

The 02 sensor and the MAP could be diagnosed with a digital multimeter but you would need the wiring schematics and specific knowkedge of what to look for. We checked them on cars that way (back in tha day) before most shops used oscilloscopes and pro scanners.

As Ian says, the Dr.H is the way to go here if you can swing it. The diagnosis fee might end up saving you money in the long run.

Good luck.
 
Been trying to get back to the site to post an update but my browsers keeps giving me a redirect notice and wont load for some reason...

Changing out the O2 sensor seemed to fix the issue. No more surging felt on the last test run... If the weather holds I may take her out offshore next weekend for one last fishing trip before she (hopefully) sells.....

thanks again for all the help and advice...
-Danny
 
Thank you for the update dcastillo. Here's hoping your sea trial and sale go well as a result the O2 replacement.
 
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