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2010 BF150 miss at 4100-4400 rpms only

C

codycat

Contributing Member
I'm starting a new thread here because I believe I've ruled out all fuel delivery issues. From new tanks to fuel injectors.

My port motor will miss and drop rpms when cruising between 4100-4400 rpms. The volt Gauge and trim gauge will drop and the rpms will drop 500-700 rpms. As soon as you apply pressure to the throttle with 1 finger, it goes away. It will run all day without skipping a beat except in that range. 4000 no problem, 4500+ no problem

I have put new trim switches in and eliminated that.

Is there any sensor like a throttle position sensor or the neutral safety switch on the motor that could be doing this? Any help would be greatly appreciated.
 
Well, just a guess but you might be on to something when you mention the TPS.

They are just variable resistors and they do get "bad spots". Nowadays everyone checks them with an oscilloscope but you might catch it acting up with an ohmmeter.

That or maybe the throttle body is dirty and that can affect incoming air. Probably wouldn't hurt to clean it anyway.

Good luck.
 
jgmo said:
Well, just a guess but you might be on to something when you mention the TPS.

They are just variable resistors and they do get "bad spots". Nowadays everyone checks them with an oscilloscope but you might catch it acting up with an ohmmeter.

That or maybe the throttle body is dirty and that can affect incoming air. Probably wouldn't hurt to clean it anyway.

Good luck.
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Looking at a schematic online, and in my service manual, I am only seeing the MAP sensor and the air temp sensor. Is it the map sensor?

It is the BF150 AKO CA
 
Is this it on the side of the throttle body?
1000003998.jpg



Seems to be non removable. Does that mean to replace it I'd need to get a whole new throttle body?
 
Yes, it's integral to the throttle body. That's why it's important to test it instead of guessing.

You may be able to use an ohmmeter to "sweep" it through it's operating range and catch it "glitching" but as I mentioned before, hooking up an oscilloscope and testing it while it's being powered is a much more reliable method.
 
Sadly, that TPS looks like one that was replaceable at one time and was held on with machine screws. You might even find an exact match at a Honda car dealer but then you would find that the threaded holes for the screws aren't there anyway.
So, if it's bad, it's probably best to just get a new throttle body and be done with it.

Although ....I'm stubborn and might try doing something "different".
 
jgmo said:
Sadly, that TPS looks like one that was replaceable at one time and was held on with machine screws. You might even find an exact match at a Honda car dealer but then you would find that the threaded holes for the screws aren't there anyway.
So, if it's bad, it's probably best to just get a new throttle body and be done with it.

Although ....I'm stubborn and might try doing something "different".
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Interesting that you say that. If I look in thru the slotted holes, I can see threads. On the outside it looks like a "head" was cut off so they couldn't be removed.

So if my engine is a 2010, I should be able to go to autozone and get one from same model year? I'll need to figure out what liter size the 150 is.
 
I'm not so sure it would be as simple as that but.....maybe.

My guess is that it's probably from a much earlier designed car than 2010.

But....just a guess.

At any rate, you really need to know if that's the issue before possibly chasing something that might not actually fix it.

Additionally, many "aftermarket" electronics parts are very suspect these days so that could also trip you up if you go that way. Standard Automotive Products components are reputable though so you might want to keep them In mind.
 
jgmo said:
I'm not so sure it would be as simple as that but.....maybe.

My guess is that it's probably from a much earlier designed car than 2010.

But....just a guess.

At any rate, you really need to know if that's the issue before possibly chasing something that might not actually fix it.

Additionally, many "aftermarket" electronics parts are very suspect these days so that could also trip you up if you go that way. Standard Automotive Products components are reputable though so you might want to keep them In mind.
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So Update:

I went ahead and ordered a throttle body last week, it arrived yesterday and I threw it on today. I figure I plan on keeping these motors a while, so no hurt in having extra parts.

I did decide to test the TPS, and using the ohm meter, there seems to be a bad spot in the circuit. Using alligator clips and leads, I was able to slowly open the butterfly using both hands and a steady rate. I was able to see the resistance rise and fall steadily as I actuated it. In a spot, it loses connection and screen says OL, which as in there is no connection, then as I let it move, it goes back to a resistance figure.

Am I right in thinking, since even with butterfly closed there is still resistance, that when it loses connection at that point in the throttle opening, that it could be affecting the ecm making the motor mis fire?

The 4100-4400 rpm range is the best crusing speed for the boat, as at that speed, it handles most seas. As you said earlier could this be that bad spot in the Throttle position sensor?

New throttle body is installed, and going to try and take it to the lake tomorrow
 
Well, in my. opinion, I think you have firmly nailed the problem.

Yes, that sounds exactly what a bad spot in a variable resistor, which is all a TPS really is, looks like.

Here's hoping that your sea trial proves that out tomorrow. I think it will.
 
Almost forgot to say that there may be a base idle adjustment that you need to do with changing out the part. I don't know. I don't have the shop manual.
Just be aware that, if it doesn't idle properly then that could be the issue.
And, that adjustment, if necessary, is more complicated than simply turning a screw. It should NOT be attempted without consulting the service literature.

Good luck
 
jgmo said:
Almost forgot to say that there may be a base idle adjustment that you need to do with changing out the part. I don't know. I don't have the shop manual.
Just be aware that, if it doesn't idle properly then that could be the issue.
And, that adjustment, if necessary, is more complicated than simply turning a screw. It should NOT be attempted without consulting the service literature.

Good luck
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It fired up and idled fine on the muffs today, but I have the book if it doesn't match the other engine when I'm on the lake tomorrow
 
Well, I'm pretty confident it was the throttle position sensor. I'm still on the lake now. Been running for probably 10-15 miles. Kept her at 4100,4150,4200,4250,4300, 4400 rpms and no issues. Gonna keep running for a little while more.

To be fair, it has never acted up on the lake. But with how smooth it usually is, I'm running 4500-5000 typically.

Thank you for all your help Jgmo!!!

And the idle is exactly the same as the starboard motor, so it came pretty well set from the factory
 
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