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2000 BF115 rough idle and fouled plugs

W

wrcook

New member
A friend gave me his pontoon boat and I've been trying to get the motor to run properly for several weeks now. The boat had been in the water for approximately one year with the motor trimmed down with the foot in the water. After one year of not being run we put a new battery on the boat, turned the key, and the motor fired right up. It had a rough idle and wanted to stall when going into gear but we managed to get it going and I drove it to the boat ramp where my trailer was waiting.

I pressure washed the algae off of the pontoons and decided to see if adding fresh gas to the tank would help clear up the rough idle. There were approximately 5 gallons of gas in the tank that had been treated with stabilizer a year ago. I added 15 gallons of fresh non-ethanol fuel to the tank and drove the boat until the tank was almost empty. At the end of the trip it still had a rough idle but seemed to be running well at WOT. I did notice the RPMs would not exceed 5k. I repeated filling the tank and running it almost empty a few more times and the idle never cleaned up. My friend who gave me the boat said it sounded like it was running like he remembered at WOT. He also said it had always had a very smooth idle and it was definitely not idling like it had in the past.

Since then I've done the following to try to get it to idle well:
- replaced the plugs - they were dry fouled
- replaced the fuel filter
- cleaned out the water separator resivoir
- was puzzled by engine fuel components not matching service manual diagram - discovered it had new VST / fuel pump installed
- removed and cleaned out the VST - it had very minimal patchy residue of some kind in the bottom
- replaced the fuel injectors with rebuilt injectors
- tried to measure fuel pressure but could not find proper fitting. determined special gauge/fitting required.
- replaced the fuel pressure regulator
- replaced the ECT sensor
- replaced the IAT sensor
- cleaned and inspected the IAC valve
- tested the overheat sensor (because I originally thought it was the ECT sensor)
- removed and cleaned the MAP sensor (sprayed MAF sensor cleaner into the sensor)
- removed and tested the thermostat - it is within spec
- checked compression - didn't realize I needed to have throttle wide open - cold, with throttle closed, all cylinders were 115psi
- read in some forums that plugged exhaust could be a possible issue. Dropped the foot and inspected exhaust ports from the bottom. All clear.

After all of that the motor still has a rough idle and I'm running out of ideas. Any help is greatly appreciated!

Thanks,
Billy
 
Can get expensive replacing parts in the hope of fixing the problem. You either have too much fuel at idle or not enough air. Fuel pressure needs to be checked and idle air control (IAC) needs to be cleaned. Your compression should be around 180 - 200 psi with throttle open.
 
Yes, I have managed to get really good prices for the parts but it is starting to add up. I'd like to check the fuel pressure but can't find an adapter for the small fitting on the VST. The correct Honda fuel pressure test gauge was more expensive than the fuel pressure regulator so I decided to give that a try instead.

For the IAC, I already removed and cleaned it. I also removed it and used my hand in place of the IAC to see if I could cause it to idle properly. No luck, still won't run well with my hand being the IAC.

I plan on re-testing the compression with a warm engine and the throttle open.

Could a bad MAP sensor be the culprit? I removed the MAP sensor from the throttle body and linked in my multi-meter via some jumpers. I put my vacuum test pump on the MAP sensor inlet and as I drew pressure the voltage changed so it is at least somewhat working. I have not been able to find specifications for the MAP voltage at different pressures so I have no idea if it is operating within specification. I don't want to buy one without being sure because it is an expensive part.

Thanks,
Billy
 
I agree with lang6766 on the valve clearances. Also check the timing marks. If it jumped time by one notch, it can make a big difference in idle and high speed.

Mike
 
Thanks for the suggestions. This afternoon I'll warm up the engine and check the compression. If that is normal I'll check the timing marks and then later when the engine is cool I'll move on to the valve clearances.

Here is a video I took of the engine idling. The microphone on my phone cut out some of the frequency range but if you turn up the volume you can hear it skipping. https://www.youtube.com/watch?v=CoCHEXIt0xo. After letting it run for several minutes the plugs are dry and loaded up with carbon. I've cleaned the plugs numerous times now.

Thanks,
Billy
 
Well sure enough the timing was off by four teeth. I adjusted the belt and now it idles like a sewing machine. I was buying new engine oil and a filter for it today and mentioned your suggestions to the person at the marine store. He said mud daubers often build a nest on the inside of the timing belt and that will cause the belt to jump. We have a lot of those bugs in the area and I had to remove a lot of nests from under the engine cowling when I started working on the motor. https://en.wikipedia.org/wiki/Mud_dauber

Thanks again for all of your help. My wife thanks you too so I can stop obsessing about fixing the motor. I'll be interested to see how it runs at top-end when I take it out on the lake tomorrow.

Thanks,
Billy
 
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