Engine Missing?

97 SN GT 40 EFI

I had the boat in the water of the weekend and noticed my tach was reading a bit high. Tach was reading over 1100 at idle but was actually aroung 700-800. At full throttle, tach was reading around 6500. Boat redlines at 5800 normally. It was not a big deal deal to me at first. The RPMs seemeed to clear up over time. She started "missing" every couple of minutes. When the boat would stumble, it was very bad. The boat would slow so fast, my buddy hit his head off of the windshield. It felt similiar to hitting the speed limiter in a car.

Im not sure if the tach and the miss are releated or not. My initial thought was bad gas. Also, do these engines have a rev limiter?


Thanks
Shawn   

Check your plugs could be detonation causing the knock sensor to retard the timing. (I just went through similar symptoms)
As for the 5,800 redline what MPH are you running at that RPM. I'm thinking your tach is reading incorrectly, the GT-40 has a rev limiter set at 5,200.

I didn't mean change them, I meant check them as in look at them for symptoms of what could be causing the miss.
I had some plugs get the electrode ruined during detonation from bad fuel. After I got rid of the fuel it ran OK but not quite right I pulled the plugs and that’s when I found the bad electrode.

lots of problem with gas lately, or this boats sit during long periods with untreated gas?
Poor quality gas pump, ethanol?

I´m surprised with the low quality fuel down here, I have never experienced bad fuel symptoms in my engine! my boat is used year round at least twice a month so i´m always adding new fuel...thats probably the reason though...

Its time to change the plugs anyways. Im hoping it is just bad gas. There is definetly something wrong with the tach though.

Thanks for your input.

kapla wrote: lots of problem with gas lately, or this boats sit during long periods with untreated gas? Poor quality gas pump, ethanol? I´m surprised with the low quality fuel down here, I have never experienced bad fuel symptoms in my engine! my boat is used year round at least twice a month so i´m always adding new fuel...thats probably the reason though...

Kap
My boat sat in the garage for only about 3 weeks or so but I have no idea how old the fuel was when I bought it. The last fill-up was at the lake and could have been the bottom of the tank.
So much for Star-tron put it in when I filled up and it didn't do sh!t I think I'm going back to Sta-bil marine never had a problem with that.

TRY REPLACING THE DISTRIBUTOR cap   our friends boat had a hairline crack in their cap and #7 fired with every other plug so we put the old one on and it ran beautifully

The tach issue could be as simple as some bad isulation on the plug wires or a bad cap.

Does the tach behave if you poke on it?

I hate that you have a problem and have to wait to work on it. It makes time crawl by.

I had the boat out for the first time this year. The water is already 73 deg!! I believe I fixed the tach issue...bad connection on back of tach.

The boat seems to be running good, but its still stumbling once in awhile. It usually occurs after WOT after the boat gets down to 30-35 MPH.

I filled her up with 93 octane and added injector cleaner and fuel cleaner. I ran for about an hour and only about 5 "misfires".

Im gonna check the plugs this week.   I will also pull the tach wire off of coil.

Ill report back with plug conditions.   

I had the boat at Tionesta Dam. I couldnt believe the temp. I also heard Pymatuning Reservoir was 74 over the weekend, but it is a very shallow lake.

We pretty much stay a Tionesta even though its not good sking on the weekends.

Do you have good camping on Brady?

Boat has been running about 4900.

I removed and inspected the spark plus. The color looked good on all of them, but the ground electrode on one of the plugs was slightly bent to the side. Im not sure if it was put in this way or if it could bend while running???

Anyways, i got some Autolite AP103 to try out; its a platinum plug. I wanted 764s, but they were out of stock.

We'll she how she runs this weekend. Still betting its bad gas, but Im usually not right.

where does the tach wire feed from?

I forgot I replied to this thread last year. Sounds very similiar to my issues.

Similiar Issue

Where is the distributor stator located and is there a way to test?