BIG 1996 Shamrock 220 WA Project

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
Now that I'm thinking about it more, it may not be the transmission after all.

Basically what happened is I'd advance past 2000 rpms and it would cut the power, the revs didnt rise but fall. I would think if the trans slipped the rpms would rise instead of drop.

So I suppose I may have some sort of electrical sensor issue with this TBI system. Would this engine maybe have a limp mode that it's activating? Not sure where to start with these sensors.
 

TK246WA

Well-Known Member
Aug 18, 2020
147
17
South shore, MA
Now that I'm thinking about it more, it may not be the transmission after all.

Basically what happened is I'd advance past 2000 rpms and it would cut the power, the revs didnt rise but fall. I would think if the trans slipped the rpms would rise instead of drop.

So I suppose I may have some sort of electrical sensor issue with this TBI system. Would this engine maybe have a limp mode that it's activating? Not sure where to start with these sensors.
Not sure about the limp mode, someone else may know more. I’ve learned that pumping the oil and transmission fluid out rather than draining is better (for me anyway) so I can put the exact amount I pumped out back in. An example is I just changed the transmission fluid and filter on my hurth. Everything I read said 2.13 quarts but it actually took almost 3 whole quarts which is what I pumped out.
 

deputyrpa

Well-Known Member
Supporting Captain
Aug 28, 2010
1,195
85
Fort Ann, NY
I've not been paying attention to this thread for a while. I agree with others here that you've done an amazing job with this boat. She's beautiful, and you should be very proud!

I'm not fixated on the tranny in your case. I've had one slip, and I've had one internally destruct. You are correct that the revs spike during those events.

Now to throw some things out regarding the rpm dive. Fuel pressure and volume are the most common causes of low rpm. If your fuel pressure or fuel flow is good at idle, either or both may drop off at WOT. I remember you have the new fuel pump (because I bought one too!), but I would check the fuel return lines, fuel tank valves,, and most importantly, the fuel tank vents.

But before you go taking stuff apart, get a 5 gallon (or so) gas can and take her out for a spin running off the gas can. If she revs fine, you will know that the issue is in the fuel lines, filters or tank vents.

Lastly and maybe... did you mess with or adjust the engine timing (should be 10°BTDC)? Is it jumping around at idle? If so, the computer was not put in diagnostic mode first in order to set the base timing. Does she rev up and hold revs fine in neutral?
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
I've not been paying attention to this thread for a while. I agree with others here that you've done an amazing job with this boat. She's beautiful, and you should be very proud!

I'm not fixated on the tranny in your case. I've had one slip, and I've had one internally destruct. You are correct that the revs spike during those events.

Now to throw some things out regarding the rpm dive. Fuel pressure and volume are the most common causes of low rpm. If your fuel pressure or fuel flow is good at idle, either or both may drop off at WOT. I remember you have the new fuel pump (because I bought one too!), but I would check the fuel return lines, fuel tank valves,, and most importantly, the fuel tank vents.

But before you go taking stuff apart, get a 5 gallon (or so) gas can and take her out for a spin running off the gas can. If she revs fine, you will know that the issue is in the fuel lines, filters or tank vents.

Lastly and maybe... did you mess with or adjust the engine timing (should be 10°BTDC)? Is it jumping around at idle? If so, the computer was not put in diagnostic mode first in order to set the base timing. Does she rev up and hold revs fine in neutral?
Thank you very much! Appreciate the advice.

She does rev up fine in neutral, which is what has me perplexed. Idles and cruises around slowly SUPER smooth, it's just under load that I'm having the issue.

Have not messed with the timing so hopefully that's not an issue. I did check the vent as well.

It definitely feels like the motor is getting a bad reading and cutting power under load. Has a new temperature sender so that shouldn't be it, also just put in a new oil pressure sender this morning- hoping that was the issue as it did stop working yesterday.
 

deputyrpa

Well-Known Member
Supporting Captain
Aug 28, 2010
1,195
85
Fort Ann, NY
Are you certain that the new fuel pump you installed can actually deliver the pressure @volume necessary?

If it runs the same off a little gas can, you can narrow it down a bit.

Also, use the DIY code reader I explained in the Mechanic thread and see what codes you get.
 

Fish Witch

Well-Known Member
Apr 1, 2008
1,121
132
Anchorage and Seward, Alaska
You can look in the air intake to see if both injectors are firing when the rpm drops to see if it's in limp mode. Happened to me on my last boat and drove me nuts. And a code reader won't tell you anything with limp mode problems as it's doing what it's supposed to - duh! After spending $600 on a Rhinda laptop analysis program I tracked it down to a bad oil pressure switch. It's a NC switch that opens with pressure and if it doesn't cuts one injector out. A temp sensor does the same I believe. Pulling the lead to the switch will keep it out of limp mode, but be sure it has good oil pressure. Swapping injector leads will tell you if it's the injector or limp mode btw. Good luck and great job on your boat. And the picture of Pt. Pleasant brings back memories. I drove a Pepsi truck during college delivering up and down the shore during the summers.
 

boataddict

Well-Known Member
May 19, 2020
170
33
Point Pleasant, NJ
Well, this is certainly the happiest of my updates so far. It turned out that the new fuel pump I originally purchased was not functioning properly. I don’t know why or how, but I replaced it with Carter pump number P5001 and had immediate success.

I’m happy to say that after a little less than a year’s work I finally got her out and up to cruising speed. Thrilled to say the least.
IMG_20220531_200803.jpeg


What a phenomenal boat. Love the handling, and she’s super comfortable cruising around 3000 rpm’s and makes about 20 mph comfortably in that range. How many gallons per hour do you all typically get at cruise? I’m curious.

Having only owned a 20 foot Wellcraft V20 Steplift previously, which was a great handling boat for its’ size, this boat is a big step up in pretty much every way. I’m taking it easy on her at first, trying to ease into running regularly and going on longer and longer rides.

Still have some miscellaneous things to take care of, like fixing the gauges (all but the tach stopped working) and the lights, but overall I’m very happy with where it sits to enjoy it this summer.
 


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