GT-40 RPM SURGE

[randall]

HELLO NAUTIQUE DEVOTED- I am the new owner of a 96 sport nautique with a efi pro boss gt-40 it has 390 hours. My problem is the engine is surging up and down I usually feel it with crusing speeds - It starts about 10-15 minutes after the engine is running. I have change the plugs -FCC filter -oil -trans fluid and impeller. I am at my wits end!!! I noticed the sherwood water pump is leaking- could that cause a surge I wonder? I dont have a perfect pass.

[Rock_Toy]

That's one of my symptoms as well, along with backfiring and the engine dying. Could it be bad gas?

[Teleman]

I just called Adirondack Marine. He said to try to clean the Idle valve ind the injectors.

[schiffsnautique]

gt-40 rpm surge

i have a 93 with the 351 and coil pack. i have noticed surges as well at long cruising. luckily, i don't cruise much, but wondered what would cause this issue. i've never had the engine stall out but had a loud pop a year ago when the engine was under strain from pulling a skier. it turned out to be a loose ceramic on one of the spark plugs. the boat always fires immediatley whether in the water or on the "fake lake" in the driveway. i've had problems with coils on vehicles and have read that the coils on these boats are so called "bulleproof" , but why does skidim have the option to revert back to a distributor? you can guess.. are the coils causing a miss that the engine would surge or not want to run it all?? i'm not a fan of coils by any means..., but a distributor maybe an option for some of these older models. i would love some feedback

[DavidF]

RE: gt-40 rpm surge

You have the ProTec ignition system and PCM no longer manufacturers parts, so they make you convert to conventional (old school) ignition should a component fail as they will not sell replacement parts to you. However, if you have a TBI engine with the Protec, then PCM will indeed sell you new old stock parts they are hording for the TBI owners. I sold my TBI boat a couple weeks ago. Two times out and the new owner experienced a coil pack failure. He was able to get it replaced. So, the coil packs are anything but bulletproof.

[nms1991]

RE: gt-40 rpm surge

First you need to check your fuel pressure when it is surging. Aslo what octane fuel are you using?

[Teleman]

RE: gt-40 rpm surge

Just Cleaned the intake and injectors yesterday (Ran sea Foam right into the gas line) let sit for about 5 min. (It obviously mixed with the remaining fuel in the FCC). While appart I was checking the Idle valve. Noticed if I put my finger over the intake to the idle valve it starts to surge. Anyhow, I cleaned the filter on the output side of the idle valve port and it appears to run smooth. It looks like that filter can make or break the idle (and midrange) smoothness. It seems to get mucked up with the valve cover vent that goes into the intake. Why can't that vent go to somewhere outside rather than to the intake? It seems to just clog everything up. Maybe a small air filter in-line with the vent hose to remove all the oil mist that vents out.

[Rock_Toy]

Glad to see that you got your problem fixed. I'm with you on the vent line running up to the filter. Bet yours wasn't nearly as bad as mine was!!!

[Teleman]

Not even close!! Looks like you had it running in a dust storm!! Try taking off the idle valve and cleaning the filter. I used laquer thinner to clean it out. It is a stainless steel ball of wire that is used as a filter. About 1/2" thick. It just slides into the port but the gasket will have to come off too, the filter is bigger than the hole in the gasket.