View Full Version : throttle surge
06-09-2013, 11:38 AM
My 05 XStar with 8.1L Indmar has been acting up last two times out on lake. I do not use the perfect pass, so I use the hand throttle to "manually" control speed, rpms, etc.
Recently, when I throttle up hard to pull skier or boarders, the rpm's drop and the engine does not respond/recover until I back off the throttle and "gently" throttle up to approximately 3800 rpm's. Engine doesn't "cough" or sputter, it just refuses to accelerate aggressively.
I replaced fuel pump last summer and also had MC dealership update the software codes. In the past month, I've noticed a slight whine that I attribute to the alternator bearing going bad. Otherwise, 496 engine has just had routine maintenance and oil changes every 50 hours since I've owned boat.
Any thoughts or ideas?
06-11-2013, 12:45 AM
06-11-2013, 09:36 PM
Just had a similar issue on my boat. I cleaned all the fuel filters and inlet screen on the fuel pump and it fixed my issue. I was skeptical that this would fix my issue but it did. I guess I didn't realize how much trash was in my fuel tank. Ps. I had replaced my fuel pump less than 2 hours before this problem started, so it definitely could be your issue.
06-11-2013, 09:38 PM
Mine had the same exact whine as well and it was the fuel pump starving for fuel.
06-12-2013, 07:47 PM
Thanks for reply Tateau18. I'll clean the fuel filters and fuel pump screen next time out and see what happens.
I started troubleshooting by checking the Perfect Pass and had there tech services walk me through a control test and a series of reprogramming. Nothing seemed to make a difference with engine surging, so I disconnected DBW Master Module to send in to PP for software update.
Unfortunately, the throttle surging continued after removal of PP, so it's not going to be that easy of a fix. The Perfect Pass technician sent me this tech bulletin so I might give it a shot before having to haul boat 3 hours away to a MC dealer.
06-12-2013, 10:31 PM
I'll add the link to my post about the issue I had, it sounds identical to your issue. The problem is the ethanol fuel eating the inside your fuel lines and getting stuck in the pump inlet screen most likely. In that post is the link to the how to thread on cleaning the filter. It took me about 20 minutes to do. Good luck.
06-17-2013, 06:25 PM
Tateau18 - sent you a PM.
I noticed my fuel gauge had dipped below the 1/4 full marker, so put 20 gallons of non-ethanol gas in boat Friday night. When returning to boat slip from gas dock (5 minute ride), throttle surging was still present. Before l left marina, I cleaned the electrical ground on engine block with battery corrosion cleaner and a wire brush. It was getting late so I didn't take boat for a drive after cleaning corrosion off engine ground.
Today I took boat out on lake and the engine purred with no hint of surging! I throttled up 8-10 times from 0-35 mph in the few minutes I had to be out on the water and the 8.1 never surged. I'm returning to the lake tonight to confirm the surging has been resolved, but I'm cautiously optimistic it will be.
Any ideas what was causing the throttle surge and what I did to fix it? In 16 months owning my boat, I have never let the fuel tank get this low (always refuel to full tank when gauge is half full).
08-22-2013, 08:40 PM
Previous post was "accurate" for exactly one month and then the surging started again while on week vaca at TRL in late July. When surging returned, it was not remedied by filling fuel tank full. I changed the fuel filter (old filter was little dirty, but not bad) and engine still surged.
Long story short, a MC dealer friend let me borrow his fuel pump compression gauge which lead us to the culprit. At key up, fuel pump pressure was 35psi (should be 50-60psi for my pump) which was suspicious, but when engine started it immediately jumped to 55psi. I had to launch boat and run it down lake to cause surging and SURE ENOUGH, engine surging directly correlated with compression gauge dropping down to <25psi.
I had replaced fuel pump with auto parts store carter pump last summer, so I decided to take a 4 c-note upper cut to the chin and purchase a new MC fuel pump (complete fuel pump and hardware) this time. The day the MC pump was suppose to arrive, Dave mentioned he had seen black tubing kink inside fuel pumps on other MC's and recommended I check that before installing MC fuel pump system. He gave me a $0.50 corrugated tubing to replace the black thicker tubing inside the fuel pump.
VOILA - it worked!! Thankfully, the owner of Ski-N-Sports didn't mind keeping the new MC fuel pump and it only ended up costing me 60 bucks for the overnight shipping charge.
A few weeks later, I saw the fuel pump thread in which the "hose" issue is addressed with great info and pics on the first page of post.
08-22-2013, 09:02 PM
This video of me running fuel pump compression test sucks, but it's all I've got. When vid starts and engine is on, the dial on gauge is in 1:00 o'clock position (58psi) but once I throttle up to 2500 rpm, the dial drops to the 10 o'clock position (25psi).