Yamaha, 2002 4 stroke 115 stalls on acceleration

tonyv138 · #1 December 29th, 2008, 02:14 PM

Hi,
I had this motor for 1 season, after trolling at just above IDLE, trying to accelerate to WOT, motor dies. It restarts right away and runs just fine. It runs fine all the time otherwise... I checked sparkplugs, they look clean, even thougfh 1 & 2 are a tiny bit dirtier than 3 & 4.

Any suggestions what to look for would be gratly appreciated.

Thanks, Tony

rodbolt · #2 December 29th, 2008, 07:29 PM

this will require some testing with equipment you may not have.
what happens on rapid throttle opening is a sudden loss of intake vacum resulting in a very lean unburnable air/fuel mix in the intake.
during normal running the injection is synchroeous,meaning the injectors fire in pairs at a predetermined pulse width. during rapid acceleration,rapid throttle opening, the ECU VIA the TPS is notified the shutters just got altered drastically. the ECU then fires all injectors asynchroeously as well as synchroeously to add fuel. the pressure regulator sees a drop in intake vacum and closes, spiking fuel pressure on the rail, thereby adding even more fuel for the same injector on time.
one of these is missing.
I would check the VST and fuel rail pressures as well as TPS and TPS reference voltage for proper spec at rapid throttle opening.
you may also wish to check intake vacum at variances at the fuel pressure regulator.
this is a rather unique issue that has affected almost all brands and sizes of 4 stroke EFI motors.
it can be maddening.
my personal F150 will do it occasionally and so far I cant find out why.
my 175 E-TEC does it at slow throttle up about 2700 RPM. makes loading it on the trailer interesting occasionally.

pine island fred · #3 December 29th, 2008, 08:14 PM

Just what RODBOLT said ! I was going to respond with the same thing but go into more detail !!!! You should try to follow him at the BLUE CRAB after a few brews. Good luck. What he is saying is that you have a FADIC engine. Full authority digital intergrated control. So there!!!
RODBOLT, see you sometime in the late spring when it gets warm up there. Did you ever get married? regards FRED

tonyv138 · #4 December 30th, 2008, 01:22 AM

Genleman, thank you... Looks like a trip to a shop is in my future... Need to find a re[utable Yami shop in the Dallas area...

One question: it seems to me, based on the explanation, this should happen every time, but it does not, only after trolling. Seems that there is a good chance I am in for an interesting experience hunting this issue down... I would be gratful for any suggestions how to hunt down this sort of problems