1994 225HP Yamaha surging

My port Engine, Yamaha Mod L225TXRS will no run smoothly between 1400 and 3200 RPM. it seems to run fine below 1400 and above 3200 but if you try to run in between it surges back and forth between the two speeds. The dealer rebuilt the carbs, changed all three fuel pumps, tested compression and vacum, changed all spark plugs, ran combustion chamber cleaner, replaced water separators and filters, replaced electric primers with bulbs and after having the boat for 3 weeks charged me $1600.00. Said the motor ran fine. It does not. After this I did the following, all with no improvement.<br /><br />-removed, cleaned and re-attached all grounds<br />-swapped computer module from starboard motor<br />-swapped all coils from starbord motor<br />-swapped crank sensor from starbord motor<br /><br />When I try to run between the above rpms and put a timing light on the motor, the timing jumps beteen 4 DegBTDC to 4 DegATDC, Runs up in rpm at 4DEGATDC and drops in rpm ar 4degBTDC<br /><br />Questions:<br />-Could it be the throttle position sensor?<br />-Can I bypass the sensors (throttle, temperature) so that the computer cannot cause these wild timing swings and if so how?<br />-Any other suggestions?<br /><br />Need help Please

Re: 1994 225HP Yamaha surging

it could be the TPS. it can also be a temp sensor telling the motor its cold. use the test harness to isolate the TPS. watch the TPS voltage as the engine surges.<br />also test the crank position sensor if equipped.and now I will ask the killer question<br /> is this a 2.6L motor or a 3.1?<br /> that will be critical<br /> post us back with that and we shall see what we can deduce<br /> good luck and keep posting<br />]

Re: 1994 225HP Yamaha surging

Thanks for responding. How do I isolate the TPS?. I already swapped crank sensors between motors so I dont think that can be a contributing factor. Also I dont know if the motors are 2.6L or 3.1L. THe model number is 225TXRS, does that tell you the size? Also I believe from the shop manual I have that it is a 76 deg V6 not a 90 deg and that it is the same as the 250HP. Would that mean it is a 3.1L<br /><br />Thanks in advance

Re: 1994 225HP Yamaha surging

Rodbolt, or others please reply....<br />I have 1994 twins same engine, with erradic surging also between 1500-3500rpm. 450 hours, not used often, plugs look pretty good, tank ran to bottom recently. Just bought the boat.<br />Also, my idle is low @ 500rpm. High speed seems to run well.<br /><br />Other engine is a whole other story....I'll post that in a new thread.

Re: 1994 225HP Yamaha surging

the v76* motor is rather uniqie in the fact that the carbs can have the fuel flow altered slightly by the computer based on a few inputs. if the computer senses a rapid acceleration by the TPS it will add about 20%more fuel to compensate. also if a t-stats sticks open it can drain the #6 fuelbowl at high speeds. the knock sensor if triggered will retard timing and cause some erratic functions. if dissconnected it will lock the timing at about 7*btdc. the TPS on those engines did give some troubles. monitor it with an analog meter to look for fluctuations. set it with a digital but what the analog will show is rapid fluctuations. the wiper arm on some of the early ones was not strong enough. this motor also has the capeability to have a diagnostic lamp attached. it usually only tells you what is not broke but nevertheless its an invaluable time saver. but you must first eliminate all the mechanical 450 hours in 10 years is almost neglected. make sure the fuel pumps are rebuilt or replaced and clean out the carbs. test the sparkplug caps. the other issue we had was stator failures.<br /> sometimes it will take 20 or 30 min to find but if the test equipment is left attached and you see the stator CD charge voltage going from 150 to something about 70 to 80 volts replace the stator.<br /> usually that will show up as a random cyl plug fouling.<br /> good luck and post back a bit more info.

Re: 1994 225HP Yamaha surging

To clarify the previous post, there is a wire going into the computer module (I forget the color) which you can disconnect if you are having problems that are causing the computer to set the timing so wrong that the engine won't run - instructions for disconnecting it are in the owner's manual - it will cause the timing to be fixed at 7 btdc so you can get home. But you are not having a problem that severe so disconnecting the wire won't prove anything - it won't isolate which sensor is the problem, if any. The ohmmeter test is the one to do on the TPS. I am on my third TPS in 11 years (375 hrs) and I am almost willing to bet it is your problem. You do need the test harness and a DVM to calibrate the new one, although the physical replacement is trivial. The service manual describes the calibration - it is very critical - don't try to use a cheap voltmeter.