2003 SX150TXRB HPDI running erratic

[Captain RW]

Runs fine sometimes and short on power at other times. When it is low on power the tach is very erratic like when it should be showing about 3700 it will go up to 6000 then it may come down to 5600 then go back up again. The erratic readings on the tach seem to coincide with the low power problem. Recently cleaned the O2 sensor and VST screen and installed new NGK BR7HS-10 spark plugs all of which seemed to improve the running just slightly but not completely correcting the problem. Compression was 119-124. Ran fine since new until this fall. Any suggestions will be greatly appreciated as the local Yamaha "GURUS" are just itching to change the ECM or do a "complete rebuild". Hoping everyone is having a great holiday. Best regards, Capt. Roger

[rodbolt17]

find a real technician.
and please put the PROPER plugs in your motor
the BR7 is the complete WRONG plug and was never used in any HPDI.
RPM information is sent to the ECU via a pulser coil, from there the ECU converts it to a tach drive signal.

find a real tech that has access to tech bullitens,the single driver HPDI motors could use 1 of 2 plugs depending on the coil connector color.
you MUST go by the coil connector color to insure the correct spark plug. sometimes the decal and the service manual are WRONG.
the tech bulliten has the correct information for plug selection on the single driver HPDI.

look on your "guru's" wall.
look for current master tech certificate or at least electrical and fuel training certificates from Yamaha.

if they are not there find a real dealership.

[rodbolt17]

oh, and something is wrong with your model number.

its either an HPDI OR an SX.
cant be both.

[boscoe99]

Methinks it is an OX66 and not an HPDI. Reason being is that the SX150 does use a BR7HS-10 spark plug.

[Captain RW]

You are correct OX-66 my bad.

[rodbolt17]

ok,
but still look for the certificates on the wall.
the OX66 motors used the same pulser coil to ECU and ECU to tach arrangement.

could it be the ECU?
in the 10+ years of the OX66, and most my work is 150 + with twins, I have seen two ECU failures.
one had the oil control module go bad the other shut down one bank of cylinders below 1800 RPM.

I would be surprised if its an ECU failure.

[Captain RW]

Rodbolt17 does the erratic reading of the tach suggest anything.

[rodbolt17]

suggests you may have an erratic pulser coil signal,a voltage loss issue dunno, that's why dem dar wall cerrts are rather impotant. unless you just wish to insert the knife between the second and third rib.
what brand and type of tach is it?

[Captain RW]

. Analog Sea Pro. Yes I already know if a cheaper one was available they would have put it on there.

[rodbolt17]

that tach is very sensitive to voltage issues. so is the electronics on the engine.

double check all battery cables/connections and all ECU ground wires.

[Captain RW]

CaptSolo there is no change in RPM's just a change in the tach reading during the same time the engine has a slight loss of power. Other times the engine runs fine with no erratic reading on the tach. I normally run at or near 3800 RPM's and saw a reading of 6000 for a time yesterday when it was running poorly without changing the throttle position.

[boscoe99]

Do you get any codes on the tach? Put it on the YDS and check for Codes.

Problem sounds like a fuel issue to me. A slight restriction will cause the RPMs to drop from 6000 to 5600. Look for fuel leaks around the hoses around the VST and the HPH on top that feed the rails and injectors. I've had "leaks" on the high pressure hoses (they are found on top of engine on my F225s) that caused stalling issues at idle. Also kept me from getting the top RPMs (6000) I was looking for. Fuel leaks can cause a fire. I had one of those, so check for gassy smell and dripping around the cowling while at idle. When fuel hoses leak gas you can see (drops), smell and taste the gas. Then you look for the source. On the HP hoses the leaks are around the OEM fittings and the clamp is often the culprit. Cheap fix.

Another thing to try: Run the engine on a dedicated 5 gallon gas can. If the problem (surging - drop in RPMs by 400 for no apparent reason) goes away with the gas can, the problem is before the engine - i.e., the RACOR filters or hoses; the fuel tank pick up clogged causing a restriction, the primer ball. or water in fuel.

Run a can of Yamaha Combustion chamber cleaner for $9. Run the stuff through the (4) intakes at 2400 RPMs. Go intake to intake. When can is empty, shut it down and let sit for 24 hours (i.e., engine in the running position). Don't tilt up engines. On start up, let run for 30 minutes at idle or take it out front and go WOT under load, then change the plugs. It will run better for sure after the Combustion cleaner.


GLTY

YDIS is not operable with an SX150 model.

What tachometer will work with an SX150 and display codes?

[Captain RW]

No spun hub and no increase in RPM's just an increase in the reading on the tach. My good ear is probably more accurate than the Sea Pro tach.