98 OX66 225 fuel concern

[23Contender]

Ok guy's really hope I can get this solved. Having a issue with a high idle(1200 rpm's) and won't rev over 4200 under a load. Parts replaced low pressure fuel pumps, VST filter, on the motor fuel filter, water separator filter and housing, spark plugs and a cleaned O2 sensor. What I have found is even after pumping the bulb when the motor starts the fuel level in the on the motor fuel filter drops down to about 2/3's full and that's when it idles high and won't rev over 4200. Now if I pump the bulb when the motor is running the on the motor filter will fill up and the idle drops down to 700 and she will rev out to 5500 and runs like a raped ape. Fuel pressure is at 36 psi at idle even when acting up. The guts to the check valve between the on the motor and low pressure fuel pump have been removed. Not sure how to go about isolating why the level of fuel in the on the motor pump drops after its started after its off for more then 15 or 20 minutes. Oh yea compression is between 120 and 125 on all cylinders. Thanks for the help guy's.

Don C

[rodbolt17]

as its on the SUCTION side the fuel filter cup runs at about 1/2 full.
not your issue.

the primer bulb is also in the suction side and no it wont stay hard while running.

have you checked the ign timing while its idling high.
have you checked O2 sensor output voltage?
TPS voltage?
a quick check with the diagnostic test lamp would be nice.

[23Contender]

as its on the SUCTION side the fuel filter cup runs at about 1/2 full.
not your issue.

the primer bulb is also in the suction side and no it wont stay hard while running.

have you checked the ign timing while its idling high.
have you checked O2 sensor output voltage?
TPS voltage?
a quick check with the diagnostic test lamp would be nice.

Thank you for the reply. How would I go about checking timing?
I will check the TP and O2 voltage the next time I put it in the water. It's about to storm here any minute so I can't do it tonight. I also don't have access to a test lamp. Is it possible to make one myself?

Now my question and believe me I'm not doubting you about the fuel thing at all, just trying to understand, When the fuel level in the motor filter is low it has exposed the filter element. Now as soon as I pump the bulb and fill the filter on the motor the idle comes down and I get full power. I'm guessing the O2 sensor is giving funny readings and the "extra fuel" richens it up enough to get it out of open loop. Just trying to rap my head around what's going on. When I get it in the water I'll check those voltages and let you know.

Don C

[23Contender]

Ok took the boat out tonight, had a break in the weather. Got to the ramp ready to check TP and O2 sensor ran great at the ramp. Let it idle for a little bit and shut her down, started back up ran great. I put the cowl back on and went for a little ride all was good shut her off sat for a few minutes. Shut her down again and drifted few minutes started it back up and again was great. Rode a few more minutes and then drifted 15 minutes. When I fired her back up she was at the high idle and no power. I tried pumping the ball and still had the concern. So I shut it off and fired her back up and idle was normal but when I gas it throttle it took a lot of throttle before it "kicked in". I shut it off and it was ok again. I didn't get to check it, the rain was coming so I put it on the trailer and came home. When I came home I swapped out the O2 with a known good one I had. Tomorrow I will swap out the TP with a good one I have and retry. The more I think about it I think I have a bad TP because of the way the throttle seems to be delayed. If that doesn't fix it I'm going to have to buy a flash tester to check codes. Any more idea's you guy's have I'm open to any info. Thanks

Don C

[rodbolt17]

don't know what you have, your taking the splatter gun approach at trouble shooting.
couple that with no clue of what your troubleshooting and expensive things happen.

start with basics.
compression.
spark.
lift pumps
IF and only IF a sensor,other than O2, fails or gives an out of range feedback base ign timing goes to 7*BTDC and idle speed increases.

that motor does like to eat lift pumps.

O2 sensor is NOT monitored for faults or failures.

[99yam40]

a timing light is used to check timing just like on your automotive motors

[23Contender]

don't know what you have, your taking the splatter gun approach at trouble shooting.
couple that with no clue of what your troubleshooting and expensive things happen.

start with basics.
compression.
spark.
lift pumps
IF and only IF a sensor,other than O2, fails or gives an out of range feedback base ign timing goes to 7*BTDC and idle speed increases.

that motor does like to eat lift pumps.

O2 sensor is NOT monitored for faults or failures.

I have gone over the basic's several times
Compression is at 120 on 4 cylinders and 125 on the other cylinders.
The low pressure fuel pumps are brand new Yamaha units.
The VST filter is Brand new not cleaned.
Water separator filter is brand new and the housing is new
Fuel pressure at idle it is 37 psi at full throttle when it was happening it was 33 psi.

I don't have a diagnostic tester to get a code. I have a shop manual and according to that the temp sensor, TP, crank sensor, Knock sensor will cause the high idle and dropping of two cylinders. I have checked the temp sensor as per the manual, I have checked the knock sensor as per the manual and both passed. I don't have the test harness for the TP so I have to check it on land by back probing the harness. The problem is intermittent so it makes it difficult to have everything set up to run test when it happens. I can be out all day and it happen once or twice.

I replaced to O2 because I have a known good one and I have a known good TP so I can set it up on land and if it's the problem then yea me. I'm a tech for cars and truck by living. This is far from the ideal way to try and perform a repair but short of paying someone to fix it for me I have to make due. I thought it was a fuel problem when the filter on the motor had the little bit of element exposed, so my thought was it was getting air into to fuel system.

Thanks for everyone who has given help with my concern.

Don C

[rodbolt17]

reread that manual.
the ONLY thing that causes 2 cyl top drop on an SX or S OX66 is the CPS and the ECU.
AND its designed that way.

between 600 and 800 RPM it drops cyl 5.
between about 800 and 1800 it drops 2 AND 5.

its called CCS.
VX OX66 motors DO NOT use CCS.

if any sensor faults occur base ign timing reverts to 7*BTDC and all cyl fire.

that's when it idle high.
typically the base idle timing is ECU con*****ed and is about 7* ATDC.
the pulser coils are physically mounted at 7*BTDC.
the ONLY sensor not monitored for failure is the O2.

depending on the sensor ign timing may or may not advance and top speed may or may not be reached.
other than that its a simple closed loop speed density EFI setup.
unlike a car it will try to alert the operator that there is an issue and it does have various defaults for a sensor failure.

don't believe me?
simply unplug a sensor,other than O2, while its running and watch the ign timing and the idle speed.

[23Contender]

reread that manual.
the ONLY thing that causes 2 cyl top drop on an SX or S OX66 is the CPS and the ECU.
AND its designed that way.

between 600 and 800 RPM it drops cyl 5.
between about 800 and 1800 it drops 2 AND 5.

its called CCS.
VX OX66 motors DO NOT use CCS.

if any sensor faults occur base ign timing reverts to 7*BTDC and all cyl fire.

that's when it idle high.
typically the base idle timing is ECU con*****ed and is about 7* ATDC.
the pulser coils are physically mounted at 7*BTDC.
the ONLY sensor not monitored for failure is the O2.

depending on the sensor ign timing may or may not advance and top speed may or may not be reached.
other than that its a simple closed loop speed density EFI setup.
unlike a car it will try to alert the operator that there is an issue and it does have various defaults for a sensor failure.

don't believe me?
simply unplug a sensor,other than O2, while its running and watch the ign timing and the idle speed.

Please don't think I don't believe you, if I thought I knew it all I wouldn't be asking for help diaging my boat. I have come to the realization that I'm going to need to buy a diagnostic lamp to get an idea of what's going on. I had her out today for some striper fishing. It ran bad at 5 am so not much to do revved it hard ran great the rest of the day except for a stall at idle and didn't want to restart for a few minutes. Started then ran great again. It never happens when I'm at home in the river, just early in the morning. Will it store a codes like a car or no? Again I'm am happy for the help you have given me. I have to stop thinking of it like a car.

Don C

[rodbolt17]

next time your at your car mechanics shop.
ask the tech a question.
tell him your car runs well for a few minutes at 5000 RPM then loses power.
watch the blank stare.
yes you auto will run 10-15 minutes or longer with no issues at 5000 RPM.
however jonny law may have an issue with it.

no that ECU wont store a code.
it will only display an active code.
if more than 1 code is there it will only show the lowest numbered code.