Yamaha 98 250 EFI V76 driving me crazy

[joserrr]

I have a Yamaha 250 EFI 1998 that has raw fuel comming out from the exhaust. Have replaced injectors, ecu, both low and high press fuel pumps, flywheel, trigger coil, crankshaft poss. sensor, all 6 coils, ox sensor is within specs, throttle poss sensor adjusted and in spec, motor was rebuilt, starts right away, timming is at 24 degs instead of 7 at idle, please help my mechanic has over 25 years of experience and has good knowledge of yamaha outboards.

 

[huanca]

Re: Yamaha 98 250 EFI V76 driving me crazy

why the timimng difference? stick to he original specs. <br /><br />are all cylinders firing? seems like one or more is missing. you have 6 cyls so your enigne may be running on 4 and you might not notice it. with the enigne running at idle and in nuetral, unplug each spark plug wire (careful not to get a shock) and see if it makes a difference on the sound of the eninge. if it does, that cylinder was firing, so plug it back on. try the next one. eventually you will reach one or more where unplugginf the spark plug makes no difference. that of those ones were not firing. once you know which one it is, see if there is a spark to the plug (hold the plug cable close -1 cm- to the engine and you will see and hear the spark if there is one). if there is no spark, try switching complete cold and cable assemblies form a working plug and cylinder (dont just cross connect them, rehook it up). that will determine if the problem is the coil-cable assembly or the spark plug or the cylinder. if this does not pinpoint it, try the spark plugs. if this does not do it, run a compression test on all cyls. good luck

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

test the throttle position sensor again asa well as the crankposition sensor. also check the needle assy in the VST also test the fuel rail pressure regulator. the 24 degrees idle timing indicates there is a serious problem. that motor only idles on 5 cyls and drops another between 850 and about 1800 RPM. <br /> the main timing control is the TPS also test the thermosensor. has anyone used the diagnostic lamp on this motor? if they are not familiar with yamaha and the CCS and SMART systems it will toss you a curve ball.<br /> good luck and try to find a tech that is trained in yamaha EFI that incorperates the CCS

 

[bigbrownbuku]

Re: Yamaha 98 250 EFI V76 driving me crazy

i would check the needle in the vst also. the overflow is typically straight into the intake.

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Hi, we have used the test lamp and is giving code 1 wich is all ok, the crankshaft poss. sensor is new, the fuel press is 36pounds, the VST was replaced with a good one and kept doing the same, the thermosensor is within specs, the tps also on specs, also we are being advised by the master mechanic on the distributor here in P.R., havent taken the boat there because it is about 2 1/2 hr drive. Any help will be aprecciated.

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

hello<br /> find another master mechanic. has anyone indexed the flywheel? the 24*advance indicates there is a problem. or you can replave the entire powerhead and the problem will be solved. please post the test results from all of the running readings. high and low speed charge coil outputs,temp sensor out put as well as tps and o2 sensor outputs while running. parts swapping is a waste of time. trouble shooting is much quicker and easier.<br /> good luck and keep posting

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Hi, the os output was .50-.60 volts at idle, the flywheel was indexed and the timming was correct at tdc on cyl 1, we are parts swapping because I had access to the parts at no cost. The powerhead was rebuilt and when we started the engine the light gave the code of the cps so it was replaced. I'm missing a tach on the boat so there is no rpm reading, the tps reading at idle was around .50-.53 volts. <br />Thanks

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

the correct test for running on the o2 sensor is to remove the airbox and with the engine running and the meter attached close the airhole in the #1 butterfly with your finger. the o2 sensor should react and react again when the finger is removed. test all orange wires for 5V dc the orange wire is power for the sensors. also test the red spark plug caps.<br /> has fuel rail pressure been tested?<br /> with the timing at 24* at an idle the idle speed should be very very high and unstable. so that tells me the CDI is either broke,recieving bogus TPS information or the flywheel is not properly indexed to the crank.<br /> good luck and keep posting.<br /> PS any sensor failure that affects timing will lock the ign at 7* BTDC.<br /> creating a high idle so at 24*BTDC the idle will be almost uncontrolable.

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Hi, will test the os that way, Im using the Yamaha service manual but it does not explain very much on troubleshooting and how to do the tests. The cdi or ecu was replaced and did the same. The fuel press is 36 pounds before the reg. What can be causing the timming to be so high, idle is very rough and raw fuel is comming out of the exhaust, the spark plug caps tested ok before the coils assy were replaced.

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Just a follow up. Bought the test light to read codes, gave the code to the TPS, replaced the TPS, went to the water to test the boat and the boat ran fine for a while, stopped for about an hour then the engine did the same problem, installed the code reader and TPS came again, changed spark plugs and started right away removed TPS adjusted out from holder idled ok, reinstlled and went for a ride, rangreat for about 2 hrs did 45mph by gps. Tried trolling and full throttle rus ok, when ready to load the boat engine didnt want to accelerate. Any clue to why its giving TPS code with a new TPS, all the engine harness is ok no corrosion or broken cables teste it myself. <br />Thanks

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

hello<br /> check the orange wire in the harness for 5 vdc.<br /> I am suspecting you have a bad splice somewhere. it must be checked while the engine is acting up. the ecu sends a 5vdc reference voltage to all the sensors. there are a few splices under the blacktape in the harness. they are not sealed well and are prone to corrode.<br /> good luck and keep me posted.

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

another check the book does not list.<br /> the tps is just a variable pick off resistor<br /> from black to orange should have a fixed resistance, from orange or black to red the resistance should vary smoothly when the tps arm is moved. do the test with the tps disconnected and with an analog meter. digital wont work.<br /> good luck and keep posting

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

ooops<br /> on my last post I printed the wrong wire colors<br /> pink is pick off for ECU feed back. orange to red should be 4.75 to 5.25 volts. the pink wire wipes a resistor and that varies the current and thus the voltage.

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Hi, just a follow up, Checked the tps harness and looked OK, spliced new wires from TPS to CPU and didn't give TPS code(18)then adjusted TPS to specs and gave code again and black smoke came out, adjusted by ear and ran ok, this was done out of the water. Went to the water ran good up to 3/4 throttle at full throttle died back to 3/4 ran ok, trolled for about 30 mins. and fouled the spark plugs, replaced spark plugs ran fine to the ramp. Took the boat to another mechanic about 2 hrs away adjusted TPS to specs, code 18 again did some spark tests and said stator is bad not enough power to coils, the batt charge coils are good 14.2 volts at batt. Can that be my problem. The stator was the only part I didnt exchange.

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

hello<br /> a bad stator should not give a tps code. however if the voltage to the coil primarys is failing it will cause plug fouling. while not common there were some stator problems that showed up only when warm and will pass the resistance test but not the voltage output. if the output voltage to the CDI is below spec when warm then its quite possible to have a bad stator.

 

[rodbolt]

Re: Yamaha 98 250 EFI V76 driving me crazy

hello<br /> another thing. all the computer sees is the improper TPS voltage, the 5 VDC reference is generated inside the ECU and fed to all the sensors. the computer looks for a return within a specified range. therefore when getting a code for TPS its imperitive to test the 5 volt reference on the orange wires as well as the pick off signal going back. usually if everything tests good you will find a bad splice in the main harness. the only good way to find the bad splice is to untape the entire harness.<br /> remember all the engine sensors,well most, recieve the 5 volt reference signal via the ECU on the orange output line.

 

[joserrr]

Re: Yamaha 98 250 EFI V76 driving me crazy

Hi, just a follow up and the end of this saga. Had the stator rewound, the shop guy said that the coils where bad so that probably was the problem, installed it and the motor sounded stronger but had the same problem. A friemd gave me a new engine harness and some sensors also ordered a new temp sender installed temp sender and harness and atlast there was no raw fuel thru the exhaust. Went to the water today and the engine ran perfectly, 45 miles by gps. Thanks to everyone who helped.<br /><br />Thanks Jose

 

[John from Madison CT]

Re: Yamaha 98 250 EFI V76 driving me crazy

Jose: I've been following your saga for sometime now and am happy to hear you have found the problem.<br /><br />Wow, I never thought a problem like yours could be a Temp Sender and harness.<br /><br />John