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2008 Yamaha WR250x won't start

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Straight to the point.  Have had the bike for a year or so now, ran relatively strong besides some bogging and flaming out (only happened a few times) within the first 15 minutes of riding. Rode it home from work, everything seemed fine on the ride; next morning, wouldn't start. It turns over just fine, even got it to start for a bit, but would slowly die. Things I've done so far..

1. Replaced the battery

2. Replaced the spark plug (check the spark and it seemed good)

3. Pull the fuel injector, cleaned it and it seems to be operating normally (hooked up the electrical with it out and turned it over - injector seems to open)

4. Replaced the fuel pump and filter - cleaned out the fuel lines and replaced the fuel

Still have the same result.  The strange thing is, I can get the bike running and stay running by spraying seafoam into the airbox and pulsating it every second or two. Once I stop supplying the seafoam, it flames out. Anybody have any ideas?

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The Seafoam trick makes it very likely (better than 95%) that the problem lies in fueling.  It can be complete failure to inject fuel, wrong amount of fuel, or improperly timed injection.

 

Poor pressure, poor injector trigger waveform, and injector defects can often be confirmed by examining the spray pattern of the injector.  Typical faults shown in this video:

 

You can test with the injector removed and attached to the bike's harness, but it is dangerous to be spraying fuel.  Use all reasonable precautions to reduce the chance of fire, and have a fire extinguisher handy in case.

 

You can use the built-in diagnostic mode to trigger the injector.

 

Info here:

 

 

Use youtube search function with "Yamaha fuel injection testing" to bring up some factory videos.

 

 

Lastly, you may be able to see the spray pattern installed in the bike with a USB Endoscope. About $30 on Amazon.  I have not used this method, but it seems possible.

Edited by BluePill

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The '08's had fuel pump issues , I see you replaced it . A used one or new ?   The above info is good ^ .   For watching injector spray use a clear glass or plastic tube and hold the injector at the top opening and the other end down in a gas can or something to catch the gas , then the mist/spray is confined inside and the gas get collected without being airborn .

 

You can also trigger injectors by a simple 12 volt wire running from a battery to the 2 contacts on top the injector , however the fuel needs to be connected to a pump that's pressurizing it same as in the bike . Probably easier with the onboard diagnostics since this bike has it , some don't .

 

 

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Update - I took the injector out of the motor, while it was still connected to gas and electric and tried to start it. The spit seemed weak, so I ordered a new injector and threw that sucker in and it started up and ran for a minute or two and flamed out. However, the idle was quite high and the slightest throttle would bog down the idle. 

I feel like this is electrical at this point - ECU or stator?. Would anyone else agree with this assessment?  Does anyone know if you can troubleshoot a bad ECU through the built in diagnostics? 

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4 hours ago, Skloops said:

Update - I took the injector out of the motor, while it was still connected to gas and electric and tried to start it. The spit seemed weak, so I ordered a new injector and threw that sucker in and it started up and ran for a minute or two and flamed out. However, the idle was quite high and the slightest throttle would bog down the idle. 

I feel like this is electrical at this point - ECU or stator?. Would anyone else agree with this assessment?  Does anyone know if you can troubleshoot a bad ECU through the built in diagnostics? 

1. Based on your bog problem: Possible that with all your work you may have created a vacuum leak in the intake, or the TPS is out of range.  Recommend a visual check of the intake tract and injector seal to look for any place where air may be sucked in.  Do the diagnostic test #1 to be sure that the TPS has proper range.  Also do the coolant and air temp. sensor tests. Wiggle the connectors at each component while testing, in case you have a bad connection. You should not get any change in readings when you wiggle.  Make sure that any connections to the throttle body (Vacuum hoses) are proper and secure.

 

2. ECU would be unlikely, but it is always good to unplug it, clean both sides of the connection carefully with a bit of Electrical Contact Cleaner, then blow off with low pressure air.  A hair dryer set on low or no heat works if you don't have a compressor available.

 

3. Stator could be a problem.  Easy test.  #1 = charge the battery overnight with a proper low rate charger or maintainer.  #2 check the voltage at the battery while cranking - it should stay above 9.6 volts.  #3 = Start the motor with the Seafoam and verify that the voltage goes up to 13.8 to 14.6 volts.  If so, stator is most likely good.

 

Question: Was the Stator recall ever done?  If you are not sure, a dealer can check with your VIN for completion.

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If you want to look for stator failure, just remove the left crankcase cover.  If the stator coils all are light brown like the photo below, it is probably good. If some of the coils are dark brown or black, it's bad.  There is oil in there, so you will either have to drain it or lay the bike on the right side before removing the cover.

 

S1r8yDL.jpg

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Just remembered.  I had a Pressure Sensor fail on my old WR.  It caused the bike to stall and bog, but ran OK at high speeds.  The book test is useless, but I removed the sensor and bench tested it by applying variable vacuum and found that it failed at high vacuum (Idle and low speed conditions) but tracked ok at lower vacuum (equal to higher speed with larger throttle openings).

 

I diagnosed and repaired it soon after the symptoms showed up, so I never got a total no-start condition.  From your original description, possibly yours had been intermittent for awhile, and has now gotten worse.

 

This is my video of the failed sensor:

 

 

Note how the bar graph on the meter suddenly jumps to zero at higher vacuum.

If you have or can get a hand vacuum pump (Mityvac) you can do the test yourself.  You will also need a standard USB 5 volt power supply and a digital meter for the test.  I can give you the hookup info if you want to try it.

 

For comparison, here is the same test with the new sensor:

 

 

Edited by BluePill

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I appreciate all the feedback.  I'll report back as soon as I get through these tests.  Thanks again!

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So you were right about the vacuum leak - my injector wasn't properly sealed. Fixed that and it returned to running strong, with the addition of sea foam in the air box, of course. I tested the voltage and took a peak at the stator and everything seemed good. Judging by the stator's condition, I believe it was replaced because it looked brand new. 

What you described with the pressure sensor failure is familiar to how my bike has ran the past year. I always assumed it was acting that way because of it not being hot yet (maybe this did play a part in a way; usually within the first 15 minutes of riding), but occasionally the bike would stall after letting off the throttle and sometimes would die on idle at a stop light (again, no throttle input). Sometimes giving it throttle when idling, it would stall as well. However, it never bogged at regular/high speeds when throttle was actively given.

According to the codes:

13 - Intake Air Pressure Sensor (Open or short circuit) - IAP Sensor open or short circuit detected - Can be started? Yes - Can be driven? Yes

14 - Intake Air Pressure Sensor (Pipe System) - IAP sensor-pipe system malfunction (clogged or detached hose) - Can be started? Yes - Can be driven? Yes

Is Yamaha indicating, that the bike can function without the sensor all together? If this was the case, would the sensor be influencing the operation of the engine that much? (sorry for the noob question, haha)

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I reviewed my notes from when I had the problem.  Codes 13 + 14 came up more than once.

 

My notes:

12-15-2014
Dirt slides in Milton.  MIL on, rough idle and stalling.  Somewhat better after trip home.  Wash bike.

12-16-2014
Read out code 16 (TPS)  Add free play to throttle cable.  Try to perform idle reset, but stalling.  Disconnect battery and jump +/- cables.  Road test local.  Idle seems ok, but MIL on with code 13. Pressure sensor wiring.  

12-29-2014
Rode about 75 miles.  Possible bad gas?  Mil came on a few times for a short time.  Stalls at stops at times, other times is OK.  Holding throttle partly in neutral give effect like Honda EFI cut out - ie revs, then drops, repeats.  Noid lite diagnosis?

1-1-2015
Flushed fuel tank. No water seen.  Change spark plug.  Lube and clean connectors at ign. coil, MAP sensor, ECU, injector.  Road test. Sets code 13 again.  Runs OK at high cruise, Mil comes on when closing throttle and coasting down from speed. Still stalls and runs rough at idle/low speed. Need to check for vacuum leak or jumpy MAP voltage at high vacuum.
(Possible that MIL is set by rationality check of MAP voltage vs. TPS position?)

 

After this, I did the vacuum test and confirmed the pressure sensor (MAP) was faulty.  A new one cured the problem.

 

If you backprobe the connector wiring at either the Sensor or the ECU, you should be able to monitor the voltage while riding.  If you see the sudden jump at higher vacuum readings, that would verify a defective sensor.

 

RE: your question about running with a bad sensor.  When failures are detected in many of the monitored circuits, the ECU will often switch to a default program that tries to guess the approximate values needed to keep the motor running.  It will substitute calculated values based on the other inputs (speed, rpm, TPS, etc.).  This is called "Limp Home Mode".

 

More Here:

https://www.quora.com/What-is-limp-home-mode-in-a-car

 

 

Edited by BluePill

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Well, just swapped out the pressure sensor with a fresh one, with the same result. This one definitely is lost on me - it definitely seems to be a fueling issue, but I feel like I've hit every major part in that system.

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OK.  Back to basics.  Did you do the TPS test (Diagnostic test #1)?  If so, try it again about 20 times in a row and look for erratic numbers.

 

Besides the TPS and the Pressure sensor, the Coolant and Air temperature sensors have considerable authority over fueling.  If either of those go wonky at times, the A/F ratio will suffer.  You can substitute a fixed resistor for both sensors in order to test.  Choose a value of 80 degrees for the air and 180 for the coolant.  Bring the motor up to temperature, then shut down and put in the resistors.  Otherwise you may have a problem starting from cold.

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