CB900F (919) running rich - ECT? - Wrist Twisters
 
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post #1 of 14 Old 10-28-2014, 04:14 AM Thread Starter
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CB900F (919) running rich - ECT?

Hey Guys, Need help with my '05 919

A few months ago the Honda snapped a throttle cable. I tried to hook a new one up with the throttle bodies still on but just could not get it in the hole/slot so I stripped it down to remove the throttle bodies (TB) as per the service manual. I was not confident of getting the TB off without damage because they were stuck on pretty good so I trailered the bike to a local shop to pull the TB off and fit the cable for me. Job done I trailered the bike home and put it back together.

While apart I took the opportunity to check valve clearance, change plugs and replace all fluids. It was due for a service.

When I get it back together I had the common issue of a slight misfire between idle and about 3500 rpm. I had to ride the clutch a bit more to take off. Above 3500 rpm it was running fine. If it was a carbied bike I would suspect that the choke was still engaged on a warm engine.

I took the bike back to the shop and got informed that it was the MAP sensor. I brought a second hand one, at least thinking it would make a difference. No difference. The shop then started blaming the TPS. I found the brilliant thread where you got the Honda Civic one and modded it (thanks guys it saved me a fortune). This made no difference. By this time I was starting to loose faith (and money) and decided to do the diagnostics myself and save the money.

Judging by the plugs it appears to be running rich. when I pulled the plugs out after about 100km plugs 1,2and 4 were covered in carbon but they were not consistently across all 4. I cleaned them up and reversed the order of the plugs (plug 1 into cyl 4 and so on) to see if it was the plugs or fuel. It appeared one plug was pretty much stuffed as it was the worst of the lot in cyl 1 and cyl 4 but any plug in 1 and 2 cylinders were fouled up as well.

I have had a good search of this forum which has been a great source of info and have checked many things.
There are no alarms on the MIL. I cleaned up the ground on the frame.

I checked the FPM for leaks. None apparent. I checked the voltages and resistance on MAP, TPS, IAT and ECT. They all were withing tolerance with the exception of the resistance of the ECT. The manual 2.3-2.6K Ohms @20 deg C. The ambient temp was about 27 deg C and I got a resistance of 1.83K Ohms. This seemed a bit low to me even with the temp difference. This was backed up by the fact that the bike seems to run a lot cooler now according to the gauge. I had it running for at least 5 min with some generous blips of the throttle and the gauge barely made it over the cold engine line. The fan did not start at all.

I seem to remember reading somewhere( but cant find it again) that the ECU uses the ECT temp to change the ECU map to richen a cold engine to effectively be an electronic choke. Please correct me if this is wrong. If this is the case could the ECT sensor be the issue with my running rich problem? Not sensing warm engine and not changing the ECU map

Sorry for the long winded explanation. There are some pretty knowledgeable guys on the forum so I am hoping someone Can help with this. I need the Honda up and running for work and riding it in peak hour like this is a bit risky.

cheers

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post #2 of 14 Old 10-28-2014, 05:51 AM
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The MAP Sensor is what the ECU relies on at lower load/RPM, which works off of engine vacuum, so the shop was on the right track looking at the MAP Sensor. My guess based on your sequence of events (the problem started after some work was done) is that something wasn't put back together properly and you have a vacuum leak somewhere. Since both you and the shop did the work it would probably be tough to pin it on them. I would check all of your vacuum connections and the intake boots on the throttle bodies. You could do a visual and check that the clamps are all tight and also spray some carb cleaner at the connections with the engine running and listen for changes to try to pinpoint the leak.

Best of luck!

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post #3 of 14 Old 10-28-2014, 06:06 AM
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Quote:
Originally Posted by marylandmike View Post
The MAP Sensor is what the ECU relies on at lower load/RPM, which works off of engine vacuum, so the shop was on the right track looking at the MAP Sensor. My guess based on your sequence of events (the problem started after some work was done) is that something wasn't put back together properly and you have a vacuum leak somewhere. Since both you and the shop did the work it would probably be tough to pin it on them. I would check all of your vacuum connections and the intake boots on the throttle bodies. You could do a visual and check that the clamps are all tight and also spray some carb cleaner at the connections with the engine running and listen for changes to try to pinpoint the leak.

Best of luck!

I second the motion! Its possibly a vacuum leak ... damaged intake boot or cracked vacuum line etc.

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post #4 of 14 Old 10-29-2014, 05:34 AM
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If you had a hard time taking off the TB, then the boots are probably rock hard and no longer providing a good seal.

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post #5 of 14 Old 10-29-2014, 03:14 PM Thread Starter
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Thanks for the replies guys. I have some spare time today so I will try the carb cleaner on it.
When we I was looking at the MAP sensor I gave all the vacuum lines a visual check and they looked OK.
I will give the boots a good hose down with the carb cleaner and see what happens.

cheers

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post #6 of 14 Old 10-30-2014, 03:33 AM Thread Starter
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I got the bike up and running and sprayed carb clean all over the TB boots, MAP sensor vacuum tubes, No change to idle speed. I did replace the plugs again and today it was running reasonably. I will take it to work tomorrow (60km round trip) and pull the plugs out on the weekend and see how it is going.

Can someone please explain how the ECT effects the air/fuel ratio. I measured it again today and the resistance across the sensor is way down on spec. It is starting to warm up here (Australian Summer) and the temp guage is barely getting above the cold engine mark.

cheers

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post #7 of 14 Old 10-30-2014, 06:50 AM
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When you fuel pump primes, does it have 1 solid tone or does it change tones midway through?

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post #8 of 14 Old 10-30-2014, 07:23 PM
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Quote:
Originally Posted by RobR View Post
I got the bike up and running and sprayed carb clean all over the TB boots, MAP sensor vacuum tubes, No change to idle speed. I did replace the plugs again and today it was running reasonably. I will take it to work tomorrow (60km round trip) and pull the plugs out on the weekend and see how it is going.

Can someone please explain how the ECT effects the air/fuel ratio. I measured it again today and the resistance across the sensor is way down on spec. It is starting to warm up here (Australian Summer) and the temp guage is barely getting above the cold engine mark.

cheers
Some info here on how the ECU uses coolant temp to adjust fueling. Normally adjusts fuel on warm-up or overheating.

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post #9 of 14 Old 10-30-2014, 07:57 PM
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Have you checked the Fuel Pressure Regulator?

Those are a known weak spot in those bikes.

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post #10 of 14 Old 10-30-2014, 10:07 PM Thread Starter
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Quote:
Originally Posted by marylandmike View Post
Some info here on how the ECU uses coolant temp to adjust fueling. Normally adjusts fuel on warm-up or overheating.
That was a great article. Thanks. So if the ECT was reading a low temp. It could effectively be making the A/F ratio richer.
The thing that has be stumped though is if the resistance over the sensor is low the less voltage drop across the sensor which would mean higher voltage across the gauge which is theory should read high not low. Basic Ohms law.

I checked the guage and it reads full scale deflection as per the service manual when shorted. It would be worth changing over the sensor but it is an $85 part in Oz.( Not to mention the wait time because they are never in stock).
I would be prepared to pay the cost if I knew it was definitely the problem.

cheers

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post #11 of 14 Old 10-30-2014, 10:13 PM Thread Starter
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Quote:
Originally Posted by Sniper View Post
Have you checked the Fuel Pressure Regulator?

Those are a known weak spot in those bikes.
Yeah I did read this on the forum and did suspect it might be the problem so I did the standard checks. Warm up differential on the pipes. Not conclusive. Sso I moved to the vacuum line and replaced the Number 2 cylinder tube with clear as it was getting more carbon that Number 3. No sign of fuel.

I'm not sure if it is a valid test but I even put a vacuum pump directly to the FPR and applied some vacuum. There was no leak down on the pump gauge. Like I said I do not know if this was valid as I did not have the 50psi fuel load applying pressure to the other side of the diaphragm. FPR was off the bike.

cheers

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post #12 of 14 Old 10-31-2014, 04:11 AM
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Quote:
Originally Posted by RobR View Post
That was a great article. Thanks. So if the ECT was reading a low temp. It could effectively be making the A/F ratio richer.
The thing that has be stumped though is if the resistance over the sensor is low the less voltage drop across the sensor which would mean higher voltage across the gauge which is theory should read high not low. Basic Ohms law.

I checked the guage and it reads full scale deflection as per the service manual when shorted. It would be worth changing over the sensor but it is an $85 part in Oz.( Not to mention the wait time because they are never in stock).
I would be prepared to pay the cost if I knew it was definitely the problem.

cheers
I'm not sure exactly how the circuit works between the sensor resistance and the gage, but it's very common with the 919 that the temp never hardly gets off the cold mark, unless you are riding in traffic.

I pulled and tested my thermostat in a pot of water on the stove and it was right on spec (180 F). I changed out my thermostat for a 195 F one and my bike seems to be running less rich because I can no longer smell the exhaust stink and the temp runs at the 1/4 mark on the temp gage. I have the 900RR headers so the stink was no longer a big problem, but I could still smell it at stoplights and in the garage before the thermostat change.

I never had any of the symptoms like you are describing though.

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post #13 of 14 Old 11-08-2014, 01:01 AM Thread Starter
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Thanks for the helps so far. I have been away working for a while so I haven't had a chance to work on the bike.

I put in some new plugs and have ridden approx 100km. Ran find initially with a slight miss down low. I just kept the revs a bit higher than usual by staying in a lower gear.

See the attached picture of the plugs after 100km of moderate riding.
Plug 1 is about right. Plug 2 is very rich, Plug 3 is very lean, and plug 4 is a bit on the rich side. These plugs were brand new.

Any suggestions welcome.
Attached Images
File Type: jpg DSC_0478 (640x360).jpg (114.1 KB, 26 views)

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post #14 of 14 Old 04-12-2017, 01:00 AM
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Hey, I wonder if there is any update on this.

oryrider.blogspot.com
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