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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #1  
Old 31st July 2008
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Default Function of the MAP sensor?

What exactly is the function of the MAP sensor on my 2006--what does it sense, what does it do, what might cause it to malfunction or send a trouble code? Does anything revolving around this sensor have an effect on the leanness/richness of either or both of my cylinders? Part of this question comes from the fact that I once upon a time got a P0107 code, but what does that mean??

I hope this isn't another stupid question.
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  #2  
Old 31st July 2008
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The MAP sensor is the accrostic for Manifold Absolute Pressure.

It is connected to the intake manifold on both EFI and Carbureted engines to monitor the changes in the vacuum (-ve pressure) that are occuring as you ride change speeds and vary the load via the throttle position. It is temperature compensated and uses a complex algorithm to help offset the pulsating wobble effect of the HD V twin's assymetrical firing setup.

It is a very major component of the final speed density calculation that ulimately determines the injector's pulse width required to sustain the best A/F ratio at any given time - for EFI setups. In Carburetor versions it assists in monitoring the degree of advance for the timing of the spark plugs.

There are several codes that it can throw out such as:

P0106 MAP Sensor Rate of Range Error Carb
P0107 Map Sensor Failed Open/Low Carb
P0107 Map Sensor Open/Low EFI
P0108 Map Sensor Failed High Carb
P0108 Map Sensor High EFI

The P0107 indicated that the reading was either absent or fell below the minimum range for a some period of time.

If not calibrated correctly or working properly the ECM will fix a canned value and use the other inputs to adjust the A/F ratio. It will in an EFI setup greatly affect your richness/leaness if it is skewed or not registering accurate readings.

I hope you have the sequence for checking the DTCs both current and historical as they have been posted several times on this forum in previous threads.


You will need to perform the DTC diagnostic trouble code check using the historical mode to see if it is still there. Then errase the error code, ride around and see if it returns.


More advanced systems also use a second sensor to just monoitor the Barometric Pressure and then use it as an offset depending on your elevation and the local atmospheric conditions.

There may more that others can add but this is the basics of the MAP sensor.

Cheers;
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Old 31st July 2008
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An 06 does not have EFI so the MAP sensor helps determine which advance curve the ignition will use. Mine failed and was replaced about six months after I bought the bike under warranty. If I remember right the bike seemed a little sluggish and was flashing lights at me showing a fault. Other than that it did run with no other apparant problems.
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Yup, on the carburated 04 and later bikes, the spark timing curve is selected by the Ignition Module from RPM input and manifold air pressure input (from the MAP sensor).

In other words, engine rpm and engine load (manifold air pressure) both play a role in determining what spark timing is needed at any given situation.
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Cool, thanks for the info!

Checking the codes, the P0107 no longer exists. This code popped up after I took a ride in mid-80 degree temps and was cruising at about 90 for ~3 miles when I had my engine light pop on and my engine cut out briefly. I checked my oil temp--250. This was the first time anything like this had happened. It happened again in slower conditions a couple of months later. That was two months ago.

Since then I have been trying to diagnose why my oil temps have climbed 30+ degrees since doing a Stage 1 change (or trying to determine if these two things were simply correlative rather than causative). My rear cylinder goes way lean after about 75 mph while the front remains steadily slightly rich. I'm trying to determine what's going on that one cylinder is fine and the other is starving for fuel. Could this be caused by an ill-informed spark timing curve?
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Bumpty bump...
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Did you happen to change the brands of oil and/or the filter at or around the time of the sudden rise in oil temperatures?

Having too little total advance would add some heat overall when travelling at the speeds you mentioned you may want to do a full advance reading to be sure.

The disparity in front to rear A/F reading is more suggestive of a leak in the rear intake manifold allowing for a leaner mixture to the rear and disproportionate amount of fuel to the front cylinder.

I would re-set the intake couplings and switch the spark plugs front to back and see if it repeats the colour variation.

These symptoms can sometimes be very hard to prove until you have tried every possibility.

I hope one of the above will point you to the source -maybe.

Cheers;
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Quote:
Originally Posted by Fe Head View Post
Did you happen to change the brands of oil and/or the filter at or around the time of the sudden rise in oil temperatures?
No, I had the initial heat rise and engine light occur at roughly 8k miles while still running HD dino oil. I had recently performed my Stage 1 prior to this occurring. I switched to semi-synth Castrol Actevo at my 10k service, but my high temp phenom still occurred.

Quote:
Having to little total advance would add some heat overall when travelling at the speeds you mentioned you may want to do a full advance reaing to be sure.

The disparity in front to rear A/F reading is more suggestive of a leak in the rear intake manifold allowing for a leaner mixture to the rear and disproportionate amount of fuel to the front cylinder.

I would re-set the intake couplings and switch the spark plugs front to back and see if it repeats the colour variation.
I checked for intake leaks with WD-40 to no avail. Reseating the intake was something I was thinking of doing, in hopes that this might solve the issue. At this point, it's about the only thing I can think of, aside from something internally wrong.

Thanks for the suggestions!
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Old 31st July 2008
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I've checked for leaks before using WD-40 or a propane torch and though they can show you for sure that you HAVE a leak, I don't know that the test tells you for sure that you DON'T have a leak.... i.e. unless you're running the motor at 4k rpm under a load when you do it (and I doubt you'd notice the result as well then), I'm thinking there could still be a leak that shows up only under load...
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Quote:
Originally Posted by Kev M View Post
I've checked for leaks before using WD-40 or a propane torch and though they can show you for sure that you HAVE a leak, I don't know that the test tells you for sure that you DON'T have a leak.... i.e. unless you're running the motor at 4k rpm under a load when you do it (and I doubt you'd notice the result as well then), I'm thinking there could still be a leak that shows up only under load...
Agreed. So do you think reseating the intake to the head is the best approach to (hopefully) address this? Would it be worthwhile to replace the seals while I'm at it? I'm just trying to reduce the number of times I have yank stuff off.
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