MAP sensor wired backwards

[Susty]

1985 VMax purchased from my cousin Walt w/abt 35K mi on it in 2007(?). Ran good at high speeds or wide open but poor gas mileage, and backfiring and running rough at low speeds. In Fall 2011 found MAP sensor plug wired backwards with sensor output where +V should be & vise versa. Appears to have come from the factory this way. Did web search and could find no other listings with this problem. Anyone else heard of this? Didn't drive bike much due to this problem. Now repaired, runs great, primary bike when not cruising for which I use an 06 FJR. :clapping:

 

[naughtyG]

Welcome to the site! Never heard of your problem but it's very interesting to know. I'm wondering, what is the MAP sensor and where is it on the Max?

 

[wildweasel_pt]

Its the Boost sensor and its on the front coils rack hosed to the front left intake manifold...

 

[naughtyG]

Aha, boost sensor - that makes sense now.

 

[Susty]

MAP= Manifold Absolute Pressure. Does not effect Boost. Adjust timing by sensing manifold pressure. Boost sensing uses RPM and still worked fine when MAP wired incorrectly

 

[naughtyG]

Ok so you mean the unit that attaches to the vacuum hose from carb 1 right?

 

[Susty]

No, vacuum hose comes from the #2 intake manifold on my bike. #2 cyl being front left by my book

 

[KJShover]

No, vacuum hose comes from the #2 intake manifold on my bike. #2 cyl being front left by my book

Normally there is, It's possible the previous owner or the bikes mechanic was changing things.
Dyna makes reference to the tube as well, in the dyna 3000 instructions. Maybe that's why it worked with the MAP not wired right, cause it was never getting the vacuum it wanted, so it didn't give you any ignition advance. So there might be a chance, you have been missing out on a little bit of power. :rocket bike:

 

[naughtyG]

My bad on the cylinder numbering - I did have a blink about it trying to remember the 1-2-3-4 order on the Max!

Of course it is

front wheel
2 3
1 4
rear wheel

so the vacuum hose is on #2 :worthy:

 

[Susty]

To KJShover: My hose is connected exactly as your photo shows. Attempting to install a Dyna 3000 and using the indication LEDs on the Dyna pointed me in the correct direction to find the MAP plug wired backwards. There was absolutely no indication that anyone had previously modified the plug wiring which leads me to believe it came from the factory this way. Because of the way it was wired it was making the "brain" give full advance timing (checked with voltmeter), that's why it would run well at full or high throttle and poorly otherwise. Its too bad it took so long to find.
The bike is running on the stock "brain" at this time. After I repair the front brakes (so it stops as good as it goes) I will re-attempt to install the Dyna. Will the Dyna make a noticable improvement?

 

[KJShover]

To KJShover: My hose is connected exactly as your photo shows. Attempting to install a Dyna 3000 and using the indication LEDs on the Dyna pointed me in the correct direction to find the MAP plug wired backwards. There was absolutely no indication that anyone had previously modified the plug wiring which leads me to believe it came from the factory this way. Because of the way it was wired it was making the "brain" give full advance timing (checked with voltmeter), that's why it would run well at full or high throttle and poorly otherwise. Its too bad it took so long to find.
The bike is running on the stock "brain" at this time. After I repair the front brakes (so it stops as good as it goes) I will re-attempt to install the Dyna. Will the Dyna make a noticable improvement?

sweet, so no chasing other's modding ideas. I hate that, I've done it on a few of my old bikes and it's no fun.

As far as a noticeable difference. Dyna folks say a 2-3hp increase depending on the curve. but that's not going to be noticeable. (I'm using curve setting #4) What I did notice was a little bit better mileage (about 2-4mpg), easier starting, and a more crisp throttle. I mainly bought it for the ignition retard modes and the rev limiter. The shitty thing about it is that for the early Gen I's the dyna had a two-step, but they dropped that feature for the later Gen I's.

Them ignitions that Dingy scored, sound like a kick ass unit. If I were to have to replace my Dyna, I would go with one of them.

 

[Nielsen]

What do you mean with "the early Gen I's the dyna had a two-step" feature ? What is two-step ?

 

[KJShover]

What do you mean with "the early Gen I's the dyna had a two-step" feature ? What is two-step ?

A two step rev limiter is something that is used in drag racing.
How it works is when its switched on it, at first it wont go over a certain RPM, like 6000. This is the first step.

So when your at the staging beams, you crack your throttle and it wont go over 6000. as soon as you launch the bike will now go into the second step which is the high rpm revs, like 9500.

Its great for consistency and motor protection.

If you watch some prostock motorcycle or prostock cars or other classes that use them, just before the lights fall, you'll hear them go up against the 1st step of the 2 step rev limiter.

http://www.youtube.com/watch?v=JTY4kaBLnhA&feature=related