Bike was running a bit crappy lately, so decided to check the settings on the fuel injection in accordance with service bulletin M-1105 and YouTube videos. Was a simple procedure, and now the bike is running like a contented kitten with a belly full of cream. Most here dont care for the Magneti Marelli injection, but its actually a pretty simple beast, akin to an electronic carburetor. There are really only 3 adjustments that can be made without an aftermarket tuner.

1st off, Throttle position sensor, needs to be set to .275 volts with throttle blades fully closed. VERY IMPORTANT!!. a lower voltage will skew the mixture leaner (ECU thinks the throttle is more closed than it is) a higher voltage will skew richer (engine thinks throttle is further open than it is). being that these bikes are a bit lean normally, err to the higher voltage when adjusting (within reason) The ecu takes tps voltage to point to a section of the fuel map, if this is off, you are looking at the wrong part of the map, causing poor performance

2nd, cold Idle adjustment, needs to be about .670 volts for proper cold idle. easy peasy

3rd, warm/hot idle, set to 950-1050 rpm for proper charging and oil pressure.

Mine was WAY out on all specs, save warm idle (which was out of whack when the others were recalibrated)

TPS was at .230 volts, which was way lean (probably causing the decel pop, and generally running like ****) mounting screws still had the factory sealant in them, so this was probably off for the life of the bike. (remember, Harleys are usually tuned lean, and this confirms it)

Cold idle was way low

Warm idle was way high after fixing the other two.

 

Interesting info here. Glad you got her dailed in.

 

Thank you for posting, always interesting to hear about a system and service procedure that I new nothing about.
Mike

 

My MM tweeked & Dyno tuned is running like a champ in the black hills of South Dakota. It's sucking gas and hauling ***, over a thousand miles from home. 118,xxx miles on bike. Make no mistake these 88's like a oil cooler and the fan on it was needed on this trip a few times, dam the jam's. This is a mountain climber with the Tw21.

 

I wish I'd known this back in the day when I had one; I knew part of it. Where do you measure the cold idle voltage?

 

I measure the cold idle voltage on mine using a breakout box. Most people don't have one. You can also do it with a scanlyzer but nobody has one of them. The other method is to put a pin in the wires that go to the TPS. Look for the youtube video on how to do that. Not hard.

I had the same issues with my bike as the OP did. I made the adjustments and it ran much better.

carl

 

like the previous posters said, breakout box or through the wire. I went through the wire (grey one) to get the voltages. Bike runs like a raped ape now, and I dont have to downshift as much when I go to pass, just roll on the throttle, and she goes. Probably didnt amount to much difference in injector pulse width or timing, but seat of the pants, made one hell of a difference.

 

Ah...it's starting to come back to me. I recall back-probing a purple wire somewhere near the TPS... .

 

Like you say..almost like a mechanical fuel injection without jets to stop up and a needle float to cause problems. People just don't take the time to understand it and paid mechanics don't have the time to adjust it.

 

well said. couple that with being out of use for going on 20 years, and having some hard to find parts is a final nail in the coffin for many. I have the luxury of having the manual, a good working knowledge of the systems (generic fuel injection and electrical systems) and the time to fiddle with it. when it works, its a good system for what it is, an open loop EFI, basically just an electronic carburetor. I plan on getting a tuner, with those, its the equivalent to a jet kit