2007 Street Glide. Possible Coil Issue?

[texas_medic85]

I recently bought a new bike from a private owner. Last week I picked it up and rode it home with no issues. Friday I went to go for a weekend run and barely made it out of the neighborhood before I had a considerable decrease in power. Engine light comes on at high RPMs The bike seemed to get bogged down. Turned around, got home and proceeded to check spark plugs. Inline test shows weak spark to rear cylinder compared to front cylinder. I replaced the plugs and the wires since the bike had been sitting for a while. No fix. Checked the DTC code: P1356 - No combustion rear cylinder. Swapped the plugs and wires (front to rear) same issue: weak spark rear cylinder. The bike starts and runs but the rear cylinder/header pipe is cold. I smell fuel so am thinking the injector is ok.

Is this a possible coil issue? If so how do I test the coil? I heard there was a resistance test you can do but don't know where to start. The coil has already been removed. It is the stock single fire coil P/N 31743-01. Got a run this weekend and I already sold my other bike. Any help would be appreciated.

 

[Hoople]

I recently bought a new bike from a private owner. Last week I picked it up and rode it home with no issues.
**since the bike had been sitting for a while.**

Resistance checks on coils just about tell you nothing. Especially with a problem such as yours. Did you use Genuine HD spark plugs. It sure could be the coil but since the bike has been sitting awhile, is the fuel fresh? Did you just add new fuel to the old? If the fuel has been sitting for awhile, get it out of there.
Before changing any parts, I would drain the tank and start fresh.
How did you check spark? Adjustable spark tester?

 

[texas_medic85]

...Did you use Genuine HD spark plugs. It sure could be the coil but since the bike has been sitting awhile, is the fuel fresh? Did you just add new fuel to the old? If the fuel has been sitting for awhile, get it out of there.
Before changing any parts, I would drain the tank and start fresh.
How did you check spark? Adjustable spark tester?

Thanks for the reply...

The spark plugs are HD and I tested them with an inline spark tester between the wires and the plugs the light flashes nice and bright on the front but barely visible on the rear.

The fuel is fresh...when I got the bike the fuel was right on E. Filled it up with 93 octane. The fuel has since been drained since I snapped the plastic nipple on the main fuel supply line trying to raise the tank slightly in order to gain access and make sure the wires on the coil were seated properly.

 

[Hoople]

Would you happen to know if there is a fuel enrichment "black box" on the bike. Previous owner had to install something to enrich the fuel. Do you know what was installed.
Not too many bikes remain bone stock from the factory.

 

[texas_medic85]

Not too many bikes remain bone stock from the factory.

Indeed...
The previous owner was a gear head (races drag cars) he installed the Vance and Hines Dual Head Pipes and a Dynojet Power Commander. I bypassed the power commander and still the same issue. The power commander seems to be operable since it shows the throttle position as I twist the grip but I don't know much about them so I could be wrong.

 

[Hoople]

I bypassed the power commander and still the same issue.

When you say bypassed, you now have the factory wiring harness plugged directly into the factory ECM.
Until you get this problem resolved, I would leave the Power Commander disconnected and out of the picture. That is a must. Then once you get the bike running again, it's OK to re-attach the Power Commander.

The neon testers are OK but I would get an adjustable spark plug tester similar to the one here. Thexton 404 Ignition Spark Tester with Adjustable Gap

You need to compare the front and rear spark in free air. The fact that the front cylinder has combustion, it will have more spark duration, hence a better glow. A free air test makes both tests equal. The adjustable type will also allow you to test the dielectric strength of the coil. Set the gap to about .050" or .060" and get a visual of the available voltage and spark strength. If the spark jumps the gap and you see a little bit of orange in the spark, your probably good. A thin blue spark is weak. Thick barrel shaped orange spark is picture perfect. Use it on the front, then the rear while cranking. Leave the plugs installed in the cylinders. When testing front coil, leave rear wire connected to the rear plug. When testing rear coil, leave front wire connected to it's plug. Connect the alligator clip of the spark tool to a cylinder fin. Do not connect the alligator clip to the spark plug installed in the engine. This is not an engine running test like your tester is.

I know you said that you smell gas but I would also pull the plug just after running the engine to see if the plug is wet. Before I spent $100 on a new coil, I would cross check everything I could. Cross check the coil using the gap spark tester. Cross check the injector by checking for a wet plug.
What's the mileage on the bike.

 

[texas_medic85]

When you say bypassed, you now have the factory wiring harness plugged directly into the factory ECM.
You need to compare the front and rear spark in free air.
What's the mileage on the bike.

Yes the factory wiring harness is now plugged directly into the factory ECM.

Makes sense...I'll get this tester in the morning.

The Mileage is just over 15,000.

I really appreciate your input.

 

[texas_medic85]

Ok. So spark wasn't the issue. It was the power commander all along. I went out and disconnected the power commander again like you suggested in order to eliminate it from the equation. Now the damn thing fires right up and runs fine. Hook the power commander back up, no rear cylinder. OK so the problem is the power commander. Why would it affect the rear cylinder and how do I fix it? The bike runs fine but there is a noticeable difference in throttle response/power.

 

[Hoople]

That's good news. It could be a number of things about the PC. It could be corrupted software, corrupted firmware, or just a plain old hardware issue within itself.

Knowing it's not the bike when in factory form is great. It is not a big deal to fix because you have lots of choices. Do you have O2 sensors on your year bike.

 

[Jack Klarich]

Ok. So spark wasn't the issue. It was the power commander all along. I went out and disconnected the power commander again like you suggested in order to eliminate it from the equation. Now the damn thing fires right up and runs fine. Hook the power commander back up, no rear cylinder. OK so the problem is the power commander. Why would it affect the rear cylinder and how do I fix it? The bike runs fine but there is a noticeable difference in throttle response/power.

That's good news. It could be a number of things about the PC. It could be corrupted software, corrupted firmware, or just a plain old hardware issue within itself.

Knowing it's not the bike when in factory form is great. It is not a big deal to fix because you have lots of choices. Do you have O2 sensors on your year bike.

This is kind of like when a Dyna S ignition system fails it almost always takes out the rear pick up , least that is what I looked at when working on my buddies bikes back in MN. They all had to have them thinking H D was not good enough. In fact at the time (dual Fire) was not good enough. Like Hoople says it could be any number of things and ya know he is right JMO