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Discussion Starter #1
Hi all,
I have a 07 street bob that only starts about once every 4-5 tries.
New battery, new plugs, fuel pump ok, fuel lines without pinholes...
I pulled the spark plugs and grounded them to the cilinders and I can see that only once every 4-5 tries i get spark...the rest of the time there is no spark. However, once it starts, there are no misfires or anything, engine runs ok after starting up.
I ve replaced coilpack, crankshaft sensor also..same behavior.

Any ideas?

Thank you!
 

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Grounding the plugs won't produce a spark. There has to be compression for the ECU to generate spark, so you need to use an inline tester.
Like bobf said, check the ignition switch. Also check the ground cable connection to the frame. If it's loose or dirty it doesn't matter how new the battery is. Even then, I wouldn't trust a new battery unless it's load tested after a full charge.
 

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Discussion Starter #4
Thanks for the replies, guys!

I have tried connecting it to my car battery also and i get the same behaviour.
The ground connections I have also checked and cleaned..

Thanks
 

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Test the charging system, a faulty regulator can cause the symptom you describe.
Also you shouldn't connect your battery to your car's battery.
 

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Discussion Starter #6
@SCHMIDTY thanks! Could you explain a bit further, I'm not so good at this stuff..

How could the charging system interfere with the cranking?
Also, once running it runs smooth and never shuts down..

I really appreciate your help, I would really like to understand this problem.

Thank you!
 

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A fully charged battery can keep the bike running for quite a while, the starter uses most of the battery's energy at startup. The starter can pull more than 100 amps whereas the ignition circuit can use as little as 3 amps.
When starting the engine the battery volts can drop down to less than 10 volts. If the battery drops down below 9.5 volts the starter will turn the engine over but there's not enough left over volts to trigger the ignition circuit to fire the plugs.
That's why I suggest testing the charging system, not that difficult,
 
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Discussion Starter #8
@SCHMIDTY understood, i will test it right now.

The thing is I've tried with 2 new and charged batteries already and the behaviour is the same..if it would be the case of the battery being drained over time, I would imagine at least the first few cranks it would produce a spark, but it doesn't...

Thanks!
 

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Discussion Starter #9
@SCHMIDTY I've measured the charging voltage and while idle it's 14.2 volts..that would be reasonable I guess...

Is it true that during cranking the ECM needs to also read correct compression to produce spark or is it just using just the crankshaft sensor to determine the correct timing?

The thing that bothers me most is that I don t get why it only starts very rough but then while running there is no misfire, engine runs smooth all the time, no shut down, plenty of power..

Also, no DTCs! It says "none" when I read them out...

Thanks!
 

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Hi all,
I have a 07 street bob that only starts about once every 4-5 tries.
New battery, new plugs, fuel pump ok, fuel lines without pinholes...
I pulled the spark plugs and grounded them to the cilinders and I can see that only once every 4-5 tries i get spark...the rest of the time there is no spark. However, once it starts, there are no misfires or anything, engine runs ok after starting up.
I ve replaced coilpack, crankshaft sensor also..same behavior.

Any ideas?

Thank you!
Ignition
 

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Hi all,
I have a 07 street bob that only starts about once every 4-5 tries.
New battery, new plugs, fuel pump ok, fuel lines without pinholes...
I pulled the spark plugs and grounded them to the cilinders and I can see that only once every 4-5 tries i get spark...the rest of the time there is no spark. However, once it starts, there are no misfires or anything, engine runs ok after starting up.
I ve replaced coilpack, crankshaft sensor also..same behavior.

Any ideas?

Thank you!
not fer nothing... do what he said ck all ground wire, but more important; ALL the hot wires.... it could be a intermittent short; like wire insulation or connector going bad,
 

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You can't check for spark with the plugs out of the head. Use a spare plug or better yet a spark tester. Harbor Freight for $3-$4.
Harley has some way of detecting compression, no compression, no spark.

Sent from my VS995 using Tapatalk
 
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