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post #1 of 7 Old 01-28-2019, 10:57 AM Thread Starter
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questions. intermittent spark, bad coils, crank sensor related

I think this is my first post here, ill try to be as thorough as I can be. I bought an 08 brute force project bike that has an 840 kit, snorkels, whole 9 yards. the motor was out of it, but assembled, so Ive got the engine in and cranking over, just cant get it to start. I had a friends brute force to reference when hooking up sensors and harnesses, and ive got it all together where its not throwing an FI light. it cranks, fuel injectors fire, but have intermittent spark. will usually spark one good time when i first start cranking it over and it wont fire after that. if i spray starter fluid down the throttle bodies it will backfire (probably compression igniting)

before i got to this point i pulled the valve covers back off and verified it was in time. when you line up the rear camshaft and have the stator on TR, and bar it 3/4 of a turn over clockwise, the front cam lines up, and is on the TF mark. I know it is very easy to time it wrong, but that to me tells me its correct. the pistons are at TDC when the timing marks are lined up. Does anyone know if the cam marks should line up with the TF and TR marks every single rotation? mine only lines up like that every other rotation.

The 2 wires to the coils were hooked up backwards, according to the manual. so the ground and power were switched around. when ohming coils out, i get 1 ohm too much on the primary side, and 1000 k-ohms over on the secondary on both coils. so they are both bad by ohms. my buddy and i went through everything that the power to the coils goes through and load tested the wires, everything is good there, but when we hook up the coils and try to fire them manually by giving and taking ground away at the ECM plug we cant get them to fire. We have 12 volts at the coils until you try to crank it over, then voltage disappears. so I'm in for 2 coils and will most likely get an automotive straight boot so i can get away from using the post style plug. does all this check out in theory to you guys?

the crank sensor ohms out 2 ohms short of spec (I think spec is 423-537 ohms and I get 421) but what is more concerning is that i get maybe a half a volt when cranking it over. service manual says I should have 2. I have tried it with 2 different volt meters, one of which records peak voltage. Is this voltage so fast that a volt meter wont see it and i need an Oscilloscope ?

last question, does anyone know what the vehicle down sensor actually disables when it isn't at the right angle? I feel like Ive read everything from it wont let it crank, to no fuel, to no spark. I can crank and i can see the injectors firing fuel, and i get intermittent spark, so I feel like mines working?
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post #2 of 7 Old 01-28-2019, 01:15 PM
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Sounds like youíve done a lot of troubleshooting on the bike.
As far as the coils go, I recently check both my coils and on the primary windings I was in range but on the secondary side I was reading 2k ohm high on both my coils. And thatís on a running brute for your reference.

Also, And when my roll over was not working correctly it stopped the injectors from firing.


Do you know for sure your fuel pump is good ?


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post #3 of 7 Old 02-06-2019, 06:39 AM Thread Starter
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I have not done any fuel pump tests, mainly because I can see the injectors firing. I would feel better about going towards the pump if it would fire up and run on ether, but it wont because of the no spark issue.

can anyone confirm that thats how timing looks when a bike is in time? one time the tf and tr marks line up the cams and then the next rotation its off?
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post #4 of 7 Old 02-06-2019, 07:53 AM
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Quote:
Originally Posted by fivespeedsteed View Post
I have not done any fuel pump tests, mainly because I can see the injectors firing. I would feel better about going towards the pump if it would fire up and run on ether, but it wont because of the no spark issue.

can anyone confirm that thats how timing looks when a bike is in time? one time the tf and tr marks line up the cams and then the next rotation its off?
TF stands for Timing Front and TR stands for Timing Rear. When either is lined up to the case mark, that will be a TDC (Top Dead Center) on either the Front or Rear cylinder. HOWEVER, there are two "TDC" positions on either cylinder- one is the one you want, Compression stroke, the other is the exhaust stroke. In either position that mark will line up with the case mark. Sense the intake stroke always precedes the the compression stroke you always rotate the engine in it's normal directions watching for the intake valve to go down(open), then back up(closed). Once they are fully close it starts the compression stroke. That's where the piston travels from the bottom of the cylinder to the top..and the top of that stroke is TDC on the compression stroke. A few degrees before that is where the plug fires and although messy, if you put a timing light on that cylinder's plug and shine it in the hole, you will see that cylinders timing mark just a few degrees before the case mark. This is of course spark advance. If a plug won't fire, look to low coil voltage first, then CPS or the pulse coil, then the ECU/CDI. Of course it also just be a bad plug or coil.

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post #5 of 7 Old 02-15-2019, 05:31 PM
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A coil sparks by grounding and removing ground just like you were testing. seems like a bad ground "maybe" ECM engine ground.
Or the crank position sensor. You dont need an scope. Thats why it lists a cranking voltage. if your sure you have full battery and cranking voltage coming out of crank is low then thats probally the issue. just make sure your testing it rite. some engines its a AC voltage not DC. The crank is telling the ecm the engine is turning @ x RPM and ecm starts fuel and spark. some engines have a cam sensor as well you need to check on.
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post #6 of 7 Old 03-01-2019, 06:00 AM Thread Starter
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Confirmed again its only making .2 volts on the crank sensor when cranking. pulled the stator cover off and found that the crank sensor was leaning back a little bit (away from the pickups) took it off and found that the mounting plate had come up and let the sensor rock back. got a new crank sensor on order, i think the distance between crank sensor and the pickups was too much not telling it to spark.
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post #7 of 7 Old 03-01-2019, 06:50 AM
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Quote:
Originally Posted by fivespeedsteed View Post
Confirmed again its only making .2 volts on the crank sensor when cranking. pulled the stator cover off and found that the crank sensor was leaning back a little bit (away from the pickups) took it off and found that the mounting plate had come up and let the sensor rock back. got a new crank sensor on order, i think the distance between crank sensor and the pickups was too much not telling it to spark.
Makes sense..most likely it.

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