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Discussion Starter #1
I have an 08 750i that has been having issues starting in colder weather (40-50 F) I pretty much have to drain my battery to a pump where it needs a jump to continue trying to start. I eventually get it after using a little starting fluid and it’ll start great after that when it’s warm.
In warmer weather I don’t have to do anything but crank it for a second or two and it’s fine.
Shouldnt the ECU compensate for this?
My question is what are some things to check as far as starting issues when cold.
I’ve adjusted the valves with men 10hrs so maybe I need to check that again.


Thanks


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With the EFI you won't have the cold starting issues a carbed machine may have as it has fuel right now but..the effects of low compression and/or low fuel pressure will still have an effect on the cold. I suggest you do a compression check...and a fuel pressure check...as the 08s were known to have pump problems...and re-check those valves.
 

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Discussion Starter #3
I guess a compression check would kinda let me know if the valves were tight right, should be lower with tight valves I’m assuming.

I’m gonna check that pump out while I’m at it like you said. I checked the follow of it awhile back and it was in range but never did check the pressure.


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A little update on the troubleshooting I’ve done. I’ve checked all the ignition components and the test out to be within range of the manuals specs. All except the coils. I’m reading 18.3 instead of 10-16 k ohms that the Manual states. Not sure if I need new coils. I’m getting a decent blue spark with iridium plugs.
I’m gonna do the plug wire mod to see if it helps with the starting issues.

Also I checked the compression on the cylinders and they came back 50psi-front and 80psi-rear.
36-66 is the range from the Manual.

Wondering why the rear is so much higher. And if this could attribute to my issues.


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A little update on the troubleshooting I’ve done. I’ve checked all the ignition components and the test out to be within range of the manuals specs. All except the coils. I’m reading 18.3 instead of 10-16 k ohms that the Manual states. Not sure if I need new coils. I’m getting a decent blue spark with iridium plugs.
I’m gonna do the plug wire mod to see if it helps with the starting issues.

Also I checked the compression on the cylinders and they came back 50psi-front and 80psi-rear.
36-66 is the range from the Manual.

Wondering why the rear is so much higher. And if this could attribute to my issues.


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Although it isn't unherad of for them to be over the 66psi, the fact that there is such a difference does tell me there is something afoot. I am assuming you pulled both plugs, held the throttle wide-open on both and that you charged the battery back before doing the other one. If so, then there may be a ring, leaky valve or a spring on one comp release issue. Need to do a leak-down test next. Most often with EFI engines, hard starts are related to either compression or timing issues...of course there are always the possibility of low fuel pressure or supply issues but I'm sure you have checked all that already.


The coils can show higher voltage then the rest of the electrical system usually when there is a grounding problem or the coil is charged but hasn't discharged as it is the ECM or CDI that provides the ground for discharge. Your tester may be providing a ground that it shouldn't .Test the coil voltage with the leads off the coil is always best.
 

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Discussion Starter #6
So I was working on installing my plug wires and new sparkys tonight and as I finished up, thought I would recheck the fuel pressure as it had been sometime since I had done so. Well sure enough,
the pressure only came up to around 34psi and also dropped down rapidly upon the fuel pump shutting off. New pump is on order.
Pretty sure this is my issue all along. But at least I know every inch of this thing on the bright side.

Thanks for all the tips and I’ll post back when I get it installed.



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Discussion Starter #8
Update:
Got the pump in there and fuel pressure is at 44 psi atm.
Seems to start a little better but still doesn’t start right off the bat.
When I jump it with my portable booster set it cranks immediately though. Now I’m wondering if the battery voltage is dropping too low for the ignition to fire causing it not to start.

Anyone know what the minimum voltage for the coils to fire is. ?? Might hook up one of my Jetski batteries to see if that helps it out in the morning.

The battery is a yausa maybe a year or two old. Bought it new when I bought the bike.


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These coils have a problem charging below 11.5 volts. You may have a bad battery or maybe just a bad connection somewhere. Also, if the starter ever got water in it it will rust-up and pull extra amps pulling the battery down farther and faster.
 

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Discussion Starter #10 (Edited)
Ok that does make sense. I was wondering if the starter might be going bad from so many prior starts on the engine.

Another thing I found today while rechecking all the connections and cleaning and applying dielectric grease around the plugs, I found that the coils on both cylinders were wired backwards according to the manual. So I swapped them both and it seems to be starting a little better. Not really sure if this matters or not. Would it really matter if the wires were crossed. ?

Still don’t see how it was running to begin with.


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as a rule of thumb with any ECM engine. if you connect an electrical meter and set it to minimum VDC. crank the machine and if it dips under 9vdc you need a new battery. under 9vdc you start loosing electronics, relays, ecms. there cut off voltage is usually about 9vdc. if you dont have a meter with min/max just attach the probes to battery and watch the meter cranking.
 

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as a rule of thumb with any ECM engine. if you connect an electrical meter and set it to minimum VDC. crank the machine and if it dips under 9vdc you need a new battery. under 9vdc you start loosing electronics, relays, ecms. there cut off voltage is usually about 9vdc. if you dont have a meter with min/max just attach the probes to battery and watch the meter cranking.


Thanks for that info. I was wondering what the actual cut off was.


Update:
While I was reading on another post, I read that the coils need to have at least 10.5 V to operate correctly. Well after seeing that And testing it on my quad, I found that I was dipping below the 10.0 V range from the battery while cranking. So I decided to check my starter and see if there were any issues in there causing it to draw excess amperage pulling the battery voltage down. I found some amount of corrosion on the hot wire to the starter and cleaned that up. Took the starter apart, cleaned all the dust from the brushes wearing in, and put it back together. Also cleaned the contacts on the back of the stator where the brushes make contact. And the starter spins so much more freely now that when cranking it only drops down to about 11v.
And as of now I’m getting good results starting. The bike starts right up and runs great. Keeping fingers crossed that I’ve fixed all the issues that have kept my bike from being easy to start.




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Discussion Starter #13
Yet another update on this bike.lol

Even after all the previous work I did to the bike it still wouldn’t hardly crank up when it was cold or without a boost on the battery.
I got my Multi meter back out and started troubleshooting connections and making sure my readings were according to the manual. Not too far in, I found that my crank position sensor was giving me only .5 volts to the peak voltage adapter that I was using on the meter. Manual states it needs to be above 2v to operate. Well I took the magneto cover off and lo and behold I found a problem with it.


It was backed off enough to reduce the voltage generated by the sensor that is being sent back to the ecu.
Well I had one on hand that I had bought off a friend from a used bike and installed it. Checked the peak voltage once again, and it was reading 5v. Perfect.
Added oil and coolant, and tried to fire the engine up, and it cranked without hesitation, also being 48 F outside.

My guess is that the extra speed the motor was turning over from being boosted on the battery was just enough to allow the cps to generate just enough voltage to start the engine and run.


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