916 Starts Then Dies...

The battery is FUBAR, change it, do not go down any rabbit holes until youve done that. I speak from experience, had a battery giving exactly the same readings as yours snd gad exactly the same inability to start. I changed plugs, swapped coils, removed, cleaned, refitted and tested injectors, changed the CPS. All rcause si was convinced my battery was fine. In the end I did the test I set out above, then bought a new battery, guess what? It started first time and I’ve had no further problems.

You’re possibly bent/damaged valve is a different issue.

BTW, the fuel pump doesn’t know when it’s at 3 bar on key on it’s just programmed to run for x seconds at key on then run continuously once the engine is running.

I’d wager your fuel lines are fine, get a new battery first

 

I disagree about the battery, it's not a certainty that it's no good just because of those voltage readings, i've had a 1098 show similar, and it's continued to start the engine for a further two years. There's nothing wrong with changing it just as a way of ruling it out, but cranking speed is good.

 

If you are sure your timing is good, and you're getting sparks and fuel, then start to think about the sensors.

I just had a very similar experience last month with my '94 916. After checking the above, I connected the laptop to the P8 and found that the coolant temperature sensor was under reading, which I expect was affecting the fuelling and making it difficult to start. Replacing the coolant sensor fixed the problem completely.

 

I had a similar problem with a 999S many moons ago. Long story short- it was the starter.... but when cranking, it seemed fine.

 

I agree the cranking speed is good, I’m just going off my own direct experience Chris. In my case the situation was exactly as described by the OP and in his video. The bike would almost start but just wouldn’t. Someone suggested to me it could very well be the battery but, as the voltage across it was good and as it was always kept on an optimiser, I dismissed that suggestion. I must have gone down every single rabbit hole I could to track down the issue , just could not locate it. In the end I did the test I outlined above, got similar results to the OP, bit the bullet and bought a new battery. I was gobsmacked when the new battery read 13.1 v and still stayed well above 12 v at key on (and my lights are set to be on at key on as well for DLR purposes). In fact it barely dips below 12v when starting and started first press of the button.

I even made a little video of it for my home movie collection

Voltage drop on starting


The old battery fell below 11v on starting.

 

Ditto, and not meaning to stray off topic, but what was the bike? I can see that using an accurate meter helped, and (not saying you did) starting straight after a good charge would also show favourable voltage during cranking. I don't know what time of year it was, but would be interested to see your cranking voltage at say, 3 deg C cranking from cold, on a battery that hadn't been charged for 48 hours (just being devil's advocate). You can sometimes get a whole group of ingredients not behaving as they did when new, and the battery replacement might appear to "cure" the whole problem, but really it was just the straw that broke the camel's back and other factors also contributed to the overall failure to start/run/etc.

 

That was about a month ago, I’d guess the air temp was around 8c. The photo with the multimeter at 10.87 was what the old battery dropped too when cranking (I said starting above) but it always struggled to start. I’m now convinced it was because the battery had insufficient power to feed the starter and power up the coils with anything more than what would result in a really weak spark as I found no other faults anywhere. Oh, the bike is my Monster 1100S.

Re cranking after not charging, I know the new battery still cranks and starts the bike after a week of not being connected to the optimiser (I forgot ) although what the voltage was I don’t know as I wasn’t testing it then. The old battery, which I thought was perfectly ok, drops to 10.5v after a couple of days, even though it’s not attached to anything, and then just sits there at that level; it’s on the workbench now for testing things.

 

You could try turning the key on, let the pump prime, turn the key off, then on again so the pump primes again, do it 3 times then hit the starter button. Each time the pump primes a tiny bit of fuel is sprayed into the cylinder to prime it. By repeating the on/off you’re increasing the prime into the cylinder. It’s a 1 min thing to try.

If that fails then the next thing I’d do is to check the injectors are firing and dispensing fuel as they should, unless you’ve done that already. The simple way is to remove the plugs, get some dry cloth or tissue and push it into the plug hole, just make sure it can’t get sucked in. Crank the engine and see if the cloth/tissue gets wet with fuel.

The alternative is to remove the tank and airbox, disconnect the injectors from the throttle bodies (I don’t think they’re shower type on yours are they ?), reconnect the tank and then crank the engine, does fuel spurt from them?

Assuming the fuel is getting into the cylinder and plugs are sparking with a big fat spark and it’s still not starting then I think there has to be a timing or sensor issue.

 

One other simple thing to try assuming you have fuel at the plugs is to put the old plugs back in and try then. At least that will eliminate any issue with the new plugs you fitted.

 

the fuel pump doesn't sound very laboured does it. i've no idea on the layout, but if you can get to a pipe post pump i would be checking the pressure in someway or another (carefully) what are we thinking, 2.5-3bar, 30-40psi? it should pish out at quite a rate when priming.

 

I didn't know this? My 916sp requires the fast idle on to start - in the vid I thought he knocked the fast idle off - looked like he rolled the throttle shut, which we know knocks it off, I didn't see him pushing the button? But my bike will struggle to fire up like that without fast idle on.

 

My 916 is like Lazza's too. 1998 916 Bip. It needs the button for a few moments. Wont start without it. (from cold)

And from someone who's knicked the green o-ring on the push in fuel thingy, the fuel pisses out at a good rate when the pump is and has primed. It pishes everywhere.

 

Check your temperature sensors, if you haven't already. The ECU will likely start with after-start enrichment for the first little while in order to help with cold startup, before leaning out the mixure to a more normal level. If one of your temperature sensors is out, then it might start with the ASE, then be unable to idle with an incorrect mixture.

 

yes and from my other thread - fuel pump is fine but I also didn’t get the o ring in right and petrol pissed everywhere - well, I got a call at work from Mrs saying the house stank of petrol? (Garage is linked to house) When I got home, I took tank off, I had put about 4litres in, there was about half a liter in it! The rest had dripped / run out, engine was wet! So reusing the o ring wasn’t best idea I’ve had!! ESP as I found I had a new one in my box of spares!

 

Got to say it but I think your compression figures are low

 

11:1 if I remember? 11x 14.7 equals... 160 ish psi.
Check me out. I'm old and my slide rule has seized.

 

Valve timing double, treble check time? Thinking out loud again one tooth out? More and you would have an interference motor.? Maybe someone else can confirm the compression ratio and relative PSI?