Beema98 Posted October 15, 2007 Posted October 15, 2007 Ever since I bought her, I have had the problem that, when starting after it has been left overnight, I notice that when starting (fast idle on first click) that about 5-8 sec after it starts (no problems) it gives a prodoinate miss as if she were starving of fuel. I over come this buy holding the fast choke right on full for 10 seconds however at that 5-8 sec mark, revs drop to from around 1800 to 1000 with no problem after it gives the miss. Just wondering before I start looking at cause. I beleive it to be a loss of vacume in the fuel system someware. (no apparent leaks). Has 85,000 km on the clock and has been through the 0=0 process. Any suggestions would be helpful. Many thanks.
T__ Posted October 15, 2007 Posted October 15, 2007 Ever since I bought her, I have had the problem that, when starting after it has been left overnight, I notice that when starting (fast idle on first click) that about 5-8 sec after it starts (no problems) it gives a prodoinate miss as if she were starving of fuel. I over come this buy holding the fast choke right on full for 10 seconds however at that 5-8 sec mark, revs drop to from around 1800 to 1000 with no problem after it gives the miss. Just wondering before I start looking at cause. I beleive it to be a loss of vacume in the fuel system someware. (no apparent leaks). Has 85,000 km on the clock and has been through the 0=0 process. Any suggestions would be helpful. Many thanks. Trev, I doubt it is a vacuum problem in the fuel system as your motorcycle has a high pressure fuel supply system that operates under pressure not a vacuum.. It seems that some BMW boxers act just like your bike does.. My older R1100R acted the same way.. (ie start fine then go through a rough period for a few seconds then operate good the rest of the day).. It could be a slug of air in the injector line(s) but most of that should purge out as soon as the fuel pump runs (except the last few inches of line).. It could be a timing chain tensioner bleeding down overnight then re-pressurizing with oil after a cold start (I believe that was the problem on my 1100).. It could be an algorithm in the fueling computer to keep the Cat converter from over fueling after a cold start (if your bike has a Cat & related CCP).. Could even be thick motor oil that loads one of the oil pumps about 5-8 seconds after starting (probably take about that long to fill the oil cooler on a cold start).. Maybe rig up a fuel pressure gauge on one of the injector lines to monitor that on cold start,, maybe try some thinner motor oil as a quick test,, listen for a timing chain clatter on cold start & if heard possibly a tensioner bleed down overnight,, maybe try a different CCP or no CCP.. What happens if you key up 2 or 3 times before actually starting? That should run the fuel pump each time you key up & possibly purge the fuel regulator & related lines better? Maybe try adding about 300-400 ohms of resistance in your AIT (air inlet temp) circuit,, that will add a little more fuel on cold start as the Motronioc will think it is colder out.. Probably wouldn’t hurt to test your Air Inlet Sensor for correct operation & smooth resistance change also.. Maybe make sure you TPS is set correctly.. If the Motronic sees below .4 volts & above 1500 RPMs it can shut the fuel off as it thinks it is in decel mode.. If you have a fuel controller installed try turning that off as a test as those things can sometimes cause problems.. Twisty
Woodie Posted October 15, 2007 Posted October 15, 2007 Mine does it too. Sometimes it stalls, sometimes it doesn't...but there's definitely a drop in RPM shortly after starting.
Beema98 Posted October 18, 2007 Author Posted October 18, 2007 Thanks guys for the replies. Twisty, especially such a detailed responce. Has given me some thing to look at. Many Thanks !!
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