Erm... hesitation

[Richard Russell]

My '94 1100GS has been running beautifully smoothly for the last few months due to a combination of Brisk plugs and me getting better at doing OVAD and throttle body sync.

But... for the last few days it's been hesitating, much as described by others in previous threads. It runs ok at low engine speeds, but when accelerating it hesitates at 3 - 4k before picking up again, albeit more roughly than before. On the motorway it surges and lurches when before it would have held a constant speed, but strangely it's not vibey. It feels most like a carburated engine when cold with not enough choke.

I've changed the plugs (Brisk again) and the air filter (from OEM to K&N - for the service life, not for the airflow). The air filter made no difference. I thought the plugs had fixed it, but back on the motorway it was clear they hadn't. The RH plug was in good nick, evenly browned next to all four lobes of the electrode, but the LH was somewhat charred next to one lobe.

Based on a search of the accumulated wisdom of the board, it's obvious that the fault is either in the HT leads, the coils, the new plugs, the fuel filter, the injectors, the Hall sensor, or something else.

I feel as if whatever order I try replacing all of the above, the thing that's broken will be the last thing I try, leaving me with a large Visa bill and a pile of very serviceable but worthless second hand parts. Any hints on diagnosing the fault without spending any dosh? Can BMW / anywhere else test HT leads, for example?

Cheers,

Richard

 

[Richard Russell]

oops

I've been un-forum-sponsored. Sorry Paul... just renewed it now

 

[Fanum]

Not sure if the 11 has the same style coils in the plug leads but my Adv had symptoms just like that and the coils in the leads that sit on top of the actual plus in the cylinder recesses were to blame.

I was luckuy enough to have tippytoes around, who kindly lent me two good ones to try, which ionstantly cured the problem and i was able to get two brand new ones to replace his under warrenty.

Might be worth finding someone locally with an 11 and borrowing theirs for a few minutes......zero cost, zero tools test with instant results

 

[(RIP) Kaister]

if you've just changed something and the problem has started - then that's the problem.

Put your old plugs back in - and check the caps are seated really well.

report back all info...

 

[Richard Russell]

Thanks for the replies.

Fanum, I haven't noticed a separate coil on the end of the HT leads. They seem to be a single unit, but maybe I need to look more closely.

Motomartin, I hadn't changed anything for ages before the problem started. Changing plugs and filter was an attempt to fix it.

I'll let you know how it goes...

 

[Steptoe]

swop the injectors around - see if the problem moves with the injectors .

swop the HT leads around, see if the problem moves with the leads .

swop the HT lead connectors around into the coils ( it's a wasted spark ignition so it'll still run) , see if the problem etc etc .

 

[Richard Russell]

Cheers Steptoe,

I haven't been able to localise the problem to left or right. It's a bit tricky since it only happens under load at 3k revs and above, i.e. when I'm riding it.

I could whip the plugs out and see if one spark is visibly weaker than the other... is that what you had in mind? Or have you got special powers of perception that allow you to tell which side it's misfiring on? It's not obvious to me - perhaps I'm just being thick

I could borrow working HT leads from my mate's 1150R, but it's a twin spark. Does this have leads that would fit the 1100, or does it use Y-shaped leads?

 

[Richard Russell]

Well, I'm not much further on after a couple of hours tinkering tonight. I swapped the leads over as suggested, but I still can't tell which side is misfiring. Maybe both, which might indicate a fuel supply problem?

I thought it was the left side for a while, as blipping the throttle sharply from idle seemed to make it pop on the LHS, but then I realised I was listening to the air intake...

The fuel filter is due a change anyway, and I've got a spare in the garage, so that sounds like a job for the weekend, especially as the tank's nearly empty. I'm not too hopeful this will cure it though - the problem started too suddenly for this to be the cause, I think.

I still think the HT leads are the most likely cause, but I'm reluctant to shell out £30 until I'm sure. Can anyone Saddleworth / Oldham / Manchester area spare theirs for half an hour in return for the satisfaction of helping out a fellow GSer?

OK then, how about in return for beer?

 

[Frank Warner]

Can you measure the resistance of the leads?

Does the problem only occure when warmed up or is it there when cold too?

 

[Taipan]

You can get your HT leads checked. Any garage with a electronic tuner such as a sun tester can check them for you. They connect a probe each end and wiggle the leads. You should get a resisatnce reading based on length of lead. If the lead is knackered, this normally shoots of the scale, ala >999

You can probably do this yourself with a digi multi meter if you have one? Just see if there is any difference in readinsg between each lead, assuming the leads are teh same length.

Sorry, I'm miles away from you darn sarf or I'd hapily let you borrow miy leads. Keep us posted.

 

[billy-joe]

hi there rich

i had the same prob on my 94 1100 a few months ago. it turned out to be a broken wire on a plug on the lh throttle body. it sits on the lhs of the lh throttle body. peel back the rubber cover thingy that the plug is attatched to and you should be able to see wires going into the plug. this is where i found the broken wire.

a quick fix that i am yet to fix properly is just to bridge the wire into the plug.

hope that made some sense. if not, pls feel free to pm me and i can try to describe it to you over the phone.

good luck
bj

 

[DrAlf]

Check or replace the little rubber caps on the throttle bodies - the ones that you remove to balance the throttle bodies. Mine started to perish away last year which produced the same effects that you describe. I replaced them and the problem went away. Cost bugger all and well worth a shot.

Good luck

 

[bmwrich58]

But... for the last few days it's been hesitating, much as described by others in previous threads. It runs ok at low engine speeds, but when accelerating it hesitates at 3 - 4k before picking up again,

I was thinking fuel filter myself,as if it's "starving for gas" while under load.....

 

[Richard Russell]

Some progress

I changed the fuel filter on Wednesday night, and noticed two interesting things:

1) the existing fuel filter was fitted the wrong way round (arrow pointing against the direction of flow).

2) one of the breathers was clogged with rusty crap at the point where it passes out of the tank through the metal plate. I had a go at unblocking it with a length of wire, but I suspect it may still be blocked further up.

The problem was still there the next morning, so changing the fuel filter alone has not fixed it. On my way home from work yesterday I rode the first few miles with the filler cap ajar to bypass the breather, and hey presto the problem was gone.

Problem solved, I thought, so I closed the filler cap and waited for the problem to return... but just to confuse me even more it carried on running fine all the way home, with maybe just a hint of the previous problem after 15 minutes or so.

Next job is to have a proper go at unblocking the breather. Could this explain the problem?

 

[Richard Russell]

Problem solved

Just following up in this old thread to let you know the outcome.

The problem turned out to be water in the tank, most likely caused by a blockage in the filler cap drain hose. When I siphoned the petrol out of the tank I found about half a pint of brownish water in the bottom. Presumably this was just below the level of the fuel pump intake, so small amounts of were being pumped through in certain conditions (riding uphill, hard acceleration etc), hence the intermittent nature of the problem.

I took out the fuel sender plate, hoovered up the remaining water using a big syringe (easy with the tank on its side and the plate off), used compressed air from a bicycle pump to remove the blockage (rust in the pipe where it passes through the sender plate) , refitted the sender plate using a new o-ring and new external drain & breather hose, and poured the clean fuel back in.

Riding to work this morning everything was fine. Thanks for all the suggestions

 

[T900]

i strongly suggest you put a fuel system cleaner in at least one tank of fuel as this will break down any remaing water that could be in the injectors,
most car accessory shops will have it, only use a brand name such as castrol, stp as they have lubricants and detergents in them for fuel injectors , most others are high strenght solvents,
believe me you will notice the difference