ER6 Low RPM trouble

Scrap · L Plate Warrior Joined: 14 May 2020 Karma :

Hi all. I have a 2009 ER6 with 60k on it, normally used a few days a week and earlier this week the bike suddenly started playing up.

At low or idle RPM, the engine is intermittently dropping revs, like a on/off switch - one second it's ok, next second it's dropping revs; it's either dropping revs or it's ok - there's no middle occurrence where RPMs drop slightly. Pulling out of a T junction for example, the bike can stall because RPMs can drop at the same time I let the clutch out, so I have to give it a load of throttle and keep the clutch in for longer.

At over 2.5k-ish RPM the problem goes away. No dropped revs, no skips. I have noticed that when the revs drop, the exhaust can pop, and I can smell unburnt fuel.

On idle, the revs can intermittently drop to about 700 rpm. Revs can quickly bounce between normal 1.1k and 700 so sounds like a rough idle. With a little bit of throttle, it will bounce between, say 1.8k and 700 - it will 'sit' at either and not in between.

It did this on my 20 min journey to work and also the way back, it wasn't a particularly hot day - I've had the bike out doing the same journey when it has been much hotter.

I suspected the throttle position sensor might be bad. So I did some back-probe diagnosis using an oscilloscope on the connector at the TPS and the ECU:

- 0V and 5V are good and stable, when the key is on engine off and engine on.
- When the key is on engine off and engine on, the idle position is dead on 1.0V as per the spec in the Haynes manual, and the sweep is nice and smooth up to 4.4V with the throttle fully open, again exactly as per spec.
- There is no sign of the signal or voltages dropping, the curves are smooth and consistent.
- The readings are the same at the TPS and ECU connectors.
- Connectors at both the TPS and ECU look good, no sign of debris or corrosion.

And of course, the problem has now disappeared... Maybe a crap connection which I've wiggled when diagnosing and inadvertently made better.

So while I wait for the symptoms to come back and do my diagnosis again, what else should I look for? I've ordered a TPS connector adapter so I can probe more easily next time.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Battery holding a good voltage?

Maybe try a new set of plugs in it, could be dropping a cylinder?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Scrap · L Plate Warrior Joined: 14 May 2020 Karma :

Battery is good, charging system is good.

NGK Iridium plugs were last installed 6,000 miles ago, so relatively fresh. I'll pull them to have a look next time.

I think it's possible that a cylinder is momentarily dropping, I wonder if this was the case, what could be causing it to only happen sub-2.5k rpm? Could dodgy spark plugs or ignition coils do this?

blurredman · World Chat Champion Joined: 18 Sep 2010 Karma :

Air leak between carb/barrel perhaps.
____________________
CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 - 40k, 1989 MZ ETZ251 - 52k.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

On the previous models (er5 and GPZ500) they did sometimes have a problem with the coil earths. They attach to the frame with a bracket and it would corrode under the bracket, eventually giving a poor connection. I'm not as familiar with the ER6 so i don't know if it's a similar setup but it's 17 years old and in the UK so corrosion is always a possability.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Scrap · L Plate Warrior Joined: 14 May 2020 Karma :

No carb in the ER6, it's fuel injected. Doing a visual inspection and a firm grip and wiggle of the throttle body, it all looks solidly attached and I'm reasonably confident there aren't any leaks downstream of the throttles. Fuel injectors and their connector contacts look fine, for what that's worth.

I balanced the throttles two years ago, I'll check throttle balance again, later.

The connections from the ignition coils go directly to the ECU according to the wiring diagram at the back of the Haynes manual, i.e. no direct frame earth connection.

Corrosion has certainly been an issue! The swing arm had to be replaced and cut in to pieces before it could be removed; holes had corroded though it and the pivot was completely seized. I have replaced about a dozen electrical connectors, chopped off the rectifier connector and soldered the wires directly after needing to deal with a corroded connector for the third time. I eventually took everything off the frame, sanded the frame back and painted it, every bearing was replaced, rebuilt the front forks, new stanchions (old ones had rust pitted), re-built the brakes with new pistons (again rust pitting).

EDIT: I've also ordered a diagnostic connector adapter, to OBD2, hopefully I can use that to read some PIDs.