Help Please - 998 Misfire Woes
 

Hi Guys,

Apologies in advance if this post is a bit long, but I want to give all the details so that anyone with any advice for me knows all the relevant info.

The bike is a 2002 998 Bip, DP performance upgrade kit, PC111.

The problem is that when the bike revs to a certain point, the ignition seems to cut completely for a moment, resulting in backfiring, and the motor not revving any further.

The misfire starts at about 5,750 revs, and seems to come down a little to 4,750 as the bike gets fully warmed through (15-20 mins). At lower revs, the motor runs perfectly.

The problem first occurred after giving the bike a good wash and clean. It went away after a few days, so it seems pretty certain to be water ingress somewhere. A couple of weeks later, cleaning again after a very wet ride, and the problem is back, and now it is not going away.

Further info:

• The rev counter instantly falls right down when the misfire ocurrs, well below the drop in revs.
• Other electrical components, headlights, instrument lights are not affected.
• I have isolated the Power Commander and re-connected the original loom to the fuel injectors, but the problem is still there, so it’s not the Power Commander.
• Both cylinders are affected.
• I have removed the plugs, plug leads, coils, disconnected every electrical connector I can see/reach, cleaned all connectors and liberally dosed with water dispersant spray.
• For once, it is not an intermittent fault – eg: I can start the bike in the garage, warm her up, and the symptom is easy to demonstrate revving the bike on the stand.

I am reasonably handy with mechanical tasks (I can strip/reassemble a chassis and remove/replace a motor competently), but I am useless with electrical problems.

The last time I had a misfire type problem, it cost me over £800(!) to find out I had a dodgy Power Commander fitted, so I’m hoping that someone may be able to give me some pointers where to look to try to diagnose the problem.

Any advice or questions to help solve the problems will be gratefully received.

Spin

I guess that you've checked all connections!

Make sure all the earths are clean & corrosion free.

Do the yellow cables from the rectifier get hot?

when did it last have service...blocked fuel filter or dodgy spark plug..Just a thought mate

Had a similar problem with a customers 998. The ECU was returning error on the crank sensor. Replaced that and set the air gap and all was well.
Have you had the ECU interogated for error codes? Worth doing first before you go and start replacing sensors etc.

Thanks Guys for your suggestions:

Chaz – the rectifier cables show no signs of the insulation melting, although the block connector has “darkened” around the terminals, suggesting to me it does get hot.

Daz – Defo not the plugs. I will change the fuel filter (good idea), although the symptoms are not at all fuel starvationy.

Naz - sorry, Nelly – I have a spare 996r ECU (bikes runs R ECU and cams), and will try that. I may see if my local dealers are prepared to read the error codes for me, and let me have the results. How does you go about checking the “air gap” and where is the crank sensor located please?

Any other tips, hints, suggestions are more than welcome.

Spin

I'm Still trying to work out the drop in Tacho reading
Maybe its linked to the Multi-pin connector Just above the battery.
As you can see in the excel doc a lot of signals runs through there.

I'll post the ECU pin-out when I manage to locate it

Fairly certain the Tacho signal comes from Pin 9 of the body connector as its referred to

The feed for the tacho is taken from the crank sensor, via the ECU.

Crank sensor is in the Alternator cover, just forward of the waterpump cover. there's a blanking plug in the forward face of the cover that you remove to check the air gap between the face of the sensor and the idler gear that drives the cam pulleys. Need the hoses out of the way to get at it properly

does look as if it could be crank sensor related and maybe the washing of the bike has coincided with the crank sensor going down or damaged the connections between the crank sensor and the ECU.

Nelly do you have figures (i'll check my manual when I'm at home) for checking the Crank sensor such as Inductance & impeadance.

only figures i have are 680 ohm across 2 of the three pins. That's at the nominal 20 degrees C.
Tbh, that doesn't always prove a fault as the thing can/ could be breaking down under temp.

Just a thought, do you have an alarm fitted? You probabaly don't need one on the Channel Islands.

My 996R had a mystery problem like yours and it turned out to be the alarm at fault. I've seen been told by a Datatool fitter that once the units are a few years old and been subject to V twin vibrations the contacts get a bit iffy and the result in my case was an intermittent misfire/cutting out as you've described but only at certain revs which in ny case was always in between 5 and 6,000 rpm.