2002 ST4s: erratic rev counter - Ducati.ms

Ascalon · Jan 27th, 2012, 1:17 pm

The rev counter on my ST4s has become increasingly erratic.

Sometimes the bike will start from cold and be ticking over on the fast idle lever and the rev counter won't read at all then it will jump to the right reading after a minute or two.

Other times I'll be cruising and change up and it won't register the rev change immediately, it will stay at the previous indication and then drop suddenly.

Now, I think the rev counter was replaced at some point because the two wires that connect it have bullet connectors on them, but these are clean and corrosion free and well insulated.

I have also noticed on occassion, at ticker over, that when I flick the full lights, the rev counter needle will fall back to 0 for a minute or two but when the revs rise beyond tick over as I pull away, it will start to read properly.

Anyone else noticed this behaviour? If so, what can be done about it?

Cheers,
A

Shazaam · Jan 27th, 2012, 1:34 pm

Electronic tachometers give erratic readings when the base/reference voltage is low, usually caused by a loose battery connection. The worse situation for low voltage is at idle when the alternator output is at it’s lowest or during a voltage drop when the 55W headlight is switched on. You may just need a new battery or a good charging.

If it's not the battery:

Most likely - Intermittent power or ground connection
Next likely - Intermittent rpm signal connection
Least likely - Tachometer internal problems

Check for a loose or corroded electrical connection at the battery, the fuse, and any in-line connector. Check the two battery connections first, next the connector at the instrument cluster, then at the fuse, and lastly at the wiring harness connections.

Next, since the bike is running OK, the RPM sensor gap, the sensor itself, and wiring back to the computer are not the problem. So you need to check the connectors between the computer and the tach.

The tach could have electrical contact issues inside. The tach itself is held with three brass screws against a white plastic housing that forms the base of the tach. These screws vibrate loose and sometimes need to be retightened.

Finally, try to borrow a tach to verify that it’s actually the problem, before buying a replacement.

Ascalon · Jan 27th, 2012, 1:53 pm

Quote:

Originally Posted by Shazaam

Electronic tachometers give erratic readings when the base/reference voltage is low, usually caused by a loose battery connection.

Thanks mate,
a few things worth checking there.

Yeah, the bike runs fine and and the battery is good too as she starts from cold easily and I have a charging lead on it so I plug it in to charge if it is not run for more than a weekend.

I actually forgot the damn connector further down the wire from the bullet connectors!

Is there a way of wiring in another ground, bcause i have been told before that aluminium engine casings are far from an ideal ground.

Have you heard of someone doing a bdniing jumper to the frame too? Steel being a better ground.

A

tonered · Jan 27th, 2012, 2:10 pm

Before you start rewiring, check the brass screws on the back that Shazzam mentioned. Here's an easy way to tell. When it acts up and you push on the lens, does it go back to functioning normally? If so, tighten them up.

Have a good one.

Ascalon · Jan 27th, 2012, 2:18 pm

Quote:

Originally Posted by tonered

Before you start rewiring, check the brass screws on the back that Shazzam mentioned. Here's an easy way to tell. When it acts up and you push on the lens, does it go back to functioning normally? If so, tighten them up.

Have a good one.

Indeed, it can corect itself with a tap on the glass.

Righto, will do that.

Cheers guys,
A

volleykinginnc · Jan 27th, 2012, 4:18 pm

hey bro....I had the exact and I mean exact same symtoms. This happened for a couple of weeks then I started to blow relays. So naturally I thought it connections and hit them all with dieelctric grease. It continued and every week or so I would blow the same relay. Then my ecu crapped. I replaced it with a DP Ecu and haven't had problems until about a week ago and it started doing it again.....grrrrrr....anyway here's hoping it's nothing serious for you.

tonered · Jan 27th, 2012, 4:46 pm

Quote:

Originally Posted by Ascalon

Indeed, it can corect itself with a tap on the glass.

Righto, will do that.

Cheers guys,
A

Saaaaaweet. Super easy, but time consuming fix. Add a slight smear of dialectic grease to the instrument lamp holders to get them in an out easier.

That has me thinking of bagels and schmear. Yum.

Quote:

Originally Posted by volleykinginnc

hey bro....I had the exact and I mean exact same symtoms. This happened for a couple of weeks then I started to blow relays. So naturally I thought it connections and hit them all with dieelctric grease. It continued and every week or so I would blow the same relay. Then my ecu crapped. I replaced it with a DP Ecu and haven't had problems until about a week ago and it started doing it again.....grrrrrr....anyway here's hoping it's nothing serious for you.

Sorry to hear about your ECU, but it would not be the first time that two parts behaved abnormally on a Duc for different reasons.

Have a good one.

Ascalon · Jan 27th, 2012, 6:02 pm

Well about six months ago the immobiliser unit went and I had to get a new one, but apart from that I have not had much in the way of elecrtical issues.

The rev counter thing has been a steadily worsening issue for half of the 4 years I've had the bike. But over the last six months I have been fixing niggles as I have decided to keep it for another year or two and the rev counter is now top of the list.

Anyway, will have a fiddle with it tomorrow and see how it goes.

A

mbevans · Jan 28th, 2012, 12:52 pm

When the 2002-2003 ST4's were still in the world of warranties they had an unusal amount of "BAD" tachometers, and even afterwards from my research.

Most of the time they can be fixed with tightening the screws on the rear of the unit.

Sometimes people have been successful cutting carefully the back of the housing in half checking the circutboard for loose connections (poor solder jobs) then expoxing them back together.

I had a tach on my 2002 ST4s that I did both to without success, as I lived with a bouncy one for quite a while also!

The good part is there are quite a few new tachs on dealers shelves in Europe, and can be had for a good price, (<$200.00usd) delivered, which I bought one from ultimately.

Here in the states many dealers want $350.00++ for one. Remember they are the same as the 998 Superbike (only)......

Good luck with yours!
M

Ascalon · Jan 29th, 2012, 6:44 am

Right, just put it all back together after removing the rev counter.

The three little brass retainers were not loose but they were very corroded on the tips. I took them off and used contact cleaner and a tap to ensure they were all clean as I could not see if they were actually providing some electrical function or just structural.

I cleaned all the contacts in and around the rev counter and greased the rubber inserts for the dash lights too.

When I started it up, I could instantly see that the rev counter seemed to be more responsive than previous, more closely matching what I could obviously hear the engine revs to be doing.

The next question is, the temp reading on the dash is very erratic too and will jump anything up to five degrees when the fan or the headlights are turned on. I know this is most likely an earthing problem, but the main earth by the right foot peg and the battery terminals are all clean and corrosion free.

Cheers,
A