techo/mpg gauge is doing whatever they feel like..?

Post Wed Oct 31, 2012 3:36 pm

Ok so next on my list of annoyances are the tacho and MPG gauges.

The tacho is not accurate, if I hold revs at 1000rpm, the needle will wander back and forth around 800-1200 rpm.

My understanding is the MPG gauge takes its reading from the speedo and tacho and then gives a result.? So if either one isn't working as it should the MPG gauge will be off.?

Where do I start checking to fix this tacho issue?

(I replaced the SI batteries a month ago, tested and working)

Post Wed Oct 31, 2012 6:59 pm

Just reading up on possible leads, saw this on on r3vlimited; this valid?

"The coding plug fixes an issue where the tachometer is working but not accurate."

Post Wed Oct 31, 2012 7:18 pm

The coding plug is located on the cluster.

Post Wed Oct 31, 2012 7:22 pm

Thought so, 2 types for 4 and 6 pots. Mine was a 325i so should be ok.?

Hmm what else can I test?

Post Wed Oct 31, 2012 7:23 pm

The brass nuts behind the gauges??? Have you checked to see they are tight?

Post Wed Oct 31, 2012 7:26 pm

Yeah checked them, can't hurt to check again as I have the clocks out anyway.!

Oh rav, look at this mate. My car doesn't have No10 breather tube. No8 in mine is just a straight pipe. Where does No10 go, somewhere on the intake manifold?

Post Wed Oct 31, 2012 7:29 pm

No 10 is a vacum hose, mine doesn't have one either.

Wonder if it's for slushbox cars?

Post Wed Oct 31, 2012 7:31 pm

Could be oil vapor vent hose for slushbox cars yeah.

Post Wed Oct 31, 2012 7:50 pm

Mines got one, as I replaced nymber 8 with a new one from BMW, my engine is from a late manual car, can't remember where the other end goes though sorry!

Post Wed Oct 31, 2012 8:28 pm

Mines a late manual engine too, you couldn't have a little peek could you Jer?

Hate to be cheeky!

Post Wed Oct 31, 2012 8:39 pm

Iirc that pipe goes to a little stub under the inlet manifold.

Post Wed Oct 31, 2012 8:51 pm

Ah, I'm off to the garage to tinker, I'll go take a look now.!

Cheers Lee

Post Wed Oct 31, 2012 9:59 pm

A bit eager

Post Wed Oct 31, 2012 10:46 pm

I do most of my tinkering at night, only bit of peace I get.!

Right so yeah, I do have the little tube, its been plugged and tucked away under the inlet manifold. It's not leaking any air in so not doing any damage?

I've also looked again at the cluster grounding nuts, cleaned the threads again and replaced the nuts with shiney new ones. Still no improvement with the wandering Tach and econo gauges

Beginning to think the tach is dodgy.

Post Wed Oct 31, 2012 11:03 pm

I would put it back where it belongs, maybe it's sucking in air causing the tacho to rise and fall, which an air leak would do

Post Wed Oct 31, 2012 11:07 pm

its well blocked off, the crank case breather that its supposed to go to has been replaced with a straight pipe, so no join on it.

The tacho wanders about, but the idle remains stable. Like I say I can hold engine revs at a stable 1000rpm and the tacho needle will wander - + 300 rpm.

Not the engine revs, just the tacho needle.! Mad.!

Don't forget to look for those things for me Rav.!

Post Wed Oct 31, 2012 11:09 pm

I'll do it tomorrow, hopefully it won't be fooking raining

Post Sat Nov 03, 2012 5:55 pm

Hey fellas, a quick vid of this mad gauge issue I have. As you can see the Tach and econo gauges dance about and the temp flickers. The engine idle speed is very stable as you can hear.

[youtube][/youtube]

Post Sat Nov 03, 2012 6:12 pm

Your car is possessed!

My temp gauge does a similar thing once it gets aboult half-way, I always thought this was down the the brass nuts on the cluster but not checked it yet, but you say you have checked yours.

Could it possibly be an earthing problem? Just guessing though, maybe you could try running a seperate earth to the earth connector on the cluster? I've done this before to eliminate problems with electrical faults

Post Sat Nov 03, 2012 6:43 pm

It's worth a punt, which earth point on the cluster are you referring to Jer?

Post Sat Nov 03, 2012 6:59 pm

I don't know mate, as I haven't taken the clocks out of mine yet! If you've got a Haynes or Bentley manual you might be able to figure it out on a wiring diagram?

Post Sat Dec 08, 2012 4:30 pm

Ok had something strange happen last night, drove home sticking to 30mph as there are cops everywhere here in December.

The lights went really dim for about 2 miles and when I arrived I shut the car off only to find it wouldn't start again...! I let the battery sit for 5 mins then tried again whist giving it gas and it fired up all lights nice and bright and the tacho and econometer working accurately!!

So today I ordered a new alternator regulator/carbon brush set and fitted it. The car is perkier but the tacho and econometer now are flopping about again. Bah

I'll post this in the technical help section too..

Post Sat Dec 08, 2012 4:54 pm

Also, I replaced SI batteries a couple months ago with these,

http://www.ebay.co.uk/itm/VARTA-CR1-2-A ... 19c587595e

The inspection light stays off too.

Post Sun Dec 16, 2012 9:50 pm

Ok so over the past week or so since I changed the alternator brushes the tacho and econometer are working great.! Also not getting that strange light dimming after driving around.

Not sure if it was the brushes or the fact the alternator connections have been freshened up thats done it. Ah well another problem taken off my list.! Woot.!