mx5cartalk.com

Evening guys,

I had a browse through here and the big forum but could not find what I was after.

Over time my instrument cluster has developed some mental issues... Car is a 1990 NA6 with 202,000 on the clock.

First one is the Tachometer. On freeway driving, it will sit at it's usual position, however, occasionally it will randomly jump around in 1000-3000rpm gaps without changing how the engine acts, purely a visual problem. Tonight, I noticed that the car was reading around 800rpm lower than normal through out the entire rev range, this means that idle was now 0-50, 5000 was now 4200 etc. This stayed for around 20 mins, jumped around like mad for a few seconds, then went back to normal.

The next is the Speedo, not so bad but it has the shakes on very rare occasions.

The other one is the oil pressure gauge, it's seems to read quite a bit lower than a normal one, at optimal running temp, it sits at 1. I have been reassured by numerous people that these are troublesome things and they are not worth worrying about, however, I'm quite fastidious about how my car is and I would rather it work that be faulty.

Has anyone ever had issues with these gauges before? I heard dirty terminals can cause erratic behavior on other parts of the car, maybe this could be the same?

Thanks for taking the time to read this

Cheyne

Im going with bad earths. Have you pulled out the cluster and double checked the connections?

I had a typical famous na dodgy oil pressure guage and it was just a dodgy connection at the pressure sender. Its perfect now. If its connection is bad, the increased resistance will lower the reading, but you may also have low oil pressure.

Anyways, id suggest getting a mate with another na over and trading clusters and checking the earths.


Easy and will pinpoint the area its causing it.

Dann

Thanks Dann, you know your stuff ;)

Where can I find the earthing points, If I can get in there, I'll give them a good clean, anything you recommend to clean them with?

I am almost certain that the oil gauge is the issue, it had the same problem with the old engine and still sits low with the new engine. I know for a fact it's a good motor.

I want to avoid pulling the cluster out as the standard meter hoods break quite easily and can only be replaced with an ugly matte item...

Im actually not 100% on where the specific earths are for the tacho and speedo. But there are a couple under the dash. One like... 45* degrees up and right from your right calf when flooring it. its a 4mm or so black wire, theres also one in the exact same position on the other side. Also clean the earths just forward and to the left of the crank angle sensor, its a general ignition earth, but one would assume seeing as the speedo is having the same issues, its the dash end that of the equation that has issues.

As for removing the cluster, I know they are fragile, mine has zero tabs actually, and i managed to use regular silicone for tiles or whatever to glue it back on. Its hidden, strong, eliminates vibrations and its comes off if you pull on the hood firmly for say, 30 seconds as it slowly peels away. I know your cars smick and mines not but I guarantee if your careful with the silicone it looks factory. Just in case you snap one.

As for the actualy oil pressure guage, even though the engine is new, the spade connection on the wire going onto the oil pressure sender might have a rusty, high resistance surface. Its easy to check, cut off the old spade and crink a new one on, sand the male spade on the sender to get it clean, and bobs your uncle!

Dann

I had a weird jumpy tacho when my alternator stopped charging correctly. When this happened the battery light didn't come on until the battery was almost flat but the tacho was doing all sorts of weird things.

Solution: I replaced my alternator.

As for earthing points, I think the main earth for the cabin loom is the on the back of the head?

Cheyne, in case you didn't see some big forum threads Guran recently posted on a jumping tacho: viewtopic.php?f=55&t=43726&p=594225&hilit#p594225