Tach issue and 4wd/abs light out of nowhere

[GTR203]

Need some advice on this one. Car has been driving very good no issues at all then today on a drive I look down and tach is jumping all over the place. It will drop to zero them back up and hop around and then drop back to zero. Btw the engine is running fine and NOT following the tach the car runs and drives no issues. At the same time I noticed my 4wd and abs lights are on. I've never had a issue with the 4wd before and checked all fuses and looked for loose grounds but all good. I had one blown fuse in the fusebox that was labeled ( car electrical or somthing along those lines) replaced it and nothing still the issues. Ill be testing the attesa ecu soon as well. Thanks in advance for any help

[AL91GTR]

I have had the same issue with my tach for a little while too. I've been looking around here, google, etc... and found no answer at all. I checked all connections behind the dash and as much as I can see under the hood and nothing seems to be an issue. My engine runs smooth, steady and does not jump at all.

My abs and 4wd lights don't come on but i noticed last week that the tach even started jumping after i turned the ignition to the 'on' position before i even started the car.

Any advice on this would be greatly appreciated as well.

[caliber676]

Try pulling codes out of the attessa ecu. I would start there. If nothing is wrong I would start looking at input signals for the tach and see what components are linked between that and the attessa/abs. It's safe to say some electrical component is not receiving a proper signal or able to flow to a solid ground.

[GTR203]

I went and started the car and everything was back to normal? Ill have to drive it abit tomm to see if it reoccurs we had alot if snow so Mabey somthing got wet

[caliber676]

Resistance values can be effected by temperature in some cases which could cause your random signals. If you suspect a leak best to check your trunk and door seals.

[GTR203]

Yea I'm going to check everything over and test the ecu drive fine for 15 mins today no issue them the 4wd abs light came back but tach was fine? Ill have to test it. I've just parked it and took the 240 out for now as I don't like driving the gtr in the snow

[caliber676]

Gotta love 20year old electrical gremlins.

[GTR203]

So I'm not pulling any codes from the ecu no lights. I just found a fuel leak that was leaking on my alt and I heard a bad alt will throw the lights with no codes. I replaced the fuel lines ( we're just replaced 3 months ago) and it stopped leaking cleaned the alt with electrical cleaner and went to run errands no light the whole time turned the car on and off multiple times. Pull in my driveway turn the car back on and lights are on again. I'm pulling 14v on my guage and have no symptoms of a bad alt.

[GTR203]

Car was fine for 3 weeks no issues then last night in the rain my power steering went numb ( like if the speedo cable was broke but it isn't I just replaced it and speedo works fine) but no lights. Today I run to the store everything is fine I park start my car back up and my abs and 4wd light is on( steering has been fine all day so far) it definitely has so thing to do with the rain. Back to sqaure one.

[h4X6]

trace all wiring related to power steering, might have a frayed wire and its shorting...

[GTR203]

I think I may have found the issue, I have a plug on the rear wiper and it was leaking a tad bit I'm assuming dripping on the hicas ecu I dried it out everything works fine I sealed up the plug and so far so good. Lets keep our fingers crossed!

[AL91GTR]

Everything on the back of the dash here is good. No codes from ECU or Attessa in the trunk and no appearance of water leaks. All wiring etc... looks fine. My car has been parked in the garage for a few months and is completely dry. I think I'm just going to install a new (used) tach and see if that helps.

Anybody else have this issue wiht a jumpy tach? Seems like it would be more common on a 20+ year old car.

Anybody know shich wire is the signal wire for the tach and where it originates in the engine? Seems most likely that there is a bad wire or ground related to the signal hitting the tach.

[GTR203]

My tach only jumped around that one time when I made this that was weeks ago never happen again, however my light came back on yesterday. It only happens the 2nd time I turn the car on, so say I start the car it will not have a light ill go to the store turn it off when I restart they will be on. If I shut off and restart the car they will remain on buy if I let it sit for an hour or so and start it they will be off again

[rob_96]

update

[AL91GTR]

I'll give a Tach update I guess. It's still pretty much crazy. As soon as the ignition turns to 'on' it Jumps around all over the place but after driving for a while and once the car is fully warmed up everything settles back down to nomal. I think it's once the dash, interior etc... warms up and actually has nothing to do with engine temps.

My friend owns a speedo repair/conversion business and at a quick glance the other night he thinks it is the motor that drives the tach inside the cluster that is messed up. I might just take the cluster out in the fall and have him look at it ...