Advice on Jumping Tach

[Gibby]

Hi All,

I am very new to this--both the car and the forum--, but hope to get some help or advice. I have a datsun 280zx which I love to peices, but recently as I am driving I notice the Tach start to jump all over the place right about the time the car starts to get warmed up, then the car starts to run rough, and dies. It's consistently happening if I rev the engine to high as well. But, I never have a problem starting the car. I have replaced the battery, battery cables, coil, fuel filter, spark plugs, spark plug wires, cap and rotor. Any ideas?

Thanks all for any help you can give!!

Gibby

[ajmcforester]

Well it sounds like you went the expensive way to eliminate spark as the problem. That leaves compression, fuel and air. My bet would be fuel, check the fuel filter, if you haven't replaced it recently put a new one in, I'd try that first. Then check fuel pressure then clean the injectors. It realy sounds like a car starving for fuel. If the fuel filter is relly bad you might need to clean out corosion in the fuel system to fix the problem

[FastWoman]

The tach can jump (at least sometimes on some cars) when the cylinders misfire. That can cause premature termination of the spark, such that all the pent-up energy rings at high voltages in the ignition coil. That results in double-triggering of the tach. If you straighten out your running problems, the tach will probably stop jumping.

It sounds like fuel starvation to me too. It could also be a failing fuel pump.

[ajmcforester]

The tach can jump (at least sometimes on some cars) when the cylinders misfire. That can cause premature termination of the spark, such that all the pent-up energy rings at high voltages in the ignition coil. That results in double-triggering of the tach. If you straighten out your running problems, the tach will probably stop jumping.

It sounds like fuel starvation to me too. It could also be a failing fuel pump.

I agree, but try a fuel filter first its cheaper than the fuel pump. Is your timing at factory specs?

[IdahoKidd]

Hi Gibby, welcome to the forum and to the Z world! What year ZX? turbo or non? Auto or stick?

Will the car just set and idle along fine? When it starts missing, does it do it just revving the engine or when it is under a load (driving). Does it ever reach a point it doesn't do it any longer (driving down the road at 55 for example, or after it runs for 20 minute)

How familiar are you with cars? Can you tell if it sounds like fuel or if it sounds electrical? I can often tell the difference but probably can't tell you in writing how. Just an ear thing. I see you have changed the fuel filter. What is the history of the car? Has it been a daily driver all along, has it sat for some time, did the PO mention any issues? Did it work fine for a while and then the problem arise? Check obvious things like loose wires at the coil and distributor, pull the dist cap and spray the inside of the cap and the distributor itself with WD-40.

At the top of the page is a "search" option. It is picky and will only find the exact words you put in. Search things like 'erratic tach' 'bouncing tach' 'engine miss' fuel starvation' etc and read through some of the posts. You'll find phrasing that will lead you to a different search and more information. I've seen this symptom listed a lot but have never followed through. I don't know if it is proper etiquette to refer you to a different site with more/different info, but at hybridz.org, there is a lot more zx information. Those guys are over the top anal about the search button and a vast majority of their cars have been altered, but still a lot of reading available and by association of similar problems, you might figure it out. It isn't likely a major issue, just a matter of finding it.

I just re-read your post again. It isn't over-fueling by chance? These cars have a sensor in them that enrichens the fuel injection when the motor is cold and then turns itself off when it warms up. If it fails, it might lead to symptoms of having the choke on.

Good luck and do let us know. The next guy that has the same problem and uses the search will find your questions and perhaps the answer.

Leonard

[IdahoKidd]

Holy crap, anyone see the date on the original post? August 05.:stupid:

[adamr]

8-19-2005!

Gibbie, do you still have a tach problemLOL

[FastWoman]

Good lord!

More to the point, what did the problem turn out to be, Gibbie?