[nickmil]

This has been bugging my, ever since I bought an ATX Focus (ZX3 '01) 3 years ago - an unusual tachometer behavior.

For instance, in second gear, I would lightly press the accelerator, and the tachometer needle would quickly go to around 2000 rpm. I would slowly keep pressing accelerator, the speed would rise from ~25 mph to ~35 mph. But, the tach would stay basically the same, around 2000 rpm. I always thought this is caused by the torque converter and it is normal for automatic. Is it?

What got me puzzled is when I got a coolant flushed a month ago. My car behaved totally differently for the next week or so. Throttle response was so much better, much similar to the manual transmission cars, tachometer was actually following my accelerator input closely. But, this lasted only about a week[] .

I have no idea what happened[dunno] .

Is this how automatic transmissions (mis)behave?


- Nick

 

[nickmil]

One other thing that might be related.

No matter how slowly and lightly I press the accelerator, engine would immediately rev to around 1800 rpm. When car decelerates RPMs would fall in low 1000s, as well, and it will show correctly on the tachometer. (Digital tach shows the same data.) But, if I press accelerator again, it goes to, at least, 1800 rpm.

What can this be?
- worn/sticky accelerator cable
- sticky throttle body (butterfly)
- bad TPS
- something else??

Thanks!

 

[iminhell]

Check your engine grounds and improve them if possible. Might be a bad TPS, but I'd almost lay money on a poor ground.

 

[nickmil]

Thanks, I'll do that - as soon as I figure out where to look[:I]

The whole engine is metal, and conductive, should be on the same ground level as '-' on my battery. Should I just poke around to find any difference in voltage?

Is there any wiring between battery '-' and engine, for the ground purpose?

Thanks again!

 

[iminhell]

The main engine ground will be connected (or should be) just under the ignition coil pack, bolt on the case of the trans to the engine block. That one should run right to the battery "-". There is also one on the top passenger side that bolts to the head just above the fuel rail and attaches around the strut tower area.
Both should be removed and cleaned, emery cloth and dielectric grease for reinstall.

There are also a couple inside the car, but I don't think those would be an issue, you'd see other problems as well.


This may help some:
http://www.focuscanada.net/forum/index.php?showtopic=8122

 

[nickmil]

Awesome! I'll redo my grounding cables - rep-ed.

Thanks!

 

[nickmil]

I've connected my OBD scanner and found some interesting data.

Put my car in neutral and observed the following values for absolute throttle position (TPS) and RPM:

ATP RPM
18% 750
30% 6000

Idle is always at 18%. Pressing accelerator to the floor (engine off) shows 92% for ATP.

Throttle is very touchy, just barely pressing it jumps to 2k rpm. Has anyone checked these values using any OBD scanner, and noted their values?

Is this faulty TPS or something else? I might grab some resistors and try to modify what TPS shows to see if it helps - but that would have to wait until weekend.

Thanks!