Bad Earth????

[AttaBoy]

I read somewhere here in this forum that bad earth can cause rough idle???
So where can I find the earth point in the engine bay?? I tried injector cleaner, new leads and sparkies, tried different fuel, pump seems to be working.

So where is the earth point and how can I fix it?

Thanks, the rough idle is driving me nuts!

[Murdoch]

Maybe your thinking of the O2 sensors having a bad earth? I think its common on VS's. I know i have read it in the forum some where.

I earthed my VS O2 sensors at the memcal box. I did this as my O2 sensors were reading intermittently, this seemed to fix the problem. From memory i just used my Gregories manual to locate the eartth wires at the memcal.

[kopper69]

A faulty wire is likely to go faulty either at the connector, if it is stressed, or at some other point where it is stressed. If a wire doesnt get stressed, it wont have any reason to go open circuit (unless it is corroding). If you have a multimeter, you can test wires in a fraction of a second, it is rare that they do open circuit though. I would aim for something else, unless your car was sold cheap because of water damage. Can you describe the rough idle, we might be able to point you in a better direction.

[AttaBoy]

A faulty wire is likely to go faulty either at the connector, if it is stressed, or at some other point where it is stressed. If a wire doesnt get stressed, it wont have any reason to go open circuit (unless it is corroding). If you have a multimeter, you can test wires in a fraction of a second, it is rare that they do open circuit though. I would aim for something else, unless your car was sold cheap because of water damage. Can you describe the rough idle, we might be able to point you in a better direction.

When I bought my car I got it for $9,900 and at that time, she ran so beautifully and so smooth and had no probs with her for like a year!! I was actually very surprised!!!! But in the last few month she rarely misses and gets very rough idle (Worse with A/C on). She now cranks a while before the engine fires up, before the car just fires up under a sec but not any more?? This happens when I haven't driven her for few hours but fires up quickly after like 1/2 hour since been driven!!
Anyway I'm just getting more worried cos soon I'm gonna supercharge her so yeah..... What could it be??

[fitzy2005]

could be your fuel pressure regulator, crank angel sensor, coil pack etc. fair few diff things could cause it

[AttaBoy]

But what is most likely to affect it?? Coilpacks?? Can't really be fuel regulator cos the engine runs fine its just when I put it in Drive it idles rough like at the lights.

[kopper69]

Sorry mate, no easy answer. I would start off simply with your battery and battery terminals. If the battery is >2years, replace it. If the wiring to the battery terminals isnt rock solid, get them fixed up. If you have a multimeter, meausre the voltage. Let us know how you go with that.

[Burt_vn]

yeah i was gonna say check the resistances through all your leads, check the coil pack...check the spark your getting from the leads... but as said before it could be a few things, hopefully just a weak spark.

[AttaBoy]

But my leads and sparks are pretty new!! Anyway will check it. Don't really know how old the battery is but looks ok to me.

[Burt_vn]

get your multimeter out, check the batteries voltage with the engine off, then check it while the engines running.. around 13.9 i think is perfect voltage ( dont hold me to that, im a bit rusty) and check your coil out too. Just some ideas mate, based on what you said about it rarely missing, but a miss is a miss. As for the rough idle im not too sure, idle circuit solenoid, O2 sensor, try cleaning your throttle body out, etc. Mines just started to idle rough as well, gonna check it over on the weekend, ill let you know if i find the problem

[AttaBoy]

get your multimeter out, check the batteries voltage with the engine off, then check it while the engines running.. around 13.9 i think is perfect voltage ( dont hold me to that, im a bit rusty) and check your coil out too. Just some ideas mate, based on what you said about it rarely missing, but a miss is a miss. As for the rough idle im not too sure, idle circuit solenoid, O2 sensor, try cleaning your throttle body out, etc. Mines just started to idle rough as well, gonna check it over on the weekend, ill let you know if i find the problem

Thanks let me know how you went.

[Michelson4301]

I've had a rough idle since I bought my VS, it's common for the ecotec to slightly burn valves, also it's a common problem to have an earth problem with the oxygen sensors, you could ground A1, A2 and D14, D16. The first 2 are engine earths, I had like 5.5ohms resistance, checked and cleaned all body earths and engine earths but this didn't fix it so i've made a earth to the body from the PCM end. D14 & 16 are the oxygen sensor earth references for the computer I also made jumper wires and fitted them to the body at the computer plug end. This seemed to make the car more responsive and did reduce the severity of the missfire. Last of all i'd do a compression test test on the engine to confirm the engine compression is good. This will tell you if you've got unbalanced cylinders or low compression. If only 1 or 2 cylinders are down on compression add 10ml of oil to the affected cylinders and repeat compression test. If the compression suddenly spikes then you've got a ring sealing problem, if little to no change is made then you have a valve sealing problem.