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HQ355 wrote:I could be wrong but it may be the brand of tacho's your running, speco and calibre are really nothing special, a mate had the same prob years ago with delco injection on sbc, went through atleast 5 tacho's until he got a decent one and never had prob again

Yeah I realise I could potentially buy an autometer branded one or something and have it work straight away, but this one is fitted in the dash and matches the others.
Plus it was working when installed, and still works on other holden V8s so something is wrong with my car somewhere.

On another note, whilst going through my loom I checked for continuity between various plugs and pcm, and found some wires eg one from the ignition module (white with violet) had around 1 ohm resistance, which is quite high for a short length of wire. Others wires next to it read basically dead short circuit to pcm as expected.
Is it worth replacing the wire with the higher resistance or is the current from sensors generally so low that it won't cause any voltage drop issues? If it was one of the heavier brown or blacks wires obviously designed for higher current I would replace it, but when they're just signal wires does it matter?

1 ohm is really irrelevant in the context of a signal wied. Most multimeters have lead resistance in the order of 0.5-1.0 ohm

Simon

Thanks Simon but the meter leads were zeroed and the adjacent wires of similar length had lower resistances.

But in the context of a signal wire, 1 ohm will be insignificant. If it is the MAP sensor then the source impedance is about 1K and the input of the ECU is almost certainly >10K, then the effect will be in the order of .1% if I remember the theory correctly.

Simon

Yeah cool well thats basically what I was wondering. Being just a signal wire a resistance of 1 ohm is insignificant. If it was a 1 ohm resistance in the power wire supplying injectors etc then that would be a problem.

Well, you would probably see 1 ohm or more there as well. The fatter the wire the lower the resistance but 1-2 maybe even 3 ohms is pretty normal for a wire of that kind of length. It also depends on the quality of your multimeter. Cheap ones in particular are not so accurate at such low readings, and things like multimeter battery voltage thats a bit off due to it being on its last legs can affect it too.

Nah 1 ohm on a wire like that is way too high!
Eg ignition coil power wire or injector power wire carrying roughly 5 amps. 1 ohm resistance would equal a 5 volt drop. That's huge! I'm an electrician by trade so I do have reasonable quality meters. Resistance of a wire like that should be less than 0.1 ohm for wire in good condition IMO.
Anyway, not really relevant but I was just making sure that particular wire was only used as a signal or reference, not heavy current carrying.

I guess I should have said to see up to 3 ohms is normal. But it sounds like you know what your doing and have quality equipment that can accurately measure low ohms.

Hey mate, I have the same issue with a vp v8 in a cv sle tacho flicker above 3000 rpm and feels down on power in the top end, however it made 134rwkw in this state, I also of late have had the tacho start to drop even sit on 0 rpm occasionally whilst driving car still drives but spits n farts but feels way down on power, I'm thinking it's earth too, I put a 120a alternator on mine as it seems to get worse when I have the stereo going amps etc, but once it starts even the indictaior will cause it to stutter drop rpm etc.i need to log a bit more, but the laptop has a busted screen ATM and I haven't done. Much with it of late. I know it doesn't solve your problem but know you are not alone.
Cheers Gareth

Sort out the basics 1st. Earth leads, power feed leeds (202t will back this up)and get your screen fixed ! Otherwise your shooting in the dark, keep us posted