rev counter still fluctuating badly
Discussion
hi guys, hoping someone can help, have tried loadsa things to try and find out why my rev counter has started fluctuating badly. there is something interfering with the signal, it jumps and varies by about 500rpm randomly.
it started a few weeks back.
so far, ive changed the plugs,battery, put new bosche leads on, new plug extenders, dizzy cap, alternator, starter, rotor arm.
Ive also put on a set of known good magnecores, cap plug extenders, coil and ignition amp module.
none of these made any difference. On the wiring side, i have checked and cleaned up the 2 earth points inside the car and checked the wiring plug on the back of the rev counter.
im running out of ideas for what it could be? does anyone else have any ideas for things i could try?
thanks
it started a few weeks back.
so far, ive changed the plugs,battery, put new bosche leads on, new plug extenders, dizzy cap, alternator, starter, rotor arm.
Ive also put on a set of known good magnecores, cap plug extenders, coil and ignition amp module.
none of these made any difference. On the wiring side, i have checked and cleaned up the 2 earth points inside the car and checked the wiring plug on the back of the rev counter.
im running out of ideas for what it could be? does anyone else have any ideas for things i could try?
thanks
Anything like this? http://www.pistonheads.com/gassing/topic.asp?h=0&a...
I never got to the bottom of why mine did it but it has been behaving itself recently. I did get a throttle control unit from the 'bay but I haven't swapped it out yet (mostly cos I can't get the dash off
)
I never got to the bottom of why mine did it but it has been behaving itself recently. I did get a throttle control unit from the 'bay but I haven't swapped it out yet (mostly cos I can't get the dash off
)It'll be pick up from the eht circuit.
check and move the plug leads, especially the coil lead to try and get rid.
Also magnacores are prone to this, IMHE even though they shouldnt be.
You can have a diode put into the line to remove the spikes, this can be done by the dial company...ETC??? something like that but I'd gues you could do it externally across the rpm i/p line easy enough.
A
check and move the plug leads, especially the coil lead to try and get rid.
Also magnacores are prone to this, IMHE even though they shouldnt be.
You can have a diode put into the line to remove the spikes, this can be done by the dial company...ETC??? something like that but I'd gues you could do it externally across the rpm i/p line easy enough.
A
The rev counter picks up the spikes in the coil primary that are caused when the coil discharges, typically these are about 200- 300 volts and swing to and fro as the magnetic fields die away in the coil, so the voltages dies away pretty rapidly, so it should only pick up the first pulse . The problem occurs when these spikes are larger than usual so that the rev counter picks up more than one of these "ringing" pulses, so it gets a double trigger pulse. The reason why its not always apparent is the voltage needed to ignite the mixture varies with compression and the amount of fuel, so the peak HT reached before the coil fires varies considerably, which effects the level of the spike in the primary, and the trigger points accordingly. As already mentioned increasing the HT resistance by whatever means reduces the spike size, or you could try putting a resistor inline with the rev counter input, although I cant give a value as I dont know the rev counter resistance. You could try putting say a 1 meg ohm 10 turn resistor inline with the input, and simply wind it up until you get a reliable trigger. Also as mentioned a diode will stop one side of the ringing pulse, that may be enough.
This trace shows the big primary spike, followed by the ringing pulses that need to be controlled (not the coil oscillations, the ones to the left):
This trace shows the big primary spike, followed by the ringing pulses that need to be controlled (not the coil oscillations, the ones to the left):
I had this problem many moons ago when I has a 94 chim 4.0l. Coil went and after fitting a new coil I had the same problem. Long story short, a coil from a similar era car with original coil was test fitted and rev counter as steady as a rock again even though same part number IIRC. Never did find outs the cause but above explanation seems to make sense.
Im confused now- you have two posts, and the other says the car is running poorly....if you get a misfire it can make the ECU overfuel the engine, and soot the plugs (assuming its not a precat. If the plugs are bad on one side of the V8, and OK on the other then the misfire is one of the 4 leads / plugs on the side that is sooty.
hello,
yes, its running poorly, very very lumpy on idle, a lot is masked when running on non-cat map. It will only hesitate when going on the throttle when running on the cat map. So probably more of a hesitation due to fueling than a real misfire, just to clarify, on full load no misfire. The rev counter bounces around not in time with the engine tone - if that makes sense. if i rev it lightly for example to 3k rpm ish, the needle will fly round to 6k.
I thin its difficult to determine whats causing what now on this one lol.
yes, its running poorly, very very lumpy on idle, a lot is masked when running on non-cat map. It will only hesitate when going on the throttle when running on the cat map. So probably more of a hesitation due to fueling than a real misfire, just to clarify, on full load no misfire. The rev counter bounces around not in time with the engine tone - if that makes sense. if i rev it lightly for example to 3k rpm ish, the needle will fly round to 6k.
I thin its difficult to determine whats causing what now on this one lol.
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