e30 rev counter incorrect

[iam]

I just made a run up the motorway to my nearesst Euro car parts store for the e30 temp sender and at one point gave the throttle some beans (floored it) in 3rd gear. The rev counter went past the 7 and the red line and didn't 'bounce' so i assume the rev counter isn't calibrated for the engine. Fairly obvious but any idea how out it is? I'm thinking of temporarily knocking up a stick on of some sort to correctly gauge what the actual revs are. Any have any idea how 'out' the e30 rev counter is?

Cheers

Iam

[e30trooper]

I just made a run up the motorway to my nearesst Euro car parts store for the e30 temp sender and at one point gave the throttle some beans (floored it) in 3rd gear. The rev counter went past the 7 and the red line and didn't 'bounce' so i assume the rev counter isn't calibrated for the engine. Fairly obvious but any idea how out it is? I'm thinking of temporarily knocking up a stick on of some sort to correctly gauge what the actual revs are. Any have any idea how 'out' the e30 rev counter is?

Cheers

Iam

it could be that or ... you a chip with no rev limiter. passing 7200 on a stock engine will start breaking things.

[E30SPDFRK]

Nah, the tach is calabrated for how many cylinders you have. If the car was a 4cyl to start with, it's now reading double. If it was a 6 cyl its reading 4/3's.

Mine does this too but I haven't done anything about it yet. I think it's possible to run a resistor inline to the tach wire but I'm a noob to electrical. Maybe someone with more electrical experience can chime in.

[nando]

a resistor won't work. it's a digital pulsed signal from the ECU.

[1mz]

has this car been swapped? do you have the correct coding plug?

[E30SPDFRK]

a resistor won't work. it's a digital pulsed signal from the ECU.

Know of any other ways of doing it then?

has this car been swapped? do you have the correct coding plug?

This thread is in the m60 subforum

[nando]

I don't know, it must be done. I'd assume a 4cyl plug wouldn't work? wouldn't the RPM read half, not double? since the coil fires half as often per engine revolution?

if there's not a V8 coding plug that will work (E34?), there's probably a way to double/divide the signal with some hardware and coding..

[E30SPDFRK]

The 4 cyl tach reads double because theres now 8 coils instead of 4. You bring up a point about 6cyl tachs though, I just assumed it would read like the 4cyl one does.



The e34 and e32 coding plugs don't fit in e30's.

[nando]

right, I was thinking backwards. there are twice as many coil pulses per RPM.

you'd need a frequency divider circuit. it's a low current, 0-5v signal. shouldn't be that hard to do.. dividing by half would be simpler than 3/4.

[E30SPDFRK]

Warning: typing out loud ahead.

I just did some studying up, it doesn't seem that complicated but I'm not sure exactly how to hook it up. One thing said theres 2 imputs, one is the signal you have now and the other gets grounded via a diode? I don't see how that would be an imput though.

Going off this drawing, where do J and K go? or are they just there to act as a display for the signal.

The drawings just show a box for the frequency divider, I just have a hard time wrapping my head around what is in the box.

[dirty30]

I have the tach signal converters for sale. $100 shipped.

[E30SPDFRK]

Any insight into how you hook it up? Or what it looks like even?

[dirty30]

Red – Power Supply (12V on ignition position)
Brown – Ground
White – Input rpm-signal (from engine control unit)
Yellow – Output modified rpm-signal (to instument cluster

[slammin.e28]

I need one of those. I got your PM, just not the $$.

[dirty30]

I need one of those. I got your PM, just not the $$.

Its cool... tell you what...

I need an M60 oil filter housing, I'd trade you one straight up for it. We aren't very far from each other so we could meet. LMK