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[willo]

I have a problem in that my TJ is all clever electrickery and the pcm sorts stuff out after taking readings from things such as speed and revs. Now as Im sure you are all aware I ave recently fitted a Dana 300 transfer case, and it is the old stylee and as such only supports a spinning mechanical speedo cable. So the problem tat I ave is tat if the pcm uses speed to adjust valve this and that, it is now unable to as there is no reading going to the pcm from the TC.

Now, this afternoon, I have fitted my Brantz tripmeter wich uses one of these on the mechanical speedo cable, and the Brantz has a digital readout with speed in one of te boxes......So my logic is that somehow I am getting a pulsed (or similar) readout from said above connector and I am wondering if I can somehow use this to send some kind of speed info to the pcm..........thoughts please

[Dave The Sparky]

I would suggest that first you need to know what frequency the pcm requires at a set speed and mimic that.

Once you know that the simplest way is probably to to make a toothed wheel to match the above and then fit one of these with the correct voltage to read it and feed back into the pcm http://uk.rs-online.com/web/p/inductive-proximity-sensors/0198661/.
If the pcm wants a 5V signal then you would need to fit a resistor in line to save frying your pcm with a large voltage.

I could use a programmable controller to accept your pulses multiply it by whatever and whack out an output frequency instead but it wouldnt be cheap!

Some electronics genius may have a better idea or you could just fit an engine with a carburetter or even better fit a nice diesel instead and bin the electronics 

[willo]

or perhaps one of these would work:

#54MG. Eight pulse signal generator for your electronic speedometer head. This goes behind your dash and plugs to the head and drives off of your old speedometer cable. Doesn't include the cables. Can be installed inline for both mechanical speedometer and pulse generator. Can be screwed directly to the transmission at the speedometer housing. Works for GPS, EFI or Cruise. Cost $78.00


from here (scroll down a bit to #54MG)

[Dave The Sparky]

#69 would be a better bet Willo or email them and tell them what you are trying to do im sure it will have been done before.

[dtooth]

i might have one or two of those eight pulse things lying about as they are used on renix engined jeeps

[willo]

i might have one or two of those eight pulse things lying about as they are used on renix engined jeeps

well let me know if you ave and in the meantime I will try and find out how many pulses the tj pcm needs

[dtooth]

nope can't find them i think i've pasted them on ,sorry .

but the diffinatly look the same they control the cruise control on the renix jeep

[willo]

nope can't find them i think i've pasted them on ,sorry .

but the diffinatly look the same they control the cruise control on the renix jeep

ok thanks for looking

[willo]

so I asked a similar question on Pirate, and got directed to this, which will allow me to use both the leccy for the speedo/ecm and still use the brantz offof the mech speedo cable:

http://hescosc.com/shop.asp?action=details&inventoryID=43100&catId=7902

[wildwood]

right then.....just arrived at this thread.....

but just at the right time....

I have one of those in my Dana 300 and or course it was once screwed into your Dana 300

it does work.....but sometimes if you come to a stop from higher speeds to a dead stop you might still get to stall.
got used to it once I got used to its behaviour......

T o read speed I went old school and bought a speedo cable and for $100 a CJ speedo. on 35s it was accurate up to 30
Which was all I cared about cos of plod and after that became more optimistic......

[Dave The Sparky]

I believe my way although crude is still cheaper and more accurate 

[willo]

I believe my way although crude is still cheaper and more accurate 

thort you said it wouldnt be cheap

[Dave The Sparky]

Using just a proxy and a toothed wheel would cost you the switch (£30) a bit of wiring and a bit of time making the toothed wheel (or maybe a lot of time depending on how many teeth it needs!)

However it would be neater to buy the proper speedometer gear for your tyre size and the hescosc adaptor then you shouldn't have any problems as presumably the speedo system will be fooled into thinking it is back to where it was from the factory and send the correct pulses for the speed you are doing.