Please Help: Where can I find the pulse wire/tacho wire?

[Aussie XLT]

Hi all,

Just completed a LPG conversion on my 1999 Ford Explorer XLT 4.0 SOHC but I can't find anywhere to tap a pulse wire (tacho pulse) from for the gas safety switch. We've tried wrapping a wire around the lead/s, tried going from the coil pack and still having no luck.

I thought there might have been that white diagnostic plug in the engine bay like Aussie Falcons but as yet I haven't been able to find one.

Any ideas?

[Turdle]

Could you tap of the synch signal from the camshaft position sensor?

[wood1]

I have used a fuel injector wire to supply automatic car starters with a tach signal. They need to be programmed to recognize the frequency of the pulse at idle though. I'm not familiar with the LPG conversion so I don't know if this will help you or not...

[Aussie XLT]

Thanks guys, jtsmith I'm not sure to be honest but even if we can I'd need to know what colour wire I'm looking for and unfortunately I dont have a workshop manual. We've had a go at the crank angle sensor but again no luck.

wood1 we tried to tap from an injector but that didn't work not sure why.


Any more ides? Anyone?

[rwenzing]

On US-spec Explorers, the factory wire from the PCM to the tach is tan/yellow. You can find it at pin 48 of the PCM, at the 42-pin main engine connector or behind the instrument cluster.

[Turdle]

Pin 85 on th PCM plug--Should be Dark blue with an orange stripe.
This is the Camshaft position sensor signal wire--

I'll try to find the actual tach drive signal--give me a minute

[Aussie XLT]

Thanks guys!!!

I was hoping to find a wire in the engine bay to use but I guess I'll take what ever I can get.

[Turdle]

Originally Posted by Aussie XLT

Thanks guys!!!

I was hoping to find a wire in the engine bay to use but I guess I'll take what ever I can get.

You will find this in the engine bay--
oh wait--you have right hand drive yes?

where is the main PCM plug? Ours is on the passenger side firewall

[Aussie XLT]

rwenzing am I right in saying I can find tan/yellow wire on the big square engine loom connector on the top of the engine/rocker cover?

[Aussie XLT]

Im not sure jtsmith

[Aussie XLT]

jtsmith just had a look at the Explorer and as far as the engine bay goes the easiest place for me to get to wiring is that massive black square engine loom plug that sits on top of the engine/rocker cover (U.S. drivers side)

[wood1]

Hmmm, if you already tried the tach signal from the coil pack, and you had the correct wire, (it should be a tan/yellow at the coil pack and I would probe it with a logic probe and insure it pulses at idle) maybe a tach signal generator?

I have literature that says that that the wire at pin 48 of the 104 pin connector at the ECM that is a White/Pink or White/LtGreen is a tach signal. I know that Bob has this wire as being tan/yellow and he may be right. I haven't had to go to the ECM for a tach signal on an Explorer.

Sorry I couldn't help more...

Chris.

[Aussie XLT]

Could the tacho pulse be digital? maybe that's the issue, maybe my safety switch doesn't recognise it

[rwenzing]

Originally Posted by Aussie XLT

rwenzing am I right in saying I can find tan/yellow wire on the big square engine loom connector on the top of the engine/rocker cover?

That is the 42-pin connector that I referred to and it should be there. The tach wire is shown as being tan/yellow in the 1999 Explorer Ford Wiring Manual (North American).

The tach signal is generated by the PCM solely for the tachometer and trip computer, so it is likely to be digital. It has nothing to do with the coil pack which has its own independent ground triggers from the PCM.