High RPM misfire - may have found something, need help!

[dog man]

I took to going through the ECU fault finding process chapter of the bible and I found on pin 39 where I should have been getting battery voltage I was only seeing 9.5. This is fed from the low tension side of the coil and tells the ECU what the engine RPM is.

At the coil end of the same wire I've got 12.6 volts. The battery is days old BTW

So after the wires leave that side of the coil, they disappear. Two wires come off that same side - both white with black tracer - the same colour as at the ECU end. Doesn't one of those go from the coil to the ignition module?

Does it run under the inlet manifold as it makes it way to the loom/ECU?

Obviously at some point it becomes one wire so, what might be happening between the coil and the ECU to be robbing nearly 3v?

[Ozstyle]

I think that is correct, the wire from the coil to the ECU has a dropper resistor in it (6.8K ohms I believe). Sure I've about read this in other 14CUX related articles. If you have the Haynes Land Rover Discovery manual the wiring diagram clearly shows a "fuel injection resistor" between coil and pin 39 on ECU.

[dog man]

Thanks. I think I've read the same somewhere too!

Had a look in the passenger footwell loom area, couldn't find it. Might try to probe deeper today.

Still unsure weather I should be following the bible - i.e, I'm 3v down at pin 39 or is it actually fine at 9.5 and the bible is wrong?

Could someone measure pin 39 on their Chim please? Ign on, pin 39 and earth (I earthed from battery)

[Ozstyle]

The resistor (actually 2 of them) in question is in the LT wiring to the coil in the engine bay (close to the coil), usually taped or cable tied to the pcv tube that runs in front of the plenum. The resistor is rectangular and black and has a spade connector at each end, female loom spade connectors have black covers.

[dog man]

Yep I think mine is taped to the bit of the loom that goes to the AFM, I've just remembered seeing it. I remember thinking it was my 100amp fuse.

[dog man]

Found it. Measuring about 7140k ohms. Bit high?

With ECU plug disconnected I get nice 12.66v at pin 39 and connected it's reading 9.5 ish varying slightly.

Would the seeming extra 340ohms resistance cause the voltage to drop 3v when the ECU is plugged in?

Sounds a bit unlikely but it's the only thing I've found wrong so far!

[dog man]

Gave pin 39 12v by bridging the resistor...problem still there.

[blitzracing]

Bad idea, that resistor is there to limit the 150- 300 volt pulse you get back from the coil primary when the coil fires so it does not fry the ECU!

[dog man]

Really?

blitzracing said:

You could not blow the ECU what ever you did to the coil, as its either 12 volts (plus spikes) or 0 volts being fed back to the ECU, and it will cope with both quite happily. Unless of course you connected the king lead to the ECU input!!!

Well it's back as it was now, no harm done.

What the feck is causing this guyyyzzz!!!!!!!

[Alexdaredevilz]

Bite the bullet and give it to a specialist,

There's only so much you can do at home armed with pistonheads manual forum

[dog man]

I have done! I took it to Bespoke Performance and it has them stumped.

I have a few other places to see next!

[Bassfiend]

Ozstyle said:

The resistor (actually 2 of them) in question is in the LT wiring to the coil in the engine bay (close to the coil), usually taped or cable tied to the pcv tube that runs in front of the plenum. The resistor is rectangular and black and has a spade connector at each end, female loom spade connectors have black covers.

Well that explains what that grungy mass of crap is that I had always wondered about...

Thanks

Phil

[v8 racing]

dog man said:

I have done! I took it to Bespoke Performance and it has them stumped.

I have a few other places to see next!

I would be intrigued to have a look for you if you fancy a trip to spalding? as my previous post some weeks back i would lay money on a bad rotor arm, but if you fancy a drive out feel free to come over and i wont charge you a bean! i am kind like that sometimes!