tune resistor

toughy V8 · Post by **toughy V8** » Thu Mar 15, 2007 9:13 pm

whats this inline resistor i keep hearing about sopposed to be near the air flow meter thats meant to go to the coil all i have is a relay with a single wire coming from it

ramon alban · Post by **ramon alban** » Thu Mar 15, 2007 10:27 pm

toughy V8 wrote:whats this inline resistor i keep hearing about sopposed to be near the air flow meter thats meant to go to the coil all i have is a relay with a single wire coming from it

On the standard Rover Efi system as fitted to the SD1, (and earlier RR Efi systems) when the engine is either cranking or running the engine speed is signalled by a trigger connection from the negative side of the coil via a 6.8K ohm "inline resistor" (sometimes confusingly labelled a "ballast resistor") to Pin 1 of the ECU via a White/Black wire.

The purpose of the resistor is simply to protect the ECU from receiving too much current from the ignition system in the event of a fault.

The maximum current that could flow into the ECU is limited to approx 13.6v / 6800 ohm or 2 milliamps. (not very much), but in the case of high induced voltages from the ign coil primary winding, the protection is critical.

Without that signal the ECU will not fire the injectors.

Without the resistor, a direct connection could wreck the ECU.

It sounds like you may have a direct connection

You can see the item labelled as "fuel injection trigger" item 452, on the circuit diagram seen via this web page.

http://www.vintagemodelairplane.com/pag ... uit01.html

Ramon

http://www.vintagemodelairplane.com

Eliot · Post by **Eliot** » Fri Mar 16, 2007 6:57 am

Which isn't called a tune resistor. The tune resistor is a seperate resistor on the hotwire setup that tells the ecu whether it has cats or not.
You need both. A trip to maplins will usally secure the correct part.

Tune resistor specs and full diagnostics info can be found here, grab it before i delete it:
http://homepages.nildram.co.uk/~eliotmez/efi_test.zip

ramon alban · Post by **ramon alban** » Fri Mar 16, 2007 7:57 am

Eliot wrote:Which isn't called a tune resistor. The tune resistor is a seperate resistor on the hotwire setup that tells the ecu whether it has cats or not.

Whoops, sorry about that! didn't mean to draw a red herring across your problem.

Ramon

ChrisJC · Post by **ChrisJC** » Fri Mar 16, 2007 8:26 am

And for the record, the 6.8K resistor that Ramon refers is not necessary (at least on a Range Rover ECU).

Following a discussion on the previous forum, I took apart my ECU and sketched out the circuit. It was clear that the resistor did nothing useful.

I do not have one fitted, and have had no problems.

The only way that it could protect anything is if the wire to the ECU became shorted to ground, it would protect the ignition amp.

But as already stated, this is NOT a tune resistor.

Chris.

toughy V8 · Post by **toughy V8** » Fri Mar 16, 2007 6:59 pm

i failed to mention its a flapper system from a range rover,

this part of the wiring instructions has confused me

In engine bay there will be a single black/white wire usually with the airflow meter loom, this has an inline resistor MAKE SURE THIS IS FITTED, this then goes to the negative side coil for efi ignition trigger to tell the ecu engine is running and to fire the injectors

ramon alban · Post by **ramon alban** » Fri Mar 16, 2007 9:45 pm

toughy V8 wrote:i failed to mention its a flapper system from a range rover,

this part of the wiring instructions has confused me

In engine bay there will be a single black/white wire usually with the airflow meter loom, this has an inline resistor MAKE SURE THIS IS FITTED, this then goes to the negative side coil for efi ignition trigger to tell the ecu engine is running and to fire the injectors

OK Toughy - back to square one, its a flapper and it seems we are talking about the "trigger resistor" or "inline resistor" or "ballast resistor" which are all the same thing as mentioned in my prior post.

It's usually 6800 ohms and Rover fitted it for some sort of protection.

If not for the ECU then for the Ignition Amplifier (which makes more sense)

Given the choice I would still make sure it was fitted.

toughy V8 · Post by **toughy V8** » Fri Mar 16, 2007 10:54 pm

is this the mentioned resistor

ramon alban · Post by **ramon alban** » Sat Mar 17, 2007 12:48 am

toughy V8 wrote:is this the mentioned resistor

It could be - there is a white/black wire going into the loom and it looks like a two terminal component in a 3 terminal socket. The white/blue wire prolly goes to the coil negative.

Mine does not look like that but hey its an SD1.

Why dont you measure it with an ohm meter?

Eliot · Post by **Eliot** » Sat Mar 17, 2007 6:54 am

Looks like a relay to me - and ive read about an anti run-on relay that was used to prevent - well,... run-on!
Just had the run-on problem with my mates RV8 - but we cheated and fitted a diode on the brown/yellow wire leading to the alternator.

ramon alban · Post by **ramon alban** » Sat Mar 17, 2007 12:30 pm

Eliot wrote:Looks like a relay to me - and ive read about an anti run-on relay that was used to prevent - well,... run-on!
Just had the run-on problem with my mates RV8 - but we cheated and fitted a diode on the brown/yellow wire leading to the alternator.

Good thinking, or possibly the Range Rover engine over-run relay that is operated by a vacuum switch on the inlet manifold so that at high manifold depression (throttle closed at high engine speed) the relay is activated and disconnects the engine running signal on the white/black wire going to the ECU to cut fuel supply, thereby, eliminate popping and banging in the exhaust on over-run and to save fuel at the same time.

ChrisJC · Post by **ChrisJC** » Mon Mar 19, 2007 10:27 am

That is the overrun cutoff relay, which interrupts the low tension coil signal between the coil and the ECU. It is cut off as already stated when the manifold vacuum is high (i.e. coasting) to save fuel and improve emissions. The resistor is a 2 terminal device, I would be interested to see one....

Chris.

ramon alban · Post by **ramon alban** » Mon Mar 19, 2007 12:21 pm

ChrisJC wrote:That is the overrun cutoff relay, which interrupts the low tension coil signal between the coil and the ECU. It is cut off as already stated when the manifold vacuum is high (i.e. coasting) to save fuel and improve emissions. The resistor is a 2 terminal device, I would be interested to see one....Chris.

See a temporary image of one here:
http://www.vintagemodelairplane.com/pag ... dia01.html

ChrisJC · Post by **ChrisJC** » Tue Mar 20, 2007 8:22 am

Ah, yes, that looks like a resistor.
Not sure why it's called a ballast resistor - that could be misleading at best!

Chris.

ramon alban · Post by **ramon alban** » Tue Mar 20, 2007 2:23 pm

ChrisJC wrote:Ah, yes, that looks like a resistor.
Not sure why it's called a ballast resistor - that could be misleading at best!Chris.

I agree with you, it is misleading, particularly as the term is commonly used for another function associated with the ignition coil, but I have seen this item described 3 different ways in various Rover publications. Trigger, Ballast and Inline. Now further to be confused by this thread calling it a Tune resistor?

I think the word "Ballast" must crept in the back door via the long-standing electrical practice of protecting an electrical component with a resistor in series with the load. Rover also used the same term for the resistor in series with the instrument panel light used in conjunction with a dimmer control.

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