S4 secondary injectors and their resistor

[stevefh 9]

Hi all, looking at Sheet 4 of the wiring diagrams, the positive to the resistor comes from the inertia switch (ow),leaves the resistor (ou) to the secondary injectors and then(LGG) to the ecm where it will be earthed as required.

 I take it the resistor reduces the voltage going to the secondary injectors in parallel.When tested my resistor originally appeared to have infinite resistance but after a good shake l could not make it anything but about 3 ohms, which Andy told me should be 3.3 ohms 10 amps.

 I take it this means I must not test each secondary injector using 12 volts from my battery.Please confirm that if I put the resistor (if about 3ohms)in the circuit before the secondary injector it will simulate when on the car. I am expecting to hear a click to indicate that its solenoid is working before I use the gizmo to clean them.

The resistor (nla   I will try to fix it later)and the resistors are off the car. The injectors are still in their housing as I am having difficulty getting the M4 x12 button screw out without damaging it, thanks to the permabond it is in f-tight. Thanks for any help or comments 

 

 

[AndyPG 50]

3 hours ago, stevefh said:

I take it the resistor reduces the voltage going to the secondary injectors in parallel.When tested my resistor originally appeared to have infinite resistance but after a good shake l could not make it anything but about 3 ohms, which Andy told me should be 3.3 ohms 10 amps.

Hi Steve,

The ballast resistor should measure 3.3ohms and has a rating of 10w, nothing to do with 10 amps.

You can test the secondary injectors directly with a 12v supply as normal.

The ballast resistor doesn't reduce the voltage to the secondary injectors, it simply satisfies the ECU by giving it the total circuit resistance it likes to see. It's a borrowed unit that was previously fitted to many american cars.

Andy.

Edited September 22, 2020 by AndyPG

[stevefh 9]

Hi Andy, thanks for enlightening me.

[AndyPG 50]

No worries.

You definitely need to re-flow the soldered joints inside the resistor though.

Your continuity tests almost certainly indicate a cracked joint.

It's a likely contender for the code 26 you've experienced.

Andy.

[fjmuurling 65]

The Resitor is there in order to Limit the max. current so the Quad driver inside the ECU doesn't get fried.

[stevefh 9]

Hi. Have taken the cover off the resistor, I will try to work out how to upload my first ever photo and then discuss its contents.

[stevefh 9]

As you can see the rear of the 3 pins are set in a resin with metal “tracks” running down to the front edge of the board. I have no understanding of the metallic looking bottom with 2solders with what looks like channels cut into it. Only the pair of lower pins are used.Comments please.

[stevefh 9]

Another photo 

[Escape 776]

The metallic looking path is just that, a metal film on the circuit board. The channels are cut to form different pathways for the different components/pins. This is a very simple circuit, with only 2 paths, each going to one end of the actual resistor (the block on the other side), connected by the 2 solder joints. I think you'll find the right pin is not connected to anything, just a standard connector.

IMHO 3.3ohm is close enough (10%) to the target value to leave it alone. That is if you get a consistent reading, even when shaking etc. Open circuit measurements are often due to poor contacts with the multimeter probes. You can use clamps for better/consistent connections or even dedicated lead with spade type connectors. Or try to measure directly on the circuit board through the solder joints.

For the record, the resistor does limit the voltage available to the injectors (as part of the available battery voltage is used to overcome the resistance), but as said above that is merely a side effect and not the main purpose. Without the resistor, max current would be higher and the ECU would not like that.

Filip

[AndyPG 50]

9 hours ago, stevefh said:

Comments please

Hi Steve,

Difficult to see on the pictures but the soldered joints where the PCB attaches to the terminals looks dodgy and that's there mine had cracked. Reflow them if you suspect they are.

It appears your car has a 3 ohm resister where as mine was 3.3 ohm. As @Escape says, nothing to worry about. In any case, IMO the resistor itself will be fine.

Andy.

[stevefh 9]

Hi both, the 3R3 means the resistor is 3.3ohms. In the second photo the dark green lines appear to be metal cut out to form narrow channels whereas in  circuit boards I have seen the narrow channels of metal are used. I could be wrong but it looks like the wide areas are used and the pins to the left and right are the pair with about 3 ohms resistance . I can clearly get at the 2 large solders but not those set in resin that are at the edge of the board joining the base. I will learn how to re-flow the 2 large solders and have a go.

[stevefh 9]

Ok ,read a bit.Can I just melt the existing solder on the resistor ends or do you recommend removing most of the old and re-soldering from the bottom. . I am wary of taking the resistor tails out altogether in case I damage the pcb connections.

[AndyPG 50]

31 minutes ago, stevefh said:

Can I just melt the existing solder on the resistor ends or do you recommend removing most of the old and re-soldering from the bottom

The resistor ends will likely be fine. It's the other two joints that give the trouble. No need to remove any old solder. Just apply a smear of flux and reflow. Add a little extra solder if you like.

Andy.

[stevefh 9]

Hi Andy,the resistor is approximately 38x7x7mm ,out of interest does that make it 10watt, also I think I have plumbers flux somewhere ,can I use that with “string” type solder.Thanks again for all your help.

 

[AndyPG 50]

No problem Steve,

I recognize it as a 10w resistor. I researched mine when it was apart. Deffo 10w.

Plumbers flux is fine. You only need a light smear.

When you say "string" type solder I assume you refer to "wire" type which is fine. Best if it's proper cored electronics stuff.

TBH, you only need to apply a little flux and reflow the joints. Adding more solder is fine but optional.

After all this, I hope the ballast resistor is the cause of your intermittent code 26.

Andy.

[Clive59 115]

1 hour ago, stevefh said:

plumbers flux somewhere

don't use plumbers flux, it is NOT for electronic use. Use proper rosin cored solder.

[stevefh 9]

Hi Clive, has rosin cored solder got the flux in it? Ebay has 1m 0.7 mm for £1.25 or 1.0 mm diameter for a little more.

[Clive59 115]

1 hour ago, stevefh said:

has rosin cored solder got the flux in it?

yes, it sure does. 0.7mm is probably best for that job. I would suggest getting lead/tin solder if possible, much easier to rework than the lead free, and the existing board is most likely lead solder.