Hey All,
I need a little help from the 240 group Please.
I need a resistor pack for the fuel injectors of a late 240 to enable a conversion of my B20E to a megasquirt system.
Could anyone give me a lead please? This is the last piece of hardware for a project nearing completion.
Sorry for the glibs in message, difficult computer to use at work.
Thanks
Joel
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Antique Swedish Steel 71 142E color V#102

I got my info from a webbsite outlying the equipment needed, it stated
"I found a suitable resistor pack in a pre-95 volvo 240 at the junkyard for $1. It looks like a metal cage with 4 white finger-sized resistors on it - bolted on the driver's side fender close to the headlight. There are 5 wires. The middle connection gets switched 12V, the other 4 each go to an injector"

Can anybody fiqure this out?

Thanks Joel
--
Antique Swedish Steel 71 142E color V#102

Joel:

Let me ask the question a different way: What year and model 240 did you get the injectors out of? Another question: What is the resistance of the injector coils, measured between the 2 pins where the connector mates up?

If they are out of a late 240 (last year made was 93, not 95), then you don't need a resistor pack!

Peak-hold (low resistance) injectors normally measure around or below 2 Ohms, where saturation injectors measure above 10 Ohms, typically around 12 Ohms.

Now, based on my memory on Megasquirt, it is designed for saturation injectors (10 Ohms or above). If you hook up a peak-hold low resistance injector without a resistor, you will fry the drive transistors that run the injectors. On the other no-no end, if you have high resistance saturation injectors and add a series resistor of around 10 Ohms, the injectors at best will fire late but most likely won't fire/open at all.

I will state this again, measure the resistance of the injector coils and tell us what the reading is, then we can help further.

jorrell
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92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

Jorrel
I did not specify that I am using the Bosch injectors that came with the B20E.
Currently I have 8 injectors at Cruzin Performance to match up 4 injectors for my system. I cannot measure resistance across the pins.
My reference (1800Philes.com in the megasquirt section) had run the stock injectors with megasquirt and developed flyback issues. These were resolved by adding a resistor pack from the 240 to the injector circuit for the stock bosch injectors. I wish I had a diagram of the circuit, I could probably make one.
I am at work so I will have difficulty determining the stock injectors resistance across the pins, but during the sweet 16 games tonight,as the Tar Heels dominate, I will look up and respond to that question, (properly phrased for a non mechanic like myself). This system is a challenge for me, and a great learning experience. Thanks again for the help.
I am also amazed by all the activity in the 240 forum, I wish the 140-160 had as much going on.


Later Joel
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Antique Swedish Steel 71 142E color V#102

Hello,
I found a reference for the resistors required for the 2.5 Ohm Bosche injectors. 25W 6 OHM power resistors are required. I presume the supposed reistor pack from a 240 has similar values.

Joel
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Antique Swedish Steel 71 142E color V#102

Joel:

Thank you for clarifying the details... and sorry for the delay in my response... interview in Raleigh NC today (went very well) but I hate the thought of moving!

Now, onto the injector issue, you have 2.5 Ohm peak-hold injectors that the megasquirt system can't deal with. For the answer, I will rely on a little math and experience from boosting my 2000 Eclipse (which involved going from 12.5 Ohm injectors to 2.5 Ohm peak-hold injectors. For these calculations to work, you will have to assume that each injector has its own separate resistor (typically 4 resistors in a pack). The big difference between the eclipse and your setup is that the megasquirt has non-sequential injection (all 4 injectors fire at once) where the Eclipse fires one injector at a time based on which cylinder is about to start the intake stroke.

Now for the calculations, don't worry, I'll tie it all together in a few minutes:
These are all WORST CASE calculations with the injectors turned on 100% of the time, this approach provides significant design margin.

Worst case assumptions:
14.5V maximum battery voltage when running at any time. NOTE: This is a DC approach and does NOT take into account the favorable issue of inductive charging rate.

Target resistance for each injector is 12.5 Ohms but your injectors are 2.5 Ohms. This means that you need to add 10 Ohms in series with each injector.

Now lets calculate the worst case current through each injector/resistor pair:
Current = Voltage / Resistance
1.16Amps = 14.5V / 12.5 Ohms
Since the current through the injector and the resistor must match, lets
calculate power dissipation in the resistor (how much heat it has to be able
to get rid of):
First, figure out the voltage across the 10 Ohm resistor at 1.16 Amps:
Voltage = Current * Resistance
11.6V = 1.16 Amps * 10 Ohms
Now we can figure out the needed power rating of the resistor:
Power = Current * Voltage
13.45 Watts = 1.16 Amps * 11.6V

The above says that each resistor (so it is "bullet proof") will have to be rated to 15 Watts at 10 Ohms on a heat sink. Now bullet proof is a relative term, on the Eclipse I wound up using 10 Ohm 10 Watt Dale heat-sinkable (aluminum shell with fins and mounting ears) resistors from Digikey, I have been running them for 2 years and they are doing just fine sitting on their heat sink that is bolted to the firewall. Key point here is a 10 Ohm resistor with a power rating of 10 to 15Watts will serve you well.

Now for the wiring. One connector pin of each injector must go to ground, the fuel rail mounting points on the intake manifold are perfect for this. The other pin of each injector must go to one pin of each separate resistor for your setup. From there, there is probably a single output pin from the ECU (with megasquirt, there are two, but you will probably only use one), so that ECU output must go to the remaining unconnected pin of all four resistors.

I hope the above has been clear enough and not too fundamental (sorry, don't know your background), and on top of that, it has been one heck of a long day. If you want a picture of the resistor setup I used on the Eclipse and the www.digikey.com part numbers, let me know, I'll pipe it off to you in a separate email unless someone else on the BB pipes up and wants the info as well, then I'll reply to this post. My email address can be found in my profile.

Hope that helps,

Jorrell
--
92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

The late 240s didn't use them, as Jorrell pointed out. If you do end up needing them, they were used in the late 940 turbos, and are likely to be plentiful in boneyards.

Good luck!

Late model yellow top injectors on B230F engines do not require a ballast pack as they are the high resistance type. To verify this, measure the coil resistance of the injectors and see if it matches up with the megasquirt spec.

jorrell

--
92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!