Need help w/ a resistor

[spadnos]

Originally posted by gt40
typically the maf has a signal return (GND) signal line (0-5V) which is dependant on actual airflow, a reference voltage line (5v) and a 12V power line.
And actually it would only be a voltage divider if he did this:



MAF signal====-----[ | | | ] ---------------====Piggy back
................................................|
................................................|
...............................................|-|
...............................................|-|
................................................|
................................................|
..............................................GND

I think you are confusing the MAF line as being an Input, when in fact it is an output.
Basically the piggy back unit modifies the signal from the MAF going back into the ECU

Ah - OK. I had noticed the resistor arrangement, but for some reason it didn't manage to affect my brain before posting.

I wasn't sure if the piggyback was just a monitor, or if it fiddles with the MAF output.
I'd guess that the resistor goes in series with the piggyback. It may be as simple as converting a current output on the MAF to a voltage input on the piggyback.

It seems to me that a resistor to ground would either (a) reduce the output level from the MAF (constant current from MAF going through lower equivalent resistance) or (b) just cause it to have to output more current, which wouldn't be too useful.

(I still don't know what I'm talking about )

- Steve

(incidentally, if you view your original circuit diagram with a fixed pitch font, the resistor to ground is on the right side of the series resistor)

[gt40]

bah, that's why I suggested talking to the manufacturers of the the piggyback.
without knowing the actual dynamics of the electronics involved, it's really just a guess.
I was just trying to make an educated guess based on some limited knowledge.

putting the resistor in series wouldn't serve much purpose unless the piggy back drew excessive current.
putting the resistor in parallel really shouldn't hurt and would make sense if the output was an open collector/emiter (which might also mean the resistor was tied to Vcc).


-----aaaahhh, best to just get ahold of the aftermarket piggyback manufacturer .

[Kooldino]

Ok, I wired in the resistor, and the car is very tempermental.

It likes to go REALLY lean (19:1 AFR) at 500-2000rpm under light throttle. This resistor is screwing with things.



The reason I need the resistor in there is because the MAF is an "amp meter, not an analog meter. So we need a resistor on the line to turn it into an analog output."

Does that make sense to anyone?

[Tjalfe]

looks like what you need it to do is have the resistor to ground, having the current ( AMPS) from the MAF create a voltage across the resistor which is the analog output you are looking for.
the circuit you suggested would be the correct one for that.



ECU wire #88:

MAF------------------Piggyback
.................|
............... [ ] <--resistor
.................|
.................|
.................- <--Ground


edit: corrected the circuit

[Kooldino]

That's how she's wired in right now, but I think the 1K resistor is drawing too much from it?

What are some smaller resistors I can try?

Does wattage matter?


Right now I have a 1K .5W resistor.

[gt40]

can you provide a link to the piggyback unit?
I'll see what info I can dig up on the MAF.

a smaller resistor will draw more current, producing a smaller voltage, going more lean again.

wattage refers to how much current the resistor can handle before it self desructs. Anything above 1/4 watt for your app is ok as long as the value is 1K or above.

[Kooldino]

Originally posted by gt40
can you provide a link to the piggyback unit?

http://www.perfectpower.com/products/smt6.asp

I'll see what info I can dig up on the MAF.

a smaller resistor will draw more current, producing a smaller voltage, going more lean again.

So a 500 Ohm resistor will produce a smaller voltage than a 1K resistor? And a 2K resistor will produce a larger voltage than a 1K resistor?

wattage refers to how much current the resistor can handle before it self desructs. Anything above 1/4 watt for your app is ok as long as the value is 1K or above.

Side note: Looks like I'm back to square one here. I don't think the piggyback will do what I want it to do.

So i need something that takes an input of AMPs, and outputs the same as the input, until the input exceeds my defined limit, in which case it would only output my limit.

What a pain in the arse.

[Wombat]

Then you're looking at using an amplifier circuit of some type.

[gt40]

try calling pro-flow, if anyone know MAF's they do.

It looks like your MAF has a current output, so ANY resistor will effectively make it go lean, because you are effectively shunting some current to ground, instead of feeding it to the ECU

[Kooldino]

I think the extra MAF I have IS a pro flow It's just not wired in.

[gt40]

the pro-flow may offer less restriction, if it is calibrated as the original, it will yield the same problem.
if you have one that is calibrated for larger injectors, then it is already scaled up and just switching to larger injectors would solve your problem.
don't be afraid to call them, they are usually very helpful and may offer a solution.

[Kooldino]

I'll keep that in mind. Although I couldn't imagine them configuring it perfectly...

BTW, I emailed my piggyback company, here's what they had to say...

"Firstly: cut the wire from the MAF sensor. Now solder the blue wire and the 1k
resistor to the maf sensor wire. So you have a split wire now, one going to the
SMT and a 1k resistor hanging in the sky. Now using the violet wire. Using
another 1k resistor, solder this to the end of the violet wire. Then solder this
wire to the ecu side of the MAF signal wire. So the violet wire will have a 1k
resistor in series to the ecu. Now place the blue wires 1k resistor on the join
of the purple wires resistor to the standard ecu.
So when you now follow the maf signal wire it will look like this: Maf sensor-1k
resistor in series-ecu. Then two wires will be Teed into this set-up. One blue
wire Teed into where maf sensor joins 1k resistor, and another resistor with
purple wire attached Tees into where 1k resistor joins ecu. "

Now, I was able to translate that about 90% of the way, but there are a couple of things I'm not sure about. Anyone care to try to decipher it and sketch up a skematic?

[gt40]

looks like this to me:
but someone may want to double check.

[spadnos]

(protel 99SE, anyone )

That looks right (according to the description).

That lets the MAF sensor output essentially straight through (if the blue wire is high impedance, and the violet wire can be put into a high-Z mode. Or, when the reading gets too high, they can lower the potential of the violet wire, and sink some of the current that way, so the ECU gets a lower reading (or raise the voltage, to add a little extra current).

The two resistors basically sum the current from the MAF sensor and the violet wire, and the blue wire is a sense input for the piggyback.

- Steve

[Kooldino]

spadnos - Can you dumb that down a bit for me?

gt40 - i THINK that we have the same idea in mind here. Take a look at mine and let me know what you think.