what does the ECU need to see to trigger an injector pulse? from what i've read, flyback voltage will trigger it, but i don't know the wave form or voltage limit it needs to see. also would this "trigger" be something like what you'd see on the negative side of an ign coil?
basicaly i need to know how the injector system works on the 2.5 so that it could be used in another vehical.
------------------ Arty: a.k.a. FestYboy or Fieroman87 '87 GT 5 spd. (soon to be 3.6L TT 6 spd.), '88 Festiva 5 spd. rockin' a high revin' 1.6, '87 Scirocco 5 spd. (VR6 swap?) AIM: FestYboy88L
there's no crank trigger on the 2.5.... at least not on the blocks/years i'm looking at.
i know there's a trigger from the distro, but i don't know the spcifics to it. i'm looking to substitute a trigger from the engine i'm using to pulse the injector but i need to know what the ECU wants to see.
------------------ Arty: a.k.a. FestYboy or Fieroman87 '87 GT 5 spd. (soon to be 3.6L TT 6 spd.), '88 Festiva 5 spd. rockin' a high revin' 1.6, '87 Scirocco 5 spd. (VR6 swap?) AIM: FestYboy88L
The ignition module in the distributor sends the reference signal to the ECM. This is a simple square wave 0v to 5v signal. As soon as the ECM sees these pulses, it will start firing the injectors. (Of course, how long they're fired will also depend on other inputs like coolant temperature, MAP, etc.....)
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10:26 PM
Mar 31st, 2008
fieroman87 Member
Posts: 647 From: Lancaster, PA Registered: Nov 2003
the idea is to use the 2.5 TBI and mount it to my carbed Festiva intake. all i'm looking for is to trigger the injector at the correct frequency (RPMx4).
i want to replace the carb with an injection system with as little intrusion as possible... that's the jist of it.
i don't need the electronic timing because the festy engine has vac advance (less to integrate).
the reason for using the festiva carb intake? it has shorter, larger runners than the EFI intake (better for higher rpm).
------------------ Arty: a.k.a. FestYboy or Fieroman87 '87 GT 5 spd. (soon to be 3.6L TT 6 spd.), '88 Festiva 5 spd. rockin' a high revin' 1.6, '87 Scirocco 5 spd. (VR6 swap?) AIM: FestYboy88L
You could (potentially) use one of the sensor 5v reference lines (MAP, TPS) as your source. You'll need to make sure that your new circuit doesn't load the ECM down too far....
Unless you already have a crank trigger solution, another possibility is to use the ignition module from the 2.5. Effectively, all it does is take a variable reluctance signal from a pickup coil and convert it to the 5v squarewave. You'd just need to feed it the +12v, ground and VR plus/minus signals to get it to work.
The ECM will do its calculations on the falling edge of the reference signal. Since you're not worried about spark timing, a 50% duty cycle signal will keep the ECU happy.
I would say to use a simple ADC with a tach pulse input and the output going to the ECM. A simple op-amp with no feedback will provide a good 5 to 0V swing.
I believe the tach signal output is nothing but the output of the coil with a large resistor in series. (Do correct me if I'm wrong!) If that's true, I think this should work:
You will need to experiment with Cb and Rb. Rb should be high enough to just make it past the forward bias voltage of the diode. The diode will keep the input voltage fairly low so as not to overload the op-amp. The capacitor will denoise the circuiit and protect against voltage spikes. Cb should be slightly lower than just enough to get a good signal to the op-amp.
D2 makes sure that current only flows forward and the Zener clamps the maximum voltage at 5V. This way you have a full swing of 0 to 5V at the output. The output may need a capacitor between the op-amp and D2 to ground.
Is this a ECM controlled carb? You still need TPS, MAP, and O2 or the ECM wont know what pulse-width the injector needs.
EDIT: The ratio of Ro1/Ro2 needs to be a little less than 3/1 and the resistors should be in the hundred kOhm range.
[This message has been edited by AP2k (edited 04-02-2008).]
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11:07 AM
Apr 2nd, 2008
fieroman87 Member
Posts: 647 From: Lancaster, PA Registered: Nov 2003
the carb has SOME ecu control, but as far as i know, all circuits are a 12v or B+ source.(will have to verify later)
the TPS, IAT, MAP, and CTS will all be sourced from the 2.5 (the first 3 being intigrated into the TBI unit). the only thing not being used from the 2.5 donor will be the ignition system (as stated earlier, already taken care of).
81tta: you stated that i could potentially use the ign mod from the 2.5... i can feed it B+, ground, and a pick-up signal from my distro. all those are available right now. which pins need to go where or get what? there are 6 pins on the 2.5 ign mod and 2 of them are a high and low, do i need to worry about these?
AP2k: you're right about the tach signal. but what are Vss and Vdd on the op amp (it's been quite a while since working with amps) and is what you're showing me what the ign mod does to the VR signal from the pick-up? or is this something i have to build to come off the ground side of the coil?
------------------ Arty: a.k.a. FestYboy or Fieroman87 '87 GT 5 spd. (soon to be 3.6L TT 6 spd.), '88 Festiva 5 spd. rockin' a high revin' 1.6, '87 Scirocco 5 spd. (VR6 swap?) AIM: FestYboy88L
AP2k: you're right about the tach signal. but what are Vss and Vdd on the op amp (it's been quite a while since working with amps) and is what you're showing me what the ign mod does to the VR signal from the pick-up? or is this something i have to build to come off the ground side of the coil?
Its pretty close. The reluctance pickup looks like a triangle wave and when it gets picked up the signal gets turned int a digital signal pulse. This circuit, however, uses the tach signal coming from the coil instead of the pickup from distributor. Does the distributor even have a pickup? seeing as though it uses vacuum advance and all.
Vdd and Vss are drain and supply voltages for the op-amp. They are specific to the op-amp, though. A quick gander at some typical op-amps say the voltages are Vdd = +20VDC and Vss = -20VDC. A dedicated op-amp power supply can source this.
Also, I've revised the schematic. Seems I forgot about overloading real parts.
Do note that the ECM normally sees a reluctor pickup as opposed to coil output, so there is a small chance the engine wont run as well as it should. Hopefully the runner length will minimize the injector lag.
[This message has been edited by AP2k (edited 04-02-2008).]
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04:33 AM
PFF
System Bot
fieroman87 Member
Posts: 647 From: Lancaster, PA Registered: Nov 2003
Distro HAS a pick-up, and it's very close to the 2.5 pick-up coil system. even with a vac advance, the spark can be retarded via a signal from the knock control on the carb (I know, this system is WIERD).
saying that i can utilise (sp) the reluctor, what are the chances that i could use the 2.5 ign mod to generate the 5v square?
note: i'm not against using the op-amp idea, but the less i have to build, the better. plus it'll save me time in the build (RadioSchmuck doesn't carry parts like this anymore)
I didnt expect the distributor to have a reluctor output since it had vacuum advance, but since it does you should definitely use an ignition module output. That and you should definitely post pics when its done.
[This message has been edited by AP2k (edited 04-02-2008).]
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03:27 PM
fieroman87 Member
Posts: 647 From: Lancaster, PA Registered: Nov 2003
now it's time to go shopping!!!! list: TBI unit, 92 ECU, harness, MAP, CTS, IAT (all 3 comming from my 2.8 fiero or spares), and NEW inline fuel pump
things to fabricate: TBI to intake adapter plate, adapted harness, fuel pump bracket, CTS pipe and bung
this may be easier than i thought..... then again...
one final question, (i swear). how much fuel pressure can the TBI regulator handle, OR, what pump can be used (external inline)? i'm told the pressure at the injector needs to be between 9-13 psi. what is the line pressure before the regulator?
[This message has been edited by fieroman87 (edited 04-03-2008).]
