Can You Use a 7 Pin Distributor in Place of 3 Pin Ignition Module
V3 MicroSquirt® - QuickStart Guide
Full general Motors HEI Ignition Control with your MicroSquirt® Controller
Tuning Software
There were a number of dissimilar kinds of General Motors HEI modules:
- 4 pin module - electronic ignition, simply doesn't do computer timing control, elevation left
- 7 pin module (large) - electronic module that does timing command, used with coil-in-cap distributors, superlative right
- vii pin module (small) - electronic module that does timing control, used with some external coil distributors, bottom right
- 8 pin module - electronic module that does timing command, used with most V8 external curlicue distributors, bottom left
- 5 pivot module - rare and not discussed here. not shown
When using the HEI-seven or HEI-eight pin modules, you need to set your MicroSquirt® controller to:
| Parameter | Value |
| Ignition Input Capture | Rising Border |
| Cranking trigger | Trigger Ascension |
| Coil Charging Scheme | Standard Curlicue Charge |
| Spark Output | Going High (Inverted) |
The 7 Pin HEI Module
With a GM HEI vii-pivot (and viii-pin modules), the ignition module wires you need to know about are:
- tach bespeak is a imperial wire with a white trace [pivot R] goes to Ampseal OPTOIN+ pivot #30 (ground the Ampseal OPTOIN- pin #31 at the benefactor)
- accelerate control bespeak is a white wire [pin Due east] goes to Ampseal pivot #12
- override (cranking) signal is a tan wire with a black trace [pin B] goes to Ampseal pin #vii (with a 1.0K resistor pull-up to Vref on Pin #28) if using the FIdle as a spare port for this function.
- ground is a blackness wire with a red trace [grounded to benefactor case]
The 4-pin HEI uses a negative-to-positive transition, while the 7/viii-pin uses a positive-to-negative transition (though this *might* have changed in some applications). Thus polarity of the reluctor bespeak is critical to proper function.
In the GM 7/8-pivot HEI, the module converts the AC indicate from the variable reluctor pick-upward {on pins P & Due north} in the distributor to a 'square wave' tach signal {on pin R} suitable for your MicroSquirt® controller. The falling edge of this foursquare wave is used as the trigger upshot (which becomes the rise edge when the input excursion inverts the point).
HEI does not employ the reluctor for dwell control, this is accomplished in the module. Dwell needs to exist contained of RPM. Variable reluctor output is RPM dependent with regard to both its width and aamplitude of its output. The only matter constant with a variable reluctor output is the location of the zero crossing point with respect to the passing tooth.
Be sure to get the variable reluctor pick-up wires connected properly. Reversing the variable reluctor sensor wires and thus the polarity of the sensor causes the leading voltage to go negative starting time and the electronics ignores the positive going transition. Thus trigger point, if ever recognized, is the falling border of the voltage as the cease of the tooth passes.
The but way to become proper triggering at the center of the molar is to accept the positive ½ cycle first (tooth approaching) and the negative ½ bicycle final.
The 'trigger outset' in TunerStudioMS is the number of degrees before TDC at which the VR sensor output goes from positive to negative, and the falling edge of the square wave is sent from the seven/8-pin module to your MicroSquirt® controller. This tells your MicroSquirt® controller where the crankshaft is positioned so that timing advance tin can be calculated appropriately. (Note that since the optoisolator (U4) inverts the trigger signal, you specify 'Ascent border' for the 'Input Capture' in TunerStudioMS, which refers to the betoken at the processor.) Positive trigger offsets are used to specify the number of degrees before meridian dead middle (BTDC), negative numbers are used for triggers that occur after elevation dead eye (ATDC).
The vii/viii-pivot HEI uses a "next cylinder" advance calculation method. That is, you go the square wave out of the module at (say) 10° BTDC which is used for cranking and limp habitation mode. To advance the timing your MicroSquirt® controller waits until the Side by side cylinder to fire to provided an altered signal to the ringlet.
Reference (tach) pulses come into your MicroSquirt® controller from pin R at 10° BTDC (this kickoff can exist calibrated using TunerStudioMSII and so that the spark table values match the actual accelerate). At each reference pulse, the menstruum between it and the previous reference pulse is calculated. The departure is used (with a time interpolation technique) to ready the timing pulse for the next ignition event. Specifically, the reference period is added to the time of the current pulse, a calculated amount subtracted for the advance, another amount subtracted for the dwell to decide the ascent time.
When the bespeak is 'high', electric current flows. When the indicate is pulled low, electric current stops, the magnetic field in the coil collapses, and a spark is produced. Thus, the HEI module fires on the 'trailing edge' of the advance signal. The advance signal is generated by your MicroSquirt® controller from the tach signal by modifying its duty cycle (pulse width). Larger duty cycles hateful less advance, as the spark is delayed by a larger amount.
The ignition indicate going to your MicroSquirt® controller comes from pin R of the 7-pin HEI module and goes to the Ampseal VR1IN+ pin 32. Exit the VR1IN- pin #33 unconnected (exercise not ground information technology).
The timing of the trailing border determines the corporeality of advance: a longer pulse width ways a more delayed, 'retarded' spark, while a shorter pulse width means an before 'avant-garde' spark.
In a GM vehicle, the override signal is zippo volts during cranking (less than 400 rpm or 5 to 15 seconds), then at that place is 5 volts on this wire afterward the engine starts to betoken the 7-pin module that information technology should utilize the indicate on the white wire to control timing. Yous need to apply a 5 volt bespeak hither in order to command the timing while running. A wire can be run from the 5 Vref for the TPS (Pivot 28 on the Ampseal connector) to the HEI pivot B through a relay that is switch from a source that is hot in RUN just not Crank (meet the diagram beneath). Most cars have a source like this, check your service transmission.
Alternatively, you tin can utilise the spare port settings to send a v Volt point. The FIdle ports grounds the FIdle, so you lot'll need a ane.0K Ohm pull upwardly resistor to a 5V source (such as from the 5Vref).
And so set up the port conditions (rpm < 300) and settings (check these carefully), and you take the pin B betoken on Ampseal pin 7.
The FIdle is particularly useful, since most GM ready-ups use a stepper, not the FIdle port. However y'all may already exist using the FIdle output for a TCC (in which example you lot'll take to employ one of the other ports like knock enable and add together a transistor).
(Note that the vii-pivot HEI module also has 2 pins for the variable reluctor choice-up ([pivot P] and [pin N]) likewise as one each for the whorl [pin C] and +12 volts [pivot +] from the battery. Together with the spark timing signal [pin E], Ref (tach) [pivot R], and crank override [pin B], there are 7 pins in total ).
(Shown is the large 7-pin HEI module. The small vii-pin HEI module (used in Vauxhalls in the Uk and is listed for the 1.6i Cavalier) is wired to the same pins, but the pins are grouped differently. P, North, E, R are on the right, +, C, and B are on the left)
Virtually whatsoever engine equipped with a variable reluctor benefactor and a single coil can apply the seven-pin HEI module to interface with your MicroSquirt® controller. These have the advantage of existence cheap, widely available (in North America), and reliable. These are available as:
- Echlin TP47 ~$seventy at NAPA OnLine
- Standard Motor Products LX315
- Accel 35363 ~$50 at Summit
- Holley 891-102 ~$27 at Summit,
- General Motors 1976908
HEI eight-Pivot Module
In addition to the module shown in a higher place, yous can employ the HEI 8-pin module from the "small-scale cap" HEI distributor. This was used on 1987 through 1992 Camaro/Firebird Tuned Port Injection V8 engines, likewise every bit 1987 to 1993 full size cars and 1987 to 1995 pick-up trucks, and V6 MPFI cars (such as the Fiero). Information technology uses a remotely mounted coil (i.east., not in the cap), which is typically is bolted to the intake manifold. The distributors are used primarily on roller cam equipped engines. Note that the GM 8-pin HEI module is basically the same every bit the 7-pin, except at that place is one extra pin: the extra pin is 'G' and is used for a ground. The viii-pivot module has 2 'mushroom' way connectors. I has 2 pins, it is used for the curl. The other has 4 pins, and is used for the electronic timing control. The timing control wires are unremarkably the aforementioned colors equally described above for the 7-pin module.
You tin can buy the 8-pin module as:
- Wells: DR133, DR135, DR138, DR140
- Niehoff: DR408, DR410, DR411
- Standard: LX339, LX340
- Echlin: TP22, TP24, TP25
- ACDelco: D1943A, D1948A, D1960A, D1978, D1980, D1984-A, D1990, D1993
- Borg Warner: CBE25, CBE27, CBE28
The iv-wire connector to your MicroSquirt® controller can be bought as:
- GM: 12126487
- Air-conditioning Delco: PT757
- Motormite: 85135
- PICO: 5602
The two lead connector for the small cap module is the aforementioned as the recommended CLT sensor connector:
- GM: 15306195
- AC Delco: PT1350
- Wells: 254
- NAPA: ECHTSC200
- Motormite: 85100 (~$nine @ Autozone (PN 047131))
The VR pins can utilise 1/8 " spade connectors.
There are four pins on the external ringlet used with the viii-pin HEI module. These are tied together in pairs (so you lot'll see cypher resistance between them). One gear up of 2 is on the +12 V positive side (electrically), the other is on the negative side.
- 1 pin on the positive side is used to have 12 Volts to the scroll. The one continued to this takes 12 volts to the 8-pin module (+ pin).
- One pin on the negative side is used to ground the coil (C pivot on the module). The other is used for the tachometer signal for the nuance tach.
In OEM applications, if you lot await at the curl connections with the high tension terminal up and the 2 connectors on the lesser (with the atomic number 26 core horizontal), that:
- meridian left is 12 Volt supply to the + pin on the module (black/ppl),
- bottom left is the ringlet ground wire to C on the module (brown),
- elevation right is 12 Volt supply from the ignition switch (pink wire),
- bottom correct is the tach signal (white).
You should notice about 0.four Ohms between these ii sets of pins (the coil'due south chief resistance).
For the OEM HEI coils, gear up the dwell to
- 3.5 milliseconds for an in-cap whorl (7-pin module),
- 2.5 milliseconds for a pocket-sized cap distributor with an external coil (seven-pin module).
If the amount of desired dwell is longer than the remaining amount of time available, the dwell fourth dimension is shortened and the amount of time available is used (otherwise the timing would exist increasingly delayed).
Setting the Trigger Commencement
After installing the your MicroSquirt® controller and HEI, be sure to utilize a timing light to verify that your 'trigger outset' is calibrated. Changing the Trigger Kickoff in TunerStudioMS volition not change the displayed advance, instead, it changes the actual advance every bit seen with a timing low-cal. Your goal is to make these two friction match.
To practise this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then utilize a timing low-cal to verify to be certain your actual accelerate as shown by a timing light equals your the advance brandish on the accelerate gauge in TunerStudioMS. (Note that positive numbers denote BTDC, and negative numbers denote afterward TDC.)
The trigger get-go value can theoretically be ready anywhere physically, even so, since it may be used for cranking and 'error mode' timing (depending on how you have wired the bypass pin), it is best to fix it at a reasonable number for cranking and idle, ordinarily about ~eight° BTDC (or whatever is recommended past the module'due south manufacturer). Check this with a timing light. To get the trigger kickoff to this value, you may accept to physically rotate your distributor.
If yous aren't certain where your trigger is physically located, you lot can ready the trigger offset on your vehicle (with the 7 or eight pivot HEI module):
- Bring the engine to peak dead center on cylinder #1 by rotating information technology in it's normal direction (usually clockwise when viewed from the front, except for some Honda engines). I remove the spark plug from cylinder #one, and feel for compression, and then you know the engine is at TDC on the compressions stroke. Rotate the engine a flake more than until the timing indicator lines up with the TDC mark.
- Rotate the distributor to marshal the VR sensor teeth. In the HEI distributor, in that location are 8 sets of teeth, all of which align with i other tooth simultaneously. Lock the distributor down.
- Whichever concluding the rotor is pointing at is now cylinder #1. The rotor should be much closer to one terminal than the others (information technology will probably take gone by one of the cylinder'southward terminal by a bit, that'due south okay - it means it will line up with a chip of advance - you tin rotate the engine through very nearly 2 consummate revolutions to cheque - get it to nearly 25° to xxx° BTDC and it should marshal with the terminal). If the rotor is pointing between cylinders (i.due east., the phasing is off), then information technology'due south likely that the distributor is off by 1 or more teeth at the camshaft (in a V8 HEI install, at least). On a pocket-size block Chevrolet, for example, the distributor should exist installed and so that the rotor is pointing a little in front of the #1 cylinder when the engine is at TDC on the pinch stroke for cylinder #1 - all other positions will create phasing bug.
- Install the remaining plug wires in firing order around the distributor, being very conscientious about both the management and the society. On a small block Chevrolet, the rotor spins clockwise when viewed from in a higher place, for instance.
- Start the engine with the B pin disconnected, and fix the timing as seen on a timing light to the trigger offset you desire to use by loosening the distributor and rotating information technology. Usually you volition want a value between 0 and 10° BTDC. (I apply 0.)
- Connect the B pin to 5V (letting MegaSquirt® control the timing), and outset TunerStudioMS, verify that a timing lite and the trigger wizard give the same number. Change the trigger offset value in TunerStudioMS a chip to make them friction match, if necessary.
There are many more parameters to set up and melody to use the GM HEI effectively, come across the:
- V3 MicroSquirt® configuration page,
- V3 MicroSquirt® Tuning page.
If you have whatsoever questions or problems that can't exist answered from the links above, or a search the MicroSquirt® transmission:
yous can ask questions at the MicroSquirt® support forum which is at: world wide web.microsquirt.com Click the links for more information.
MicroSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
MicroSquirt® and MicroSquirt® controllers are not for auction or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MicroSquirt® or MicroSquirt® controller is legal for your application.
©2004, 2022 Bruce Bowling and Al Grippo. All rights reserved. MicroSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of V3 MicroSquirt® boards from Bowling and Grippo.
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