MSefi.com read only forum (Jan.15,2018)

I do not know my next step. I have a 1978 transam with GM TBI MS II version 2.905. I initially had it tuned without the Ignition and it ran fine. At that time the mechanically distributor was set at 18 degrees without vacuum and had 50 degree at idle with about 45 kPa of vacuum. The mechanical advance provided 35 degrees by 2700 rpm. I installed 7 pin GM module (had to adapt it for a Pontiac). It started fine and I set the trigger so that it was providing 20 degree at idle. The car idled fine and I was playing with the ignition timing at idle from 20 to 40 degrees, when the engine crapped out. I set the timing back to 20 degree but the car would not start. The next day I was able to start the car but it ran poorly. If I disconnect the 5v to the module, it may have run better at idle, but not great. I get spark to all of the spark plug and the timing light still shows 18 degrees without 5volts and 20 degrees with the 5 volts connect. I have tested the injectors and they seem to work fine. However, the car will not run and I do not know where to start to trouble shooting. Although, it seems more like a fuel problem than a spark, but I though I would start with this board. Any thoughts would be appreciated.
John

Post up an msq & log so we can all have a look, John.

What version of ms are you using?

Ken

I am using MS board V3. I have attached the msg and the log file. Unfortunately, the car runs so bad, that I can not keep it running to warm up. Therefore, I am not quite sure AFR is accurate as the unit may have not warmed up either. Although, I have the IAC motor all the way open, I have to give it 30% throttle to keep it run. Therefore, it is not "idling" in the normal cell. When it was running, I would have it idle at 1000 and 45 kPa with AFR of 13.1. It is not a pretty picture, any help will be appreciated.
Thanks
John

The thing that jumps out at me immediately is the rpm continually spiking to zero. Let's see what the gurus have to say, but I'm leaning toward problems with your hei setup.

Ken

The RPM signal is going haywire - how exactly is your RPM input set up?

I used these direction below:

It is so confusing, it is hard to know what to do next. They give some option if I am having problems with my tach signal, but I really don't understand them.

To install the Hall/optical input circuit (or points without a coil connection):

Install and solder R12 {390H-ND, 390 Ohm, ½ watt, orange-white-brown}. This is installed between the resistors you have just been installing and the CPU socket. This resistor should be mounted roughly 1/8" (3mm) above the surface of the PCB. Also, the value of this resistor may have to be changed if you trigger from the negative side of the coil depending on application - start with the supplied value, and if gets hot while the engine is running, then increase the value, in steps, up to 10K (like 470 Ohms, 560 Ohms, 680 Ohms, 1K, ...), or even more in some applications (consult the MegaSquirt Forums list for advice). However, do not adjust this resistor on assembly, unless you have a good reason to do so.
Install and solder R13 {4.7KEBK-ND, 4.7k, yellow-violet-red}. This is located 3 places close to the heat sink than R12 (which you just installed).
Install and solder C11 {399-2075-ND or 399-4326-ND, 0.01µF, 103 marking}. This installs at the top of the row of 'vertically' oriented capacitors above "e;Bowling" in the copyright notice.
Leave the C30 location empty - DO NOT jumper it.
If you have a Hall sensor or optical sensor, do not install D1, put a jumper in its place. It is located beside R12, further from the heat sink.
For most installations, diode D2 {1N4001DICT-ND, the marked 1N4001} is not needed. Do not install D2, install a jumper (made from a snipped off lead) in its place. It is located beside D1, closer to the heat sink.
Note: this diode (D2) is needed only if the ignition system has a large offset bias - most systems do not have such a bias. So, to start, you can either solder in a jumper wire in this location, or, you can install the diode D2, and then install a jumper around the two leads of the diode - in effect shorting it out. The latter will allow you to snip the jumper later on if needed, putting the diode back in circuit. Solder the diode in observing the banded end as on the board, then solder a wire jumper across the diode itself.
Install/solder opto-isolator U3 {160-1300-5-ND, 4N25). This is located near the center of the PCB. If you have bought a socket (AE7300-ND or AE10021-ND ) for this component, solder it in place instead, then insert U3 into the socket. Observe the proper orientation (notch matches PCB - towards the heat sink, or dot for pin #1 which is the square pad on PCB at the notched end of the silk screen). If neither are there, hold the chip so that the writing is facing you and the right way around. Pin #1 is on the bottom left.
Leave the C12 location empty - DO NOT jumper it. This is located above "e;Bowling" in the copyright notice. This capacitor may need to be installed and/or the value increased if there are noise problems with the tach signal - values up to 0.1µF will work. The 0.001µF value is a good starting point.

You might want to try our alternate HEI mods here:

http://www.DIYAutoTune.com/tech_article ... _v8_v6.htm

They give a bit of a stronger signal.

Matt:
I just tried the alternate HEI mod as you described and there was no improvement. Any other thoughts?
John

I continue to try and trouble shoot my issue. I have concluded that the basic problem is a poor tach input signal. The reason I came to this conclusion is that when I put 5 volts to the module I get a very erratic tach signal, which is caused by the Megasquirt having trouble deciding when to fire the ignition. If I do not put 5 volts, the module will firing the ignition at 18 deg without Megasquirt. My tach looks fine, but the engine runs poorly. I have switched the Megasquirt back to get the tach signal for the negative side of the coil and left the module unconnected and it runs ok. I have captured the output from the module tach pin and I get a strange signal. My software only captures 250p/sec, so that may partially explain why the signal looks funny, but something else is going on. Any thoughts would be appreciated. Or should I be looking at a different cause for my problem?

Could be a faulty module - or you could try using a spare output so the MS only sends 5 volts to the module once RPM goes over 500.

I have replace the module and the same thing happens. I have the tach cutting in and out about 1000 rpm, so I do not think senting 5 volts after 500 will solve my problems. Does anyone know what the actual tach signal looks like coming out of the module?

I want to test my VR sensor signal before it goes into the module. I am going to pull my distributor and connect the VR wires to a circuit to see if the VR is functioning. Does anyone know of a simple circuit I could use to test the VR function as I assume the signal will need to be amplified if I want to be able to measure it.
Thanks
John

I am still trying to solve me rough idle/ignition problem. I bought a better PC oscilloscope so that I could see the tracing better. I pulled the MS unit from the car and hooked it up to a spare distributor. I spun the distributor with a drill at about 900 rpm and saw a nice tach and ignition signal (see dist.jpg). Therefore, I assume the unit was ok and I expected a very noise tach signal when I re-installed the MS unit is the car. I measured the signals at the MS unit and when the car was “idling normal”, I saw a nice tach and ignition signal (see idle.jpg). The tach signal was nice and clean, no noise. However, the timing between the two signals was somewhat inconsistent. When the car started to idle very rough, the tach signal was good, but the ignition signal was dropping out (see rough.jpg). So I have concluded that the problem was not a noisy tach signal, but something with the way the MS unit is triggering the ignition signal. There seems to be a misconnect between the timing of the tach signal and the ignition output. Any thoughts???
Thanks
John

Could you post a data log of what happens when the ignition signal cuts out and a copy of your MSQ? This will give me a better feel for what's going on.

The files are located in the third entry of this thread viewtopic.php?f=89&t=40583.
John

Try switching the board over to VR input - this will let you adjust the trim pots and use them for noise filtering.

Matt:
I might try that, but I do not think that my tach signal is the issue. As I have a GM TBI, which are low impedance injectors, I temporarly added a 10 ohm resistor (1/4 watt) to the circuit to make them "high impedance" and the ignition signal is now fine on the bench test. The car is put away for the winter so I will not be able to test it on the car for awhile. Do you know how big (watts) the 10 ohm resistor needs to be to change from a low to high impedance set up. Is there any down side to adding the resistance to the injector circuit and do I need to change anything on the board or with the software?
Thanks
John

It's still a tach signal problem, just that it may have been caused by injector noise. I'd go with a 5 watt resistor to be safe.

It is definite the injector causing noise. But I still think it is effecting the ignition signal, and not the tach. If I limit the current to less than 15% the problem seems to go away. Also when I did the modify flyback circuit, it seem to go away. Unfortunately, I broke one of the transistor pins doing the modification and I had to order replacement. I am going to try this modification first. However, I did order 10 watt 10 ohn resistors as my back up plan.
Thanks
John

Sorry, I meant the MegaSquirt's internal tach signal.