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

This MS-I worked fine for many years, then it started flooding the engine. When ever it was powered up it woud ground the fuel injectors and cause the engine to flood. the U7 chip looked a little burnt and has something to do with injector output, so I replaced it. That fixed the flooding, however there is no out put to the injectors any more. The injector LED on the MSI blinks but the inj LED on the stim does not. How do I narrow down the problem from here? Thanks!

Joffrey wrote:This MS-I worked fine for many years, then it started flooding the engine. When ever it was powered up it woud ground the fuel injectors and cause the engine to flood. the U7 chip looked a little burnt and has something to do with injector output, so I replaced it. That fixed the flooding, however there is no out put to the injectors any more. The injector LED on the MSI blinks but the inj LED on the stim does not. How do I narrow down the problem from here? Thanks!

The MS LED shows injector output stage control input - the stim LEDs show the output stages are actually working. Failure of both output devices at the same time is slightly unlikely, so I'd check the common things like supply to them and their drivers.

Thanks for the speedy reply. I am confused - you state "the stim LEDs show the output stages are actually working."
By this you must mean they would if they were blinking? "Failure of both output devices at the same time is slightly unlikely" By "both" do you mean the stim as one of the 2 output devices? The stim worksfine with a different MS plugged into it. The car works fine with another MS plugged into it. Is the U7 the other output device or the whole MS1? I would like to check to check what is going to and from the U7 but don't know what i should see at each pin. "so I'd check the common things like supply to them and their drivers." It seems like you are saying there are two things that not working and that they both have drivers. Would replacing a U7 require that the code be reinstalled on the ecu?

If the injector LED on the MS is flashing when you have an ignition tach signal present from the stim suggests the processor is ok up to that point. it can be configured to use this single 'pulse' to provide alternatives to the two driver circuits - like simultaneous or alternating,etc. So you need to check these two signals from the processor through the output stages to see where the problem is. If the injector LEDs on the stim ain't following the one on the MS it means there is a problem somewhere.

Using the circuit diagram in the manual check for a signal at the inputs to U4 (pin2 circuit A, pin 4 circuit B) With the rpm set slow so you see the LED on the MS flashing, you should also see these inputs going low and high. A scope is best - but a decent DVM should also work.
Check also there is 12 volts between pins 3&6 (U4 supply)
If you're not seeing them switching, try altering the output configuration in software say from alternating to simultaneous. If they are switching move on the the outputs from U4 and through the rest of the output stages.

If there's no inputs to U4, I'd re-load the code before going further.

do you mean U7 rather than U4?
Looking at a schematic here:
http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf
U4 seems to be part of the input circuitry. U7 has power across pins 3 and 6. My digital volmeter is not reading inputs to U7, but it dosn't read power arcoss the blinking LED either.

Joffrey wrote:do you mean U7 rather than U4?
Looking at a schematic here:
http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf
U4 seems to be part of the input circuitry. U7 has power across pins 3 and 6. My digital volmeter is not reading inputs to U7, but it dosn't read power arcoss the blinking LED either.

Yes - I was going by my MS2 V3. So transpose everything to U7.

Slow the RPM down as far as possible - your DVM should then show it switching. Hopefully.

Have it slow as it will go, 200 rpm, cant read it. Is it like the injector output, an intermittant grounding? so I put my volt meter to a sorce of 12v on one lead and the input on the other? One odd thing I came across is that when I check the U7 output that goes to Injector 2 it causes the led on the stim for that bank to start blinking. I tried hooking up an audio amplifyer to the inputs I can hear the changing tone as i speed up the rpm. One input to the U7 is much louder than the other. Not much comming out of it. Maybe I overheated it when soldeering it in? Static damage? will play with it some more

I'm gonna put this on the shelf for a while. I'll take another look when I get some extra time and set up a PC based ocilliscope. thanksfor your help!

Joffrey wrote:Have it slow as it will go, 200 rpm, cant read it. Is it like the injector output, an intermittant grounding? so I put my volt meter to a sorce of 12v on one lead and the input on the other? One odd thing I came across is that when I check the U7 output that goes to Injector 2 it causes the led on the stim for that bank to start blinking. I tried hooking up an audio amplifyer to the inputs I can hear the changing tone as i speed up the rpm. One input to the U7 is much louder than the other. Not much comming out of it. Maybe I overheated it when soldeering it in? Static damage? will play with it some more

How is set up in software? Squirts per cycle? Alternating or simultaneous?