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

Trying to get a GM 3.8l started with MS1-MSnS-e.

It just cranks and cranks and no signs of firing.

But if I take ajumper wire and ground out the INJ1 bank to ground I manually open the injectors for a split second and then next crank it fires and runs for 1-2 seconds. I used a second battery hooked up to the injectors and by tapping the wire against the abttery I can get the truck to idle Although it would be nice if I could get the MS box to do some of the work

I tried putting cranking pulsewiths to maximum 20ms just to see what happens and same thing, cranks but no fire.

I have narrowed it down to 4 possible scenarios:

1. Fuel pressure regulator or fuel pump not working correctly. maybe it is a much lower fuel rail pressure than it should be and I really need to prime the hell out of the engine to start it? I can geta tester on it tomorrow.

2. Crank pulsewidths too lean. I tried 24mS cant go any higher!!!??

3. Cranking voltage too low to open injectors. I'm using a brand new optima red top battery with charger hooked up set to 10A charge. Voltage is 12.5V, drops to about 10.5 when cranking. I think this might be part of the problem. To test this thoery I took a spare battery I have and drained it down to 10V when under the load of my electric fan. Hooking up the injector wires to this battery I can't get them to open. How can I test this problem further or possible ways to solve it?

This last one would make sense as I'm using full battery power to open the injectors with the engine off, then when cranking the voltage drops, the engine runs for a second or two on the heavy heavy priming pulse I just squirted and soon dies. The time I was able to get the engine to idle I was actually using another battery to "manually control" the injectors.

Can anyone help out with this?

If I install a jumper wire from the INJ1+2 screws on the relay board, and use that wire to touch ground while the engine is cranking, it will NOT open the injectors. There should be a tiny spark and a click and there is neither its like the wire goes dead.

When I stop cranking the engine, and continue to tap the wire to ground it will not make a tiny spark indicating teh injectors are opening UNLESS the fuel pump stops (a bout a seconds after stopping cranking). This also corresponds to when battery voltage goes up over 12V again.

My immdiate reaction was a wiring problem that does not give the injector 12V supply any power during cranking. To thet that theory I hooked up a voltmeter and tested voltage during cranking. About 10.4-10.5 when cranking. After cranking it goes up to about 11.4 until teh fuel pump turns off and goes up over 12V, this is when I can start manually opening teh injectors.

Is it possible these injectors require 12V+ to open? That seems bizarre.

If you have access to an oscilloscope, it is easy to see if the injectors are being pulled low by the MS. If your voltmeter has a peak hold function, you can see what the max and min voltages are that are being seen on the low side of the injectors. You could try using the AC volts range, which would tell you if anything is happening or nothing.

What is your fuel pressure?

0.6V seems like a lot of voltage drop just due to the fuel pump. What gauge wire runs from the battery to the relay board and from the relay board to the injectors?

I assume that you have checked the wiring from MS to the injectors for continuity?

If your injectors need any more than 8-9V to open, you won't always be able to start the car.

BAH figured it out. Wired the injectors in series instead of parallel. I guess that created a ton of resistance to overcome and created a higher than usual minimum voltage to fire the injectors. Rewired them and got the engine to idle so THIS is how its supposed to work! engine starts up and idles effortlessly and I haven't even messed with the tuning all that much!!!