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

Ok, here is the short and sweet.

Project: AMC 401, Holley TBI, HEI. The project was put on hold for the winter (minus 0 deg cold), Jeep started and ran fine before layup. Only changes done was new LC1 wide band O2, now I can only get the MSII to talk to my laptop while I crank the engine, and the injectors stay on with the ignition on (and not cranking) and blow 5a fuses which it has never done before. Pulled the box and powered it up with the stimulator and everything seems fine, communicates with laptop, and injector led’s flash in relation to RPM. Reinstalled and it does the same thing, disconnected power to LC1 and no difference, put 10A fuse in the injector lead and the injectors stay open while ignition is on, checked power to the box that is fine, it will cycle the fuel pump. Opened the box and looked at everything under a magnifying glass and didn't see anything burnt, discolored or bad solder joints.

Help, my scalp is getting sore from scratching it.

MSII Rev: 2.92000

Are you using high or low impedance injectors?

Low, the TB is from an old Holley Projection kit. The engine ran fine and there was nothing changed in the program other than adding a LC1 wide band O2.

chiefmiller wrote:Low, the TB is from an old Holley Projection kit. The engine ran fine and there was nothing changed in the program other than adding a LC1 wide band O2.

I think I see where Matt is going with this and I will leave the response for him.

In the mean time, can you post your msq?

Ken

FWIW, I also run a Pro-Jection tb.......

EDIT: Do I correctly assume that you are driving those injectors with PWM?

EDIT: Do I correctly assume that you are driving those injectors with PWM?

My setting are:

Injector open time (1.0)

Batt voltage correction (0.20)

PWM current limit (28)

PWM time threshold (1.0)

Injector PWM period (66)

But I still don't know why I'm having communication problems.

Thanks

The PWM current limiting is rather noisy, and can cause communications to shut down if the grounding and power isn't perfect. I'd recommend trying this noise reduction mod:

1. Cut the center leg on Q9 and Q12 or desolder it so it does not reach the PCB.
2. Run a length of jumper wire from the center leg of Q9 and Q12 to an unused pin on the DB37 connector.
3. Wire this pin to a 12 volt source in the wiring harness, separate from the Megasquirt's power supply wire.