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

I have a MSII/V3 running a SBC 383 with TPI in a 1977 Blazer. It was previously running fairly well (about 2 years ago before I overheated the engine). After a fresh rebuild of the engine and rewire of the chassis, I can't get it to idle without an irregular miss. This seems to be related to ignition because I see tach dropouts. I've tried a spare module and coil, and the problem persists. The plugs, cap/rotor and wires are all new. I need to get this running well enough to get across town to our new house, please help.

In the datalog, you can see that the dropouts go away when the rpm increases above ~2000rpm. The tach dropouts seem to go away when I disconnect the vRef signal from the module. I generate the VRef using the fIdle instructions.

Thanks for any help.

The tune is messy, but I need it to run without missing to fix it...

How is your input circuit set up for the HEI?

The input circuit on the V3 is set up like the megamanual says to set it up.

Like this.

V3.0 main board:
DB37 pin #36 to the E pin on the HEI module
DB37 pin #24 to the R pin on the HEI module
On the V3.0 main board:
use the 'Hall sensor circuit' (step #50 in the assembly guide),
jumper OPTOIN to TACHSELECT on the bottom side of the PCB, near the DB37 connector, opposite the heat sink,
jumper TSEL to OPTOUT on the bottom side of the PCB, near the center.
jumper JS10 to IGN (this uses the processor port for the outgoing timing signal directly),
jumper XG1 to XG2 on the bottom side of the PCB, near the 40 pin socket,

Try these mods:

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

We've found they give a stronger signal on many installations. You need to change the Ignition Input Capture to Falling Edge with them.

I changed the input using those guidelines and it still gets the same tach dropouts, unless I disconnect the timing override plug. When it's disconnected, I don't get any dropouts.

Well,, thanks for the help. I'll check back in later if I am still having the problem after I figure out why the No 2 cylinder was full of coolant on my new rebuild. Hopefully it's just the intake gasket...