engine dies as soon as vacuum is connected to map

[swisssquirter]

hi there.

MS-II - V3 - Megatune V2.25
350 V8 Vortec Port injected high impedance, HEI 7.

after fixing several bugs, i now believe my ms2 works, although i had to fix a bug in the relay-ecu connection cable. one pin didn't make contact. i hope it's only one.

it started real nice and idled fine. i use all the standard settings.
after a while i notice the map wasn't going nowhere, still at 91. i'd forgotten to hook up the vacuum line. i hook it all up but the engine revved up and sputtered and died. after this the engine is hard to restart, but after a while it does and i let it run for a while without the map hooked up. i can put a plug in the vacuum line, it idles fine. but, as soon as i hook vacuum up the map sensor, the engine will run very rough, and gradually die.

does anyone have an idea what this could be?
i will be switching over to wideband this week, too. this logfile is still with my narrowband sensor.

[Philip Lochner]

i hook vacuum up the map sensor, the engine will run very rough, and gradually die.

I did not look at your log BUT Without MAP connection your MS is using values off the ignition map (if your ms is controlling ignition) and the VE map AS IF the engine is at full throttle.

When you hook up the vac line MS jumps to the map bins associated with whatever manifold pressure it measures. It seems to me that the low manifold pressure bins of your maps hold values that your engine is not happy with at idle - most likely VE is too low.

[renns]

It's tuned too lean at idle. The 'rpm increases then stalls' characteristic you mentioned indicates that pretty clearly. When you connect the map hose, the sensor now detects the lower manifold pressure, and pulls VE from a lower section of the table, transitioning from rich to lean to stall.

Since this is a startup condition, check after-start and warmup enrichment settings. This process is detailed quite thoroughly in the manual here:

http://www.megamanual.com/ms2/tune.htm

Roger.