Scanmaster wigging out

[Razor]

helping a friend, car is an 84 GN with the conversion to 87 ecm, MAF, and coilpack/ign module.

Problems are two fold, Battery readings on the scanmaster are low. Like 11.5-11.9-12.3 yet on the battery of the car it reads 13.9-14.0. Also if you put the car on bat and do a run, it blinks and goes to the main O2 screen. Or any other function. It goes to the O2 sensor reading. Will show KR while decellerating yet the motor has no kr. And its intermittant, yet duplicatable under different circumstances. There is no low fan relay.

How does the scanmaster detect voltage? I presume its of the aldl line. But the ecm at its man power connector has 13.8 volts.

Car is cutting of at high boost as well. Like if there is an electrical problem. Grounds were added from motor to chassis. Battery to chassis. ecm to chassis using heavy 8 guage wire, same problem. Alternator was replaced as well. Grounds redone on the scanmaster. Replaced ecm, MAF, plugs, wires, battery, alt,.. out of ideas.

So how does the ecm detect voltage to display those lower numbers?

Any help would be appreciated.

 

[TurboBob]

The ECM measures the voltage from the pin that comes from the Ignition key.

This same wire feeds the coil pack (in an 87...). I fixed a car once with low voltage displayed, it was a bad fuse holder. It was breaking up under boost also.

The scanmaster has no automatic return-to-main-screen function so I assume it's resetting. Probably low voltage.........

The scanmaster does not measure voltage, it is displaying what the ECM transmits (data).

You've got a bad power wire somewhere.... In an 87 I'd say look for the positive battery cable grounding to the header under acceleration.

Something could be 'clunking' under deceleration.....

BTW, ever put alky on a twin turbo Stealth?

Bob

 

[Razor]

Stealth Alky.. not yet But space is an issue.

My Mom one time had a Jeep Cherokee.. and it had similar issues. It was a bad ignition switch now come to think of it. The contacts were arcing.

So if the ignition switch or fuse/wiring to it were flaky, all of this would be very well possible.

Thanks Bob.. time for a voltmeter check.. i'll post what it was in case I find it...