minimum required voltage

[KMinAF]

Trying to diagnose a no start problem.

The engine seems to crank over normally but when cranking I noted the voltage as indicated on the dash meter is reading as low as 6 volts. I tried jumping the battery with another just to see if it would change the voltage reading. It didn't. I will take the cars' battery in to work to do a draw test just to make sure it is ok.

I believe the ECM requires a minimum voltage to operate, what is that voltage? I am assuming it would be checked at the IGN and BATT pins of the ECM? Is the 6 volts a "normal" reading? If not, where would you suggest I begin looking for the voltage drop? I am thinking a faulty battery?

I have followed the TFSM step by step verifying coils, ignitor, CPS, etc. I have verified timing belt/cam timing and recently replaced a faulty fuel pump which now cycles/operates normally. I get an occasional backfire through the intake and intermittent cylinder fire but never more than one or two at a time.

My thought is that a low voltage condition would result in a weak or intermittent spark. Am I on the right trail? I am open to suggestions.

1987 NA that has had a 7MGTE installed by a previous owner and has never run since the swap.

 

[jetjock]

11 for the ECU. Fwiw voltage (measured at the battery) should not sag below 10 when cranking. If it does the battery is either discharged or has gone tango uniform...

 

[IndigoMKII]

Hiccups in the intake aren't supposed to happen while cranking.

 

[3p141592654]

The voltage regulator internal to the ECU will operate properly with only 7V battery voltage, and the injector calibration table goes down to 6V, but I wouldn't know if the car would actually run with voltages that low. 6V is definitely not going to work, but 7V might. But as JJ says, it shouldn't drop below 10V during cranking if things are normal. I'm not sure I would rely on the dash gauge for anything though.

 

[Dan_Gyoba]

I've had the car start with 7.5V at the battery. (With a push start. I'd left the dome light on overnight. Fortunately, I'd parked on enough of a slope to be able to start it with the clutch.) This should verify that 7.5V is enough to have the ECU, ignition and fuel injectors operate. That's the lowest (Which I measured) I was actually able to get a start though.