mdj577

Had a no start issue recently. Starter motor would turn over the engine but engine would not fire. Tach would not bounce while engine was turning over. Had my mechanic check the ref sensor which ended up being fine.

After re-charging the battery, the car fired up.

Questions: Why would a low battery cause a no -start. The battery had enough power to turn the starter motor and crank the engine. Is there some threshold voltage or current that needs to be achieved to fire the plugs? Why would the tach not work with a weak battery?

snb13

It probably was weak enough the starter didn't spin fast enough.

931guru

The connection to the sensor was bad. Having your mechanic test the sensor fixed the connector problem.

User 52121

Yep that's my thought. The charging of the battery did nothing. Moving around of the connector to the sensor is what did it.

The wires corrode inside the connector, and you wind up with flaky connections. Likely you need a new sensor and new sensor harness.

Next time it happens, just wiggle/jiggle the connectors and try again. It'll probably start.

Humboldtgrin

You all maybe right with the reference connection. But I think it's the flux copasitior that was low on mojo juice. Once the mojo juice was applied the car didn't die... I could be totally wrong thou.

jerome951

What was the voltage of the battery when it wouldn't start? I know there is some safety mechanism in the DME or KLR that impacts running when the battery voltage gets too low, but not sure if that keeps the car from starting.

Humboldtgrin

It's because your starter was taking all the avalible amps from the low battery to turn the engine over. Not enough left to send to the coil. It's that easy. The coil need to see 10 volts. If the starter takes it under 10volts then a week to no spark with an engine that turns slow won't start. It can't even make enough compression. You charged the battery and you had enough to start.

Tom M'Guinn

Might be worth looking at this thread, about the supplemental cables at the battery that were loose.

https://rennlist.com/forums/944-turb...-no-start.html

Also, how did the tech rule out the speed and ref sensors and harness? You'd have to pull all 4 boots off to inspect all failure points, and even then you can't be 100% sure because the break can occur inside/under the epoxy and not be visible.

Humboldtgrin

If you got your car running and would like to check connections, or possible broken wires inside the harness, then do a wire wiggle test while the car is at idle on the reference and crank sensors.

mdj577

"You all maybe right with the reference connection. But I think it's the flux copasitior that was low on mojo juice. Once the mojo juice was applied the car didn't die... I could be totally wrong thou."


After reading about all the electrical quirks that are possible with this car that is not far from what I was starting to think as well.



It's because your starter was taking all the avalible amps from the low battery to turn the engine over. Not enough left to send to the coil. It's that easy. The coil need to see 10 volts. If the starter takes it under 10volts then a week to no spark with an engine that turns slow won't start. It can't even make enough compression. You charged the battery and you had enough to start.

I can believe this possibility.



If you got your car running and would like to check connections, or possible broken wires inside the harness, then do a wire wiggle test while the car is at idle on the reference and crank sensors.


Will do. Thanks.



What was the voltage of the battery when it wouldn't start? I know there is some safety mechanism in the DME or KLR that impacts running when the battery voltage gets too low, but not sure if that keeps the car from starting.


Don't remember. It reads between 12-14V now. Thanks. Will check it out. I think my mech checked the resistance at the pins at the connector to the DME.


Might be worth looking at this thread, about the supplemental cables at the battery that were loose.

https://rennlist.com/forums/944-turbo...-no-start.html

Also, how did the tech rule out the speed and ref sensors and harness? You'd have to pull all 4 boots off to inspect all failure points, and even then you can't be 100% sure because the break can occur inside/under the epoxy and not be visible.



Thanks. Will check it out. I think my mech checked the resistance at the pins at the connector to the DME.




Thanks to all for the speculations. I think there is no simple answer to this one. Just going to keep replacing as failures occur.