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Renix CPS crank voltage and cold weather and iced inside windshields

Ecomike

NAXJA# 2091
NAXJA Member
Location
MilkyWay Galaxy
Had two new ones this week. My daughters HVAC blower switch died and she roughed it for a week with out the blower in 16 F weather up north, till the inside of her windshield iced up to where she could NOT see the road to drive in 16 F weather. She called AAA and had her Jeep, and her bod towed to class 30 miles away so she would not miss school, LOL. Later she drove 60 miles back home, no problem. One of these days she will learn not to procrastinate on simple jeep repairs. She has the new switch now, LOL.

She now understands how bad it can get :eek: with out a working defroster LOL. Why do humans insist on learning the hard way, LOL.

Then just days before we fixed a cold weather no start issue due to a Renix new NAPA CPS low output signal in 16 F weather by replacing a 16 month old, still tested as good, Napa standard duty battery with an AZ max cold cranking amps duralast gold battery and no more failures to get spark and injector signals since then.

She and I did the debugging and testing over the phone. Interesting that the used standard duty Napa battery still showed 10.75 volts while cranking, when 5-90 use to say 10 Volts minimum was needed for the ECU to turn on and give a spark. BUT it Seems in super cold weather that is not good enough for the Renix CPS to see enough RPMs to produce a high enough alternating DC pulse for the ECU to read, thus no spark when it was that cold, unless the vehicle was jumped to boost the cranking voltage/amps!!!! The battery tested as good at AZ!!!

In this case the new AZ battery at that temp held 11.7 Volts while cranking, which gave enough rpms to boost the CPS output voltage for the ECU to see and start the engine.

A good, not very old standard duty battery was not good enough in weather that cold. She uses 10W30, about 240,000 miles on the 1989 Renix Cherokee stock 4x4.

I ran a series of tests over the years looking at the CPS output voltage and it jumps lows .20 to as high as 7.0 volts as the RPMs go from about 200 to 2500 rpm.And Cruiser54 says the CPS cranking voltage needs to reach .50 Volts AC on the test meter to always get Renix to start.

One other thing, we have found that three different brand test meters are giving readings of .20 to .50 volts on the AC scale on the same CPS and the low readings were using cheap HF meters the higher readings were using expensive high quality meters. So that is another issue we need to deal with!!!
 
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