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This thread is about Renix (87-90 XJ's) grounds (and possibly newer XJs as well) and VARIABLE low oil pressure readings and low volt meter dash gauge readings.
I have been carefully monitoring my dash gauge voltage, dash gauge oil pressure (hot engine, idle in D drive (AW4), lowest oil pressure reading), engine coolant temperature, actual engine idle speed during the readings, and whether or not I have my AC blower on high and or my head lights turned on, as well as brake lights and turn signals activated.
To make a long story short, I have determined that at an extended idle in drive (like >10 seconds), while at say +190 F coolant temp, fully warmed up oil (like after a long highway run), that my low oil pressure at a fixed engine rpm (apx 600 rpm in drive at idle), will vary, or more specifically drop about 5 psi if I turn on the head lights, the A/C blower on high speed, the brake lights (by pressing the brake peddle), and turn on the turn signal. The headlights on and blower on high have most of the impact! Then if I turn them all off, or just turn off the head lights and drop the ac blower speed one notch, give it some gas for 1 second, then go back to idle in drive for 10 seconds my lowest hot idle oil pressure will be 5 psi higher! I have repeated this experiment about 100 times for months now, so I am sure of my data. I have also noted a signifcant difference in my dash volt meter gauge voltage under the same conditions where the oil pressure differed by 5 psi. The dash gauge (which is notious for lying) would drop from about 11 to about 9 volts. With everything off except the engine, at over 1000 rpm the dash voltage reads as high 13 volts. It has been this way since I bought the jeep nearly 4 years ago, so its not the alternator, battery, ...etc, it is just a well documented problem with Jeep voltage meter dash gauges.
Therefore, I have come to the conclusion that large voltage loads on the system power grid can not only drop the system voltage ( about 1 to 1.5 volt drop is typical at idle in drive, 600 rpm with head lights on, versus no head lights and AC blower on low) but can also drop the oil pressure gauge display pressure. Furthermore I am convinced from other tests and observations I have made that it is not all caused by system voltage drops (though somne of it is!), but that both gauges are negatively affected by inadequite grounds and back voltage on those grounds during peak power usage like when brake lights, head lights, max AC blower fan, and turn signals are all running at the same time, especially the head lights and max A/C blower.
I recently tightened up one of my ground connectors ( at the rear of the engine head)and found an immediate oil pressure gauge increase of 1 psi on the dash gauge! :clap:I am thinking seriously of following 5-90's suggestions of increasing the wire gauge size and clamp-connectors on the main engine, body and battery grounds. The largest load is starting the engine, and my grounds seem to be fine for starting the engine, never had any problems there, but variable gauge readings are quite annoying, and I am now convinced that while the OEM ground wires are adequite for old style automotive starting applications, they were not and are not adequite for the instrument gauges and newer electronics (Renix), especialy when you turn on the juice like the head lights, brake lights and AC blower on max. I can actually see my dash voltage change by nearly 1 volt with everthing on (head lights etc) when the turn blikers blick!
I looked at some local automitive stores last weekend but could not find anything larger than #4 wires on the store shelves. :rattle:
I have been carefully monitoring my dash gauge voltage, dash gauge oil pressure (hot engine, idle in D drive (AW4), lowest oil pressure reading), engine coolant temperature, actual engine idle speed during the readings, and whether or not I have my AC blower on high and or my head lights turned on, as well as brake lights and turn signals activated.
To make a long story short, I have determined that at an extended idle in drive (like >10 seconds), while at say +190 F coolant temp, fully warmed up oil (like after a long highway run), that my low oil pressure at a fixed engine rpm (apx 600 rpm in drive at idle), will vary, or more specifically drop about 5 psi if I turn on the head lights, the A/C blower on high speed, the brake lights (by pressing the brake peddle), and turn on the turn signal. The headlights on and blower on high have most of the impact! Then if I turn them all off, or just turn off the head lights and drop the ac blower speed one notch, give it some gas for 1 second, then go back to idle in drive for 10 seconds my lowest hot idle oil pressure will be 5 psi higher! I have repeated this experiment about 100 times for months now, so I am sure of my data. I have also noted a signifcant difference in my dash volt meter gauge voltage under the same conditions where the oil pressure differed by 5 psi. The dash gauge (which is notious for lying) would drop from about 11 to about 9 volts. With everything off except the engine, at over 1000 rpm the dash voltage reads as high 13 volts. It has been this way since I bought the jeep nearly 4 years ago, so its not the alternator, battery, ...etc, it is just a well documented problem with Jeep voltage meter dash gauges.
Therefore, I have come to the conclusion that large voltage loads on the system power grid can not only drop the system voltage ( about 1 to 1.5 volt drop is typical at idle in drive, 600 rpm with head lights on, versus no head lights and AC blower on low) but can also drop the oil pressure gauge display pressure. Furthermore I am convinced from other tests and observations I have made that it is not all caused by system voltage drops (though somne of it is!), but that both gauges are negatively affected by inadequite grounds and back voltage on those grounds during peak power usage like when brake lights, head lights, max AC blower fan, and turn signals are all running at the same time, especially the head lights and max A/C blower.
I recently tightened up one of my ground connectors ( at the rear of the engine head)and found an immediate oil pressure gauge increase of 1 psi on the dash gauge! :clap:I am thinking seriously of following 5-90's suggestions of increasing the wire gauge size and clamp-connectors on the main engine, body and battery grounds. The largest load is starting the engine, and my grounds seem to be fine for starting the engine, never had any problems there, but variable gauge readings are quite annoying, and I am now convinced that while the OEM ground wires are adequite for old style automotive starting applications, they were not and are not adequite for the instrument gauges and newer electronics (Renix), especialy when you turn on the juice like the head lights, brake lights and AC blower on max. I can actually see my dash voltage change by nearly 1 volt with everthing on (head lights etc) when the turn blikers blick!
I looked at some local automitive stores last weekend but could not find anything larger than #4 wires on the store shelves. :rattle: