Renix grounds & oil pressure switch anomalies

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:

The biggest problem with RENIX controls and gages is, frankly, grounds.

There's a reason that stupid little ground strap is A/K/A "the RENIX Killer" - it's the only ground return for the chassis to connect to the battery. Six hundred pounds of iron and aluminum, that's usually oily/greasy, really isn't that great a ground path.

Try adding a direct ground from the battery to the chassis, and it will likely clean right up. That's why I offer one as an option (having a direct ground for your chassis will help to clean up the ground reference for pretty much all of your sensors - and your ECU.)

5-90,

My only question is what took you so long to find this new thread? LOL, 10 minutes for a reply must be a new record here!!!! LOL

I forgot to mention that tightening that ground clamp at the rear head eliminted the need to open my drivers door just to get a good radio signal, LOL!!!! It was kind of risky open the door at 60 mphs just hear my favorite radio station.

I may heve to visit your web site for some real cables real soon. :wave:

Ecomike said:

5-90,

My only question is what took you so long to find this new thread? LOL, 10 minutes for a reply must be a new record here!!!! LOL

I forgot to mention that tightening that ground clamp at the rear head eliminted the need to open my drivers door just to get a good radio signal, LOL!!!! It was kind of risky open the door at 60 mphs just hear my favorite radio station.

I may heve to visit your web site for some real cables real soon. :wave:

Click to expand...

I just happened to check, and I know you own RENIX anyhow:read:

That also makes sense (ground strap WRT the radio,) and is another good reason to add a chassis ground. Radio antennae almost depend on having a good ground plane, and the chassis is the ground plant for a BFM/BAM antenna.

That's pretty much the same reason that (assuming a good chassis ground) a CB antenna usually works better when mounted in the centre of the roof and properly tuned vice a "side mount" properly tuned.

Feel free to check - I'm not going anywhere. Worst case is I (finally!) get all set up to take a vacation without worrying about the damned City getting in my hair...

I have replaced the battery cables with large gauge crimp cables, replaced the engine to firewall strap, added a braided strap from the neg. terminal to ground, and another large crimped ground cable from the neg. terminal to the intake (to remedy a high idle problem I was having) Would it be smart to add another cable from the neg terminal to the firewall? I have noticed my idle has come back to normal and it runs very smoothly unlike before. The only real chassis grounds are the two braided straps right?

There shouldn't be any need to add yet another ground from the battery to the chassis - the usual "loop" is battery-chassis, battery-engine, and engine-chassis (the engine-chassis is a backup loop. I've done double grounds on engine-chassis before, but that's more for performance vehicle than anything else, where sensor performance and clean signals are critical.)

And, since the firewall is welded to the rest of the chassis anyhow, you really don't need to add another chassis ground there in the first place (once the unibody is welded together, it can - electrically speaking - be considered a single piece of metal anyhow.)

Originally Posted by 8mud
Exercising authority is often much like masturbating, most people do it because it makes them feel good. But it really doesn't accomplish much.

8mud.... gotta love him, and thats all I got to say bout that! LOL.

So I have been noticing some green corrosion fungus forming on the positive brass clamp on my battery the last few weeks. Happened last month on my diesel jeep battery and turned out the battery post was a little loose and leaking H2SO4 gases right under the post. The diesel battery was only 2 years old so I got a nice warranty adjustment on the cost of a new one. Today my gas 4.0 battery was already 4 years old and starting to do the same thing so I replaced it tonight. After doing so and cleaning the clamps I noticed an increase in dash gauge voltage, and my headlights were brighter.

Then I added a new 2 ga 24" long ground wire to the run from the firewall to the engine block head. Now the head lights and dash night lights are brighter, the dash volt meter reads a much higher voltage than before even with everything running like the head lights turned on. The only thing that still dims the dash lights and drops the dash voltage reading is the AC blower fan, so I am guesing I need to run a seperate ground wire for the AC blower ground wire directly to the battery and or run a larger newer ground wire from the battery to the engine block, but I am tempted to run a ground from the battery directly to the chasis instead since I do not have a direct one yet.

Just thinking out load and wondering what the back voltage on the ground was up to on the sensor grounds with all the high power gadgets turned on, the ones that were dimming the head lights and droping the dash volt meter reading from 13 to about 10 volts (which I suspect was a poor ground and not a lack of voltage) before I added the second 2 ga firewall to engine head ground, cleaned the clamps and replaced the battery which had new clean posts.

I have no doubt it was adding some back voltage and thus might have been disturbing the sensor to ECU readings say at night with all the power gadgets at full power.

If you readers of this post get a chance, try checking the voltage from the chasis and again from the engine block to the negative battery post when you have everything running at full power including the head lights and AC blower on high and see if is not a lot higher than with the AC blower and head lights off!!! Might even check the TPS idle voltage with all those apppliances off, and then with them on???

Then think about the conditions you use for setting the TPS idle voltage for instance versus the test I just suggested, or what hapens to the O2 sensor reading when the back voltage on the ground jumps up versus when those items are off or on low speed.

I am going to check mine again in the morning with the AC blower on high since it still dims the head lights and the dash gauges to see if it is voltage drop or ground back voltage increases that are still causing it.