View Full Version : renix ground testing

April 21st, 2012, 21:12
should i get an increase in ohm readings on the ground system with the key on?
testing and repairing all the battery grounds, to engine, body, and all the sensors themselves. with key off i am getting little to no ohms from battery neg to engine, body, and all sensors, telling me i have good grounds to each. with key on i get an average of 5 to 6 ohm increase at all sensors, and 3 ohms from bat neg post to engine. even if i pierce into the 2 awg neg cable 6 inches from the post, i still get a good 3 ohms resistance. key off everything is great. chasing a low idle issue and it seems the ecu is telling itself to lower the idle after a few seconds of run time. all sensors test good and most are new.

April 22nd, 2012, 19:16
That's normal.

What's been done with the oxygen sensor?

April 22nd, 2012, 20:19
actually i installed a new one. Bosch. i get a decent reading on the analog meter and it is working. but when i check the ohms with key off, i get around 8 ohms. i read they are supposed to be anywhere from 5-7 ohms. so i really am not sure what to think. i am going to run it though.
on a side not, i think i figured out my low idle issue. my timing chain is making alot of noise, which i believe the knock sensor is picking up and trying to retard the timing to cure it. that and the fact that the chain is so stretched and making my cam timing way off i believe is the cause of my poor running, low idle condition. new timing set going in tomorrow.
i also found that my egr valve was leaking. not through the main body, but through the diaphragm rod going through the case. the diaphragm was working good, and the the valve was closing all the way, but the intake side was sucking fresh air through that little shaft collar/bushing. wasnt enough to make much sound. thats why i didnt notice it. the egr system was testing good, working correctly. just when i went to clean it i found the problem by sucking air through it. ya ya ya, no jokes please. all in all i think after the new timing set, it should be running just the way i want it to.

April 22nd, 2012, 20:22
Let us know after the timing set install.

April 22nd, 2012, 20:27
will do, thanks.

August 28th, 2013, 10:41
Yes i know it is an old thread but it was asked to report after the timing set install. well the new timing set did nothing but give me less chain noise. still have the low idle, slight stumble. it revs like a mo fo at start up, holds the high rev (2k+) for a good ten seconds, then drops to 300 maybe 400rpm at most. basically just enough to stay running. i walked away from this project many months ago, but recently got back to it. swapped out the throttle body with a nice junk yard piece. cleaned it and installed new stepper motor, and TPS. repaired and cleaned up all the wiring at the relays and replaced a couple fusible links that where either bad or seemed bad. put in a good battery and fired it up. ran better than when i walked away from it a while back, but still have the low idle with slight stumble, and high rev at start up. now back to re-checking all sensors, re-checking all grounds, and continue searching for vacuum leak. i know these jeeps dont get the best MPG, but it is alot better than the 454 GMC duelly i have been driving. so it is back to chasing the gremlin in my jeep, hunting it down, maybe torture it for a few, then killing it dead dead dead.

August 28th, 2013, 13:07
Sorry to hear that.

Where are we now?

Have you done any of the things in my "tips" write-ups?

August 28th, 2013, 14:12
thanks. yes i followed alot of your tips back when i was really going after this thing hard. recently however i have taken a much slower attempt at it. first i started replacing and repairing wires and fusible links. checking cleaning or replacing all wire connections. then i replaced the throttle body since the original was very dirty and had stripped out threads in various areas. i fired the thing up so i can move the jeep to better area to work on it and found that it ran better than it did when i first parked it there. so at this point i will start back at the testing stages of all the sensors. mind you that back when i was working on this before i had borrowed a DRB2 from a member. and even with that at hand i still never tracked down my cause if issue. the DRB2 pretty much test all the sensors aswell and it told me all was in spec. i no longer have access to the DRB2 but with DMM and anolog meter i should be able to do a decent diagnostic. i tested all my sensors and such before but i remember there was a schematic that showed where to probe for testing them all at the ECU. i had it copied and in a folder but i have yet to find it. you know how garages can get. i did have a thread back then telling all what i did and what was happening. what i replaced, ect. i would hate to try and rewrite it all here. but i will take a slower attack at it this time so i make sure i do not skip anything by being in a rush. i spent a good 5 weeks straight last time and got plenty aggravated. this time i figure if i work on it i do, and if not no biggie, the jeep is still just sitting there.

August 28th, 2013, 14:14
I have the ECU pinout. PM me your email address and I'll send it to you.

August 28th, 2013, 16:12
Note from DJ for 2stix
This may be your original post

August 28th, 2013, 17:19
Yep, that is my original post. thanks for linking it. i really was not going to add anything to it untill i got some good info to report. i just found this old thread that one person asked to report after changing the timing set and i never reported in untill now.

August 28th, 2013, 23:05
Your meter may be picking up standing voltage in the Ohm mode, the voltage left over in a ground circuit after traveling through the slight resistance in all the connectors and ground points. I always switch my meter to the lowest DC voltage scale and try to measure the standing voltage.

Just for giggles, strip back a little of the insulation on your TPS ground wire (three pole connector) and run a ground wire form therewire straight to the battery negative and see what happens with your idle and that 2000 RPM hot start. I found a loose splice in the harness for the TPS and after soldering it up, my low idle and hot start issues stopped. My be your issue or it may not, but worth a half hour to check out.

Double check your ohm readings at the ground strap at the rear of the motor to the firewall. I had to clean mine three times before I was satisfied all the resistance ways gone. An invisible coat of oil (human skin oil) is enough to mess up the 0.8 volt TPS reference signal.

August 29th, 2013, 05:17
I've gotten into the habit of adding a braided cable from the firewall to intake manifold and from the passenger's side block to a stud near the upper shock mount.

Here's another test for the sensor ground circuit, the repair, and then below that the ground refreshing stuff with cable part numbers.

Cruiser’s Renix Sensor Ground Test
This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 06/12/2012

Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.
Where it's connector plugs into the harness you will see that one of the wires on the harness side is brown with a white stripe. Follow the brown with white stripe wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires with duct tape over them. They're from the TPS and the CTS. The 3 wires will be  spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.
Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires with duct tape over them. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.
You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.
Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.
Zip-tie up your new sensor loom to allow for engine movement. I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.
Revised 03-09-12

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com (http://www.kelleyswip.com/). He makes an incredible cable upgrade for a very reasonable price.
Revised 03-04-2013

September 1st, 2013, 22:20
so i was doing some testing and such with both the Dmm, and a power probe 3 when while it was running for a good 20 minutes i noticed the fuel pump ballast resistor was extremely hot. the wires weren't to bad, but i decided to check them with the tester. disconnecting them from the resistor i noticed they both showed continuity to ground. the wire to the pump had a little over 1 ohm resistance to ground (key off) and the other side that i believe goes to the relay showed about 7ohms resistance to ground. when i used the power probe to the wire going to the pump it shows ground untill i activate it and the pump comes on. (those power probes are really cool). is it possible i have connected the wires to the fuel pump incorrectly when installing the new pump?

September 2nd, 2013, 04:52
Don't the connectors have 2 different size spades on the pump? Unless, of course the spades are on wrong.....

September 2nd, 2013, 13:17
well it has been a while since i looked at it but from what i remember i did have to repair a bad connection to one of the wires. this is a dreaded airtech pump which has all wires the same color. i do have my old pump (not sure of brand) and tested the leads and the power wire does show continuity to ground. so maybe that is normal.

on a side note. not to second guess you cruiser54, but the start of this thread i asked if the ohms should increase on the neg cable when ignition is turned on. and you said it was normal. well i wanted to recheck and do something. so i removed both cables from the battery. with the key OFF i get no cont. between the pos and neg cable. what i expected. but with the key ON i get continuity with about 17 ohms resistance. this leads me to believe i have a shorted positive (12v) wire to ground somewhere when key is on. am i correct?

September 2nd, 2013, 14:24
It is normal to see a resistance reading with the key on when checking resistance of some circuits.

Unplug your fuel pump harness and see what happens to that reading of 17 ohms.

September 2nd, 2013, 15:12
so you are saying that with the battery disconnected completely i SHOULD have continuity between the positive and negative battery cable with the key on? wouldn't that mean there is a shorted/grounded positive wire somewhere?

September 2nd, 2013, 16:44
well i could not get under the jeep to disconnect the fuel pump harness. but i did disconnect just about every connector under the hood i can find (one at a time, then reconnected). most had no change, but a few did make the ohms come up. one of the two transmission harnesses and i believe it was the one going to the trans and transfer case. not the control module one. it made the ohms reach a good 35ohms. then there was one almost under the coolant bottle. it has bright blue connectors. that did about the same thing. THEN i noticed if i switched the key off and back on again i get different readings. so with the key ON, DMM set on ohms/cont, with the leads on the battery cables, i went and wiggled the ignition key. DMM jumping all over the place. i do believe i may have a bad ignition switch. it is very loose.

September 2nd, 2013, 17:30
so you are saying that with the battery disconnected completely i SHOULD have continuity between the positive and negative battery cable with the key on? wouldn't that mean there is a shorted/grounded positive wire somewhere?

Not saying that. That fuel pump harness needs to be unplugged.

September 2nd, 2013, 17:47
ok i will try and squeeze under there and unplug it, then check the DMM. and i hope you did not take that the wrong way. i am so grateful for your input on these things. i was just trying to make sure i understand what you meant. because i get different readings every time i switch the key off and on, i may work on that first. just wiggling the ignition a small amount changes the Ohm reading quite a bit. while i was sitting around i thought i would check/test all my relays. turns out that out of the 4 by the coil, 2 of them did not energize when a 9v battery was applied. one of the bad ones was to the A/C clutch, the other was either the fuel pump, or the O2 sensor. since the fuel pump was working i am thinking it was most likely the O2 sensor relay. if so this can be the root to my low idle issues. i found three good relays in the garage so i will let you know what happens.

September 2nd, 2013, 17:51
Good idea on the relays, and no offense taken.

Test after replacing them, before squeezing under the Jeep.

September 2nd, 2013, 20:08
started quicker, didnt rev as high and for as long but still pretty high. leveled off at a decent idle for a few seconds, then back down. seems to run a little smoother but not a big change. for the first few seconds i thought i was a happy jeeper. oh well i was for a couple seconds. back to the grind.

September 2nd, 2013, 20:23
Have you ever checked the O2 sensor heater?

Should be 6 to 8 ohms across the red and black wires on the sensor itself.

September 2nd, 2013, 20:31
i did back when i was working on it before. if i remember correctly it was around 7 ohms. at the time i also had a borrowed DRB2 tester that confirmed my findings on the O2 sensor. everything that the DRB2 was able to test, it did, and there were no issues according to the DRB2. for kicks i checked the fuel pressure again this evening and key on i get about 41# after start up it drops to about 36 maybe 37# with vacuum line connected to regulator. disconnected vacuum i forget but it was getting dark. again tomorrow.