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Renix running rix and underpowered?

Old 08-26-2015, 02:19 AM
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Exclamation Renix running rix and underpowered?

I have a 1988 XJ which seems to run pretty good for the most part. It has 307k on it with 31" tires and a 3" lift kit and a 3" snorkel for aftermarket stuff.

When I got it, the thing was falling apart and would barely run, so I started diagnosing and replacing things.

I installed a New fuel pump/filter/pressure reg with refurbished 703s,
cap/rotor/plugs (champion copper) wires/oil/filter,
CPS/02/IAC/TPS (what I didn't change I tested to make sure it worked)
02 was replaced 3 separate times (was trying to find the problem)

I also replaced the entire cooling system with a radiator out of a grand cherokee

All vacuum lines were either replaced with soft line, or inspected for leaks

I tested every ground I could find and cleaned them up, also added a second cable from the battery to the body (all grounds have very low resistance now)

A bit of backstory.
This was my parents vehicle a number of years ago, it ran well, had tons of power, and would get 500-600 kms a tank, it then sat for 4-5 years without starting or moving, I decided to fix it up and start driving it, but due to unknown causes (from sitting), everything just started failing.

I have replaced the things that seemed to be bad but I have never been able to get more then 250kms to a tank. There was 2 weird times when I got about 570 kms, right after I changed the 02, but the next tank it went back to 250. It also spits out a bunch of black soot and carbon from the exhaust upon acceleration, and wont go past 150km/h (the top speed may be from poor quality gas though as it used to hit 175)

What could cause it to do this?
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Old 08-26-2015, 09:04 AM
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How is the integrity of the vacuum line to the MAP sensor?

If you use all soft hose with no rigid piece in it, it can bend and reduce vacuum to the MAP.
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Old 08-26-2015, 04:46 PM
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the map hose is not restricted in any way, I routed it to a port on the top of the manifold, instead of on the side of the throttle body and blocked off the old port.

I'm pretty sure that I cleaned up all the grounds, but in case I forgot one, where does the map ground to?
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Old 08-26-2015, 07:01 PM
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Originally Posted by 95cherokee89 View Post
the map hose is not restricted in any way, I routed it to a port on the top of the manifold, instead of on the side of the throttle body and blocked off the old port.

I'm pretty sure that I cleaned up all the grounds, but in case I forgot one, where does the map ground to?
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. He makes an incredible cable upgrade for a very reasonable price.


Revised 03-04-2013


And this:

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.

Refreshing of the dipstick tube connection is covered in Tip #1, and the sensor ground upgrade is covered in Tip #6.

On 87 and 88 models, you could have a poor connection at the C101 connector as well. See Tip #2 and Tip # 27.

Revised 11/01/2014
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Old 08-26-2015, 10:42 PM
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I've cleaned up the dipstick ground, the braided cable, added a second cable to a radiator bolt, soldered most of the crimp connectors.

When I tested the resistance on the ground for the tps, it read about 2.5 ohms

is this within spec?
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Old 08-26-2015, 10:50 PM
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That's a bit high....does it change if you giggle the harness?

I don't want to "gum up" your work with Cruiser, (he may be on early AM AZ time), but...

Got a stock air cleaner? How much oil in there from blowby? At 300+...Oh snorkel.....Just sayen, that front vent tube can potentially produce a puddle or something of oil that might get sucked in and cause smoke...

Vac test for clogged cat? (or loosen header pipe nuts/bolts to let exhaust out for a quick test) With that crap blowing out your CAT could well be causing a lack of power.

Last edited by DFlintstone; 08-26-2015 at 11:03 PM.
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Old 08-26-2015, 11:13 PM
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No cat, and I have a reusable air cleaner that I cleaned recently, it gets a bit of oil on it every once and a while.

what would be the symptoms of loose manifold bolts? I can hear a sort of quite whooshing sound somewhere near the front of the engine, but I think it could just be the fan blowing air (I shoved a bolt in the clutch to make it solid till I replace it, but it was underpowered and had bad mileage before)
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Old 08-28-2015, 10:29 PM
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I threw a new air filter in there just for the heck of it, its got a bit more power, but still terrible gas milleage, I also cleaned up the main grounds a bit more and added more wires to improve the grounds. no change so far.

I tested the 02 sensor, it seems to be working... I think, it would cycle voltage every 4-5 seconds, I think thats correct...
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Old 08-28-2015, 11:34 PM
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Well, (while Cruiser is taking a nap), Here's a thread I did, it was somewhat sabotaged though. The up-shot I think is the impedance of our "cheaper" meters doesn't matter that much. Of course a low impedance meter would be better, But a cheap analogue (with a needle) seemes to work.

Rite up top is a link to EcoMikes info, a supper read for testing 02 sensors.
>>https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

In a nutshell, you want around 1 ohm, (or less) resistance, on the ground, (to bat neg). System,/12 volts to the heater, and the 5 Volt feed from the ECU, (back-probed, preferably with a $300 meter), wavering around 2-1/2 Volts, running at 2,500 RPM. (I use paper clips to back probe)

The 91 on 02 sensors.....Well ours is simply a variable resistor to ground, not sure what is going on there with there three/four wires, a very different thing there.
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Old 08-28-2015, 11:47 PM
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I used an analog meter, and the reading from the O2 was not a steady voltage, it would just jump around up anywhere from 1-4ish volts every 2 second to 5 seconds at random intervals. I think I got the ground to be as good as its gonna get, so I can probably get that out of the way.

as for the gas millage... what are the primary causes to make it suffer? could the map be slightly failing? it wont really run with it unplugged, and where does the O2 actually ground?
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Old 08-29-2015, 12:34 AM
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It should jump from .1 to 5 volts rapidly.
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Old 08-29-2015, 02:31 AM
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I think it grounds through the sensor ground circuit. For insistence, the tps ground mentioned in Cruisers #5 (IIRC), from there and battery Neg should be in the neighborhood if one ohm. What so you see on your digital?

This link here has info for the map. Fancyer stuff involves watching the Map "sweep", with an analogue. >>http://www.lunghd.com/Tech_Articles/...iagnostics.htm


At 300+ K, I might consider a wet/dry compression test. Also...is the inside of your tail pipe pretty black? Just checked mine, not really black, just grey...(photo could be better)
Attached Thumbnails Renix running rix and underpowered?-103_0018.jpg  
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Old 08-29-2015, 05:16 AM
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The tail pipe is black and sooty, it shoots out soot onto the ground when I Start it up, but just puffs clearish Grey exhaust when idling when warm, though I'm told it shoots out more black smoke when I accelerate

I'll do a Compresion test and get back to you, as well as test the grounds and o2 once more.
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Old 08-30-2015, 07:17 PM
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So it turns out my meter is not very good, it was displayed over an ohm of resistance just between the prongs, so I think my grounds should be alright.

I made a quick video showing the idle when cold and hot, I think it may be connected to the poor mileage


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Old 08-30-2015, 09:26 PM
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When my 02 was stone dead, no grounding or flux in the 5 volt feed, it ran pretty well on "default", (nothing from the 02 sensor). I suppose one unplugged would so the same.

Map/bad something with the map comes up allot with flooding. Here there are some simple tests> http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Any chance some brainchild stuck in some "inappropriate" injectors? The stock are faulty, leaky and a fire hazard. Allot of us change them, hopefully to ones with the correct flow rate. If you can make out the little numbers on the side, we may be able to figure out what is in there.

But always listen to Cruiser first!
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