calling all renix gurus and others...

89 waggy limited with a 4.0 and aw4. i got this intermittent high idle problem. the tps is adjusted as good as i could get it . input voltage is 4.7 and output is 3.9 on the square connector. i checked all vac lines and none are leaking as far as i know. i also checked manifold bolts and all were tight except for one which i torqued down.so now what?

and before you say search i did . that is how i got this far.

thank you all help will be greatly appreciated!!!

come on guys help a brother in xj's out!

I'd clean out your IAC motor. I had the same issue on my 89 and after I cleaned it out it hasn't had a high idle issue again.

You didn't mention grounds. There is a braided ground from the firewall to the intake manifold. I would clean it up as best as I could, or ideally replace it.

Another one-down on the left side of the block by the oil dipstick (where it bolts to actually) several grounds there, likely for misc. sensors. Clean that too and make sure its tight.

When does it idle high? Hot/cold or whenever?

x2 on the IAC. Throttle body cleaner is ideal, I think carb cleaner actually leaves behind a film.

Check the grounds, start with the large one on the firewall that connects to the block, then then ones next to the dipstick and (this should go without saying) the battery grounds from the post to the block and post to fender. Then clean the IAC and throttle body.

I need to learn to type faster LOL

I forgot about the grounds. Heres a site that will help ya out with the sensors
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Ground issues are common on RENIX. Reason? That stupid braided ground strap from the engine to the firewall is the primary chassis ground, meaning that the chassis is grounded through an open conductor (which collects crud) and through the engine block (that connects tends to get well lubricated as well.)

Fix? Ideally, replace all your mains - they're getting old anyhow, and the OEM stuff could have been done better. Practically? Replace the firewall ground strap (dollars to doughnuts it needs it) and add an auxiliary ground from the battery to the chassis (giving it a direct ground path.)

Why? Because the chassis ground is the common ground reference for the ECU and the engine management sensors. This needs to be a clean ground plane - if it isn't, you have trouble. That stupid ground strap is also known as "The RENIX Killer" for a reason.

I find it also helpful to dismount the throttle body and give it a thorough cleaning - clean the pintle for the IAC, clean the idle air passage, and just scrub the rest of the thing while you're about it. I try to clean out the vacuum ports with pipe cleaners, but I'm cranky. Cleaning the bore, butterfly, idle air passage, and IAC pintle won't go amiss, and it's all easier to do on the bench anyhow. The lower throttle body can get crudded up because of the damned EGR setup - I don't know who came up with the idea of routing exhaust gas through the intake stream, but it's intolerably stupid. There are better ways to solve the problem (and per emissions test results, the EGR valve isn't even necessary on the AMC242 anyhow. Neither is the "reversion timing" that ChryCo used to delete the thing.)

The Renix ground system and computer is extreemely sensitive to the quality of the ground, and consistancy of the ground. The later vehicles seem to use a common ECU ground that I suspect self corrects for a floating chasisis and or engine ground. By floating I mean small changes in the ground resistance of just a few ohms. If the ground path resistance changes by just a few ohms it changes the ECU's reading on the TPS enough to raise the idle speed significantly.

The ignition starter circuit can handle the extra ground resistance, but you want the ground resistance between the engine, frame and negative battery post to be less than 1 ohm, hot cold, rain, shine, and even over road hazard bumps.

all hail the mighty 5-90party1:


okay, i checked all grounds and cleaned them up. unplugged tps and re-calibrated it again. cleaned the distributor cap out,bunch of white gooky stuff, and i did the b+ latch ralay thing. the ground strap definetly needs to be replaced because one of the eye connectors is broke in half. the high idle seems to have left for now, oh it was about 2000 rpms. but there is this stumble type powerloss thing when cruising in 3rd or so i was thinking fuel filter or something of the like but i think ill clean out the iac and throttle body and might even go as far as the intake manifold. one question what should i replace the braided ground strap with?

almost forgot the high idle happened, happens, all the time no matter if its hot or cold and the stumble thing happens all the time too, but it feels worse if the motor is cold.

m0n3ym1k3y said:

all hail the mighty 5-90party1:


okay, i checked all grounds and cleaned them up. unplugged tps and re-calibrated it again. cleaned the distributor cap out,bunch of white gooky stuff, and i did the b+ latch ralay thing. the ground strap definetly needs to be replaced because one of the eye connectors is broke in half. the high idle seems to have left for now, oh it was about 2000 rpms. but there is this stumble type powerloss thing when cruising in 3rd or so i was thinking fuel filter or something of the like but i think ill clean out the iac and throttle body and might even go as far as the intake manifold. one question what should i replace the braided ground strap with?

almost forgot the high idle happened, happens, all the time no matter if its hot or cold and the stumble thing happens all the time too, but it feels worse if the motor is cold.

Click to expand...

Y'ask me, I say replace it with a proper cable of some variety. That stupid open braid is used because it is cheap (mainly) - I think there are some engineering reasons for using an open ground conductor, but underhood is not the environment for them (since the open braid collects a bunch of yock from normal operation, which worsens conductivity, which causes ground issues, ...)

Throttle body hold down bolts should be checked. And the EGR hoses and diaphragm for vacuum leaks.

I saw you checked the vacuum hoses, did you look at the connection on the vac ball under the bumper, too? It's behind the rubber skirting on the passenger side.

5-90 said:

I think there are some engineering reasons for using an open ground conductor, but underhood is not the environment for them (since the open braid collects a bunch of yock from normal operation, which worsens conductivity, which causes ground issues, ...)

Click to expand...

Actualy I think that the OEM open braid was stainless steel wire, (or tin coated copper?), but it is very fine, multi thread wire, which from an electron conductor physics theory is superior in several ways (and may be more expensive?). For one thing it is less likely to break from years of flex fatigue than a wire with much larger and fewer conductors. Also for the same wire size, a multicore wire with more conductors and finer (smaller diameter) wires will conduct more electrons (have less resistance) than the same overall gauge wire that has fewer larger individual conductors in the same overall gauge cable.

However, stainless steel is not as good a conductor as copper! I don't believe the outer insulation of the ground wire (lets say PVC or better) verses an oil soaked open braid ground wire (which also acts like insulation) makes any difference at all in the conduction of electrons. The oil would be no different than a PVC coated wire IMHO. In a multicore wire, or single core wire, the electrons repel each other, and thus are conducted mostly along the outside diameter of each thread of wire (conductor), that is why multicore wire is a much better conductor (less resistance) than the same overall gauge size single core wire.

In my opinion the biggest problem with these Jeep grounds is first the end connectors which tend to rust and oxidize, and the head, block and firewall (iron) also tend to oxidize at the connections, and they did not supply an OEM battery negative post to chasis direct ground strap, but instead depended on a 2 step ground path through the engine block and head of all things, and then they expected a computer and its sensers to work properly in an environment where the sensor readings go down to 0.01 volts as a significant data value, in a poorly grounded system.

Lastly they did not use large enough ground wire gauges.

The key think is to add a chassis ground directly to the battery, and to have good clean tight connector and wire on the end of all the ground wire cables and good clean tight connections between the wire connector terminations and the frame, block, head and negative battery post. With all that done a little further improvement is made by increasing the wire gauge size for the grounds. But if the connections are not kept tight and clean, it won't matter how big the wire is!

I forgot to mention that electron conduction is a surface phenomemon. The more sirface area in the conductor the more electrons it can conduct. Thus the reason that multicore wire of equal overall gauge size can conduct more amps than a single core wire. The more wires, the more surface area, the more surface area the more current it can conduct.

Also, wouldn't an open ground wire like the ground strap run cooler (disipate heat beter) than an insulated wire bundle? With all the heat under the hood that may be a mute point for us!!!!

Ecomike said:

Actualy I think that the OEM open braid was stainless steel wire, (or tin coated copper?), but it is very fine, multi thread wire, which from an electron conductor physics theory is superior in several ways (and may be more expensive?). For one thing it is less likely to break from years of flex fatigue than a wire with much larger and fewer conductors. Also for the same wire size, a multicore wire with more conductors and finer (smaller diameter) wires will conduct more electrons (have less resistance) than the same overall gauge wire that has fewer larger individual conductors in the same overall gauge cable.

However, stainless steel is not as good a conductor as copper! I don't believe the outer insulation of the ground wire (lets say PVC or better) verses an oil soaked open braid ground wire (which also acts like insulation) makes any difference at all in the conduction of electrons. The oil would be no different than a PVC coated wire IMHO. In a multicore wire, or single core wire, the electrons repel each other, and thus are conducted mostly along the outside diameter of each thread of wire (conductor), that is why multicore wire is a much better conductor (less resistance) than the same overall gauge size single core wire.

In my opinion the biggest problem with these Jeep grounds is first the end connectors which tend to rust and oxidize, and the head, block and firewall (iron) also tend to oxidize at the connections, and they did not supply an OEM battery negative post to chasis direct ground strap, but instead depended on a 2 step ground path through the engine block and head of all things, and then they expected a computer and its sensers to work properly in an environment where the sensor readings go down to 0.01 volts as a significant data value, in a poorly grounded system.

Lastly they did not use large enough ground wire gauges.

The key think is to add a chassis ground directly to the battery, and to have good clean tight connector and wire on the end of all the ground wire cables and good clean tight connections between the wire connector terminations and the frame, block, head and negative battery post. With all that done a little further improvement is made by increasing the wire gauge size for the grounds. But if the connections are not kept tight and clean, it won't matter how big the wire is!

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Perhaps. But, doesn't engine oil conduct some small amount of electricity? It's not actually designed as an electrical insulator per se (oil-cooled transformers & electronics don't use regular engine oil...) so the effects would seem to become unpredictable. This goes toward spurious signals - mainly "leakage" from the ground and a slight "floating ground" that can cause headaches.

Of course, it also didn't help that the contact area between the ground strap and the chassis amounts to the screw threads - maybe. The rest of the surface is painted, and I think the hole got squirted as well. Paint definitely doesn't conduct well!

And, adding the direct ground from the chassis to the battery is a good idea - which is why I offer it as an option (not everyone wants it, but I honestly think everyone should install it.) Of course, this means "done properly" - which does not mean just sticking the chassis end down with a sheetmetal screw. You need to strip the contact area down to bare metal and apply corrosion inhibitor to ensure good contact, else you may as well not bother in the first place.

We just checked my braided ground strap... looked fine. Then I remembered something from my old nautical days (yes, it was on the Mayflower) that "lines" usually wear from the inside out. I grabbed the ground strap and gave her a few twist and much to my surprise out came a ton of green corrosion ( maybe its magical fairy dust).
That strap will be replaced tomorrow with some 6AWG (4AWG if I have it and can get it in there) with soldered lugs.

5-90 said:

Perhaps. But, doesn't engine oil conduct some small amount of electricity? It's not actually designed as an electrical insulator per se (oil-cooled transformers & electronics don't use regular engine oil...) so the effects would seem to become unpredictable. This goes toward spurious signals - mainly "leakage" from the ground and a slight "floating ground" that can cause headaches.

Click to expand...

On the long stretch of wires between the crimp connectors on the ends you could soak the wires in anything you pleased, with no significant effect. The electrons are going to flow down hill, from the higher potential to the lower potential across the outer surface of each and every tiny wire. Does not matter if the wires are dirty or clean, it is the low conductivity copper they follow. THe more copper wires, the better, which is part of the reason your cables work better than the OEMs.

What does matter is the choke points, where there is only a small surface area for those electrons to move across, like a huge dance hall filled to capacity and then all of a sudden they all head for one small exit door. In this case the exit door, or choke point, is the actual contact points (surface area again!) where some of the wires at the ends make contact with some of the crimp connectors surface area.

Imagine 200 people per minute going in and out of one small door at each end of the dance hall. One inlet door and one outlet door, one way doors, and a room big enough for 10,000 people, but the dance hall currently only has 300 people. The bulk ground wire is the uncrowded dance hall. The doors are the crimp connectors on each end.

Then imagine someone starts a fire at each doorway, LOL. :flame:


The fire analogy at the doors is surface corrosion at the contact points between the wires at each end and the crimp connectors, and between the crimp connectors and the engine block, head and firewall contact surface.

Also note that the engine gets hot, like 190 to 230 F. Electrons don't like to travel through hot connections. The resistance goes up as the temperature increases. So trying to force them from a cool firewall through a 200 F iron head bolt on the head and through the small surface iron contact on the head, is like trying to piss on a bonfire!:laugh3:
:flame:

In summary, it's the terminations that matter the most, as they have the smallest contact surface area, and that is where the heat builds up, and keeping them clean and free of oxidation is the key to success. Green slime in the middle of a long multicore wire (assuming the green slime has not eaten through the wires!) has little effect on the ground path.

Lastly, the larger ground wires are needed to keep the ground wire back voltage as low as possible due the computer and its sensors being so ultra sensitive to as little as 0.01 volts of standing voltage on a ground wire. Head lights and brakes lights and turn signals toss a lot of electrons through the ground paths! But, you could put huge 0 gauge wire on the ground and it would be a waste if the crimp connectors were not solid, tight, and if the block, head and firewall connections were not bare, clean, unoxidized metal.

So, the bigger problem with the "open" ground strap is that it allows surface corrosion at the interface between separate conductors.

Is that what you're essentially saying, or am I missing something? I'm familiar with the idea of "conductivity being a surface phenomenon" (ever been in an airplane that was hit by lightning?) so this might be some small thing that I've either misunderstood or just missed entirely.

However, I'll stand by one assertion - an "open conductor" of any particular sort is a Bad Idea underhood. Too easy for it to get contaminated - by whatever means, and in whatever manner...

" So, the bigger problem with the "open" ground strap is that it allows surface corrosion at the interface between separate conductors."

Not exactly. But you are correct for the wires at or near the crimp on connectors!

What I am saying is that it's only a problem at the end of the wire where it makes physical contact with the mechanical crimp on connector. If that contact area between the outer wires and the connector gets corroded (which is accelerated by exposure to the elements under the hood) then you have a big problem. Thus the reason for insulating the connection area is to keep the elements out that accelerate corrosion.

You could make the point that if the wire itself is left bare, and only the terminals at the ends of the wire are sealed, that the green stuff (copper sulfate) can get into and under the sealed terminals at the wire ends through the exposed wires gaps by creeping along the wires surface, and therefore the entire wire should be insulated and sealed. But only to protect those crimped connectors at the ends! If the wire is 6 foot long I would not worry about insulating the middle 3 feet. But I would want the last 18"s or so well insulated. Probably depends on the geography. Here in Houston they never use road salt, so corrosion is more rare, except near the battery. Up north it might pay to insulate the hell out of the wires becuase of road salt, etc.

What I was trying to say is once the electrons start flowing through the separate wire threads, once they have gotten past the terminal crimp connector and are headed for the other end of a lonnnng wire, they don't care about the green slime between themselves and the other neighboring wires.

In other words 100 hundred thin wires bundled together in a full PVC jacket won't conduct any better than 100 wires bundled together and exposed to the elements, or 100 wires bundled together and dunked in oil, or green slime, although the 100 wires that are dunked in oil might be just a little bit more conductive because the oil might act as insulation for part of the area that is between each of the 100 wires because the oil would shield the electrons in one wire from seeing the nearby electrons in the next wire. Corrosion on the surface would do the same thing.

Think of it this way, take 100 wires (same size) in a tight wire mesh bundle, and then take those same 100 wires and insulate each one with a tiny film of PVC (to simulate the thin film of oil contamination effect) then compare the conductivity of the insulated bundle with the conductivity of the uninsulated bundle, and you will find out the multi insulated wire bundle (100 seperately insulated wires of the same size as the uninsulated bundle) will carry more current and has more conductivity.

Since the electrons repel each other in the same single thread of wire, they tend to get as far away from each other as possible until they reach the out surface of each thread of wire, then they see the neighboring wires electrons at any points of contact between the wires in a multicore wire bundle, and then they tend to avoid those contact points between the wires in the bundle, unless those contact points have stopped conducting and starting insulating due to corrosion, green slime, oil, or new PVC insulation a few molecules thick.

Does that make sense now?

I was also saying that once the electrons get past the end conectors into the bulk wire, they are less crowded, and therefore most of the resistance found in a ground cable (clean or badly corroded) is at the end connectors, between the wires and the end connectors, not in the rest of the bulk wire length.

You could compare the cables to a water pipe, where the end connectors are like the sharp 90 degree turns and the main wire is the pipe. In water pipe a 90 degree elbow has a pressure drop equal to about 100 feet of horizontal pipe (or something in that neighborhood, so don't quote me on that 100 ft), but you get the idea.

One other point I was trying to make, is that just like the metal fatigue we discussed about exhaust bolts and nuts, I think the OEM cale ends, crimped metal ends, are geting soft and loose under the thermal and physical stress they are exposed to, which is making the choke spot even worse with age, even without the corrosion. Therfore, larger heavy duty clamps (crimped ends on the wires), and extra large wire bundles will hold up longer!