renix fixing itself, any input? (long post)

I have an 89 laredo 4x4 with 4.0 i bought in december of last year. It started having bucking problems shortly after purchase. I tested and replaced the following: o2 sensor (precat), muffler (3 times due to detonation), air charge sensor (autozone), plugs, wires, rotor, air filter, oil change, I recalibrated the crankshaft position sensor and changed the fuel pump and mask.
Here's the problem (or maybe lack thereof). Everytime it started running bad, i.e., the bucking and / or backfiring throught the exhaust, I found one of the above to be bad. I would change a part such as the o2 sensor or air sensor and it would run great for about a week or so and than act up and I would start hitting it with the multi-meter again and find something else reading bad. When I first bought it, I asked the guy I bought it from if the battery was tired because of the slow crank time (like four cranks or so) and he said maybe. The last thing I found messed up, was the crankshaft position sensor connector was corroded. I bought some corrosion cleaner and put that on. It ran okay for a few days and the same thing. Something I need to mention, every time i changed something, I would remove the battery cable and let it set for like a day and then put it back on to "reset" the computer. I finally put that silicone spark plug sealer on over the cps connector. I think i'm in pretty good shape now but it took like a week to start to run well.
It used to crank like five or six times to get going, I am now finding when it is cold it will start right up with hardly any cranking, just like any other vehicle. When it is warmed up, it takes a few cranks or I have this new trick. When I start to crank it, if I let right off the key it may start right up. Not all the time, just somewhere around half the time.
I've checked the compression and the fuel pressure and all is great, especially considering the year (though I must say the speedo only reads 96000 miles). It has been over a week now and the rig started running better and better, no backfire and no bucking, I just keep waiting for it to start messing up again. Anybody have an experience like this with their renix?
Just to go on a little further, I made the mistake of going to the local muffler shop that has cheap oil changes to take care of that. They reccomended 5w30. It now sounds like a sewing machine. I changed it myself with 10w30 but it still sounds clackity, like the lifters are not oiled well. any suggestions?
At any rate, it seems to run fine now other than slow starts when it warms up and the occasional stall when it is cold, if i wait for a minute, it runs fine cold. The air blows ice cold (pretty awesome for a 17 year old vehicle) and the 4x4 works great in the winter, though i have to swing the wheel back and forth to put it in 2wheel (i can live with that, probably need to change the fluid).
I am sold on the renix system because i don't need a computer to troubleshoot, just my meter and a lot of time. I am sure if i went to a stealership i would have pumped a ton of money into my rig.
thanks for any of you having the patience to read this long post as well as any suggestions on keeping my jeep going for the next ten years or so!

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If you search for RENIX here, you'll find LOADS of information. In fact, we recently hashed around (again...) why RENIX has such long crank times (although, if you watch the crank pully while you're cranking, it's not usually "five or six" times around - closer to three. The engine has to start moving from not, and that takes a second...)

Also, you don't have "precat" and "postcat" HEGO sensors on RENIX, nor do you have a CEL/MIL to deal with. The RENIX system is "pre-OBD," and therefore not entirely subject to the same rules (which I always get SO damn tired of telling the smog guys around here - you'd think they'd know that, after the third or fourth time I tell them...)

With five RENIX rigs (currently,) I guess I've learned a thing or two about the system, and you're certainly in the right place to ask! RENIX was only used on the XJ/MJ from 1984 to 1990, except for the XJ/MJ V6 (used the GM V6-60 2.8L, 1984 to 1986. OBD-I GM control electronics) and the Renault I4 Turbo Diesel (don't know what it used offhand...)

The CPS sensor connector may be rebuilt (using parts found in the HELP! section at the local,) or just replace it outright if it's got over 150K or so on it. You can't use the later version (HO/OBD) to replace the RENIX CPS - the sensor works differently. Also, if you check around here, you should still be able to find a post where I describe how to "notch" the CPS bracket so that you don't have to pull the bolts off to change it anymore - just loosen them.

There was also a TSB on "Correcting a Weak CPS Signal" and wiring it directly into the ECU - there should be a copy online somewhere (I haven't had to do it yet, and I'm not sure where my copy is.)

The "long start" for RENIX, as I may have mentioned (it's getting late, and I'm getting drunk...) has been covered as recently as to-day, so search and see if you can find the post. I'm sure you'll find it informational. Also, as far as the "mains upgrade" I mentioned, there's a link to my site in my sig (below.)

If you find my post and have trouble understanding anything, feel free to ask me to explain it. To-morrow. When I've got a lower BAC than I do now (damn, but it's been a frustrating day...)

Meanwhile, welcome aboard! I'm one of the oddballs around here that actually prefers RENIX over the later OBD/HO systems - but I came up troubleshooting pre-electronic vehicles, and I seem to be an increasingly rare animal - a mechanic who can actually do his own troubleshooting...

5-90

semi off topic but may be related;
I had a problem with my motor shutting down for no reason/sputtering, being a pita, couldnt track it down to anything, but only did it when it was warm.

long story short, one time when I was diagnosing my problem for the 3000th time, I happened to put my hand on the main injector harness, and it died, so I tracked it down to broken wires in the harness, under a duct tape factory splice... it was broken but would make contact when it was cold and then the wires would become more flexible from the heat and the connection would void.

yah hows that for a pointless run on story

I was getting some violent bucking that would occur once in a while, then not happen for a few days. I started to notice that it would happen around 30-35 MPH. Above or below it was fine. I tried checking my throttle position sensor with a digital meter, but didn't see any drop off. Later I found a post, by 5-90 I think, where it says an analog meter is better for that particular test. Anyway, before I read that,I had already swapped in another TPS I had from the U-PULL-It. So far it has been running smooth throughout the entire throttle range.
Curiosity set in and I had to cut open the old TPS. Inside is a rolled piece of what looks like photographic negative, with 4 traces of resistance material printed around it. In the center is a rotating shaft with 4 pickup wipers made up of 3 tiny fingers on each. I can see where some of the resistance material is worn away at one spot,and I'm pretty sure the fingers have lost some of their tension. The whole unit is sealed from outside elements, but now I can see how normal wear will take it's toll on these sensors. I would like to post a picture of all this,but I don't know if I can on this forum.

creeperjeep said:

semi off topic but may be related;
I had a problem with my motor shutting down for no reason/sputtering, being a pita, couldnt track it down to anything, but only did it when it was warm.

long story short, one time when I was diagnosing my problem for the 3000th time, I happened to put my hand on the main injector harness, and it died, so I tracked it down to broken wires in the harness, under a duct tape factory splice... it was broken but would make contact when it was cold and then the wires would become more flexible from the heat and the connection would void.

yah hows that for a pointless run on story

Click to expand...

I had the same problem on my 87 - floating injector grounds. They're wired up on a common ground and individually switched power leads.

Another fairly common problem, but a little more random, is that the CPS wiring can slip out of it's "retaining clip" on the backside of the cylinder head, and rest against the exhaust header. Obviously, this isn't good for insulation, and you'll end up shorting the leads on the header pipe. Happens at totally random intervals, can solve itself, and can't be found without shining a light down the backside of the engine and looking (if you don't see the fault in the wiring, you should see melted insulation on the #6 eshaust tube.)

The CPS harness can be spliced and restored with any convenient wiring - last time, I use a bit of 18/2 SJOOW that I had lying about from another project (the sensor was a month old - no point in replacing it!)

5-90