The RenX Files: High idle problems

Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion. If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.
 
Actually it was a lot more fun then just bad grounds. In the final analysis, regarding the high idle and low power problem, I had multiple gremlins on board. Other than my own stupid mistakes (like reconnecting the TPS and O2 sensors backwards to their wiring harnesses which caused a cyclic idle speed) and a IAT sensor (Intake Air Temperature) sensor that died along the way (caused Major cold start problems each morning in the winter), oh and finding out that the O2 sensor and CTS were not even connected in the early days when I bought it,......, the last nearly permanent fix to my random, high idle problem was permanently fixed when I had all, I mean ALL, Oh and did I say ALL, the ground wires fixed!!!!

Then my last problem, low power, and odd shifting speeds for the tranny, was solved with a new TPS. Took me two years to figure that one out! Also the replacment TPS solved the start up, 2 to 5 second high idle, which everyone says is normal! Mine is no longer normal, it goes straight to 750 rpm or at most 900 rpm idle right away, instead of 1500 for a few seconds before it drops to 750 rpm.

Sorry, but I have not, and will not be testing the 12 volt TCU fix I just did until I have a chance (dry weather needed) to replace my A/C expansion valve and recharge the A/C. Currently driving my very COLD A/C is working now, deisel jeep. Just too Dang hot and humid right now!!! I actually just finished installing the TCU memory (D-14 pin) power switch on the dash on it last night between bouts of rain here. I still need to check the B-7 pin on my ECU to see if it has the same problem the TCU D-14 pin had. I am guessing it will take a few weeks, and a few tanks of gas to have reliable, postable data on this, unless something unexpected suddenly happens first.

mikeforte said:
Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion.

Obiwan taught me well indeed. LOL. :yelclap:

Thanks for the compliment. party1:

Actually 5-90, 8mud, langer1, lawsoncl, oldman, and half a dozen others I can't think of at the moment, here helped me get up to speed early on. I originally started this thread as a way to keep myself straight as to what I had done, and tried and in what order, and with what results as well as a place for the experts to see what I already had done and tried all in one place.

After months of sorting through one of these multiple problem beasts it is too easy to forget what you tried, when and under what circumstances you tried it, etc.

Now it has turned into what I think is going to be one of the best Renix trouble shooting threads here.

Once the FSM troubleshooting guide falls short, I have always had a nack for being able to open up, figure out, and fix what I call black boxes. Runs in the family here.... Not afraid to go beyond the FSM when it runs out of good info and develop my own tests and procedures. Been doing that sort of thing for a long time, and back in the 90's I went back to college and learned how to write well and fast so I got good at documenting what I've done.......Anyway, I got so much great help here when I first I signed up, I decided to join in and do the same.

If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.
Click to expand...
 
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i wish this thread was a little more condensed. i hae a renix and i want to solve some of these tell tale problems. The only problem with that is after reading about 4 or 5 responses the words just go in one eye and out the other. i usually find that the last few posts i read didnt register in my mind. that most likley has to do with the amount of self induced smoke in my lungs.......(hehehe)
just the same, i cant pay attention long enough to make 9 pages of this make sense. till then i will just keep fixing stuff.
Tomarrow....a timing set. OOOHH!!! loads of fun huh?
 
For practice reading (and comprehension) you could try the AW4 FSM. As I recall it is much less boring (:rolleyes:) and only something like 125 pages short, LOL.:rolleyes:

Unfortunatly this is along thread, but I spent 2 years degremlinizing this Renix beast, so 9 pages ain't that bad. Perhaps one of these days 5-90 and I will get board and make a condensed visual trouble shooting guide for the Renix.

MountainRhino said:
i wish this thread was a little more condensed. I have a renix and i want to solve some of these tell tale problems. The only problem with that is after reading about 4 or 5 responses the words just go in one eye and out the other. i usually find that the last few posts i read didnt register in my mind. that most likley has to do with the amount of self induced smoke in my lungs.......(hehehe)
just the same, i cant pay attention long enough to make 9 pages of this make sense. till then i will just keep fixing stuff.
Tomarrow....a timing set. OOOHH!!! loads of fun huh?
Click to expand...
 
I have had a low idle at start up and high idle when hot problem for over two years now! Have tryed evey tip posted on this site for renix equiped XJ's and still have the problem?
 
I gave it a short test drive today. It is working perfectly. Drives like at bat out of hell.

O to 60 in about 8 seconds now, quite a change from the 0 to 55 (top end) in 2 minutes that I got when I bought it two years ago.

The real test will be gas mileage now, that will take some time to get enough miles to see how that changed.


mikeforte said:
Ecomike,
So after all your preaching about grounds it turns out the majority of your problems were ground related. How is that dead 12v pin and switch to your TCU working? Did you have a chance to get any data on the TCUs response to haveing 12v again? Mileage?
Thanks for all your work on Renix engines and your posts here and elsewhere. You and 5-90 are the Renix gurus in my opinion. If you two should be absent an answer you dive in deep enough that is so far above my head as to impress me, which is difficult to do.
Keep up the good work.
Click to expand...
 
zero to 60 in about 8 seconds. Ditto! Sounds like that's about best you can hope for stock with 176,000 miles?? (mine)
My zero to 60 problem was my CPS, engine and tach would cut out at about 2800 rpm consistantly.
I am happy with mine now.
Just thought I'd mention here what I had found and posted in another TPS thread.
If you leave the key on for about five minutes without engine running the ECU kills the 5 volts to the TPS and you must re-initialize to continue with adjustments....
I did see some mention of this in this thread but am repeating it as adjustment procedure requires the 5 volts to be there.
 
OK I have a idle problem still. I have a 1986 2.5L TBI Renix ECU. The set up is different from later 2.5L Renix and the same as YJ 2.5L TBI Renis models. I have checked and replaced my CTS. My MAT and MAP sensors test to oem spec. I replaced all my vacuum lines (at least all I could find) except the stubs by the throttle body. I also tested and replaced my ISA. I tightened the manifold bolts as well. After all this my idle was still at around 1100-1200 rpm. I had after fire and dieseling problems during this whole time.

I then pulled off the throttle body to replace the little stub vacuum lines and reseal the throttle body. This brought my idle down to 800-900 rpm and solved the dieseling and after fire problems. I discovered the severe vacuum leak while putting sea foam through the PCV which was able to drip out at the stub vacuum connections at the throttle body. I was glad to see the idle be consistently below 1000 rpm and the engine runs a lot smoother and quieter.

800-900 rpm idle still seems high and after reading this thread my attention was brought to the TPS. Well it was barely out of spec and I adjusted it back in and it made no noticeable change to the idle.

What is the correct idle for the Renix 2.5L? I have a FSM and I cannot find the correct warm idle speed for the 2.5L TBI. The old carbureted 2.5L idle which I can find is 700 rpm. It seems that I have gone through everything but my idle is still high. Where have I yet to check? Any and all help with this PITA problem would be greatly appreciated. Thanks in advance.
 
The highest idle speed Haynes lists for the 2.5 L is 750 rpm so you are getting very close.

Have you gone through and verified all the sensor gound wires to be less than 1 ohm to the battery negative post? Also have you disconnected the battery for say 5 minutes to clear the Renix memory, and then restarted it to see if the idle drops?



tgoff said:
OK I have a idle problem still. I have a 1986 2.5L TBI Renix ECU. The set up is different from later 2.5L Renix and the same as YJ 2.5L TBI Renis models. I have checked and replaced my CTS. My MAT and MAP sensors test to oem spec. I replaced all my vacuum lines (at least all I could find) except the stubs by the throttle body. I also tested and replaced my ISA. I tightened the manifold bolts as well. After all this my idle was still at around 1100-1200 rpm. I had after fire and dieseling problems during this whole time.

I then pulled off the throttle body to replace the little stub vacuum lines and reseal the throttle body. This brought my idle down to 800-900 rpm and solved the dieseling and after fire problems. I discovered the severe vacuum leak while putting sea foam through the PCV which was able to drip out at the stub vacuum connections at the throttle body. I was glad to see the idle be consistently below 1000 rpm and the engine runs a lot smoother and quieter.

800-900 rpm idle still seems high and after reading this thread my attention was brought to the TPS. Well it was barely out of spec and I adjusted it back in and it made no noticeable change to the idle.

What is the correct idle for the Renix 2.5L? I have a FSM and I cannot find the correct warm idle speed for the 2.5L TBI. The old carbureted 2.5L idle which I can find is 700 rpm. It seems that I have gone through everything but my idle is still high. Where have I yet to check? Any and all help with this PITA problem would be greatly appreciated. Thanks in advance.
Click to expand...
 
I reset the battery after the TPS adjustment and nothing changed. This weekend I am going to thoroughly clean the grounds and recheck my TPS and hopefully that will do the trick but aside from the slightly high idle it is running very nice.

I should have fixed that throttle body vacuum leak as soon as I saw it and not put it off for almost a year but time seems to be my limiting factor during the school year. I really can't wait to finish and start making some money.
 
We call those ROUNDTOITS.

Meaning, I will do it, when i get a round to it.

LOL

Enjoy school while it lasts, someday you will miss it. :read:



tgoff said:
I reset the battery after the TPS adjustment and nothing changed. This weekend I am going to thoroughly clean the grounds and recheck my TPS and hopefully that will do the trick but aside from the slightly high idle it is running very nice.

I should have fixed that throttle body vacuum leak as soon as I saw it and not put it off for almost a year but time seems to be my limiting factor during the school year. I really can't wait to finish and start making some money.
Click to expand...
 
Just bought a 1990 Cherokee and guess what sort of problem its got? Go ahead, guess. I'll wait...

The info presented here is worth its weight in gold. Unfortunatly, I have no gold to hand out. Sorry.

Thank you guys for sharing.
 
Eliminator89 said:
Just bought a 1990 Cherokee and guess what sort of problem its got? Go ahead, guess. I'll wait...

The info presented here is worth its weight in gold. Unfortunatly, I have no gold to hand out. Sorry.

Thank you guys for sharing.
Click to expand...

Thats OK, we're not proud, even scrap copper and steel is worth money these days!:wave:
 
Speaking of copper, I just brought back about 100' of scrap 4/0 welding cable from some jobs in NE. Boss loved that! Wish I could have kept it for myself. Going back this week and will be bringing back some more (not as much though).
 
Getting sort of back on topic here, I got this beast (87, 4.0, Wagoneer, 248,000 miles) emission inspected in one of the tough Texas counties (Houston) earlier this week.

Here are the results:

High Speed: 2441 RPM
HC (ppm) was 8 and the limit was 220 to pass the test
CO % 0.04 and the pass limit was 1.2 %
CO2 % was 14.9
NOx was 0.00 ppm WOW!!!!! :eyes:
O2 % was 5.1


at 698 RPM (Idle) low speed results were:

HC (ppm) 28 with the pass limit being 220
CO % was 0.13 % with the pass limit being 1.20 %
CO2 was 14.7 %
O2 was 5.4 %
NOx once again was 0.00 PPM :eyes:

Not bad for a 20 year old jeep with 248,000 miles on it.

I also found out that since it is a 4x4 they do not run the stress dyno tests, seems the 4 x 4's are exempt for some reason, says they can not test them like they do 2 wheel drive cars.
 
90xj06 said:
clearly they do not check the nox. lol
Click to expand...

Not sure if you were joking or not. They do (did?) check the NOx.

Everthing except the engine under the hood is brand new (emissions and ECU wise, except the Renix ECU and CTS, or has less than 10,000 miles on it. The exhaust system, cat, pipe and muffler are brand new, less that 500 miles on them. New fuel injectors, MAP, O2 sensor, plugs, cap, rotor, wires, distributor, TPS, IAC, IAT, to name a few. The engine is running 20W50 dyno oil with one quart of Lucas oil additive and 87 octane Citgo gas.

Also I run a 165 F thermostat, but I had it up to 185 F running temp before I pulled into the inspection station.
 
EcoMike> If you are experiencing any or all of these symptoms. If the idle on your 4.0L Jeep motor is higher than 750-800 rpm or the idle is high and changes between 1000 to 1500 RPM after you first start the motor or stays at this RPM even after engine has reached normal operating temperature . Or when you first start the engine and it revs up to 2000 to 3000 RPM then drops SLOWELY to 1000 to 1500 RPM after 5 to 10 seconds. One thing that will also affect the RPM is the ambient Air temperature change and engine temperature changes in this condition. ANYWAY, HERE IS YOUR PROBLEM. FIX THIS AND PROBLEM GOES AWAY FOR A VERY LONG TIME. YOU HAVE A INTAKE MANIFOLD GASKET VACUUM LEAK! YOU CAN TRY RE-TORQUEING THE INTAKE BOLTS BUT THIS WILL NOT FIX THE LEAK ENTIRELY...TRUST ME ON THIS ONE. SEE, THE INTAKE MANIFOLDS ON THE 4.0L ENGINES ARE VERY PRONE TO WARPING AT THE NUMBER 6, 5, AND HALF OF #4-3 INTAKE RUNNERS. SO IF YOU TIGHTEN THE INTAKE BOLTS, ENGINE WILL RUN BETTER BUT NOT 100 PERCENT. YOU HAVE TO BUY A NEW OR GOOD USED INTAKE MANIFOLD OR IF YOU HAVE A VERY COMPITENT MACHINE SHOP IN YOUR NEIGHBORHOOD THEY CAN RESURFACE THE INTAKE MACHINED GASKET SURFACE AREA TO MAKE IT TRUE FLAT AGAIN. ALSO IF YOU OPT FOR A USED INTAKE MANIFOLD ALWAYS TAKE IT TO YOUR LOCAL MACHINE SHOP AND HAVE THEM CHECK FOR WARPAGE WITH A MACHINIST straight EDGE. AFTER YOU HAVE SOLVED THE WARPAGE PROPLEM THEN INSTALL A "NEW GASKET" AND RE CONNECT EVERYTING AND FIRE IT UP AND GO. (INTAKE MANIFOLD GASKET LEAK DOES NOT ALWAYS SHOW IT SELF ON THE 4.0L JEEP ENGINE WHEN YOU TEST FOR IT) SO TRUST ME WHEN I SAY WITH OUT A DOUBT THIS IS YOUR PROBLEM . I hope this helps and good luck and happy trails.
 
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