Rough running renix

I have a 1988 Comanche with the 4.0. The truck has sat for about six years before I bought it and put it in the road. I am used to the 4.0 HO and the power they have. My renix is a dog, and I plan on swapping it out for a newer 4.0 at some point, but would like to get the winter out of it. It starts up and idles good. It goes down the road great, but it seems to stumble or skip a beat under load and then at idle afterwards. I have replaced the gas tank, fuel pump, and fuel injectors with all brand new parts. The plugs and wires look fairly new, but I will be honest and say I haven't checked the plugs.

Any thoughts or suggestions or is this just the renix blues? It has 116k on it and is a 2 wheel drive, if that matters.

Do it old school.

Do a spark plug check.

Do a compression check. wet and dry

Do a vacuum check.

×2
Add to that a leakdown test too. Have you added any additional grounds or inspected the connector at the firewall?

Like Oldman said, and maybe pull a plug and check the spark. Weak spark often causes a crappy idle and then again acts up at higher RPM's.

I use an old plug, open it up to around .060 and look a the spark, sharp narrow blue/white you can hear crack is good. A wide yellow that you can see splash on the electrode isn't good. Ohm your spark plug cables, make sure your cap is good, no crud in the towers.

Where the coil connects to the ignition module is a good spot to check, it is a dirt trap. Check the voltage at the larger yellow wire to your ignition module, that yellow wire is prone to a rather large line loss in voltage.

Could be your O2 sensor, if it bucks around 2200 RPM +/- while cruising or mild acceleration it may be a lazy O2 sensor.

My Renix idles really good, helicoil solid core wires, stock carbon core coil to cap wire, stock Champion plugs and a good TPS ground. I installed a relay, large yellow wire trips it, power comes directly from the starter relay main power lug to the ignition module.

Renix seems a little ignition sensitive, but once you get it right it works well.

Wipe the carbon dust out of the distributor cap, look for excessive wear.

Guys talk about how much better the HO is than the Renix, Renix have better grunt, HO has a few more horses at higher RPM. At the end of a quarter mile there is maybe a Jeep length difference.

First off, hang on to that beast and fix. Once fixed it has more power than any HO engine.

Start with a vacuum gauge (dirt cheap and great easy to use tool that will tell you so much) and use the online guides to see what the data means. Google "vehicle vacuum gauge diagnosis".

Check each spark plug, replace if needed, same for the plug wires, also the rotor and cap on the dizzy may need replacing. Spark plug gap? Color? Contamination? Take photos of each and number their location and locate a photo guide on line of spark plug condition diagnosis. COSTS nothing to do!!!! It will tell you if have any engine problems. With such low mileage I suspect you have a solid engine. If it ain't broke don't fix it.

Next the Vacuum gauge test may tell you at high rpm in park if you have a blocked exhaust from bad Cat-converter. IF the cat converter is bad/damaged it blocks exhaust and kills power.

https://www.google.com/search?q=eng...la:en-US:official&client=firefox-a&channel=sb

One high probability issue is a TPS and O2 sensor problem. Start by testing the TPS and O2 sensor ground wires, disconnect the 2 sensors and test the wiring harness ground wire to the battery negative post. It should be less than 1 ohm resistance, if higher fix it, it is a big part of your problem and is very common. Bad sensor grounds are the number one problem with Renix jeeps and are cheap and easy to fix!!!

Cruiser54's site has great details on the ground issues and fixes for Renix.

Then, test the TPS, or swap it out. The testing of the TPS can be tricky, very involved, but just needs patience and and ohm meter to test. I have a thread on it here called "The Renx Files" Google it. It has test data and my war story of how a bad TPS caused your exact problem and how nothing in the Jeep FSMs or online how to test data was aware of the problem till I found it and posted the details on that thread.

RenX files link
http://www.naxja.org/forum/showthread.php?t=905849

While you may need to do repairs, and should test the O2 sensor and wiring, it does not yet sound like your problem. But you should add it to test list, google my thread by searching "O2 sensor testing jeeps naxja"

O2 sensor tests Renix
http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test

Once you have this done, the Renix has an EGR valve that could be also sticking and causing part of your exact problem, but my money is on sensor grounds and the TPS sensor.

Go to cruiser54's site and get a copy of the Renix multi-port fuel injection manual on the sensors, ECU and controls. It is the bible for the Renix and great guide to every fuel injection vehicle made since then.

http://cruiser54.com/

Keep blow by details of your tests, photos and fixes and post them back up here as you go. The worlds Renix experts are right here. I have 3 of them One has 290,000 miles on it.

I might add that 99% of Renix problems are not the engine itself!!!!! Just dirty, loose grounds and worn out sensors and consumable parts like spark plugs, plug wires etc. Cheap easy stuff if you do the proper detective work.

Thank you guys for all of the great information. I will check out the normal trouble spots first and go from there.

Do Tips 1 through 5 on my website.

New plugs NGK, wires, cap and rotor.


HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.

HO only made more HP than Renix at higher RPMs and not a bit more torque. HO had a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?

It’s only a 4% horsepower increase…..

The whole 8HP was not mostly from the head, but from the bigger TB and better exhaust manifold.

Put a 60mm TB from www.strokedjeep.com on your present manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.

HO stands for Highly Overrated.
__________________

did the Comanche have the c101 connector? and check to make sure no one fiddled with the distributor.

90xj06 said:

did the Comanche have the c101 connector? and check to make sure no one fiddled with the distributor.

Click to expand...

87 to 88