Bought a 4.0HO swapped XJ(NOx problems)

I just bought a new(to me) cherokee tonight to replace my dying one and it has a 4.0HO swapped in, which I am rather excited about ..

Looking it over it is an entire 4.0HO but retains the renix exhaust manifold and exhaust.

The vehicle has failed for high NOx emissions 1395(observed)/1115 (max)ppm.

I know the HO does not use an EGR valve so how does it reduce NOx. The toyota VVT-i does it with valve timing.. does the HO retard the ignition timing?

I was planning on just putting on a new fresh catalytic converter and run it through emissions and then putting the old one back on and save the cat for next year and so on..

Mostly cam timing, which allows a small amount of exhaust reversion (fulfulling the function of the deleted EGR valve.)

Granted, an engine could be properly tuned for both an efficiency increase and emissions reduction, but apparently the EPA (and your Canadian analogue) don't know that.

I know the RENIX and first-gen HO cams are the same, but I think ChryCo installed it a bit differently (advanced, I think) for reversion reasons as well.

If you say it retains the RENIX intake and exhaust manifolds, you should have provisions for the EGR valve, and I'd want to check the casting number on the block and head to make sure - a RENIX head will be a #2686, and a first-gen HO head will be #7120. I'm thinking the head casting number is on the driver's side, outside the valve cover, between #3 and #4 cylinders, but check around here to be sure.

I do know that it would take a fair amount of work to adapt the RENIX manifolds to the HO head (reverse of the HO manifold to the RENIX head,) because the intake ports were raised, I believe, 5/8" with the introduction of the #7120 head in 1991.

5-90

If you did use the renix intake and the renix exhaust manifold, you should be able to heat the EGR tube and bend it down to meet up with the exhaust manifold.

Also try a general tune-up on the vehicle. Make sure the plugs are clean and gapped correctly. Good wires etc.

I would try the tune up before I tried an expensive catalytic converter.

Your are not that far off. High NOx is a lean condition. Build a MAP adjuster and just turn the voltage up until you pass. I had a similar problema couple of years ago, although it was witht he original engine. My mod was the Borla exhaust header et al. + maybe injector deterioration. 5.45v worked for me.

A Mechanic (17years as DC Jeep Mechanic) put a HO head on his Renix without a problem. It was close, but there was a small overlap such that it did not leak.

Sounds like the EGR system is not hooked up. Look to see if there is a tube running from the intake manifold to the exhuast manifold. If not then you may need to adapt some stuff or go to 91-95 wiring system. If they put on an HO intake manifold, then you might have to adapt a Renix intake manifold or cut and weld the EGR boss from an Renix intake to the HO intake.
Tom

You may want to try some Sea Foam.. It claims on the bottle that it helps vehicles pass emmisions tests. It's a cheap option, about $6.50

It does not have a renix intake..

Everything is HO except the exhaust..

Before I take it through aircare I will be putting in a new O2 sensor, tuneup, new catalytic converter..

BUT... I have a thought... do emissions tests allow a higher amount of NOx for 1991+ cherokees than the 1990 and prior?

The failed result lists 1989 the year of the body..

No. Emissions failure threshholds typically go down as the vehicle gets newer...

5-90

I found the standards for the test and 1989 amd 1991 are the same for NOx..

I will be trying the adjustable MAP sensor and a new O2 sensor..

The entire exhaust is new so a new cat isnt needed.. HC and CO are sooo low richening it up a bit shouldnt be too bad..

I am a Emissions Inspector. Nox failure can usually be cured a few ways. Check your timing, retarding it will lower the Nox. Make sure that the engine is not running hot. The correct thermostat and antifreze mixture. Also since there isno EGR on the HO the catalytic convertor. O2 sensor will help with HC & CO not the Nox as will most other tune up parts.

Okay so since it had the factory 4.0 NON HO exhaust manifold...does that mean you could bolt up a factory NON HO intake to a HO head?

Yes, with a little work. It's the reverse of the HO intake on RENIX head swap...

5-90

I have been all over this site searching high and low....and from 5-90's post's its gunna be better to swap the intake and all with the head....Is there a difference in head gaskets?

The Renix (non-HO) intake has lower intake ports. Some people weld them up and recut them to adapt to the HO head. You could cut out the EGR boss from a Renix intake manifold and weld it into the HO intake manifold. Also, the exhaust ports are in basically the same location throughout the years. So swapping exhaust manifolds isn't that much of a problem, unless you try and swap the latter cast iron exhaust manifolds.
Tom