Salden Hund

Sorry this is a second run, but I lacked info and didn't get what I was looking for.

1990 cherokee loredo. 4.2 iL 6, failed smog here in CA. My numbers are:
15mph (CO2%) Meas : 13.5, (HC) Max 123; Gp 310; Meas 185,
(CO%) Max .73; Gp 2.03; Meas 2.35;
(NO%) Max 711; Gp 1800; meas 380

25mph (CO2%) Meas : 13.3, (HC) Max 103; Gp 260; Meas 196,
(CO%) Max .93; Gp 2.23; Meas 2.68;
(NO%) Max 613; Gp 1600; Meas 400

I've replaced the O2 sensor and cleaned the IAC ( it seemed stuck in the down position; It didn't move in or out when I cleaned) and have ordered a 100$ cat out of desperation (if that doesn't fix it at least it's somethin new right?!). I'm at a total loss and I'd like to fix her so I can get the free smog before the 12th of March. I've read similar posts but can't seem to narrow it down.

She idles fine, and starts up great. I'm told she is running too rich also. I'm gonna try the "run her hot on good gas " en route to smog. But I don't want a quick fix. I've also ran sea foam thru crankcase, gas, An vacum line. And for goodness sakes, please don't carry on off topic convo's here. That sh$&3s annoying.

Thanks for the looks guys/gals!

Salden Hund

D; please helppp

cruiser54

Make sure you have no vacuum leaks in the line from the throttle body to the MAP sensor and that your intake manifold bolts aren't loosening up. Refresh all your grounds per the following write-up as they can let the eCU get false readings from numerous sensors.


Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at


www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 12-04-2012

highmileage

To much heat drives up the NOX and HCs'. Something is telling the system to run rich at the tail pipe. You've already worked backwards for the cat and O2. Have you checked the exhaust manifold for cracks? The cracks will allow air in front of the O2 sensor and it will pick up on the extra air and add fuel. The cracks are usually small and narrow hard to see unless it's off or you know where to look and won't make the familiar putt-putt noise most manifolds make. also the extra air in the system adds heat and can help cook off the cat or keep it to cool to do its job.
Where are you located in Cali could be close enough to meet up and take a look?

Salden Hund

Renix; Fret not, I've read your posts numerous times. Thank you for looking. I will be doing the ground replacements today, or this weekend. After that, Not sure. But what about the IAC???? It didn't move free like I've seen in some videos. Should it?

Highmileage; Thats a good place to look, thanks for the insight!!! whats a good way to determine cracks? when I ran the seafoam thru, I noticed white/gray smoke out the pipe, but nothing unusual in the engine bay. Is there a special way to check, or just take a fine tooth combe over it? If indeed it is cracked, is the replacement easy to do? And should i just replace the whole pipe form manifold to cat?

Its disheartening because It drives fine, idles fine... occasionally on start up, i mean rarely, she'll idle really hi. restarting or reving higher usually drops it back to normal. I've been told it may be the ...(idler sensor... throttle sensor?).

Thank you for the input.

highmileage

If you got no smoke in the engine bay exhaust manifold should be okay, yeah a fine tooth comb is close because it cracks way up by the flange and by the welds makes cracks hard to see. No need to replace that much just the manifold, pending on how easy you are with a wrench dictates the removal/install difficulty. The IAC motor when pulled out will extend on its own(I believe) and has to be gingerly pushed back in before install, it will put up some resistance. The high idle can be loose intake/exhaust bolts(the back ones like to back out), MAP sensor not picking up quick enough, or the TPS.
Looking at your numbers a few more times... the CAT and a vac leak small one, the HC and NO #s' are close.
Do you know what injectors are on your 4.0? the wrong ones can throw a curve?

Salden Hund

Do you mean the make of I jectors? Idk, ill scout this weekend. I'm going to pick up some new grounding this weekend, check for cracks and locate those screws. Hopefully it will be my solution. Will keep posted!! Thanks

Salden Hund

Worth of note: Never drive without the braided cable, or equivalent, removed. Startup and operation was really weird. Light issues, nothing worked ect. Just a little scarry, but I thouroughly cleaned it and installed another 4" from same firewall placement to the top of the intake mani.

cruiser54

What's that mean?

whowey

The way I read that... He is saying don't run with the ground strap removed. It very predictably ran wierdly for him, when he tried it.

cruiser54

Makes sense to me. That ground strap was insufficient to begin with. Why use less than that?

DFlintstone

Don't take that MAP tube lightly, it's supper crucial. My (same) tube is supper brittle, cracks easily. Any flaw or blockage and you are sunk.

AC or Platinum plugs might be a problem. Can't go wrong with Champion Copper, and always check the gap is .035.

highmileage

The make of the inj. does not matter but the flow rate does. The ones that you should have are a 19 to 21lb per hour rate of flow at some electric something, if they are a higher pressure it changes fuel stuff.... there is a thread somewhere here in forum with the #s' you need to reference.
I've seen it, it exists.

DFlintstone

I guess our Renix came with 18.6 Lb/hr injectors. I didn't find that in an FSM though. I Did verify and see 16 Ohm's though on the Stock Simmons Deka. We run at lower pressure, 31 to 39 Lbs, with the line off the regulator. There's a number of "suitable" 19# with the improved 4 hole design, as opposed to the OEM one hole design, but they don't all have the slot for the clip that holds them on the rail. The EV-1 plug seems pretty common on older injectors..I really don't know there. It's what we have anyway. Oh, and a tad under 2-7/8 inches long.

Is the color on the plugs even? Double check that map tube?

Bosch injector info in post 11 here>> https://www.cherokeeforum.com/f2/199...r-swap-163105/

highmileage

The pressures in the "great info threads" about halfway down the page with a part #, but not the ohms.