hoopdaddy6

I recently bought a 1987 Cherokee Poineer 4.0 Cyl from a buddy at work. Before I bought it from him, he decided to saw off the exhaust pipes right before the catalytic converter. The cat, muffler, and pipes were badly rusted out. Since I have had it, it is idling fast, and burning waaaaaay too much fuel. Backfires when you shut it off. If I disconnect the vac line from MAP sensor, idle slows down a bit but still fast.

Also- this baby doesn't have a check engine light, or a port to pull codes from (without a DRBII scanner apprently). Renix?

I tuned it up (cap, rotor, wires, plugs, air filter, cleaned TB, seafoam, injector cleaner, new IAC, clean oil, radiator and tranny flush) and have barely driven it. It's my third vehicle just for recreational use.

I am guessing that the mileage problem is being caused by a failing o2 sensor. When I called the parts store to get a price on one, they said there might be 2, one behind the cat. So if there are two oxygen sensors, my idiot buddy chopped one off. I am also not seeing any wiring for one in that area.

In the case that there are, is there a way to bypass the second, or to install a new one into aftermarket pipes (wiring to ECM and all)?

okcjeeper

You should only have 1 O2 sensor in the down tube after the exhaust manifold but before the cat.

OnlyInMyXJ22

x2

Howler_GT

Being an 87, You have whats referrred to as a "Renix"

We have been blessed with several Renix-guys and One Renix Guru.

Have you replaced the hacked off exhaust?
New cat, muffler, and tailpipe.

ONE O2 sensor like OKC said.
Most guys at parts stores only know what the computer screeen tells them (At least MOST of them do.)

Removing the vac line to MAP sensor should cause the idle to fluctuate (up and down)
I would suspect that since its idling high, it MAY be your Throttle Position Sensor (TPS)
A Renix guy might want to chime in here. HINT...HINT..HINT.. this means YOU BLUEXJ)

5-90

One HEGO sensor in the collector. If you're working with a hacked-up exhaust and need to get bits made for it, may I suggest having a flexible coupling at the collector-to-downpipe joint? Only a few inches long, and it will save you header cracks (the XJ's rigid exhaust system means that failed/failing engine mounts will just about always take the header with them...)

Idle issues? Check the following:
MAP sensor line - the MAP sensor is mounted on the bottom of a bracket on the firewall, to the driver's side of the engine. The line is Nylon, and gets brittle and cracks with age (Strike One!) Also, the other end of the line - at the throttle body - is held in place with a rubber bung in a blind hole, and this sometimes works loose. Some RTV black on the bung going into the blind hole (not the one with the hose - the upper one) will cement the thing in place (Strike Two!)
Throttle Position Sensor. I can give the FSM procedure for adjusting it in a little while (I'm about to head out the door) if you can't find it - I know it's been posted before. I may have posted on my RENIXPower group as well (if I haven't, I should.) The function of the thing can also be tested - but that requires use of an analogue ohmmeter, not a DMM. Your TPS is on the front of your throttle body - if a manual, it has a single three-wire Weatherpack connecctor. If an auto, it has a three-wire and a four-wire (2x2) Weatherpack connector (since it reports to the TCU as well.)
Idle Air Controller - check to make sure it's not loose (it's the cannister next to the TPS on the front of your throttle body, with the single four-wire connector.) Might also be useful to remove it and clean the pintle and seat - the EGR system tends to crap everything up with carbon (I remove the throttle body and clean it on the bench every few years - acetone and an old toothbrush work well here.) Do not pull or push on the IAC pintle!
Vacuum Leak - common enough with side-draught inline sixes, due to the aluminum intake/iron exhaust combination and the length of the thing. I could go into the science why, but you'll have to ask - suffice it to say that the screws will unscrew over time. Never hurts to check torque - especially at the lower rear of the combination manifold (I'll usually find one or two loose back there - they don't get much airflow to keep them cool, so the effect of heat is exaggerated.) Torque to 19 pound-feet, and you'll find a 9/16" "flex" socket to come in handy (remove the airbox for better access.)
EGR Valve - it's stuck on the side of the intake plenum, near the throttle body. I've had the base gasket for the EGR start leaking as well sometimes - it passes fresh exhaust gas, which is rather hot. The gasket tends to burn through, causing an intake vacuum leak.

For a thorough check for vacuum leaks, have a can of carburettor cleaner handy. Start the engine dead cold (shut off for ~18 hours) and start fogging the carburettor cleaner around suspected leak sites (vacuum lines, throttle body base, manifold-to-head junction, vacuum trees, ...) If you see the fog get drawn in and hear the engine race, you've identified a leak - service as indicated.

A new vacuum line assembly can be had from NAPA under their Echlin house brand. I don't recall the part numbers (I've posted them on NAXJA,) but expect to spend about $50 for all three needed (two halves of the line assembly and the MAP sensor line.)

hoopdaddy6

Wow guys! Thanks so much for so much information and such quick replies. I am beginning to love this forum more and more.

I just found out that one of my mechanic buddies at work (supposedly) owns a DRBII scanner. The plan is to hook it up tomorrow and hopefully get some codes. So if OKC is right, I might not be in as deep as I thought.

I would really like to hear some imput from BLUEXJ (Renix expert). I don't understand why they would put so much equipment in a vehicle if it is nearly impossible to get diagnostic information out of it.

I have partially repaired the exhaust up till now. Like I said, I bought it chopped and it was LOOOOUUUD! So a bit of flex pipe, an e-bay muffler, and about 18 inches of pipe behind that, just to quiet it down. No cat. We don't have emmissions testing currently where I live. (Yes, I realize this is part of my mileage problem, but it shouldn't be this severe) The plan is to finish it off, but not until I finish with the lift (ordering 4.5" rough country the second I get my federal check.. any day now).

I don't think it is an issue with any vac lines leaking or cracked as I replaced them all with the rubber kind. Yes, I had diagrams from Chiltons. EGR feels like it moves in and out ok. I also already replaced the IAC to cure a stalling problem. As for the TPS, I would really appreciate further information on testing/adjusting. I only have a DMM, but I think my dad has an analogue one.

Let me tell you guys, this thing is getting terrible mileage. I mean about 100 miles to a tank, max! Also- I have inspected the entire fuel system for leaks. It smells like gas when it runs, but it's not leaking any. It doesn't help, that when I wrecked it a full gas can came open in the back and soaked into the carpet.. that took about a month sitting outside with windows and doors open to air out about 90%. So it's kinda hard to tell.

Sorry I'm kinda all over the place today. Really appreciate all of your help!

5-90

Nothin' wrong with RENIX - although Blue ain't the only RENIX Expert here (just ask him about me...)

You don't need fancy diagnostic equipment to sort through RENIX tho - a DMM will do all but about two of the tests that usually want doing, and the two tests you need an analogue meter for aren't done but once in three hundred times anyhow (at a guess.)

The DRB II will work, as will the MS1700 (haven't seen one of those yet) and the Snap-On MT2500 (with the base carts and the JEEP-1 adapter.) Since RENIX doesn't "store" or "throw" codes, what you get is realtime driveability data and sensor feedback - I've driven around in my RENIX rig with a borrowed MT2500 in the right seat, checking data as I go. Neat trick - I still need to get my paws on an MT2500 tho (for myself, I mean.)

I'd also like to get one because it looks like the easiest way to add a "breakout box" inline and try to rip apart the datastream - I'd like to do something akin to the old "Systems Sentry" that AMC did, but have a BASIC Stamp read RENIX realtime data and drive a display on the IP (probably where the clock module is now.) Just a blue-sky goal, but something akin to the "Driver Information Centre" I first saw on the Lincoln Mark VII.

For exhaust reconstruction, I usually use a catalytic converter spec'd for a Big Block Chevvy (it flows better) and a Walker Turbo II muffler (about $20-25,) which opens things up a bit and gives a nice note. I don't like quiet engines - I don't want "loud" - but I do like an engine that lets you know it's running without checking the gages. The AMC six on a open pipe sounds like a tractor with a thyroid problem, but an open exhaust mellows things out nicely.

Check out my RENIXPower group (groups.yahoo.com/group/RENIXPower) and, if I don't have the RENIX FI manual up there (I think someone upped it, but I'm not sure) then get it from Pirates of the Rubicon - they have a .pdf of it in their Tech section. Required reading for any RENIX Owner, and aspiring RENIX Tech.

Given the history I have with automotive controls (I go right back to the first GM/Delco HEI setups, the Ford DuraSparks, and the early Chrysler systems that were all so easy to blow up, right through OBD-I, into OBD-II - and I go back to plugs and points, even! Cut my teeth on 50's and 60's Corvettes, and 60's and 70's Camaros...) I can honestly say that I think I prefer RENIX over just about anything else, with OBD-II a close second. Then again, I'm used to doing my own thinking... I don't like OBD-I because there's no real standard to it (it was spec'd by CARB - when CARB spec'd OBD-II, SAE took over and standardised it,) and OBD-II gives you what is - at best! - a "where to look" when you have a failure. I've come across many OBD-II faults where it indicated that a sensor wanted replacing, and ended up fixing the wiring instead (oftimes after someone else couldn't figure it out, and replaced the sensor twice already. At $100 a throw.)

There are also other fori out there you may find useful - JeepForum, CherokeeTalk, and NAXJA (and, if you decide to get adventurous and get into some heavy engine mods, JeepStrokers.) If you decide to register at Pirate tho, I advise you to either make extensive use of the search function before you ask anything, or put on your nuke-proof underwears if you do not. Them bastards have no mercy on anyone (cf: "Wenzel." That's a name that became a household word after Pirate got hold of that kid, you can probably find his entry in UrbanDictionary or EncyclopediaDramatica... Pirate is almost as bad as /b/ on 4chan!)

Oh - bear in mind that, even if there isn't emissions testing where you live (you lucky pup! I grew up in IN, we didn't have that nonsense either...) you are still required to have a cat under EPA regs. Considering that it's easy enough to not lose performance with a cat - and, in some cases, gain performance (Random Technologies products come to mind,) there's really no reason to not have one. NB: If you have a stick shift, make sure you can split your exhaust system easily right around the crossmember. In fact, the midships hanger had two studs on it that served to help fasten a flange on the front of the OEM cat, and having the ability to "break" the system there makes it so much easier to change your clutch... Let's not give the Greeny Lunatic Fringe any more reason to go after us, hm? We have enough trouble with them nutjobs as it is...

radio flyer

Wealth of information in your response.. It's nice to see you share your vast pool of experience with everyone on this forum. From myself and i would think many others--Thank You!

5-90

What's the point in everything I've learned if I don't do something with it? That's why I'm working on my second and third books, first one's out (through me so far,) fourth one's an idea (hasn't crystallised yet,) and if response to my writing keeps going in the direction it has, I'll probably keep doing it!

Howler_GT

Sorry there 5-90, it totally slipped my mind about your Renix expertise.

5-90

No worries - I haven't been terribly vocal here. Just like in real life, I can be easy to miss. (6'3", 260#, and invisible. I had a Japanese girlfriend who called it the "Ninja Mind Hide" when she was all over the apartment looking for me, walked past me lying on the couch with a book for the fifth time, and almost jumped out of her skin when I asked her what she was looking for...)

hoopdaddy6

Man, u guys are a ton of help!

Still going back and forth with my buddy who (still only supposedly) has the DRBII scan tool.

The benifit I see in getting it scanned, is that there may be more issues going on that I am not even aware of.

I did find instructions in my Chiltons manual for manually testing the O2 sensor today. Plan on doing that tomorrow. I will keep you all updated on my findings.

5-90

Note that the rest really only checks the heater circuit - not the function of the sensor proper...

UserID6095

We need like a bonus point system... That was awesome 5-90!

hoopdaddy6

Ok, so I got sick of waiting so I went ahead and decided to replace the O2 sensor. It looked pretty bad when I took it out (coated thick with black, and pretty badly burnt).

No immediate effect (I figured). She's still got some issues to work out. I just hope the O2 sensor will help with the gas mileage issues some.

Maybe while I have some of you Renix guys attentions, you can help me out here.

I think it is still idling a bit fast currently (no tach), although not too bad. However, the vac line to the map sensor is still not hooked up. When I hook it up, the idle shoots right up to (my guess) about 3000 RPMs. As I mentioned before, as far as I know the vac lines involving egr, air box, tb, map, etc is all new and installed correctly. I wonder if my buddy might have unknowingly disconnected it, then somehow adjusted timing and idle accordingly to compensate? Could that even be a possibility?

A couple more things.. it idles somewhat irratically. (I think) This might be normal, but when idling the speed periodically picks up for a few seconds, then drops back down. What causes this, and is it normal? Here is a sound clip:http://www.mediafire.com/?xktfzdj9vle You can barely make it out at around :30, and about :55. Quality sucks bad, I know.. recorded it with my cell phone.

Secondly, I noticed that where the vac line plugs into the TB, there are two holes. All I have ever seen with mine, is the one line coming out of it to map sensor. I didn't realize there were two holes. Should the top one be left vacant? Or am I missing something here?

Again guys, thanks for all the help. This is all over my head.