need help with diagnosis

Sorry if this post is quite long, just want to put up all info i can initially...

I am the third owner of a '93 4wd, 4.0, 5 spd, 170k, 30 front, 8.25 rear, 3" tomken lift, 235/75/15's, VENT WINDOWS!. I am no mechanic, but i love this dark green beauty, and want to learn and heal her up myself.

engine is underpowered. runs and idles good, but weak, with some white smoke. I know that the lift and slightly bigger rubber is going to slow me down a bit, but 4th gear is needed to maintain 65-70mph on any kind of hill. loaded fairly heavy west of denver on 70, top speed 35mph.
running 89 and shell high test, alternately.
passed emissions with flying colors
-the oil had not been changed as regularly as it should, but gets 10w30 every 3k now.
-new rotor, cap, button,wires and plugs(which show consistent but modest ash deposit after 3000mi, scraped off and reinstalled.)
-new o2 sensor.
-new fuel filter
-new air filter, venturi ripped out, throttle body cleaned. body and hose snug.
-seafoamed via the fuel pressure regulator vacuum line. most of a can and she would not die, had to shut it down to soak. ran a can with 5 gal fuel through fuel tank, 1/3 can in oil for afew days before last change.
with the seafoam substantial smoke appeared from exhaust manifold area, cannot visually locate obvious crack(or really hear anything to indicate the crack is more than hairline).
-pulled codes, got #36, air switch solenoid circuit(whatever that is)
-rear ccv valve is completely clogged, line is missing, vacuum port on intake is plugged.
-a bit of oil is blowing onto filter from ccv clean air line.
fuel pump "whining" after sustained interstate speeds.

i know that i have listed a few obvious problems(which will all be rectified), and these in combo could be the culprits(and you guys tell me "fix those things first, ya geek"):
or, there could be other things at hand you all could direct me to:
or, the engine is plain tired from neglect and it's time to really dig into dino's fine articles, as well as some other sources, and start strokin'.

pondering: coil, valve guide seals, fuel pump, plugged cat, really dirty injectors, vacuum leakage
tomorrow; fuel pressure test, compression test.

sorry for the rambling, but i am learning and really want to get this little burro straightened out. thanks in advance.

treedoc said:

loaded fairly heavy west of denver on 70, top speed 35mph.

Click to expand...

i think that says it all right there.. when i went west i expected to lose some power in the higher altitudes but i never imagined it would be that bad.. i thought i toasted my tranny...

stock gearing should still be pretty drivable with 235s on the highway, you already identified a few issues you know to fix so i wont go into those.. how is the fuel mileage? does it rev freely or does it seem like it is restricted? an old cat starting to go bad will start by killing top end revs. get a tech manual and look into that trouble code too.. i have an FSM in my pc but its being a bithc right now...

fuel milage is good 18-20mpg average. revs strong and free. i've got a 93 fsm manual in pdf, maybe it will explain more than haynes re the code.

My real concern is avoiding repacing the header, valve cover and ccv lines, and a bunch of other work to realize i simply have a beat engine. i am just hoping to shortcut to the right solution(s).

my last cherokee(why did i sell it for $200!?) was an 89 2wd 215k wrecked up beater that blew tons of oil, smoked more, and made the same climb at 75.

thanks for the quick response sidriptide.

A clogged catalytic converter will reduce power above idle to so little you can't measure it -- and still pass emissions! Been there, done that.

If it idles smoothly and seems to run okay up to 30 or 35 miles an hour, then falls flat on its face, my suggestion would be to replace the converter.

thanks eagle
getting up to speed no problem. probably not the cat.
heading out to do a compression check, and get a fuel pressure gauge.

The combination of 3" lift and 29" tires on a 5-speed 4.0 XJ with stock 3.07 axle gears would be enough to force you to downchange from 5th to 4th gear on all but the gentlest of highway inclines even if the engine was 100% healthy.
It does sound like your engine is underpowered though and the white smoke from the exhaust suggests that it's burning some oil, but not enough to produce excessive hydrocarbons to fail the emissions test. The obvious things to check would be:

1. Wet & dry compression on all cylinders. "Wet" numbers that are significantly higher than dry numbers indicate piston ring blowby.

2. Intake manifold vacuum. A clogged cat could cause a low vacuum and handicap performance.

3. Fuel pressure. It should be ~39psi with vacuum disconnected from the regulator and ~30psi with vacuum attached.

Let us know what you find.

White smoke from tailpipe is from moisture, black is from fuel and blue is from oil.
Need to get the CCV stuff working correclty as a first step. Probably means pulling the valve cover and cleaning all the crap out from under there, when you pull the cover have a shop vac in one hand and a plastic scraper tool in the other, work them in tandem, prevent any small chunks of sludge from falling into the return passages to the oil pan.
You need to get it back to spec in order to really isolate any problems you may be having.
My 98XJ 4.0L 5 speed with 3:07's, 235/75R15 BFG AT/KO's has no problem maintaining 70+ mph in 5th on any of the hills here in Pa, it has over 260,000mi. Thats fully loaded with ladders on safari rack, cases of network cable, all my tools and both my teenagers when they are working with me. Same thing when we take it to Cape Cod every summer on vacation which adds two or three bikes on the tailgate rack.

If you have no CCV vacuum line there will be no place for crankcase vapors to go except into the air cleaner. You really need to fix that, I think. Also if you ripped the venturi out of the air cleaner, you may not be getting the proper fuel tank venting. I would consider putting it back unless you can point to a true performance increase from removing it.

If you have white smoke, I'd suggest compression and coolant leakdown tests next. A blown head gasket could give you poor vacuum, white smoke, and bad peformance.

Fuel pressure is spot on, 31/39. Dry compression test: operating temp, throttle wide open, all plugs removed, fuel pump solenoid off, good ground to coil, seven revos each. 147-150 (some suspense with each cylinder, like watching the bingo balls come up with your numbers). This precludes a wet test, right? Plug gaps checked. Going to test pressure @ o2 sens, replace valve cover and ccv setup, and start poking a multi meter in stuff. Intake upgrade? KN?

Exhaust manifold crack. I know i've got one: all the inline 6's in my old fords have/had 'em too. haven't put an eyeball on it yet, but it is quiet. how much concern warranted there? if replace needed, what brand, Borla? and 2000 intake to go with it?

I'm losing oil somewhere, dipstick says so. quart every 500mi or so.Some weeping on seals, no real drips. is the ccv/valve issue causing me to blow oil down my valves to burn? should i consider a valve job? Can this be done alone, or like some have told me "need to do the whole thing, the bottom will just start failing".

Going back to Utah next month want to take this truck but, i'm not doing the amish horse and buggy bit again. I have to find some more power.

Thanks for all the great input. Out of town for a couple days, but i will update next week.

reread the responses you guy gave and will do a coolant leakdown test. haven't run across a how to so far, any tips?

What might be the best way to check intake vacuum? when i pull whatever line, vac "seems" strong.

there is not much left of the venturi to but back in, it was my first "mod", and involved a hacksaw blade.

anybody know what got TC#36, air switch solenoid circuit(per haynes), might be, fsm doesn't even list it.

For coolant leakdown, you need a radiator pressure tester. This is basically just an air pump with a gauge that attaches in place of the radiator cap. You pressurize the system and then wait to see where the pressure goes. You might be able to rent one of those.

ARe you sure about that code 36? You might want to reread it. It isn't listed as a regular Jeep code, and none of the other things listed under 36 for Chryslers are present on a 93 4.0. If it really is a 36, I'd suspect some wiring or connector issues. There seems to have been a run of 93's with problems in the fuel injection wiring harness. My stepson's 93 had a bad splice that gave me a long and expensive chase. If nothing else seems to help, you might want to start tracing all the wiring with an ohmmeter and see if there's a fault somewhere there. And don't underestimate the diagnostic value of a good old fashioned vacuum gauge. You can buy one and usually on the back of the package will be a nice concise guide on interpreting the readings. It's well worth the few bucks.

If your crankcase vent isn't working properly, you might well be getting a little pressure in there, and that will send oil through the valve guides, as well as past the rings, and anyplace else it can find, a little quicker. But your compression readings suggest that the engine itself is pretty healthy.

i know it has been a few months, but i wanted to follow up.
First off, i want to express my gratitude to all the folks willing to share their knowledge and experience on this board, you know who you are. i have been searching and reading a lot, and so many of the answers(or at least the right questions) are here.
I travel a lot for work, and time learn/work on the jeep has been at a premium. at any rate i have replaced the head gasket(blowing coolant into #4) sent the head to the machine shop(the whole 9 yds). valve cover cleaned and ccv rectified, new valve cover gasket, new exhaust manifold and gasket, tune up, O2 sensor.
the results were awesome. obvious increase in power, no more oil loss, no more smoke, sweet.
thanks again to all.