interresting issues, 91 cherokee limited 4L

so i bought this thing to get me down the alcan to my homebase of phoenix, so by the end of this u will understand my frustration. by the time i got home i noticed my oil pressure dropping to nothing when idling. i read that oil pumps are a common failure on these so i checked compression, changed the oil and it didnt knock so i went ahead n bought it. put a new pump in. problem solved after that i changed the plugs, wires, cap n rotor, o2 sensor, oil pressure sensor, and fuel filter. when i took it for a test drive it hesitated a bit, n caughed a couple times accelerating, and didnt shift to second. its automatic, and its not the toyota tranny, its the other one. so when i got home i did the magic with the ignition to flash the codes and got 21 and 24, 21 is the o2 sensor no voltage. i just put a new one in...the plug looked identical, is it still possibly the wrong one? or is there other causes for this? 24 is throttle position sensor voltage too high or too low. does this mean the sensor is faulty or do i need to check other things first?. i wanted to see if they were old codes since i had just put in a new o2 sensor. so i disconnected the battery, checked the plug at the o2 sensor and it was clean n together. then when i reconnected the battery the lights started flashing, no horn but looked like alarm flashing. after that it wont start. it turns over n seems to kick but then dies. i tried disconnecting the battery again n letting it time out before putting the key in, i tried putting the key in right away, nothing seems to change. is there a valet switch or something somewhere? ive looked in the usual places but found nothing and found nothing in the chiltons or in the manual in the glove box. or is there a wire i can cut or jumper something to take the alarm out of the equation permanntly? also when it was running i checked the fuel pressure regulator on the fuel rail and it was at 31psi with the vacuum on it and 35 or so with the vacuum off. which is low, according to the book it should go up to 39. will this cause rough running or anything like that? im kinda wondering if the injectors are getting plugged up or something. i wish they were easier to pull out n "see if they're working".

well thats about it. im considering finding a different vehicle due to the trip i have planned, i really like the truck. its a shame it wasnt taken care of better. once these are gone through are they a dependable vehicle or am i looking at my future while i stare at my oil pan?

CHEERS!


*EDIT*

i just read the next post about the guy that washed out his engine compartment n the reply says he proly got his throttle position sensor wet...um...i did the same thing i think. would getting water in it cause it to not start? i need to do more cleaning, is there anything else i should stay clear of with the pressure washer?

i finnally found a post bout the alarm, and that wasmy not starting problem...WHEW...but im still stuck with the 21 and 24 codes.

i suppose my question should be...could the TPS failure cause both of the codes? as in would the failed tps cause mixture issues the computer would perceive as an issue with the o2 sensor?

I don't know about the 91, my XJ is an 88 and doesn't have them fancy codes

On my TJ though, it takes 3 no-fault startups to clear a code. So for that 02 code I would expect it to clear after a few trips around town. What o2 sensor did you use? Where'd you get it? I buy parts at NAPA or better - they're more expensive for a reason (they actually use some of that money to maintain the computer that stores your parts data, unlike Crappy Zone and Advance Auto Screwups).

As far as the TPS, you should remove it, inspect it and clean it. Chances are the throttle body is gummed up and it is sticking or not actuating properly. With my 88 you have to adjust it once it's installed, I'm not sure about the 91 but I don't think so. Do a search and you should find the answer to that one. If you do have to replace it, use a decent one as it's pretty important to have it operating properly.

A vacuum leak could cause both of those codes. Start by tightening the intake manifold bolts and the throttle body bolts. After that, look at the vacuum hoses, and listen for any whistling sounds, or sucking sounds. If that doesn't work you could try a more risky approach: get a can of spray carburator cleaner and spray small amounts at a time around the throttle body, intake, hoses, anything that can have a vaccum leak, but like I said, it carries a fire risk. :flame: I always have the fire extinguisher
sitting next to me and I also do it on the engine when it's cool. Good luck!

well, what a runaround.

thanx for all ur input guys, much appreciated. i went ahead n rolled down to napa in the little red fiero got some more parts...replaced the tps, cleaned out the throttle body. replaced the fuel pressure regulator and the fuel filter, fuel pressure on the rail still doesnt go up 10 psi like the book says. it goes up 2-4 psi, could i have a fuel pump problem as well? the only things in the line are the filter, the regulator and the pump from what i can tell. the book says it should be 39 psi on the rail with the vacuum line to the regulator disconnected, but i only get 32-34. im using a refrigeration guage and i did zero it so i know its accurate. am i just being too anal about the numbers?

i also replaced my air temp sensor on the intake manifold because it didnt operate in the range specified by the book. but the new one was reacting exactly the same way as the old one. except the old one was all gunked up so im glad i replaced it.

after all that the codes still wouldnt go away so i started going through all the wiring and found a spot on the back end of the plastic harness cover mounted on top of the intake manifold where the edge of the plastic piece had cut through the insulation on one of the wires so i rewrapped that and filed the cover down to a rounded edge. then got to testing the o2 sensor and found that the signal was reversed from what the book said. according to the book if u disconnect a vacuum hose forcing a lean condition, the signal should drop towards zero. but mine went up to .9 sumthin volts. and im checking the wire indicated by the book as the output signal wire, i dont get it.

anyway , i let it set for a half hour with the batt disconnected. the codes went away and havent come back. i have my fingers and toes firmly crossed. although i dont see why so many things arent the way the book says. i should call congress:roll:

i polished up the valve cover and put one of my sage plants on the console, just in case :roll: