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Discussion Starter · #1 ·
I have a 1996 Cherokee 4.0 that started with a CEL and a "misfire in cylinder 1". After replacing all 6 injectors, all plugs for Champion copper plugs, Bosch plug wires, new air filter, new fuel filter, seafoam in the throttle body, as well as the oil and the gas tank, and a fresh oil change, I now have misfire on 1,2 and 6. Any idea about what in the hell it could be? I'm stumped. All the wires are in the correct place, not overlapping, and I've had the CEL cleared at autozone, and the jeep ran and purred for 3 days before the check engine light coming back on. I have bought a crankshaft position sensor that I have not installed yet. I've read about the CPS, the EMC, the cat being plugged, looks like mine has been replaced already. I took it to a machanic because I was sick of throwing money at it. He unplugged injector on cylinder #1, and the misfire didn't seem to change much as it did on let's say cylinder 3 or 4. He then pressure tested the #1 cylinder and said that the exhaust valve is sticking on that cylinder. He then took the air intake tube off and proceeded with slowly pouring into the warmed, running engine while opening the throttle slightly. He said that the steam will more than likely clean up some of the carbon build up around the valves. I took the jeep home after he cleared the code. Jeep ran better than new for 2 days and then the check engine light came back on. I'm going to go buy the distributor cap for it tmrw and see if that does it, maybe even try to get the CPS on as well as unplugging the battery and trying to reset the EcM..(if that's how you do). I've read up about this misfire for 2 weeks now, and next to my machanic telling me to take the head off and take it to a machine shop and the of course I would just put everything new in the head (lifters, valves, rocker arms, head bolts, gaskets and so on) priced at about $250 for parts on Rockauto.com and about $200 for the machine shop to clean the head up. Rather than taking half the motor apart, which I can do myself but don't have time for, does anyone recommend anything else other than injectors, plugs, plug wires, and air filter that I can look into? Much appreciated, sorry about the long post, just wanted everyone to know what I've done so I don't waste anyone's time. -Adnan
 

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Have you replaced o2 sensors?
 

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Discussion Starter · #3 ·
No, but I think I may have an exhaust manifold lean that would cause the O2 sensor to get the wrong information and therefore send the wrong information back into the engine. I'm gonna try the distributor cap and coil tmrw and unplug the battery for an hour and see if that does anything. Hard to get to the exhaust manifold without taking the intake manifold off, and if I do that, might as well do the whole head and replace the valve cover gasket that's leaking as well. 161,000 miles on the jeep by the way
 

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Welcome to the Boards!

What do you mean by "exhaust manifold lean"? :unsure:

IMHO if the exhaust manifold isn't actually cracked, I'd just leave it all alone. The head in your '96 is nearly bombproof, and 161,000 miles is just the break-in period for a 4.0L!
When you replace the leaky VC gasket, i suggest dropping the $40 and install the Fel-Pro Blue.

As mentioned, the o2's "could" be part of the issue, but your Jeep "should" be throwing a separate code for that, I'd think?

Definitely cap and rotor t to see if that helps.
;)
 

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Discussion Starter · #5 ·
Exhaust manifold leak. Sorry. I'm new and saw that after I posted and didn't know how to edit the post. There's just so many things it could be, I didn't know where to start. Really weird though, when I clear the codes and reset the CEL, the jeep runs awesome for a few days and then the issue happens again and it starts misfiring pretty hard. Like I feel it in the steering wheel is how bad it's misfiring. I haven't checked the timing or wanted to mess with the timing, as I've never done timing before. Thanks for reply, and I didn't really want to to pull the head off because first it's time consuming, not very cheap, and it might not even what's causing the misfire.
 

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More trouble shooting is in order for your jeep. Its strange thatll youll only get the misfire when it throws the codes. Do us a favor and copy down every code that you get, the actual P0*** number, when you scan it and post them up on here. This will allow us to help you out some more.
 

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You also said that your mechanic is sayin you have a sticking exhaust valve? Did he perform a leak down test to declare that information? If nit, what was the compression number for cylinder #1? In fact, if you can get numbers for all cylinders that would be helpful.
 

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Discussion Starter · #8 ·
Yeah he did the leak down test on just cylinder #1, he couldn't find the hose for his pressure gauge. Rings must have been good on that cylinder because he didn't hear any blow by on the oil fill
 

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Discussion Starter · #9 ·
And I will go pull the codes later today. Have a friend stopping by with a bmw that needs help to see what her codes are and what her car needs. As soon as I get done with that, I will get my codes read and copy them on here. Started the jeep this morning and didn't misfire on the short drive to lunch with the gf. cEL is still on, but no bad misfire to the point where I can feel the steering wheel shaking or the exhaust putter
 

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Discussion Starter · #10 ·
Took the terminals off the battery, cleaned them up, took the ground wire off and cleAned up the spot where the wire touches the body, cleaned the body terminals and the battery terminals, and put it back together. No Check engine light, doesn't seem like it's misfiring, so hopefully it reset itself back into normal again. Will keep updated in a few days to see if the CEL comes back on or if the bucking comes back with the misfire. Thanks
 

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Discussion Starter · #11 ·
Started the jeep today after having it sit overnight and it sounded like **** right away. as soon as I parked it 2 mins later the check engine light came back on. Gonna go get them read and will post them
 

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If it's after you reset the computer I feel like it would be a sensor of some sort. Your jeep runs though cycles. If you reset (unhook the battery) then it resets the cycle. So whatever sensor or whatever component it is messed up, is going wrong late in the cycle. If that makes any sense. So it sounds like you are looking for a tps or a cps or O2 sensor or something along those lines.
 

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Discussion Starter · #14 ·
I've come to think its prolly my O2 sensor because of my exhaust manifold leak. I've went through the vacuum lines and the only place I've seen like it could be suspicious is on top of the valve cover. The 90 degree plastic vent caps seem like they have some wiggle to them. I've seen guys just using electrical tape on them and putting them back in place. Gonna wait until I take my manifold off to do the valve cover gasket as well as the CPS. It's a ***** to get to I think. I've bought a new exhaust manifold and wrapped it in carbon fiber exhaust tape, just because I've had some sitting around from my Go-kart, and because the intake manifold sits right on top of the exhaust manifold on these 4.0s. Thinking heat from exhaust and then warmed air going into the engine prolly isn't the best thing. Gonna do the exhaust manifold, gaskets, clean the engine side a bit, take the valve cover off and replace that gasket, (it's leaking like these are notorious for) and gonna do the CPS when I have it all off of there. Also have a transmission filter and gasket coming so gonna flush it out before winter as well. Thinking about going through the axles and flushing out the gear cases as well. I'm sure it's never been done and it's not gonna hurt anything.. Other than my wallet. If you're gonna do it, do it right? I've also had my heat take a dump on me. I'm gonna make a trip to autozone and have them read the codes that I will post today, in an hour or so. I think my heat actuator took a dump on me. The blower sounds like it's working and like it's blowing air, but when I put the control on "heat" nothing comes out of the vent. It blows on "vent" and "Ac" but doesn't blow out heat out of the vent on the "vent" selection. Thanks for the replies, I appreciate it. I've sunk a lot of money into this jeep and want it to run 100%
 

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Discussion Starter · #15 ·
I went and got the codes read today. Showed a
PO300- cylinder misfire detected

PO301- cylinder 1 misfire

"Ignition system fault-spark plug(s), ignition wires, coil
Vacuum leak
Injector fault
High or low fuel pressure"

all of the above could be the probable causes. I have no idea what the hell it could be. I replaced the plugs, wires, injectors and checked for vacuum leaks. Could the vent cap on top of the valve cover be causing a vacuum leak? I think they're a little loose fitting in the valve cover. Think I'm gonna tape them up with electrical tape when I do the new exhaust manifold and the valve cover gasket on Tuesday.
 

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the valve cover is ported to the airbox, so I don't think thats part of it.

High or low fuel pressure would show up on multiple cylinders.

Try unplugging # 1 injector and see if the sound of the engine changes. if it does, then the problem is just with that circuit. Check the rest and see if the sound changes.
 

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Discussion Starter · #18 ·
I've done that. And when I unplug #1 injector, nothing changes. Nothing major like it should anyway. When I do #3 or cylinder #4 injector, the motor really starts shaking and bucking from the misfire. It's hard to guess what it is, my machanic told me sticky exhaust valve, but to get to that valve, I've gotta tear the head off, take it to the machine shop, and while the head is off, I'd change the valves, lifters, rollers, and all the bolts. So I'm trying to leave that for the last option. I filled up the tank today and got 305 miles on the tank before the low fuel light came on. After filling 17 gallons, it came up as 18 MpG, mixed city driving with most highway miles,
(65-70). So I guess it's not that horrible, but with replacing every part of the fuel and ignition system, i was hoping for a bit better. Guess I could do an alignment also.
 

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you can do a leak down test to confirm a leaky valve and the only thing you take off are the plugs. I have the tools, where are you located?
 

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Hows the condition of the distributor cap? Maybe the post for cylinder 1 is shot on the inside...
 
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