'89 Cherokee misfire under load
 

Hi!

I recently bought myself a '89 Cherokee 2 door, 2wd, 5 speed, 4.0L Cherokee. I bought it because I had a '99 Mustang and it got totalled, but I only had $1300, so my options were kinda limited. I bought this because reviews told me that the inline 6 were bulletproof, and it should be a decent daily driver.

I bought the Jeep knowing it had a bad alternator, and a bad power steering pump. I just replaced the alternator today, power steering pump is still in the mail. It had been sitting (after I bought it) for a few days before I replaced the alternator. After I put the new alternator in, I went to drive it to make sure it was all good, and when I got to the end of my street, it stalled out. It was difficult to start, but it finally did. Misfiring like crazy. I drove it to a parking lot, and it didn't die and it idled okay for a while.

I then decided to drive it around kinda hard. That seemed to help. I took it through all the gears a few times, revved it up pretty high. These things really haul ***!

Anyway, when I got home, my neighbor and I took a look at the engine to see if we could see anything wrong. Apart from the giant clouds of oil smoke (burning off the head, the valve cover seal is almost nonexistent), and the steam from the coolant reservoir (it's split along the edge), it seemed fine. My neighbor suggested that my valve guide seals may be bad and that oil had leaked into my cylinders while it sat, and had to burn off, making it run badly. If this was the case, would the intermittent misfire under load go away after a little while? It's not a big deal, just annoying. What else could cause it to misfire like that?

Also, is the cap on the coolant reservoir supposed to be vented? I get the feeling that mine isn't, and there is definitely too much pressure in the tank. As I mentioned before, it's split on the side. It sprayed water all over the coil until I tied a rag over the split. It doesn't spray now, but I've gone and bought another one on ebay to replace it (comes with cap). I'm just wondering, the system seems to not be vented anywhere else and I don't see an overflow anywhere. What's up? Is there supposed to be an overflow somewhere? Or is the cap supposed to be vented? There is no vent from what I can see...I just hope my head gasket isn't busted. There is nothing in the exhaust that would suggest that (no white smoke), so that is a good sign.

Sorry, I'm new to jeeps :o

Hey. 5 speed 2wd. You might see better mileage than some of us. I might put a valve cover gasket on it if that's leaking. Check the condition of the plugs, cap rotor& wires. (plugs .035). It's a closed system and that's an expansion bottle, (no vent/overflow). I don't fill mine more than 1/2. Might get her cleaned up a bit, get your bottle on there and take it from there. I'm sure there are plenty here who can help you sort it out. Your "Renix" ECU does not have an engine light or store codes. Usually you need at least a cheap meter to diagnose much. Buckle your seat-belt!

Drive it around a bit. If it doesn't stop, check these out:
FSM PDFs: http://dl.dropbox.com/u/4207768/index.html
Multimeter Sensor Testing: http://www.lunghd.com/Tech_Articles/...iagnostics.htm

I figured I'd post up a few pictures.

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Gotta love how clean the interior is on a 23 year old Jeep :)

There are several things that can cause the hesitation/misfire you've described, most of which are fairly easy to diagnose. Renix engines are full of vacuum lines so that would be someplace to start. Pay special attention to the one going from the throttle body to the MAP sensor mounted on the firewall. If in doubt, replace. Bulk vacuum hose is so cheap, there's no reason not to. Also, the CPS (Crank Position Sensor) is notorious for failure. Early symptoms are similar to running out of fuel and include starting issues, misfires, rough idle, and random stalling.

There are comprehensive diagnostic procedures in the second link provided by austinjoe13. The Renix motor is pretty bulletproof but the complicated (sometimes overly complicated) electronics and vacuum system can cause headaches. Fortunately, if you're not opposed to wrenching on it yourself, the vast majority are simple fixes with readily available and inexpensive parts and the combined knowledge and experience here on CF is invaluable.

I would start off with a general tune. Replace your plugs and wires, inspect and replace your air filter, replace fuel filter and check flex lines to tank/pump for weathering or damage, especially around the hose clamps, new cap and rotor, oil and filter (WIX best, avoid Fram), and replace serpentine belt if it looks at all worn or glazed.

X2 on that map tube. brittle, it brakes.

Wow, Hey that's clean. While your waiting for the bottle, Wix filter, or Napa "Gold?" Check the condition of the old oil. T-case takes trans fluid, up to the top plug. At least top off the diff with 85-90W, or go ahead and pull the cover and change & clean it. Here's a CPS deal below. It's sort of the importance of points, with the personalty of a condenser. It tells the computer what your engine is doing. I only mention testing it on your new jeep because it really can take only a minute, and nothing will work if it's not good. Oh...whoops! Don't check the Transfer case after all!
AC voltage CPS test; Small clips on the meter leads really helps.

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps.
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low)

Mine somehow works with only .3 my wiring/grounds must be pretty spiffy. .5 seems to be a good mark. One article talked of .5 to .8.

If it's low you can modify the cps. With the next largest bit that won't fit in the hole, enlarge the hole's in the bracket just a tad. Now when mounting it's crucial to maintain firm downward pressure on it while tightening the bolts. An assistant could help with that from above.





Just in case you are looking for something to do;
That rear manifold bolt has a habit of loosening. On anything like that you NEVER want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I'd go over three times, a tad tighter each time. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension(s?). For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. :thumbup1:



Eire how your jeep is identical to mine, in every small detail!

I sold my old car, a '99 Mustang. I loved that car, but I totalled it. Oh well.

But since I sold it, I did get some spending money for the Jeep. Gonna put in a lift kit this weekend hopefully.

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These are 31" Safari ATRs. Cost me $570 (buy 3, get the 4th free) and I got 2 free tickets to Six Flags. Score!

You said water was running out onto the coil - the misfire?

I think it may have just been bad valve guide seals letting oil into the cylinders from sitting for a while. I've been daily driving it and the misfire went away. It shakes at idle a little bit, I'm not sure if that's a misfire or not, because it never stalls or anything. Perhaps just worn out engine mounts. But the misfire has disappeared. Very pleased.

Just showing the lift kit I got done.

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with the help of a friend on here, username White Elephant :D thanks again!

Also, I detailed the engine. It's a lot cleaner in person, but I'm not nearly done. I thought that heat shield over the exhaust manifold was actually painted black :icon_eek: surprise!

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Have the same problem with mine but you can pull it in gear and it misfires also updated the cooling system to the later model system and i have no problem with that delete the tank had the worst luck with that after about three tanks