Ferrel

alright guys,
So, we've got more adventures with the wife jeep. It's a 96 zj limited 4.0l. Its got the all time 4wd. It has a random miss. Seems to be worst under load and idling. It will die at stoplights.

Unfortunately, it doesn't do it consistently. One trip it'll be fine the next it will run terrible. It seems that if I run it for a long time, it get better but doesn't go away completely. It almost never likes idling at a stoplight.

I've gotten it to trip code a few times, and it's always all of the misfire codes. 1-6 and random (P0300 to P0306)

I've been working on catching up maintenance so here's what's been changed recently:
Distributor
Cap and rotor
Ignition coil
wires
plugs
fuel filter
air filter
TPS
IAC
Crank sensor
Dealt with rear main
replaced thermostat
o2 sensors
Seafoamed it (worth a try even if it might be snake oil)
cleaned the throttle body

Like I said, I'm stumped guys.
Thanks in advance for the help.

Ferrel

remembered a couple more things.
Cat was replaced 3 months or so ago. az special. Any chance it's already plugged?
Just replaced the CCV valve and elbow just for good measure.

burns some oil but not obscene
I'm hearing a hiss from somewhere very near the battery when I shut it down; hisses for a little under a minute then peters out and goes away.

dave1123

Okay, judging from your list, the only thing left is the injectors. Have you checked the fuel pressure? Low fuel pressure will change the injector's spray pattern or even the amount of fuel injected. Large droplets of fuel won't burn as completely as a fine spray. This is just off the top of my head, but it bears looking at. Go to your AZ and borrow a fuel pressure gauge. It screws onto the fuel rail test port. According to my Haynes manual, the fuel pressure on your '96 should be 37 to 41 psi idling.

Ferrel

fuel pressure is within range. I believe when I checked it it was around 50? ish? All I remember is that it was in the acceptable range. I knew I forgot to mention something. I stuck a new computer in it just in case, seems the original is still good cause it didn't change anything. if anything, it's running worse. I'll be taking the new one back out. The only sensor I can think of that would have any affect is the map sensor. Worth changing or no?

Thanks dave, I was kinda hoping you would take pity on me, I'm about ready to make a bonfire out of this jeep.

I think my next step is to pull the fuel rail and see if anything seems hinky with the injectors, or if there's maybe some nasties that made it to the rail and are intermittently blocking flow... possibly tomorrow. Gotta go to work at this point (to pay for whatever the jeep needs).

On a side note, when it misfires it seems to have a "whooshing" into the exhaust. I know vague descriptions... sorry, the wife say's it sounds like a sigh. This mean anything to you?

Ferrel

So, I ripped the new ecu out and stuck the original back in... I think someone pulled a fast one on the company cause it's been returned, and the new one looks a lot like somebody did a real good clean up job on their old one... Ah well. It's back to running "not right" as opposed to barely making it the mile to work .

I think before I pull the fuel rail, I'm gonna find a set of upgrade injectors, just for ****s and giggles. If you have to tear it apart, make it better right?

dave1123

When I changed the intake manifold gasket in my '97, I put in a new set of injector o-rings. Be sure to lube them with a little engine oil so you don't tear them going back in. I also installed them all in the fuel rail and then put the assembly into the manifold. I didn't even disconnect the fuel line. Be careful with the electrical plugs.

Red River T

The "whoosh" is likely excess gas burning off in the exhaust pipe. The fuel pressure spec for my 97 is 49 +/- 5, but they changed it somewhere shortly before 97. I'm pretty sure 95's are 37 or 39psi.

I'm battling the same problem. Clean your grounds for the negative battery cable, and the battery terminals. Clean the wiring connections on the back of the alternator. Clean the connections on the PDC behind the battery. Check the plug for the crank sensor on the wiring harness. Remove it from the plastic cover tube a few inches. A few months ago I found where mine had 1/2"+ of exposed wires between the ends of the insulation and the plug, but it was acting much worse at that time than what you describe. Use electrical contact cleaner on the contacts inside it. (and the other connections) With it idling, wiggle the wiring plugs on the PCM (behind the radiator overflow tank). If it acts up, there might be an issue with the plugs which you might be able to remedy by using cable ties to hold them more securely to the PCM, or you might have the dreaded cracked solder joints in the PCM. Also, it has been reported that the little "fingers" inside the plugs connectors get loose over time and that you can go in behind them with a dental pick (and magnifying glass) and pry them back up where they will be tight against the pins.

I bought a set of 703 injectors from "831xj" on here, but I haven't installed them yet because I am still trying to stop the dying problem. I've improved it (lessened the severity), but it is still happening.

Red River T

Your "new" ecu / pcm was a remanufactured one. I think that's all you can get anymore.

Ferrel

Thanks for the input Red. I will definitely check that stuff when I get a few. I've been a bit busy so this has taken the back burner for the moment. (Just worked a 18 hour day and am going into another one now.) I will definitely keep this thread updated on what I do, and if I find my issue.

On a side note, I helped the neighbor get his oil pan off, (his has similar miles to mine) and when we got in there we figured out his timing chain had 3/4 inch of slop. Guessing mine might too. I was pressed for time when I had my pan off, so nothing got checked. Get to tear things apart again. I'm thinking if my rig is compensating for all that slack, fixing that issue will give me a more accurate symptom to work with. Worth hoping right?

dave1123

One thing that happened to me on my '97 ZJ. The molded lead battery cables had 2 wires coming out of them. One for starter power and the other to the PDC to power everything else. The smaller wire was corroded inside the terminal so even though it cranked like a champ, it had problems starting and running because the rest of the electrical system wasn't getting the full shot. Check it out.

Red River T

I see I neglected to mention that my 97 used to give me 0300-306 codes every few days. I cleaned the PCM pins with electrical contact cleaner, and then a worn out emery board after it dried. I've only gotten 0300-306 codes once in the ensuing 6 weeks, and that was a time that it was acting up and definitely missing. I was advised later to use something like a pencil eraser to clean the pins, so as to not scratch off the coating. That's probably a good idea.

Ferrel

is there a vacuum can in the front right bumper in the ZJs like the one in the XJs?

dave1123

Good one! Yes there is and it's underneath the battery tray. It could be leaking and causing your "hiss".

Ferrel

I'll take a look when the wife gets home. Thanks.

Ferrel

Any way to test it, or just make sure the hose is plugged in and tight? It released pressure when I unplugged it.