Possible stuck valve - ZJ 5.2

Zachs

Zachs

Active Member
Joined
Mar 24, 2008
Location
Kinston, NC
ZJ 5.2 loves to run on 7cyl

Every now and then it idles smooth on all 8 cyl. Always a misfire on cyl#2. I'm not a believer in snake oils as they are almost always proved to be just not worth it, but could water or seafoam actually help in this case? I've heard the motor, at start up, just go POW and bam, perfect idle.

I've tried to move the injectors, but they stuck in and I don't want to break one.

Been battling this for months and would love some solid advice. I've done all the electrical that would fix this issue if it was electrical, but I'm not really wanted to change out any valves mostly due to lack of knowledge.
 
Have you done a compression test?

Are you sure it's always #8?

How do your plugs look? Your wires? There's a TSB on re-routing the wires due to mis-fire. I'll see if I can dig that up.

JeepForum is very active on the ZJ side.

Could be a coil on the fritz. ZJ's are notorious for all sorts of whackiness when the PCM connections are loose.

Need more info...
 
Always on cyl 2. NO compression test yet, This info is from what I remember when I troubleshooted this issue a a while back - Wires fine (changed for new ones), #2 cyl plug looks burned even though it's a new one, all other cyl fine. fuel def on plug.

If it was a wire routing issue, the cyl miss would be on different cyl randomly.
 
Alright so you have your answer pretty much... unburnt fuel in cyl 2

You can try injector cleaner, can't hurt or just pull the injector and inspect. Maybe a bad o-ring causing fuel leak down.

btw, you can swap in 4-hole Bosch #703 or 715 injectors... it's a nice/cheap jy upgrade over the stock 1-hole design

I just did this on my 4.0 a few weeks ago and it's a very nice difference, much smoother engine performance over all.
 
Gotcha, well I'll see if I can get it out tomorrow to inspect it...I've gained a lot more experience and confidence in that area since the last time I attempted to fix the issue. Found out my Celica has like 8 holes per injector. haha way to go yota

Thanks man
 
Well I pulled #2 and #4 Injectors. Attached a bottle of carb cleaner and hooked leads to the "dirty" injector (which was physically burnt looking) and ran the injector while spraying cleaner through. Fluid went from brown to clear and came out even spraying. I cleaned the mouth of the injector and all other parts on both injectors, now looking identically clean.

So I switched the two injectors and went to Advanced Auto to use their OBDII reader to clear the code so i can see if the misfire will follow the poor injector. Code comes back within a few minutes so I go back and get it read and its still on Cyl#2.

Now I'm not one to every use snake oils, but giving up all hope I buy injector cleaner and yes, sea foam. Dump the bottle of injector cleaner in hit up an industrial park that was empty due to closed business and the fact that its Saturday. I feed around 1/3 of the bottle through the brake booster vac hose and dumped the rest in the tank.

I flood that park with smoke and when I'm done the damn thing is idling smooth. Its running nice and I'm waiting to see if the code clears on its own or if the miss comes back. I'm still not convinced as popping redline may have freed up the burnt valve or whatever. Who knows. hahaha

Just sharing my experience.
 
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