Jamie57

You mentioned in another thread that the engine had been rebuilt, correct?
Did the rebuild the head? as in do a valve job?
DID THEY TEST THE SPRINGS?
That is in capitals because one of the first things I learnt in mechanics school was to test the valve springs when rebuilding a head.

I think this may also be my problem. I'll do some more research and let you know.

belvedere

The valve spring TSB applies to 1996-99. I have heard rumors of this issue on 00-01, too. However, the offical TSB says 96-99, so who knows. New valve springs did fix a stubborn #1 cyl misfire on my 98.

I feel for you, WW, and wish you the best. I'm glad the engine builder is willing to help you out.

CCKen

Word around the campus is several 2000 4.0's were fixed with new springs.

Jamie57

Crap! You're just a ray of f'n sunshine aren't you? LOL

WaY_WeiRd

Yes, it was rebuilt in October.
No, i don't think the head was rebuilt at that time.
I could call and ask, but I don't currently have a 100% positive answer to that right now.

Radi

Springs are unlikely to cause the injector fault code. Personally I'd fix that before worrying about the valve springs. Not that they aren't a possibility, but if an injector is malfunctioning, and at least one appears to be, that will certainly set a misfire code.

Jamie57

Ummm we both have rulled out an injector. Changed them with new swapped them with another cylinder, changed and swapped plugs, as well as many other reasons for a misfire.
And yes valve springs can and do cause misfires.
A TSB right from Chrysler points to that in 97-99.
We're both grasping at straws here to resolve this.

WaY_WeiRd

I'm still holding out hope for a small wiring problem. I have not had a chance to look at the wires yet, and honestly... Probably won't. I'm finding it hard to even find time to clean my house right now being the only one home with the baby this week. It'll probably go to a shop.

BUT...

I did see a post on naxja about injectors testing perfectly fine with a light, but still having a kinked or worn wire down the line causing the exact codes that I'm getting. And also something about it not being the injector itself but the harness. I'd have to search and find it again.

I will let you know when I do get it figured out, as this seems to be a problem many have.

Radi

Yes the springs are known to cause misfires. No disagreement. Problem here is she's getting P0206 (injector circuit fault #6) along with the P0306 (misfire #6). Bad spring might account for 0306 but not 0206.
P0206 is not necessarily a bad injector. It can also be tripped by a fault in the wiring harness, fault in connectors or fault in the PCM injector driver.
OP said the harness has not been opened and inspected yet and Chrysler harnesses are a known source of trouble. It doesn't make sense to me to move on to spring issues and another possible expense when the fault the PCM is displaying has not been addressed yet.

Incidentally, if you think you might have a valve spring that's become weak, another thing to look for is symptoms that get worse as RPM's increase from the valvetrain float. The misfires might steadily get worse with RPM. If you have a vacuum gauge you can see it happen, rev the engine up to 3-4K rpm and hold it steady- the vacuum reading will start to bounce if a valve is floating.

Radi

It seems to happen more with the later XJ's. Chrysler cheaped out with the harnesses. Actually much of the wiring is marginal at best.
The harnesses are exposed to engine fumes, heat, and constant mechanical vibration. The insulation (hidden under the outer wrap) becomes brittle, begins to crumble away and you get intermittent wiring shorts.
This may or may not be your problem, but it is a common problem and can cause what you are experiencing.

highmileage

throwing it out there what about the ignition relay. Had a ford do something similar and it was a relay.

Baby D

reset pcm there is a how to of how to do it it dgoes take off battery terminals hold together for 30 seconds key to run position but not on the headlights on then headlights off then key to off and u just flashed the pcm and the "adaptive memory" technolgy. if codes re appear then come back and tell us if there is a difference in them

captainwoot

Congrats on the new addition! I agree with the others, it will prob be a wiring issue to the #6 inj. All of the inj share a B+ feed (dark green/orange wire) see pic#1 .the other wire is the inj driver circuit controlled by pcm...pic#2

captainwoot

Sorry pic#2

WaY_WeiRd

So, here is an update:

With having a new baby in the house, we haven't had any time to mess with it. I did finally have time to get it to the shop that rebuilt the motor though.

It's been there almost three days now, and all they can tell me so far, is that it's not an engine problem. They're stumped too ATM, but still working to try to get it figured out. Meanwhile, I'm driving my dad's Buick. Nice car, but I'd love to have the Jeep back.