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mboone 10-13-2013 11:48 PM

2001 wj 4.7 sounds like its backfiring into the intake
I have an 01 wj with 4.7L I changed the Thermostat and when bleeding the system it got hot but didn't overheat when I started it up after it cooled down I had a miss and it sounds like it's backfiring thru the intake I changed the plugs and still have the issue. Oil pressure is normal, no coolant loss what could it be, I've been told it possibly tossed a rocker off the lash adjuster?

Frango100 10-14-2013 01:42 PM

Re: 2001 wj 4.7 sounds like its backfiring into the intake
Welcome to the garage.
If a rocker fell off, you will get a misfire and normally it will show a P030X, where the X is the cylinder number. Did you check for any fault code set doing the keydance? Ignition switch off/run three times and leave it in run at the third time. The odometer will show Done when all ok, or any fault code(s).
If there was a big air pocket stuck somewhere in the cooling system, the engine will get very hot at that spot, while the coolant temperature indicator can still show a reasonable temperature. If this engine overheats, it can warp the cylinder head(s) and a valve seat can get loose and drop. This last will cause the respective rocker arm to fall of and can cause severe piston and combustion chamber damage.
But first look for any fault code and let us know.

mboone 10-15-2013 11:54 AM

Well I've done the key dance an haven't gotten any codes, which is really puzzling because there is a definite miss. I'm hoping the valve stuck for a split second and that cause the rocker to fall off. Won't know til this weekend when I have a chance to tear into it. I did find a couple injector connections that had bare wires right at the connector which I'll also be replacing

Frango100 10-15-2013 10:26 PM

Re: 2001 wj 4.7 sounds like its backfiring into the intake
If you have a compression tester you could see if there is any cylinder with a big difference in compression. This way you know at least from which bank you will have to remove the cylinder head cover to check the rockers.

mboone 11-09-2013 05:28 PM

Ok so I figured out that it's the number 8 cylinder. After pulling the valve cover it kicked the rocker off of what I believe to be the exhaust valve. The rocker just slips right, and is all sloppy, which makes me think that either the valve spring is broken (which I doubt because I didn't see or feel and edges and it was still tight), or the valve is bent or stuck. I also pulled the lash adjuster and it appeared to be fine

Frango100 11-09-2013 07:41 PM

Re: 2001 wj 4.7 sounds like its backfiring into the intake
The 4.7 is well known to drop a valve seat when it overheats. You then get too much play, which the lash adjusters can not compensate for, and the rocker will fall of. You could press on the valve stem with some arm (only on the stem, not on the retainers) and see if the valve moves without binding.

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