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Old 04-10-2016, 12:11 PM
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Black Soot on Spark Plugs

Hello All,
I have 2001 Jeep with a 4.7 engine. The drivers side spark plugs all covered in black powder almost like soot. I replaced the engine a few months ago and redid the head the gaskets which meant I had to undo the timing chains. When I put the engine back together I put new spark plugs in and the jeep hasn't been drive but about 10 miles. I'm wondering if the cam timing is off on that side of the engine? Any help would be appreciated.
Thanks,
Scott

Some additional information about this. I pulled the valve cover on the drivers side, put the crankshaft in TDC position and the cam shaft had the V8 in the 6 o'clock position. I'm not sure how that happened as I was very careful when I replaced the heads and redid the timing. However, I don' think any damage has been done.

Just wondering that since this is a zero tolerance engine that it is possible the cam is 180 degrees off and still run (although not well) and not do any damage to the valve train or pistons.

Again thanks for the help.
Scott

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  #2  
Old 04-12-2016, 09:46 PM
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Re: Black Soot on Spark Plugs

Black soot on the plugs is normally a sign of a too rich mixture. If the timing is off, the pistons will already hit the valves, so 180 off would for sure have resulted in bend valves. Are you sure the #1 cylinder was at its exhaust stroke and not at its compression stroke TDC when you checked the mark on the cam sprocket?
Did you already check the O2 sensor on the bank #1 with a scanner?
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Old 04-13-2016, 02:08 PM
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Re: Black Soot on Spark Plugs

I may have the this on the wrong stroke, I'll double check it. I haven't put a scanner on this yet, so guess I will do that next.

I have replaced all the O2 sensors, one of them was in 2 pieces so thought it was good to replace all of them. This particular Jeep has 4 O2 sensors, 2 on each side of the engine, one upstream of small catalytic converter and one downstream.

I haven't put a scanner on this yet, so guess I will do that next to see what I can determine. I'll keep you posted on the progress.

Thanks for the reply.
Scott
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Old 04-13-2016, 04:26 PM
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Re: Black Soot on Spark Plugs

You will have to check the 1-1 and 2-1 sensors, which are the ones used for the fuel trimming. The 1-2 and 2-2 sensors (the ones after the pre-cats) are for measuring the cats performances.
You should see the 1-1 and 2-1 sensor voltages change rapidly between 0.2 and 0.8V. Then check the fuel trim figures. The STFT (short term fuel trim) should be in the single digit figures. I imagine that the 1-1 STFT will be +20 or more.
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