Random misfire/system too lean

T

Twams

New member
1999 limited. The check engine light came on with a system too lean. Then went off and came back on a couple times. Today it started shaking and running rough. With a code for random missfire, misfire cylinder 3, misfire cylinder 6, and system too lean. I am going to change the fuel filter to start but i am hoping someone may know what the problem is. Thanks for any input.
 
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Pull the spark plugs from those cylinders to check their condition/color and see if that will tell you anything.
 
3 and 6 are on the same coil pack (the middle one) so I would start there. Swap it to the front or back. Ohm check the wire, too. Check both boots and look for tracks or burns on both plugs. Any open in the waste-spark system and you lose both plugs; they are wired in series, not parallel.
 
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Thanks, I changed the fuel filter but it did not help. I will let you know on the wires and coil. I appreciate the help.
 
Clean your MAF, too. This was the cause of my lean mixture, which I imagine could then cause a misfire under heavy load. It's easy and basically free.
 
Just got home. I will pull the plugs and take a look at them, clean the mass air, change the coil to a different one, reset the codes and get the codes checked again to see if anything changes. I will update ya a little later.
 
What next

OK, Cleaned the mass air and swapped the coils around and put fresh spark plugs while i was in there. Cleared the codes and then drove 4 miles or so to get the codes check again. The only code that came up was #6 misfire0306. What should i do next??
 
What did the old plugs out of #3 and #6 look like?

Misfire is due to; a) lack of fuel b) lack of spark c) lack of compression.

If plug looked wet, concentrate on b). If dry, concentrate on a). If neither a) nor b), check c).
 
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6 looked fairly normal but did not have a white (X) across the center of the ceramic like the others did. It looked like it had a little black dot in the center instead. Also, there was a mark on the plug boot right above where it covered the plug that look funny, like it might have been arching. Plugs are Bosch Platnum +2s. I happened to have 3 others that i replaced 1,3 and 5 with.
 
No, not supercharged just a 3400 v6.

I read about spraying water at night on the plug wires to look for a short. So i tried it and could see small blue archs on 2 and 6 where the boot was on the valve cover. I also replaced a different (used) plug in 6 but it still runs bad. The spark look a little bigger on 6, but i did not get a code for 2( other than random misfire). Looking under the hood it was the first and last plug wires on the right side. New plug wires?? The sparks were very small, but i am sure not good. Why would 3 have had a code?
 
Twams said:
No, not supercharged just a 3400 v6.

I read about spraying water at night on the plug wires to look for a short. So i tried it and could see small blue archs on 2 and 6 where the boot was on the valve cover. I also replaced a different (used) plug in 6 but it still runs bad. The spark look a little bigger on 6, but i did not get a code for 2( other than random misfire). Looking under the hood it was the first and last plug wires on the right side. New plug wires?? The sparks were very small, but i am sure not good. Why would 3 have had a code?
Click to expand...

Replace the wire's and then see what happen's.
 
Twams said:
6 looked fairly normal but did not have a white (X) across the center of the ceramic like the others did. It looked like it had a little black dot in the center instead. Also, there was a mark on the plug boot right above where it covered the plug that look funny, like it might have been arching. Plugs are Bosch Platnum +2s. I happened to have 3 others that i replaced 1,3 and 5 with.
Click to expand...

I really wanted to know about the electrode end on #3 and #6. Color, wet or dry?
 
Well I am somewhat color blind but on 6 the center was darker and the metal ring around the outside was a shiny black almost wet. I will try to get this pic up the one on the right is 6.
 
Once again IMG_0046.jpg
 

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New plugs and new wires. Those have plugs have been in there a while. Again, what kind of new plugs did you put in? On the wires, I recommend either the Densos from the dealer or the NGK TE-66 set from Amazon, NAPA, sparkplugs.com or wherever. I am guessing you have factory Sumitomo's with 1999 written on the wires?
 
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No, i replaced them in 08 along with the bosch plugs. I am sure they are from Autozone but dont remember the brand.
 
I could use so brain power.

The last plug wire lost it end and i put the spark plug socket down in and wedged it. I put some pvc cement on the old wire and stuck it down there let it dry but it did not pull it out. I also tried compressed air to blow it out. I do not have one of those grab things with the three prongs but don't know if that would get a grip on it. I hope there is a easy common way people get these things out.
 
Twams said:
I could use so brain power.

The last plug wire lost it end and i put the spark plug socket down in and wedged it. I put some pvc cement on the old wire and stuck it down there let it dry but it did not pull it out. I also tried compressed air to blow it out. I do not have one of those grab things with the three prongs but don't know if that would get a grip on it. I hope there is a easy common way people get these things out.
Click to expand...

I use LONG needle nose pilers when this happen's.
 
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