I have been getting a CEL off and on for the past couple of months, first it was just 1151. I checked for vac leaks, don't think I have any. Changed the fuel filter, checked the fuel pressure. Fuel pressure was good. Had the codes pulled yesterday and now I have miss fire on #6. Now I believe cylinder 6 is driver side most forward?. I pulled the plug today and was going to do a compression test. The plug was quite oily on the threads, all the way up the threads. The compression tester said zero, which seemed wrong, tested all cylinders on drivers side, all zero. Less than year old tester, used once is dead.
Will test the compression when I get new tester.

One of the plugs I pulled I noticed the insulator had a slight crack. I've only had the truck for 10 months and the previous owner said the plugs and wires had just been changed recently, but I may need to change the plugs regardless.

The truck isn't running well, it misses on startup and on one trip it was missing for a couple of miles.

I replaced the lower intake manifold in fall, and only had a beam style torque wrench, so I'm thinking I will re tighten the manifold bolts, as I've read on other posts that if those bolts aren't within specs that can cause a lean condition. What else should I be looking at?

Sorry for the long post.

 

The #6 cylinder is on the driver side, closest to the firewall:



Is that the plug you pulled?

 

Thanks for your response, and the great diagram. The plug with the cracked insulator was #6. The plug with the oil on the threads was #4. The #6 plug the insulator was a brownish color. I'm wondering if the cylinder isn't burning lean, causing the plug to go bad, I'll have to research it a bit more.

BTW It is a 98 4.0L

Thanks.

 

I pulled all the plugs today. 1, 2, 3 all look like new. 4, 5, 6 look bad. Decided to tackle retighening the lower intake manifold bolts, they all needed tightening. Put it back together, ran bad. Ran a 1/3 of a pint of Sea Foam though, still not running right. I will change out plugs on 4, 5, and 6 and see how it works. Any other ideas?

 

I have one, but it ain't gonna sound fun. Assuming that the lower intake manifold and gasket are OK and torqued properly, then if the plugs keep fouling and you keep getting misfires on that bank, you have to start thinking a head issue.

P.S. Why did you replace the lower intake manifold last fall?

 

I replaced the gasket because I was having a coolant loss, and from what I had read on this forum it seemed that could be the problem. Of course after I changed it, I then discovered a leaking heater diverter valve. I changed that and didn't lose any coolant for a more than two months. Then the coolant started to go down again. At the same time I started having a miss at start up which was getting worse.

I changed the plugs on that bank last night, and it still ran terrible. So I once again checked the plug wires, that was probably the 3rd time, and discovered that I had 5&6 swapped around. Ran great after that. This morning there was no miss on start up. This evening it did idle rough when stopped at light with it still in drive and my foot on the brake. Put in park idled fine. That could be an IAC issue.

When you say head issue are you talking gasket, or the head its self? Wouldn't a cracked head only affect on cylinder?