I have a '90 Full size bronco with 94,000 miles, a 5.0, automatic, man. transfer, and hubs. Here's the story, the truck has been running ok, but a slight misfire could always be felt at any constant speed. Under acceleration, it was unnoticeable. It wasn't really bad, but I have replaced the following in attempt to correct it: spark plugs, plug wires, cap and rotor, set timing to factory specs. Still had the mild misfire. You can't hear it, but you can feel it. So, before I could decide what to try next, the big trouble hit. While on an hour and a half trip up and down mountain grades, it began to smoke and hesitate. This continued until I got it home and found that crankcase oil had made it's way through the breather pipe/element and into the airbox, then of course into the intake. Whala! Smoke screen! Also, and much to my dismay, I found that milky water/oil mix on the dipstick that'll have you cursing your way out of the garage. So, it looks like I'm into a new head gasket, or both just for good measure. I assume the oil in the airbox is due too much positive crankcase air pressure, from a bad head gasket. But what caused the misfire that probably burned out the gasket? The motor has fairly low miles at 94,000 and is otherwise in good shape. Anyway, my question is about the misfire, or chugging feel on the road, other than the head gasket which seems to be a result of it. Thanks a ton for any help or ideas!

 

I wouldn't jump to that conclusion yet. Really should do a compression check on each cylinder first. Why? Cuz' there may be other explanations. Like maybe the suction side of the PCV system plugged up, causing oily damp blowby gases to exit out of the intake. And combustion creates moisture, and moisture in the blowby gases that used to be swept out and burned by the PCV system aren't getting scavenged good if PCV isn't working. I'm not familiar with the truck EFI 302 PCV. Do they have it go to that screen filter stuck way down inside a well at the back of the manifold, like car EFI 302's? If so, those filters can plug, as they are rarely changed. Most people don't even know they are there.

 

I'll check the PCV, and it sure would be nice if thats all is. But there's a lot milky stuff in the oil, and the oil is clearly getting into the intake via the breather pipe leading from the oil fill spout in the valve cover to a breather element inside the airbox. I pulled the breather element out and it was saturated with oil, and so was most of the air cleaner element. Also, the engine has a bad and consistent shake. I need to find out what caused the head gasket to fail when engine never overheated. This way I don't do this twice.

 

[updated:LAST EDITED ON 04-Nov-02 AT 02:55 AM (EST)]I blew a head gasket in my 1993 Mercury sable 3.8l. They are known to do this every 35,000 miles. Anyway, When the head gasket blew. The car overheated in about 3 minutes at idle. 1 Minute at 35 m.p.h. I got a ton of white smoke out of the tail pipe. I mean people were stopping be hind me. Also I did get the milky oil. But in your case since you didn't state the color of the smoke and, you said it didn't overheat I don't think you have a bad head gasket. You might have a cracked head. That is what the mechanic that fixed my car told me. He said that if the car didn't over heat then it was a cracked head. But since it over heated he knew it was the gasket. Hope this helps any questions feel free to ask!!

 

You didn't mention where your from but I have a 91 302 efi with 146,000 on it and I also get blowby back into the airbox. I also have experienced the white milky substance your talking about on my dipstick and on the oil cap but only during winter. I know the 302 truck motor is known for blowby when you get some miles on them and I have been told that the PCV system on these is what causes the condensation in the crankcase. I was told not to worry about it and have put a few thousand miles on mine with no problems. This first happened in Feb and I like you suspected a bad head gasket and after talking with my mechanic and changing the PCV valve I experienced no more problems. I just checked my oil tonight and although there is no moisture on the dipstick I did notice a little on the oil cap. The temps here are in the 30's and I am running a 180 stat. I am going to switch to a 195 to try and prevent some of the condensation from forming. I would try the PCV first and go from there. The PCV valve on your truck is in the rear of the passenger side valve cover. Good Luck

 

The one thing I can tell you from experience is that the 302 has trouble with the 8 cylinder burnin' out. I would suggest that the oil could be passing a mushroomed or tuliped valve. I had this problem although the amount or oil was less than what you are talking about your valve could be more damaged. My suggestion would be to do a compression test then go from there and if you get it running cool I would do a code scan it could give you an indication of whats not running on point. Good luck and any help I can be if this is the case. The cat is another culprit with the 8 so if it is a valve blow by I would expect exhaust problems.