96 Bronco 302 issues

[Optikalillushun]

This is about my g/fs 1996 Bronco. Did a battery of tests and i will post the results later. Background first...

150,000 miles on the original 302. Had a bad miss at idle, PO said #7 cylinder was dead. Checked said cylinder with two different comp. testors and got the same results.

*pull oil fill and dipstick - no blow by
*pulled #7 plug - light to medium tan color. dry, no odd smell
*comp tested #7 - dead, guage reads 0
*comp test #7 running - dead, guage reads 0
*restested comp with another testor both ways, no changes
*no readily available knocking noises
*can hear a slight chuffing out the exhaust
*no smoke out the exhaust
*pulled driver valve cover, noting astray; ran engine, everything ran like normal

We also did a half assed leakdown test but those results IMO were inconclusive so im not including them (said test was my friends idea). I did note it is using a little oil, maybe one quart since she has it (about 1,000 miles). Fuel milage is poor (about 8 mpg). Just looking for some others opinions, were just going to run it until it blows. I want to borrow a real leakdown testor to verify and hook up my vacuum guage as well but i was so busy with work i didnt have time.

To me it definatly sounds like a bad or stuck valve.

 

[MUDKICKR]

put air into the cylinder. that will tell you if its a valve or rings. if air comes out the exhaust then its the exhaust valve, air out intake means intake valve, air out of crankcase then its a ring. last week at the shop a 2005 jeep grand Cherokee came in that quit going down the road. well i tried to start it and the starter was fried, replaced the starter and started it up, ran fine other then a miss and when you rev it slight smoke out the exhaust. cylinder 8 was dead, 0 compression, by 2 different gauges. put air into the cylinder and air came out the exhaust pipe. took my trusty snap on camera and looked inside the cylinder and found the exhaust valve seat came out and held the valve open.
now yours being a small block ford, i cant see the valve seat falling out, but i can see a burnt valve. also if you pulled the plug out and its dry id say the injector is bad and prob burnt a valve.

 

[Optikalillushun]

We did fill the cylinder with air but he did that test and it was fully on TDC so it was a half assed test. I let him do that cuz i was puttin brakes on at the time.

 

[MUDKICKR]

what did the air test tell you? did it leak out the exhaust or intake? anytime you put air into the cylinder it shouldn't matter where the engine is sitting at cause the air usually bumps the engine and shuts the valves for you. but there is always a stubborn engine out there where you have to move the crank to shut the valves.

 

[supachaged]

put alittle oil down that cyl. then retry your compression test,i doubt it will make a difference due to you having no compression. if it goes up then you have ring(s) issue. as far as a leak down test ive never had any issues performing one. pull the valve cover and turn engine till both valves are closed on that cyl.,if you have a bent,burnt,broken valve it will tell you. as mentionrd earlier if you have a scope you can inspect the cyl bore and piston.

 

[Optikalillushun]

Finally on a good internet connection.

regarding the compression tests, i/we did a wet test both times with both guages as well.

regarding the leakdown test, my friend (who was a GM tech) did this test while i was putting front brake pads on (was getting late). From what i rememeber, he applied air and he heard leaks from both the intake and exhaust. after fiddling with and bumping the engine to try and get the valves closed nothing really susbstantial came about. Last i rememeber was hearing the air leaking out both ends (intake and exhaust).

Another oddity i never noticed before last night. After we took it for a ride to get ice cream i went in my house while she was idling and waiting for my outside. When i came out i noticed it was smoking out the exhaust, like a white color. No distinct smell however. Only time i noticed any smoke out the exhaust. Afer going for a quick run around town it didnt smoke after that.

 

[MUDKICKR]

burnt valve.

 

[Optikalillushun]

My thoughts, heh. My friend is still hell bent on it being rings but...i did more indepth diangstics than he did in my previous job.

Now to save for a factory longblock.

 

[MUDKICKR]

then if you know what is wrong with it why ask anyone here? if your a "mechanic" you shouldn't have to ask how to diag. something as easy as a no compression cylinder.


My thoughts, heh. My friend is still hell bent on it being rings but...i did more indepth diangstics than he did in my previous job.

Now to save for a factory longblock.
http://youtu.be/5hfYJsQAhl0

 

[Optikalillushun]

Where did i ask how to diagnos anything? I was positive what it was, just looking for an outside opinion or if there were anything else i should know (common problems, TSBs, etc). Im not familiar with the 302, but i did find a TSB about the PCV and the back two cylinders (this was already fixed by 1996 MY).