Engine just developed a bad miss... ???

[Katmandu]

The engine in my 91GT just developed a miss this AM. I did a "practice" run 0-100MPH and shortly there after the engine started missing.

It's not smoking anymore than usual, and there's no real noticeable unusal engine noise. Although, the valve train on the right side "seems" a bit noiser than the left side.

I checked all the wires/boots and they're OK.

I'm going to go pull and replace the plugs right now...

I betting a valve spring maybe broke. Any other ideas of what may have happened ?

[85_SS_302_Coupe]

Could be a collapsed lifter, could be a blown head gasket. Last year mine was running like that...it would idle perfect and sound ok until you were driving it and the engine got under load like going up a hill and then it would shudder real hard and buck and didn't have any power and wouldn't rev. I bought new lifters thinking that it was a dropped lifter or two but it ended up being a head gasket.

[Katmandu]

BTW, I was (20) miles from home when it started missing and I was able to "limp" it home.

The engine runs "ok" at minimal throttle, but starts missing BADLY once more throttle/load is applied.

[Katmandu]

I bought new lifters thinking that it was a dropped lifter or two but it ended up being a head gasket.Roger that. Was your's smoking any ?

Mine isn't smoking (that I can tell).

Funny thing is, I have a H/C/I (GT40P/B-Cam/TMoss ported intake) in the garage waiting to go on! I've been procrastining getting to it! :rolleyes:

I guess now is the time huh! :HYF:

[85_SS_302_Coupe]

It would only smoke when you revved it up hard. I made this video the same day it happened, this is maybe an hour before it started the hard bucking and missing:

http://i229.photobucket.com/albums/ee275/EVIL85SSP/Mustang%20Pics%20and%20Videos/th_ModifiedFlowmasterClip.jpg (http://s229.photobucket.com/albums/ee275/EVIL85SSP/Mustang%20Pics%20and%20Videos/?action=view&current=ModifiedFlowmasterClip.flv)

Notice the white/grey smoke after hard revs...i think that was the sign that it was on its way out.

[Katmandu]

It would only smoke when you revved it up hard. I made this video the same day it happened, this is maybe an hour before it started the hard bucking and missing:

Notice the white/grey smoke after hard revs...i think that was the sign that it was on its way out.Roger that. Sounded great before it popped though! :bigthumb

I "think" I found the culprit to my engine's miss. I just yanked out all the plugs and the #5 plug (I think...PS Rear plug) was shorted out. Now, I'm not sure exactly what the debris was that was stuck between the electrodes. ??? :confused: Best I can describe is it looked like a glob of SOLDER. ??? :confused:

Most likely carbon, but all the plugs show the engine is running LEAN. All white on the noses. What's weird is that my tailpipes are covered in black soot. ?? I believe the valve seals are toast cause it does puff blue smoke occasionally.

Anyways, I need to find out how to disable the EFI/Injectors so I can do a compression test now. The fuse diagram doesn't show EFI. ?? Which fuse is it then ??

[Katmandu]

but if the engine is running smoothly and compression checks out ok, then it was just a piece of carbon or slag that got into the cylinder.Thing is back to normal! :bigthumb

Bought a compression tester and plugs and went at it.

I undid the connector behind the rear bumper (for the fuel), pulled all the plugs and got dry compression readings. Here's the result...


155
165
150
150
155
150
150
155


It was actually plug #8 that had the debri between the electrodes. Still have no idea what it was. Probably just a carbon deposit.

I'm assuming since the compression readings are very good, that the short block/piston/rings are in very good shape still as well.

I still have blow by from the bad valve seals though. This will be remedied with the upcoming H/C/I swap! :bigthumb

Today was a good learning exercise for me and really served to MOTIVATE me to do the H/C/I swap! :headopen:

[Foxxx5oh]

good to hear it was something simple! had that issue in my sol once, but it turns out a plug wire came off the dist. cap somehow and had me baffled till i started checkin plugs...LOL

[85_SS_302_Coupe]

Yeah you got real lucky! You can imagine my surprise when i pulled mine all apart to do lifters and ended up finding a blown head gasket. I almost didn't pull the heads since you don't have to just to swap lifters, but a buddy gave me some lightly ported E7s that i figured were better than my stock E5s so i swapped them...that's when i was shocked by the head gasket. It blew out between 2 cylinders so i didn't get a lot of smoke even after it blew out.