Dead Cylinder

[tercelwill]

lately my trec has been running rough. It's hard to tell because i haven't paid much attention to her in recent months other than routine maintenance so i figured i would do something about it today. when i got home i let it idle and just listened. It's not running terrible but there is valve train noise and a little vibration. i started pulling spark plug wires for a rpm drop test. pulled cylinder one. no rpm drop. pulled cylinder two, very slight drop. cylinders three and four both had a good healthy drop.

I know there is spark to all four. I could hear the tap tap of the spark on one and two but it was seemed weaker than three and four. The spark was thinner and wouldn't travel as far.

The vehicle just turned over 200K. The plugs are only six month old NGKs gapped with precision. I have replaced the igniter, cap and rotor in the last few years but not the plug wires. the wire for cylinder one actually came apart as i was pulling the wires, ripping the metal contact from the boot. but there is still spark when i jam it back together.

At this point i'm hoping the wires aren't carrying enough spark to make the plug jump but my fear is that my head is done for or my piston rings are gone. It never burns any oil. The exhaust is clear. The oil has no signs of water but the head gasket is slowly seeping oil right at cylinder one.

I'm going to put in new plug wires tomorrow and see if that makes a difference.

i'd appreciate any help you all can give, thanks

[sunray]

You can test the plug wires by misting some salty water over them using a spray bottle. Look for arching, that is bad. Then check the resistance of each plug wire with a dvom. Should be 10,000 ohms per foot but not excessive. Try doing a compression test, it will reveal the condition of the motor better.

[tercel4wdrules]

That almost sounds exactly like the problem I have with my silver '84 SR5. I had the carb rebuilt and the guy noticed my car had a misfire, I had noticed it too, it had slowly gotten more noticeable. He pulled the spark plug wires and cyl #1 had almost no rpm drop, #2 was a slight more drop, and #3 & #4 had a normal rpm drop. He checked the compression in cylinder #1 and it was fine. Next step he looked for a vacuum leak, there was one at the intake runner for cylinder #1. He tightened the bolt and the nut and it smoothed out. That didn't last long however, within a week or so, it was misfiring again, now more noticeably. In my case, it shakes at idle and continues to shake more pronounced until a bit above 2,000 rpm where it begins to smooth out. I found the cause is still a vacuum leak at the intake manifold, the stud for the manifold on the head is stripped, the nut and stud just spin. Since it looks like someone previously used JB Weld on the head I have decided I'm going to leave it alone for now until I can get another cylinder head, I don't think it's worth fixing this one, it has probably suffered serious overheating in the past. Therefore, I would start by checking for vacuum leaks around the intake manifold as the bolts and nuts like to come loose and then take it from there. If you have a decently large vacuum leak you will see it affecting the mpg too. Good luck, let us know what you find.

[takza]

I think you can get to all the manifold bolts without removing anything except for maybe 1...just be real careful about how much torque you apply...snug...not STRIPPED.

[takza]

. I found the cause is still a vacuum leak at the intake manifold, the stud for the manifold on the head is stripped, the nut and stud just spin. Since it looks like someone previously used JB Weld on the head I have decided I'm going to leave it alone for now until I can get another cylinder head, I don't think it's worth fixing this one, it has probably suffered serious overheating in the past.

If you think the head is "junk"...you might try retapping the cylinder head hole in situ for a larger bolt/stud IF it is in an accessible place. Just go up one size...metric or SAE...use a bottoming tap? Or put in a thread insert?

[Petros]

I would check the intake and exhaust manifold bolts, they tend to loosen up with temp cycling. Not all are easy to reach, you have to bend back the heat shield for the center top one (and than bend it back), use an open end 14mm. with a mirror you can reach the bottom manifold bolts with a box end wrench, also 14 mm. The rest can be reached with a 14mm socket and extension (a u-joint helps too). It is easiest if you remove the carb and heat shield, but I would not do that unless you need to remove the carb anyway.

While you are at it check all the vacuum stuff on the front runner of the intake manifold to see if any hoses or devics are leaking extra air into the front half of the manifold, making the front two cyl. extra lean.

It is possible the head gasket is failed between cyl. one and two, this is the most common place for them to fail in my experience. You also have oil leaking in this area, so that is likely. Though you usually loose water when it fails here, and you will not always find the compression test indicates bad head gasket. I would not pull the head unless you know the gasket it bad. low compression could also be because of burnt exhaust valves, cyl one and two are the hottest running cylinders and if you run the [idiot] emission spec 5 deg BTDC spark timing you could burn the exhaust valve (I have burned two exhaust valves, but none since I now run 10 deg BTDC). Either way, if you get really low compression in cyl 1 or 2 (like 0-20 psi), the head has to come off. Rings usually wear out more evenly, and not a reason to rebuild unless they are really shot.

Good luck.