bigbadon

x2 that was my first thought too. Idle speed = high intake vacuum so thinking logically there may be a co-relation.

Charlie Foxtrot

I think investigating the coil pack (and its wiring) are worthwhile, and cylinder #5 specific spark issues should be ruled out before proceeding. One would have to assume that the primary side and the coil itself would be ruled out as these are shared between two cylinders and only one is affected. Thus an ignition issue would be limited to the #5 high tension side of the coil pack/plug combo.


It is possible that there is an issue with an intake runner & oil leakage, ie: bad gasket or a crack w/oil leak above it. (this scenario is unlikely, but should be checked as part of the diagnosis)


Another non-invasive test you can try is a cylinder leak down test on #5. In a very quiet shop, roll the engine to TDC on compression stroke, prevent crank rotation, pump air into the cylinder (start low, then work your way up gradually) and use a mechanic's stethoscope (or very sensitive microphone/audio amplifier system w/headphones) and start listening for the escaping air. Go to the usual places - tail pipe (exhaust system), intake, oil sump (dip stick tube), inside valve cover. pull the rad cap off, watch for bubbles. If you don't hear escaping air (or see bubbles), you may have to take the valve cover off, and stick the stethoscope right on the valve stem/guide junction. 120 psi should be sufficient to find most leaks. If nothing obvious shows up, depressurize the cyl (let the air out) and roll the piston to BDC, valves closed. Re-pressurize the cylinder and listen to the oil pan, etc. Some time this is the only way you will hear/detect a bad lower ring(s). This is a result of changing the direction of the force applied to the ring(s).


Good luck, this is a true 'head scratcher'. Remember it's the tough diagnosis that make a good mechanic. Anybody can swap parts, mechanics diagnose and fix the 'Problem'.

dave1123

Charlie, I'm not trying to put you down, but I've been doing cylinder leakdown tests for more than 40 years, but I usually only used a piece of hose for my stethoscope! The new coil rail appeared at my door today. If the oil smoke disappears after I install it, I'll go from there. The past couple of days it's been less than 20* with light snow and I'm not young anymore! No garage, you see. Well, I do, but it was designed for a model T. I'd have to fold the mirrors to get the WJ inside, AFTER I clean it out! Not happening.

BTW, you won't hear any air leaking around the valve stem because it's inside the intake manifold and isolated from the cylinder. If the valve seat is leaking, you'll hear it in the throttle body. When doing the test, you should block open the throttle so you can hear the sound better. Likewise when doing a compression test, the most important part is the pressure on the first stroke. It should be around 3/4 of full pressure with good rings. Worn rings might give you 40 on the first stoke and pump up to 100 maybe.

The internal high tension leads in the coil rail are always a problem. Especially with #1 and #6. The lead to #6 runs all the way back from the first coil to the plug and has a history of shorting internally. This should hold true with the other coils as well.

Cleman Simpson

Good luck with it Dave and keep us posted as to what you finally discover is the culprit. I was going to work on my WJ some today but it is cold enough outside to make my arthritic hands hurt so that's off for now.

dave1123

Yup. Time to relax with a cup of Irish coffee!

Charlie Foxtrot

No offense taken. Not sure if you'd ever done a leak down. If you can use a hose, good for you. That means you've protected your ears all these years and can still hear. As for cold, it was 14F/30mph here yesterday & its 19F/calm today (snow, cold & wind was Wednesday). Most of the equipment I work on this time of year is to big to get inside. I just got my furnace installed & running in my shop on Wednesday so I understand. Of course that meant the furnace in the house decided to quit in the middle of the night (jealous, I guess). Good luck with the coil rail, hope it's the cure. Try to stay warm.

marklar134

sounds like its time for an LS swap

dave1123

Northern Illinois, huh? Funny, I spent a short time at NAS Glenview. If I remember correctly, the frostline is about 10 feet down there, right?

Why is it a furnace ALWAYS dies in the middle of the night?

97grand4.0

Dave have you done a fuel pressure leak down test to rule out a leaky injector or O ring? That's the first thing that makes sense to me given what you describe.
Carbon fouling sounds like rich, leak would make it rich, also do a great job of lubing everything to give great compression results.

dave1123

Now we're grasping at straws, aren't we? How is a leaky o-ring going to make it rich? A leaky injector will cause it to be overly rich and cause cylinder wall washdown, diluting the oil, and problems starting it. The beast starts instantly, runs smooth, and settles into a normal idle quickly. It doesn't smoke until the cylinder temp gets up to normal and the oil warms. Like maybe 3 to 5 minutes of running. I can let it idle for an hour before it starts to get whonky, then a rev-up cleans it out, usually. I'm talking 2500 rpm for about 30 seconds.

I was going to try the old flat-track trick of running a hotter plug in that cylinder, say a ZFR4N or a Champ 14, but nobody carries them and a search of the numbers brings up nothing. I can get a Champ, but not in copper core.

Hatsuwr

If the coil pack doesn't fix it... Is there any way it could be a blocked PCV building up pressure after running for a while? If I understand them right, during idle, when intake vacuum is high, the PCV flow rate is lowered. Maybe it's being stopped?

As for why cylinder 5 only... Dunno, maybe it's just the first one to give to the pressure and relieves it enough that the others don't get to the point of leaking. Not an area I know much about!

97grand4.0

Just a suggestion, Dave, you said you wanted brain storms. But if you don't have a fuel pressure tester handy, I understand

Chris Saladine

My first thought was the rings as well. Different engine completely, but I had a Chevrolet 350 with what turned out to be cracked piston rings that acted similarly. If you rev the engine in park with no load on it, does it smoke less, the same or more?

Charlie Foxtrot

NAS Glenview long gone - very expensive, upscale, high end real estate. Ditto Fort Sheridan. Hundred year old barracks turned into half million dollar condos. About a third of Great Lakes seems to have disappeared over the years also.

About 45 years ago I caught a 'hop' on Christmas from NAS Buckley to NAS Glenview on an R4D destined for decommissioning in Illinois. The plane couldn't finish the trip - engine trouble. Planes, like furnaces always die in winter, and at night.

By code, the frost line is 42" to top of pipe. Too bad that the frost can't read the code. Today was 55F no wind. Top 2" of turf = pure mud w/ice below. Furnace works great today - haha.

Any luck w/coil pack? Did you find a hotter Champ? (maybe a Champ R14YC, NGK BKR5E, Bosch FR10DC, might work??? I dunno, don't have one on hand to examine.)

Good luck, stay warm!

dave1123

My dad went to ASW school at Glenview flying the S2F Tracker learning how to track a couple of old WWII diesel subs in Lake Michigan. Being a military brat, I spent some time on base, but we lived in a trailer in a nearby park. They were putting in a new sewer service there and the ditches were 10 feet deep! If I remember correctly, this was in Lake Zurich.

I did my Basic at "The Lakes", but that time was a fog in my memory, if you know what I mean.

Everything right now is in limbo with the jeep. After idling for a while, a rev-up makes a lot more smoke, but it clears out after a bit. I'm currently keeping it from fouling by getting warm, shutting it off, getting cold, and rewarming it. My buddy's garage has a waste oil heater and I'm going there Monday morning.