ECU wet, or corrosion inside connectors of it? The ECU operates the coils with switching the grounds on/off for each of four coils, gunked up connector could make coils behave strange. Ditto for injectors, +12 volts goes to all of them, and each one is turned on/off by a ground switched by ECU. See attached.

ECU also monitors the knock sensors and adjusts timing based on them, could unplug knock sensor and look for a change in vacuum due to timing not being skewed, should turn on a check engine light.

RAVE says:

Sparks are produced in two cylinders
simultaneously, one on compression stroke, the other
on exhaust stroke. Note that coil 1 feeds cylinders 1
and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds

cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3.

 

Is sparking on the exhaust stroke done on any other engines or is it a LR thing?

 

Other engines also. But we know swapped plug wires will do it, now what natural "problem" could simulate that to achieve the low vac?

 

Lost spark is used on many engines. It is not exclusive to LR.

I recently looked at an older Town car with the 4.6L OHC. The woman was told the cam chain/tensioner assembly needed to be replaced as it was making a hell of a racket.

I first thought it was indeed junk, the entire front of the engine would need to come apart to repair that. Upon closer inspection I saw #1 plug wire looked like it was a little higher than the rest, and it was. I pushed it back down and started the car. Noise was gone, and it came right back! Pushed it down again and noise went away. What?

The plug in that cylinder suffered a total mechanical failure and lost the center electrode along with the ceramic. Compression was blowing out the gap between the ceramic top and the steel base, the top was just flopping around in the base.

The noise that sounded like a metallic knock, which was assumed to be the timing chain hitting the timing cover and everything in proximity, was actually the SECOND spark! The second spark occurs when there is no fuel in the cylinder and sounds different than a spark that ignites fuel. Or at least it does when the plug is blown up.

I put a set of plugs in it. The lady is still driving it. I still don't know where the ceramic bits and center electrode went.

The point to this long post is this. THINK OUTSIDE THE BOX AND LOOK AT EVERYTHING!

 

Hey Danny its a 1998 Discovery LE 4.0

 

Hey all, today I plan to pull each plug wire individually to see which cylinders are strong of weak. One of the coil towers is eroded(the plastic tower is sorta rotted away) down to the top of the metal connector. All the others appear normal. What'd cause this. Bad connection creating temperature issue at the tower? Without a scope to anylize the spark profile diagnosing plugs and wires continues to be throwing parts at it. The uniform compression and steady vacuum indicated sound valves and rings. The valve timing could still be wonky but that should manifest as a low compression. It's gotta be some external control issue or something like the plug wires crossing. I was wrong on the mileage it's 140,000 not terribly high. When it started acting up the previous owner thought it had maybe 5 gallons of diesel put in mistakenly by an amatuer who borrowed it. Simptoms were black smoke from exhaust and poor mileage. Previous mechanic had cleaned the plugs then given up and the vehicle sat for a few months.
How can I test the ECU without changing it for a known good one?

 

Happy Easter holidays all. Thanks a ton for all your time to diagnose and replicate problems.
Re Savannahs post on plug wires. That test says that it could be electrical malfunction. That bad coil tower could freak out that coil thus those 2 cylinders. That should make it skip but it feels like it runs too smooth at idle and off idle. Maybe pulling the plug wires today will yield more information.

 

Glad to hear of the progress and admire your determination with it.

Since you found that coil damaged/severely degraded, I would definitely plan on replacing at least that one coil pack. There are 4 separate coil packs.

I hate where they are located. It would be sweet if they were such that all the drivers side could route to one smaller bracket mounted on that side, and same for the pax side. But the grouping does not support that.

I just hate the way they are basically blocking access to the O2's and that ara down there. Anyway, I digress.

I knoww the replacements are available to just replace the damaged one, but I would consider doing all of them just to avoid doing it again later.

Hope it does turn out to be something simple for you.

The story about the 4.6 is good one to know. I wonder if that plug may have been damaged upon installation. I recently brok one of my new champions. The socket slipped a little and snapped the neck right off, but I knew that immediately.

 

Hey Danny thanks for the encouragement. THe coil pack is still loose from when I replaced the fuel pressure regulator.
Test today involved removing individual plug wires at the plug to check for cylinder hitting. All 8 are on it! Spark will jump 2 inches looks like lightning down there.
My daddy told me if you got gas... and you got spark...you gotta have an explosion. Auto mechanics class told you have to add the right mixture within limits and the right time for the spark. If there are no suggestions I'll think on it another few days. Maybe injectors?
Today I pulled all the plug wires loose and barely stuck em on there. After starting the engine(started right up) removed #1 cylinder is hitting judging by the engine noise changed, following ST Vitus dance from leaking insulation on the pliers shut down motor, reattached that wire. Restarted engine and pulled #3 cylinder, is hitting, following reversed ST Vitus dance, shut down engine and reattached wire. More tape on pliers. Tried #5, cylinder is hitting, Irish jig, pliers still leaking(gettin tired of this) #7 next, cylinder hitting, Texas 2 step.
Basically same process for the passenger side even numbers, never got used to the rural electrification experience but at least it was consistent no matter how much tape on the pliers. Dances continued to change, Scottish jig, waltz, Schottische, Western Square, The Jerk.

 

I have been lit up with 220 in an industrial setting and it does not hurt as bad as the 60,000 volt dc discarging thru your body does. I was operating a 220 volt concrete vibrator (called a donkey D**K) at Macon Prestressed Concrete yard as a 17 year old summer laborer and it was raining and we had started pouring. When you start a pour, you are committed to finish pouring.

Another worker shorted my vibrator lead to the metal bed with a huge concrete rake. I had on one of those yellow macintosh rain slickers and you could see the sparks running on the outside of the raincoat and leaping to the metal bed below.

That motor was on a strap under my arm and shocking the devil out of me. I pulled a Hulk act and rared back with the motor raised above my head and hurled it as far as I could. You have no idea what you can do when you know you must reach deep just to survive.

Some people think I am blunt and insulting. They do not realize that I am merely direct. If I think something is lame, I say so. In the same way, when I do think something is good, worthwhile or deserving of praise, I try to be just as direct.

I admit to be outspoken and sometimes a little to quick to blurt out what comes to mind. I try to say just what I feel should be expressed without falsely encouraging someone merely to make them feel good about something.

From what I understand, you stepped up to help someone when they really needed it. That alone is admirable. I applaud you and wish the best both to you and your friend in the days ahead.

I am happy to assist with your efforts.

For a sixty year old man, I feel like I am doing pretty damn good for myself these days. Just need to find a few more fun things to do. Can't wait to get out fishing and golfing soon.