2 dead cylinders
 

Last week i got my 86 series 3 xj6 registered on the road for the first time since 2007, i reringed and new bearings and the head was done at a machine shop, car ran well but have to adjust the kick down cable.
i drove about 70ks, stopped for a drink and on restart car was missing, got home and checked the obvious with the conclusion cylinders 2-3 were both 120psi when others were 150-160, when i pulled a leed on all cylinders 2 & 3 made no difference although they were getting spark and fuel.
I pulled the head and replaced the head gasket although it did not reveal any thing obvious, now the engine is all back together its still the same, 2-3 are lazy with 150-160psi.
Any ideas?

So is the compression on 2 and 3 fixed now?
If so the first thing I would look at are the leads, distributor cap and plugs (if you didn't change them already). The next would be the injectors on those two cylinders.

I agree.

With so few Kms on a rering, the rings a loooooooong way of being seated.

You did hone the bores, right??? I hope so.

If its running on 6 cylinders, give it some stick, and being Aussie you know exactly what I am saying.

Treating these engines with kid gloves will KILL them in a heartbeat.

My engines, and there have been many, have had a very hard life from revolution #1. The daughters S2 4.2 got some serious stick. How do you tell a 17YO to drive "quietish" for a few hundred KMs, HAHAHA. She was gone for 3 hours and went testing against her boyfriends Skyline, and I really DO NOT want to know, but that engine ran soooooo sweet.

If its NOT running on 6 cylinders, you MUST sort that first and foremost.

The fact its got compression, eliminates tappet clearances, so its only fuel or spark remaining.

have pulled injectors and they squirt fuel, juggled plugs and those two cylinders are still dead, 150psi on both dead cylinders.
leeds and cap are new and spark is getting to the plugs, no light show in the dark.
bores were honed
Im missing something that will hopefully click into place

150 is not dead.

That is more than enough to run, and run well.

What are the other 4 reading?

last Monday when the car was registered and first driven it was running well and later that day dropped two cylinders[no difference in running when removing leeds on 2 &3, compression test was 120psi on those two cylinders while others were all 150-160psi, so i figured the gasket was gone between 2 & 3, so new head gasket 2 & 3 now at 150-160 each but still not running

Yup. 150 is more than enough for the cylinders to run just fine.


1. What do the spark plugs look like after running the engine a bit?
fuel fouled? Oil fouled?


Try a pair of known good spark plugs.


2. Spark at the plugs isn't enough, it must get in to the cylinders.
A pair of leads that look good, but with bad ends at the plugs?


3. Two bad spark plugs. New doesn't always mean good nowadays.


4. Not sure about this idea. but, swapped plug leads does weird things??? Way back when, I finaly got my T speedsters engine to run. Preety good, albeit on only three of it's four cylinders. On a whim, more or less, I swapped number 2 and three leads, one for the other. Luck or intuition? All four chugging away. I timed it on the wrong TDC. No guiding marks on those simple little fours. 1,2,4, 3 order as I recall??


So, check the sequence at the distributor cap.


Carl

Just adding my findings over the years.

I dont use Resistor spark plugs, so in that engine NGK BP6EY is what I use.

The colour of the spark plug tips will help.

For 2 cylinders adjacent to not work is certainly odd, and the head gasket was a perfect diagnosis, but they have compresion, so the valves are sealing, the rings are sealing, the gasket is also sealing.

Just for that sake of suggestions.

Remove the leads from the cap, one at a time, so as not to mess up the sequence, and ensure that the end of the lead, and the cup in the cap, are not corroded. This has caught me out a few times.

I know you have spark AT the plugs, but when they have to "fire" under compression pressures, they can fail due to resistance in the system. My favourite engine, the V12, does this very well at 12.5:1 comp ratios.

If the plugs are fuel damp, then injection into the cylinders is happening, but there is no spark to burn it.

If the plugs are WET, then you have overfueling, and the spark will never burn that much fuel. It just floods the system, fouls the plugs.

(snicker) That reminds me of a certain red-haired teenager who took her parents' station wagon out racing her bf's mother's hot little Celica. The Celica was Much lighter and more nimble and maneuverable but the wagon had the raw power.

The race ended at the tracks where the Celica flinched for just a split second while the wagon caught air and won by a considerable margin.

Oh yeah!
(';')

If all compression's are good then have you thought about a possible air leak in the intake manifold. Breather hoses are fun things to leave off and can get the mind thinking of worst case scenarios. I was always told as an apprentice to use the KISS theory. Keep It Simple Stupid. something i always approach engine problems with.

Love it. Occasionally my natural instinct to give aging machinery an easy life goes out the window for no other reason than pure devilment.

Scenario: Young buck in his racing car (aka faded red family sedan with boom box and wide pipe) pulls alongside at the red light. Of course, he's changed lane to avoid getting stuck behind the sedate old Jag in front. He has no will to actually race, what's the point without competition? Light hits green, older Jag guy momentarily grows horns and gives her some real stick, Jag starts yelling "yeah, that's it, that's what I want, let's go for it" growling and pulling like a freight train, enjoying every second! Racer wannabe with dropped jaw still in the rear view. So much fun.

I can justify it, I can, I really can, I call it education for the young bucks - don't under estimate or mess with anything you don't understand :icon_twisted:

A pair of miscreants! you would never see me behaving like that! :icon_angel:

Odds are pretty good I'd never see you due to distance, and I'd be willing to Bet that's the reason Tony would never see you either!!

While I was growing up that was the oft repeated phrase, "If I ever catch you......" or "Don't Ever let me catch you......." So I never got caught.
(';')

:icon_laugh: you have to be careful, some people might believe that!

When I was a kid, a very long time ago, a game called "ditch'em" preceded "stop light drags". A guy who went to another school was the
one to beat. A circa 32 Plymouth tudor, top chopped, not merely lowered, gone. Sans fenders and repowered with a Dodge six cylinder
"industrial" engine. Even the city cops in their spaghetti crankshaft Plymouths couldn't touch it. I tried really hard a couple of times in my
27 hot T. Weird steering and just not enough power. But, off the line,
planetary and two speed axle shifts could not be beat. Good good about a block.... Oh, and the T's steering was too vague to match a four wheel drift on an unpaved street turn....


Oh, most of these encounters were at night, head lights off. Good to have brake lights out. Don't let them out brake you!!! Early version.
Easy for me, T had none anyhow???


How we survived ????


To this day, tis fun to show that the old brown car can go pretty durn well.


Carl

Decades later, bob of the old ply mouth and I worked together in Los
Angeles. he, Ass't Claim Manager, and I, lead Clam Supervisor.
We both drove lowly VW's as commute cars. At quittin' time, we raced from the roof top park lot to through the streets to the Hollywood freeway. Learned the cop car start there. Crank the engine with the trans in low. Just a bit of a "head start".


From time to time, we raced "slot cars" at a local track. Hand/eye coordination and reaction was the race. Just a flick of the thumb at
entering a turn. Power on/power off. Slow or miss opponent gone...
Or your car off the course... We could out brake most there. Win.
Most of the time, Bob was just a shade faster.


Messing with motor windings for more RPM, stickier tires, lighter car,
faster controller, etc... A model Chaparral, my favorite....


Carl