freddyuk

Hi all,

In dealing with replacing my dizzy caps, rotor arms and plugs, I have examined the bores on my 4.7 with an endoscope; the tops of the pistons look a bit oily and there's signs of what looks like oil dribbling from above, poss valve stem seals I'm told? Otherwise there's no obvious scoring or massive carbon build that I can tell. What's the general consensus? It's a 1985 S2 auto 4.7.

Thanks guys!

Mark

C531XHO

Check for blue exhaust smoke after pressing throttle after overun...

freddyuk

Thanks, @C531XHO I'll look for that when I next take it out

Jim M.

Do a leak down test. That's the only sure way to determine if it's rings, valve seals or valve seats.

dr bob

Hi Mark --

In addition to valve stem seals, take a look in the 'belly' of the intake manifold downstream of the throttle body, looking for oil that's carried over from crankcase ventilation. Your engine has an air/oil separator of sorts, but as the engine wears you'll find that blowby increases and that separator can be overwhelmed by the additional vapor volume. The telltale is oil puddling in low places in the intake manifold. Your endoscope should make this inspection very easy.

GregBBRD

Start with the most basic questions first:

1. How much oil does the engine use?
(A quart every xxxx miles.)

2. How many miles are on the engine?

freddyuk

Thanks chaps,
I'll poke the scope in there when the battery is charged up.

Only had the car a couple of months, driven less than 100 miles so far so no idea about oil consumption as yet. Engine's done approx 120K miles @GregBBRD

Another question, how easy is it to get the intake pipes off so I can get at spark plugs 7 and 8, as I may have started cross-threading 7! Backed off before going more than a thread or so but it's definitely not going in right, too tight, so I want to get at it vertically and try (carefully!) again. Damn!

GregBBRD

Don't worry about oil consumption, until you measure it.
Severe oiling will show up on the spark plugs. Put a new set in, go put some "real" miles on it and then see if there is an issue.

Manifolds jump off:
Remove the injector rail (with the injectors), remove the two intake bolts on each manifold, loosen both hose clamps on the rubber intake boot, lift up a little bit on the outer portion of the manifold, and pull.
At a minimum, you will want to replace the lower injector seals, possibly the fuel injector hoses (if they show any signs of cracking), and the individual intake gaskets. If the intake boots are "pregnant"....replace those, too.

Make sure you replace the injector hoses with the proper hose. And use the old "hats" on the injector and fuel rail. No clamps!

freddyuk

Thanks @GregBBRD
Great info, see the plug pic here if you have a moment. Manifolds - might try and get the plug in again straight without doing the manifold - I seem to start one small job and end up breaking a dozen other things in the process, Lol!



This is what most plugs are like, some less carbonised than others and if you scrape the carbon off they're brown underneath. As you can see there's a lot of oil on all plug threads.

GregBBRD

Looks excessively rich, especially since all plugs are the same. Check to see if the dampers or regulator have raw fuel coming out of vacuum side.
Check temperature switches for injection.
Check throttle position switch for idle, cruise, full throttle.
There is no O2 sensor to "correct" MAF on a stock Euro engine. Depending on what was done to federalize your car, this could be an issue.
True Euro injection is mostly dependent on MAF. Perfect condition is an absolute must! Some rebuilds, out there, suck!

Hope this helps.

freddyuk

Thank you Greg, I'll be honest, I'm past the limit of my knowledge at this point so I'll need to take some smaller steps to figure some of these things out.

Am hoping that I can run it for a few months, then dig into some more major work, learning along the way and renewing everything that's worn out, hoping the car is not more of a project than I can handle.


Oily coating on the piston crown, it scrapes off easily when the scope touches it.

GregBBRD

Yes, way too much fuel.
As an engine breaks in, carbon will form in the center of the piston.
As the rings seal, the carbon will form all the way to the edge of the piston.

Your engine is running so rich that the rings are no longer sealing very well, and the carbon that should be between the middle of the piston and the edge has been washed away.....and the center carbon has gotten very soft.
You need to get the fuel mixture to be leaner and allow the rings to be "happy" once again....before terminal damage occurs.

Probably the best (and not too expensive) tool you could use is a wide band O2 sensor....to see how rich the engine is. Then, when you find something that is out of specification and you change it, you will know if you've correctly repaired the car, or not.
I just realized that you are in the UK, so obviously, the car was never "federalized" for US use.
You should have a mixture potentiometer connected to the wiring over near the computers.
Try setting that potentiometer "leaner".....might be as simple as that.
(Again, a wide band O2 sensor would let you know if the potentiometer is changing the mixture and how far to turn it....other wise you are just guessing.)

freddyuk

@GregBBRD Thanks! This sounds like something that is within my capability, is there a wide band O2 sensor that you can recommend? I've never come across one before. And I assume the pot is in the footwell near the fuse board somewhere?

C531XHO

...maybe a trip to Braunton (?) for an hour or so of appraisal/diagnostics..I think they are quite close to you?

I took my last 928 to Lowe Bank (my nearest at the time) and got a very useful list to work through myself

freddyuk

Yep, have been thinking that would be a good idea, thanks matey. There's Crispin Manners at Oaktree as well, not been there for a couple of years.