Bad Valve?

Alright, start off with, no I have not done a compression test. I do not have a tool to do a compression test, I do not want to spend money to rent one, and the people I know who have one, theirs are broken. So, with that said, here is what I have. When I push the gas pedal all the way down, I get a big cloud of black smoke behind me. Would you guys say it's a burnt valve? How hard are these to fix? I do not have a Haynes manual or anything of that type (from what I have heard, I should invest in one). Please let me know what you think!! Thanks in advance.

In your other thread, the smoke out of the exhaust was blue and also came from under the engine when idling.
Better get ready to spend in piston rings and/or valve guides.
If you had a burnt valve, the symptoms would be different: some cylinder would not fire well.
What do your plugs look like? (brown/black deposits on the inner ceramic?).

I think you need to invest at least a little, and what I'd recommend for starters is a vacuum gauge. I don't think they are that expensive (haven't bought a new one in years, because they show up here and there free anyway....). If you buy a new one it will probably come with at least rudimentary instructions on using it for diagnosis. A vacuum gauge is a great tool which can detect many problems, one of the chief ones being a bad valve.

If you're getting black smoke but the engine is running evenly and not missing, my guess is that it isn't a valve.

Ditto what Matthew said.

A bad valve would result in some sort of skip or other unevennes, not black smoke. Black smoke indicates an overly rich mix. How's your oxygen sensor?

If you want to check for a valve, start the engine and let it idle. You need either an idle tachometer or a helper to watch the tach. One at a time, pull the wire off a spark plug and observe how much the RPMs drop. If one cylinder has a bad valve, bad spark, or anything else funky so it isn't carrying its full share of the load, there will be LESS of a drop when you remove the wire from the bad cylinder.

If its black smoke and not blue smoke (like in your last thread) it is most definatly a over rich fuel situation. Check the O2 sensor for carbon build up first (always start with the easiest thing first). I really think you should invest in a compression gauge (I bought mine a Sears for around $20) And do a good compression test. You could also have a bad injector as in one may not be closing all the way or has build up on it causing it not to spray properly . There are many other things you can check also . This is a great place to learn things about your XJ but nothing can beat investing in and reading a good manual and also investing in the proper tools to repair your hot rod. Good Luck!

MyLittlePony:
I would be careful pulling those spark plug wires. If you pull them loose at the plug end, you will likely get shocked. I think the system developes about 25,000 volts and doubt the plug insulators will contain it. Better to pull them loose at the distributor cap. Just keep your hands clear of the cap when the wire is disconnected.
MoFo

If you pull them by hand, you'll get a shock regardless of which end you pull. Get a set of spark plug boot puller pliers with insulated handles, or wear rubber gloves. HEAVY rubber gloves.

it sounds like the egr transducer is giong bad. i would check the egr valve also

I can attest to the fact that you will receive a shock if you just pull them off by hand. It won't hurt you but at the same time it doesn't feel really good.

OK, Pony:
Adding the info in your two threads, I gather we're all suspecting a burnt valve, a bad rear crank rear seal or bad rings/valve guides.
To discard a bunt valve: If your engine misses regularly, like once or twice per revolution, then it's probably a valve. It's unlikely that you may have burnt them all at the same time. Your engine probably wouldn't start. The selective sparkplug disconnection check can tell you which valve(s) are at fault. Also, a Vacuum tester would confirm it by showing a regular dip.
Since you report having actually seen the oil/smoke come out of your rear crank seal, that has to be fixed.
After that, if you have black smoke coming out through the exhaust, then you're burning too much fuel: your mixture is too rich and some sensors are involved. What colour is the exhaust, blue or black? How does it smell? Coast down a hill and accelerate: do you leave a blue cloud behind? Does your idle deteriorate as time passes when at a stop light?
If the smoke from the exhaust is bluish, then you're burning oil. That must come from the cylinder walls (bad piston rings) or through the valve guides.
This can only be confirmed with a compression test.
If rings and/or guides are worn, then you have blow-by that can cause all the openings in the engine to blow smoke. Blow-by is when the compression goes past the rings or out through the valve guides. Usually, also some oil stays on the cylinder walls or enters through the guides; causing blue smoke when it burns inside.
If you take the sparkplugs out (you do have a sparkplug wrench, don't you), then the colour and possible deposits on the ceramic around the central electrode may give us a hint so that we can help you.
If you don't do any of these things and let us know the results, how can we help you?

When I first got my 88, everytime I´d give it a bit too much throttle, it would throw a cloud of smoke. Turned out to be, a plugged valve cover to intake manifold, vacumn line (crankcase ventilation). Air filter was oil soaked, the large valve cover vent (crankcase ventilation), that went to the filter, would suck a load of oil into the filter/intake, most every time I´d get near full throttle.
Been many threads discussing cleaning and fixes for the oil in the air cleaner problem.
Another caution, it´s really bad technique to pull a spark plug cable with your bare hand and your crotch, firmly pressed against the fender. :repair: assgas:

Let's not forget a plugged CCV. If he has a leaking rear main, crank case pressure will spike on accelaration, forcing oil out of the rear main and onto the crossover pipe. Check for resedue inside of the tail pipe, that is a good way to tell if it's comming from inside the engine. Like everyone else has said, get a book and some tools, no matter which way you slice it, it's going to cost you money. So get the tools first before you spend money on unnecessary repairs, and then have to buy the tools to fix it anyway.

Neil

That's right... The CCV.
From your other thread ("Blowing smoke up your...."), I assume this is already done since you cleaned your valve cover. If not, it would be a very good first step.
By the way, is there oil in your air filter? If so, near what part of it?

jldiaz said:

OK, Pony:
Adding the info in your two threads, I gather we're all suspecting a burnt valve, a bad rear crank rear seal or bad rings/valve guides.

Click to expand...

No "we" are not. There's no way a burned valve, bad rings, or a leaking rear main seal would cause black smoke.

Back to the drawing board. Black smoke indicates a rich air-fuel mix. Period. So discard suggestions that don't deal with that, and focus on the ones that do.

Eagle said:

No "we" are not. There's no way a burned valve, bad rings, or a leaking rear main seal would cause black smoke.

Back to the drawing board. Black smoke indicates a rich air-fuel mix. Period. So discard suggestions that don't deal with that, and focus on the ones that do.

Click to expand...

a burnt valve would cause a misfire all the time. the earlier xj's are known to have bad egr valves causing some of those symptoms