I have a 1991 4.9. About every 9 to 12 months my #1,3 and 4 spark plugs look like this. What kind of problem(s) am I looking at.

 

Holly 5H17 that's after less then a year and it's been doing that for years?

What other symptoms does it have, do you know what spark knock sounds like?

You need to take a close look at what the deposits are, hopefully ash.

There's at least several things going on here, very likely 3 separate issues. First and most serious is detonation/pre-ignition/spark knock, all basically the same thing. Your engine will sound kinda like a diesel at times. Like it has marbles bouncing around in it.

Second, it's not burning clean, likely something along the lines of or combination of worn injectors, worn intake valve seals, and excess crankcase pressure. These things are introducing oil or liquid fuel to the cylinder and it's not burning complete.

Those plugs are likely too hot, hard to tell with the other damage, but I would definitely get colder ones.

Hot plugs combined with buildup in the cylinder will work together to cause detonation. Keep in mind what builds up on the plugs also builds up on the head and pistons, but those don't get replaced when you replace the plugs.

I'd start by doing at least 4 things, replace with colder plugs, start listening for knock, run only premium for a while, and better vent the crankcase. Several times in this forum I've written of the benefits of an upgraded PCV system, maybe find that. Last but not least DO NOT leave them in so long, pull the new plugs after about a week and take a look.

 

Pictures....http://www.aa1car.com/library/reading_spark_plugs.jpg

 

Semantics maybe but pre ignition and detonation are not the same thing. An engine can survive some detonation (still a bad thing) where pre ignition is rapidly disastrous. However for this discussion it likely doesn't matter.

Has the motor ever been rebuilt? What spark plugs are in it currently (model, so we know heat range)? Does it use oil?

 

True and true, but very hard for the average even professional mechanic to know the difference from the symptoms. They sound the same, and can have similar causes, pre-ignition just isn't as effected by ignition timing. And for this discussion that plug damage could be caused by either.

One more thing for the OP, there's a chance you're getting some oil in your intake from the PCV system, that could explain both the damage and maybe why it's only effecting those cylinders.


Edit, also please show us the other plugs, all 6, that will tell us more, if it's systemic or just three cylinders.

 

Sorry for slow response. Just finished working 3 straight 12 hour shifts. Within the last 1 to 2 years I have: verified timing; removed, cleaned and rebuilt the injectors; new PCV; new plugs, wires, distributor cap and rotor. The engine sounds and runs great. I do not see any blue smoke out of the exhaust upon starting or when idling. I didn't take pictures of the unaffected spark plugs. This is the worst of the 3 fouled spark plugs. I hear no detonation/pre-ignition/spark knock. I have pulled the plugs after 1 to 2 months of driving and they have a little deposit build-up. I bought this truck used. I have had it for 10 years. No idea if the previous owned rebuilt or replaced the engine. I do notice at times during cooler weather more vapor out of the exhaust. Maybe coolant from head gasket leak. I attached another plug photo. I did not take pictures of the good plugs. I will post the plug brand and number later today.

 

plug photo

 

Electrode looks intact, just ashy. How is your oil consumption?

 

I am using some oil. About 1/2 to 3/4 quart every 1000 miles. Losing some from rear main seal. A few other wet spots around the engine. No oil smoke out of the exhaust though.

 

This says you have some significant wear leading to excessive blow-by and excessive crankcase pressure. You need to increase the venting/PCV capacity of the engine. Stock venting and PCV is rather restrictive, designed for a new engine, and can not handle enough flow to keep up with a worn engine.

My first suggestion would be to gut the PCV valve, just cut the bottom off and let the guts fall out making it just a fitting.

 

You don't necessarily have to have excessive blow-by to have worn oil control rings. I would say almost a quart every thousand miles could possibly foul plugs like that.

I would recommend going through your PCV system, replace the valve with a new OEM Ford one, and make sure the crankcase vent is clear.

 

FWIW my line of thinking is that the leaking rear main is evidence of excessive crankcase pressure, it really can be nothing else.

That excessive pressure isn't causing an oil ring issue but a valve seal issue. Valve seals in these engines are passive, excess pressure will tend to push more oil down the intake valve guide.

Secondly excessive flow speed in the PVC/vent system could be introducing oil to the intake. This is hard to say, for me anyway, I'm not 100% up on the details of the PCV/vent in a EFI 4.9.

 

I mean, rear main seals do wear out....

 

Barely eventually, but even new the term "seal" is generous, they're more like wipers. New or completely trashed seals like rear mains whether they leak or not has more to do with the pressure difference between the inside and outside of the engine then the condition of the seal.

I'll tell a little story, the 87 F350 with a 460 in my sig I bought hmmm, maybe 8 years ago, it was a bit rough, no idea the miles, but a runner. I had about a 10-15 mile drive home on mostly freeway, that was interesting. The engine had/has so much blow-by that the rear main was leaking so bad that the cars behind me where getting misted with oil and I used 2 qts in that drive home. The first thing I did to that engine was a PCV tweak. I took where the PCV connects at the front of the carb and put a 3/8" tee on it. On the drivers side of the tee I took the vent hose that went from the fill cap to the air filter and connected it instead from the fill cap to the tee. I then took the PCV valve from the passenger valve cover and ground the bottom off of it, dumped the guts out and made it just a fitting. Basically I tripled or quadrupled the flow capacity of the PCV system and removed the vent.


From that point on for the next about 6 years I haven't opened the engine and have driven that truck all over, used it as my daily, to travel the country, etc. Over that whole time it hasn't leaked a drop of oil, hasn't fouled a plug, and hasn't used more then a quart of synthetic oil per 5000 mile oil change. I still haven't opened that engine, it's still a runner, I just don't drive it much anymore since getting the 89 diesel.

In just about any engine if you can keep the pressure in the engine lower then the pressure outside they'll almost never leak unless the hole is really big. More so if you can get/keep the pressure in the crankcase as low as the pressure in the intake manifold they'll almost never use much oil.

 

Just saying, but I've seen plenty of engines with 0 blow-by, working PCV systems and bad front/'rear seals that just dripped and leaked oil. Replacing the seal completely fixed the issue.

Most diesel engines just have a draft tube - not even a PCV system, and they don't hemorrhage oil out their seals unless they go bad.