Oil on spark plug...bad valve seal?

[Seahawk]

Want to start by saying thanks for all the info I've found on the forum so far, I believe this is my first post.

I've had my buddy's 88 Ranger 2.9 4x4 5spd in my garage for a while now, and am getting pretty frustrated. The truck was garaged because it was blowing smoke and at idle and under load also I believe, and my friend was told the rings were going bad.

I took the project over and first did a compression test, and all the cylinders showed good numbers, although cyl 4 was a tad lower than the rest.

While taking the spark plugs out for the compression test, we found oil on the #6 cyl. The valve covers were leaking very bad on both sides, so I replaced those. After putting that all back together, the water pump took a dive, so I replaced that and also the front timing cover seal, as it was leaking some oil also.

I put it all together with new plugs and wires, changed the oil and cleaned the motor up. I also checked the diagnostic codes and replaced a bad TPS.

The truck ran smoother, but only on 5 cylinders. It also really lacked power, but probably from being down a cylinder I guess. I checked all the wires for spark, all were good. Pulled the #6 spark plug out, and oil was on the new plug. The exhaust smells very rich when running, and it blows some gray smoke after the engine warms up.

The compression test on cylinder 6 was very good, so I find it hard to believe that the ring is bad in that cylinder. So my theory is that one of the valve seals is leaking oil into that cylinder, or possibly even a bent valve, and the oil is fouling out the cylinder.

Does this sound reasonable? I've read the procedure for replacing the seals, and it doesn't look too complicated, although I will have to source some tools for the job. Is there a way to diagnose a leaking valve seal without removing it? Any other theories, cracked head perhaps?

Thanks for any advice or comments.

 

[Big Jim M]

Put another new plug in there and see if the first one was a bad one. Sounds like that plug simply wasn't firing.
It is rare for one seal to go out all by itself! Plus I never saw one that would foul a plug that was firing.
Big JIm

 

[kimcrwbr1]

Bent valve = poor compression it sounds more like valve guide seals you can change them without pullin the heads put the cylinders on TDC and put 30 lbs air pressure in them I used the compression tester with a fitting to hold the valves up after you compress the spring a little tap on the compressor to break the keepers loose then compress it all the way to remove the keepers then check the valves for slop I used a skinny screwdriver to assure the piston was all the at the top in case you lose pressure the valve dont drop into the cylinder. I think I paid $20 for the compressor on ebay and after the first two the rest went pretty fast about 2 hrs total. Just curious did you do a leak down test it will give you a better idea on the condition of the engine.

 

[Seahawk]

Thanks for the replies.

Big Jim, that sounds like a cheap and easy solution that I hope works. I'll try tonight. If I still get oil on the plug, I would assume its abad valve seal. I am running out of other theories, although a leakdown test is something that I still need to do.

 

[Big Jim M]

Sea you would have to have a lot more oil than a simple valve seal to stop a plug from firing. All the other plugs are firing with the same age seals on them.. I'd be making sure that one plug does indeed fire. I would start with a different wire and a different plug.
Big JIm

 

[Seahawk]

Thanks again. Maybe there was residual oil in the cyl when I put the new plug in. Still can't explain how oil got in there in the firstplace, other than perhaps the old plug was loose and oil was leaking in from the leaky vc gaskets.

I'm just hoping its not the ring, which like I said would be hard to believe. The compression is good and for that much oil to get up there from the crankcase the compression test number should have been lower on that cylinder.

I'll pick up some new plugs on the way home today. I tested each wire for spark using my timinglight, but I will also test the continuity of that wire tonight too.

 

[Seahawk]

Well, the new plug worked! Running a lot better. Took it for a test drive and looked underneath when I got home and saw the cat was glowing red. The truck is going to the muffler shop today for a new cat and exhaust pipe.

Thanks for the help. Cheers!

 

[kimcrwbr1]

Cool keep an eye on the plugs if you have valve guide seal problems be careful because oil will destroy your new cat also.

 

[Seahawk]

The saga continues...

My buddy dropped the truck off at the muffler shop to have the cat replaced, and the guy there said that he would not warranty a new cat because he though the engine was not running on all cylinders. Apparently he has had a few 87ish Fords and thought the problem was in the engine, and not the cat.

I am certain it is running on all cylinders (at least it was last night, I didn't drive it to the shop or talk to the guy today, my friend did). It still smelled very rich last night after replacing the one spark plug.

I'm about to drive this thing off a cliff. But before I do, any advice? Here's what I'm thinking:

1. Check diagnostic codes
2. Pull plugs and inspect them
3. Compression test
4. Leak down test

If it's not running on all cylinders, would the ECU would dump more fuel to make up for the misfire? Why wouldn't this misfire show as a DTC?

 

[kimcrwbr1]

I would think it would throw a 0-2 code if the cylinder is getting fuel and spark the computer dont know it is not firing. Dont panic just yet untill you do the leakdown. You can also do a vacuum test and see the overall health of the engine and can point you in the right direction more accurate.http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm here is how you read the vacuum guage I am still hopeing for a bad seal causing the plug to foul. GL

 

[Seahawk]

Thanks for the reply. The truck is en route back to my house, and I will begin looking at it again tonight.

The engine was "rebuilt" by the previous owner, so there's no telling what has happened. The wiring harness was all over the place when I inherited the project, signs of a scrappy job in my opinion.

I'll update with some more info as I get into it.

Ben

 

[kimcrwbr1]

Yea you never know what someone else did and if it looked shabby on top who knows whats underneath. As it stands now valve guide seals would be the best senario. You said the compression was descent and if that is the case pop the covers off and check that the seals are all the way seated if one is just moving up and down with the valve especially on the intake it would suck a bunch of oil into the cylinder on the exhaust it would give alot of blowby and drip in the cylinder when the engine was off.

 

[Seahawk]

It's sure hard to diagnose the truck from 30 minutes away in my office, but I got to thinking... I noticed that the engine temp gauge was extremely slow to respond to operating temperature, and never actually got to the halfway/normal operating range while driving yesterday. Like I said above, I replaced the waterpump, and I also replaced the thermostat.

However, if the coolant temp sensor is not working, I understand that it would cause it to run rich.

As far as sticking valve guide, I pulled the driver's side valve cover off earlier this week to see what I could see, but I had no idea how to tell if the seal was leaking or the guide was stuck.

I think pulling the plugs when I get home will help. I also think I am going to disconnect the cat at the exhaust manifold to eliminate the possiblity of the clogged cat.

One more thing, I did notice that there is a random electrical connector hanging loose near the cat that is not plugged into anything. I couldn't see anything it should have been plugged into..O2 sensor, transfer case, trans, etc. I'm not sure what this connector is or what it goes to, but again, no hard codes are present that would indicate a no-response condition from a sensor.

Thanks for letting me "think out loud".

 

[Big Jim M]

I'd pull that suspicious plug first. Then I'd be looking at the firing order...NO MATTER HOW SURE I AM! Then I'd be looking into the dist..
Oily plugs aren't firing properly.. Unless the engine is completely worn out then the oil bypassing the rings overcomes the fire in the chamber. As long as the compression is adequate the fire should BURN the oil from leaky valve seals.
Big Jim

 

[Seahawk]

Firing order was another consideration, after seeing the diagram on this page http://www.therangerstation.com/tech_library/2_9_Page.html

When I took the #6 cyl wire off last night, I remember that the position it was on the distributor was closest to the front of the engine. When I replaced the wires, I did them one at a time based on how they were already on the engine before I began working on it. I never verified that they were in the correct positions on the cap!