My '85 EFI 4runner needs a rebuild I think. Per the PO, the motor was rebuilt within the last 1500 miles. Upon inspection it ran pretty well and drove even better, aside from a slight miss at high RPM that only came on once she was warmed up. Well, I decided to look into the miss thinking it was something minor and I think I found more than I bargained for.

It has new OEM plugs, wires, and cap, so I started with the simple stuff, checked connectors and whatnot, everything was good. So I pulled the plugs and found #2 and #3 gunked in oily crud, bad. No doubt it was motor oil, and a lot. #1 was just fine. As I went to pull #4, I found someone had cross threaded the plug pretty bad. It wasn't even seated all the way, but once it was out, the plug itself looked fine, just like #1.

I was able to clean up the #4 plug hole and opted to do a hot compression test since I had it apart.

#1 140
#2 150
#3 150
#4 115

A bit later and a lot cooler I did a wet test and found this. For both wet and dry I counted about 9-10 cranks.

#1 175
#2 185
#3 185
#4 180

Are these rings cooked or did they not even seat? On the first hot/dry test I was shocked to see #4 so low compared to the others so I did it twice to make sure and got the same reading. I'm wondering if the compression gauge didn't seat well enough into the goobered plug hole?

I'm assuming I have a valve issue with the oil on #2 and #3, especially #3. PO said he had a shop run the overhead a couple of weeks ago. Would poorly adjusted valves dump oil into the chamber. I would assume bad valve seals? I was getting ready to pull the head and thoroughly look at everything. Thoughts?

 

The first thing that comes to my mind is valve lash since you mentioned recent work and since the temperature was different from one test to the next.
Here's my thinking, when hot the valve stems will grow in length, if the valve lash on #4 is too tight or at least tighter than the others the valve will not be closed as long as it should, or as long as the others.
If the valve lash on all 4 cylinders it similar I would say you have an issue with the rings or you got oil on the threads when preparing for the wet test and got a better seal with the compression tester.
Also, poor valve adjustment shouldn't make any difference in the amount of oil in the cylinders. either the valve stem seals are leaking or oil is blowing by the rings or being sucked into the intake from somewhere, like the PCV system. But the PCV/intake should effect all 4 cylinders.
I'm no guru when it comes to engine rebuilds or issues like yours, but I would try hot dry compression testing, cold dry, then hot wet and cold wet if you have the time. Just make sure your battery is fully charged, throttle butterfly wide open and keep cranking till the pressure stops rising. watch how much pressure you get on the first crank and total pressure at the end. Also, don't let the cylinders wash down with fuel while you are cranking as it could give you lower results on the last cylinder or two that you test, pull the fuel pump fuse or disconnect injectors.
A bore scope might give you more clues before you go whole hog and tear the engine down.

 

Thank you. I will run the overhead again this weekend and send my camera into the plug holes to check it out. Before I started working on it, I IR'd the header at each port and found the #4 port way hotter than the others by about 50 to 60*. Not sure if that was because of the leak from the unseated plug or bad valve lash or what. Also, the T-stat was opening early at about 160*.

The more I'm finding, the more I'm leaning towards going whole hog and getting a new long block from LCE or Sunwest to just be done with it and have the confidence to drive this thing across country without hesitation. The motor pulled hard with good power and seemed to have great compression when I flogged it. Its always a gamble with a used vehicle, and I think I'm owner #4 on this one. Its my own fault as I should have done a full PPI which would have caught this. I opted not too based on the superb condition of the body, frame, suspension, and interior. I assumed the motor had been taken care of to the same degree.

Ever since I was a kid I always wanted a Marty McFly truck. But now with little ones its changed to a 4runner. I plan to keep this rig forever so I'm not too bummed to have to deal with this, as I have a good starting point, and replacing an entire engine is easier to work through than trying to cut cancer off of the chassis or fixing someone's hack job wiring nightmare. If only I could have bought my '85 new in 85.....would they have given a loan to a 5 year old?

 

Maybe a tightly adjusted exh valve on #4 could account for both the lower compression and higher measured exh temp. That’s the first thing i would look at.

How about a vacuum gauge reading? The behavior of the gauge can shed light on the health of the engine and is not mentioned often enough on our forums here.