I have a 90' 3.0L that just turned 181k. I got around to doing the 60k tune up, and in doing so decided to check the compression. What I got was not so good. 145-135psi...fairly consistent on all 6 cylinders. Test was done engine warm, all plugs out, throttle plate open. The engine starts right up, runs quite well, but other than a lopey idle and oil usage it's great.

Based on the stock compression it should be closer to 180psi. So I put about a teaspoon of oil into #5 (which was right at 140psi) and it jumped up to 180psi. So it looks like my rings are in lousy shape, valves must be in pretty good shape.

The plugs had no wet spots on them, very white on the tips and small carbon buildup. Nothing unusual.

Should I just put it back together and keep driving it for a while? Since I just have this one point of reference (never checked the compression before) it's hard to say how long it will last.

 

DOes it burn a lot of oil? Fuel? Low on power?
The choice is yours, but I remember checking my 3.0 a few years ago and getting similar compression psi, and it's still going (87 Merc Sable) at 228K. Will burn a quart in 1000 miles, and gets mid-hi 20's on highway. ENgine still stops turning NOW when you turn off the key.
I'm probably going to just let it run til something gives out. I did replace the timing set because I didn't know if it had plastic cam gear teeth, at 145K, and didn't want to risk them becoming chum in the bottom of the oil pan.
It's up to you. Find the reason for the lopey idle. I added one to mine by changing the factory coil for a "new" one because of signs of arcing. Chased that for days, and finally put the old coil back in, and it was gone. One set of plug wires, plugs, and injectors later... But, nothing really since then.
I'd be doing the standard plugs, rotor, cap replacement if you haven't and check the fuel pump draw as they will wear out and leave you where you don't want to be left.
When you did the test, did you block the throttle wide open? Did you crank it over 3-5 times to let the pressure build? Were all the plugs out of the other cylinders when you were cranking. Don't mean to be rude, but the test needs that. A better test to run is a leakdown test. You can get a leakdown tester for less than $50, and if you have your own compressor, can run the test yourself. It will tell you in % terms how each cylinder is doing compared to the others.

tom

 

That makes me feel a bit better. The motor has plenty of power, and based on the condition of the spark plugs, it could be poor ignition or fuel additives. The coil is original. Plug wires were replaced at 120k. The oil consumption is there but no major signs of leakage...reminds me of my Saturns. Rear main seal is perfect, I checked it when I had the clutch replaced.

I did the compression test correctly. All plugs out, throttle wide open, 4-5 compression strokes. The battery was also fully charged. I did notice that when the pedal was held to the floor, I was still smelling a bit of fuel. The EEC-IV system is supposed to shut off the injectors during WOT starts to clear fuel out of the cylinders (similar to a flooded carb motor) so perhaps I have leaky injectors.

Since all of the plugs looked identical, I'm not sure I'm going to worry about the leakdown test right now(even though I'd love a new toy!). I'll put new plugs/cap/rotor on and see how she does. Simple stuff first.

 

120psi isnt a problem in my book. ive got a big block that runs great on 90 psi

Matt

 

135>145 psi dry compression is fine in a high mileage 3L....just keep doing what you've been doing, all the right stuff and that 3L will easily go 300K....you'll be tired of driving the rig before it gets tired....

change the timing gear/chain set, before it leaves you stranded....only hi mileage weak point....do water pump and front seal while you are in there.

 

I already replaced the water pump at 120k as preventative maintenance. The oil seal and timing set are sitting waiting to be installed when I have the coolant drained for this season's flush and fill. Is the oil seal where all of my oil is going? It does leak oil pretty fast but it's not going out the tailpipe!

I've heard about a 3.3L stroker kit too, just not sure if I want to go that crazy. I can't imagine having much more torque that it does right now.