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Discussion Starter · #1 · (Edited)
So here's the deal,

My 85 P-Type with a 5MGE (mileage unknown, but car has around 250,000) has ran like crap since I got it. Seems to be missing and has a loss of power. It won't start worth a crap or idle till it gets warmed up a bit. I worked on finding vacuum leaks and put a new fuel filter in, cap rotor, plugs, wires....Also, I pulled spark plug wires off while running, one by one to see if there was a change in running. Then I did a compression test.

Results:

Pulling wires while running only showed that #3 cylinder didn't seem to change as much as the other ones. Barely noticeable.

Compression Test:
Cold (with dry cylinders)

#1 - 116
#2 - 100
#3 - 75
#4 - 80
#5 - 105
#6 - 120

I then added some oil to each cylinder, retested:
Cold (with oil in cylinder)

#1 - 140
#2 - 128
#3 - 96
#4 - 96
#5 - 126
#6 - 150

Definitely helped out the seal for the rings. Averaged about 25 psi increase.

I ran the car for a bit, warmed it up and retested two cylinders just to check the warm compression:

#1 - 115
#3 - 80

Soooo......it would appear to me that I have some warn out cylinder bores or bad rings/scored cylinder walls.

None of this screams blown head gasket except for the #3 and #4 cylinders being low right next to each other.

Does this all make sense that the motor is on its last legs and there isn't much to do except get a new one / rebuild this one??

As always, all info, comments, help, and jabs at something I did wrong are appreciated for the most part.



 

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Does it smoke at all, anytime, and what color if it does? Yeah, actually, all those #s are low, low, low. How many times did you bump engine on each cylinder test? Screw in, or push in tester? Did you check leakdown?
 

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Discussion Starter · #4 ·
I cranked the engine till the needle maxed out. It was obvious when it was done. I used a screw in tester with an extension to get down in the holes.

CarFreek - As for smoke, there is a bit of blue smoke on start up when cold.

83zed&supra - BHG? Even thought the numbers are so low? Just seems worn out (rings) to me. Believe me, I'd love to just put a new head gasket on, but........don't want to waste time with a worn out short block.
 

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Re test the compression, but bring the engine to operating temp before you do. Metal expands when it heats up. If the numbers are alittle low, but withing variance of each other, try the ATF trick.

If your numbers are below spec or all across the board, then do a leak down test and use a stethoscope to find the leakage.
 

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i had 245,000 miles when i did my comp. check, about 3 months ago. all mine ranged from ~140-~155 or so, with a cold engine.. so i figured that was good!
 

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first you have a 6mge, not a 5 (3000 on the intake plenum is 6mge). the spec is 180 psi
vs 160 for the 5mge.
You may also have burnt exhaust valves 3 and 4 since the oil addition barely improved those cylinders.
 

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Discussion Starter · #9 ·
6MGE? What? Honestly, I thought that someone in the past put that intake on to possibly get better air flow or more cfm or..... I guess I never looked into it very well.

Burnt exhaust valves does make some sense. I need to do a leak down test.

More to come.
 

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Discussion Starter · #10 ·
Well I'll be damned!

Upon further inspection, I do have a 6MGE. That's a great surprise!

I pulled the head today and unfortunately didn't have the "Ahhhh, that's the problem" moment. Head gasket didn't have an obvious blow out. I think maybe the valves in the head are sticky/leaking. My compression sucked. Found a donor head. Gonna get it on there once gasket gets here.

Crossing fingers...
 

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Try someone elses compression tester, yours could be fubar'd. I would suspect the rings are toast though. Congrats on your 6MGE discovery :)
 

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If its apart, put it back together properly, new rings bearings gaskets and check that head and block are flat, or have them both skimmed
 

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Discussion Starter · #13 ·
More Info, and more help needed.

Now I've got my 6MGE and a donor 5MGE torn down. Took the heads apart on both of them and need to decide which one to put together again.

Here is a pic of the 6MGE that is in my car. Can you see anything that looks bad? I didn't see a prob with the head gasket at all. #3 and #4 cylinders were really low compression.

[/IMG]

Now here is the head from the 5MGE. Seems ok except for this groove

[/IMG]

Here is the block and a head gasket prob on the 5MGE.

[/IMG]

[/IMG]

I measured the cams on both sets and they seem to be a couple thousandths off the minimum that the book states. I don't know if I'm too worried about that. What I'm worried about is why is there low compression. I'm obviously trying to not rebuild the bottom half, but I'd rather do it now than after I put the head back on.
 
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