With the 5.0 rebuild complete, just wondering about ring break in. At 200 miles, I pulled all the plugs and ran compression test. Engine run for <1 minute to get oil up. No plugs, throttle plates open.
1=100 psi
2=100
3=100
4= 95
5= 95
6=100
7=100
8=105

Running ported E7s with stock exhaust. Stock 1985-86 EEC IV
Too soon for the 175ish I was looking for? Problem?
Mustang cam set straight up on Cloyes adjustable 9-1138 True Street timing chain set.
When the engine was first fired, I had a rich condition (plugs coal black) chased down to the O2 sensor ceramic had broken. Replacement Bosch universal O2 sensor performed better but seemed very slow. Third sensor (Delphi) seems to be performing as it should.
I'm having a time trying to get this thing to idle. Runs great with some throttle opening. Closed throttle sucks.

 

I'm not much help with determining the problem, but those numbers are pretty low.

My 1984 302 in it's stock trim with very low miles (35k) made around 150psi compression. Stock heads I think D8's and 8.3:1 compression?

After a rebuild (0.020"), Comp Cam, and stock GT40 heads, my compression numbers were 170-178. Compression approx 9:1.

 

Kind of wondering if I should have advanced the cam 4°. And would that matter? I get no knock sensed at KOER goose test.

Rings were Sealed Power SLP-E-458K Premium Piston Ring Set. moly coated rings with the compression ring that has no specific up or down.

 

Ummm less than 100 psi should be a concern. Did you make certain to offset all the ring gaps? Have you driven it and made some full throttle pulls yet? Please verify your reading with a different gauge.

 

Rings are installed as they should be. Compression gauge is fine. I use it all the time. Half the mileage is back roads, lots of varying throttle position and load. Plenty of hardish pulls a few very hard pulls.

 

Compression test done with all plugs out, full battery charge and WOT?

 

Did you degree the cam? If it was seriously off, it does tend to reduce compression some. Not that much though, it would be noticeably running badly I'd think. Modern ring materials and cylinder surface finishes are supposed to be easy peasey breaking in.

Is the crankcase oil turning black or anything like that? Yeah, it's supposed to turn black, though not in 200 miles.

 

Used E4ZE cam from a '94 Bronco. Installed in stock position per Cloyes instructions. Valvoline Racing 10w-30 is as clear as when poured in.

I would have thought rings would seat quickly. Going to put some more miles on it and check again.

 

Did you do a compression test before the rebuild?
Did you check push rod length after putting cam and E7s on?

 

Did the rebuild on a '96 Explorer short block. Pushrod pre load fine

 

Could indicate a vacuum leak. Put a vacuum gauge on the intake manifold. My guess is, the gauge will show under 15, maybe even under 10.
I would check and re-torque heads.
Also, I have never done one, but maybe a 'leak down test'. You may be able to determine the problem in the top end or bottom end. Make sure pistons are at TDC for each cylinder tested.

 

Is that a brand new cam shaft, or used from a donor?
What are the cam specs, specifically the duration/lope separation of cam?

If you have lots of overlap, you are experiencing exactly what was installed, I think.

 

No vacuum leaks. As mentioned, poor idle. Possible leak was first thing I checked. All vacuum operated systems have been tested by disconnecting and plugging. Propane run around intake.

Vacuum pressure is high at 14-15" when idling smooth. (It will idle smoothly in short bursts) When idling smoothly, timing holds around 20° BTDC. Base timing set at 10°.

When the engine idles down close to dying, timing can be bumped back to ATDC for a brief moment.

Heads are sound with TTY bolts.

All spark plugs that I pulled and replaced were all tinted the exact same relatively nice, slightly dark tan. Perhaps just a bit darker than we normally see on a EFI engine.

On the leak down, that was puzzling. I added oil to just one cylinder to check. Bumped the compression only maybe three pounds. A second retest showed no gain. I expected that if rings were not seated, I should see a good size bump.

PVC system is breathing as it should. I had replaced a new BWD PCV valve with a Motorcraft yesterday in a vane attempt to see if cheap, aftermarket valve was causing vacuum issue.

So, you got me to thinking I should advance the timing another 5° just to see what happens.

Keep'em coming. No ideas are dumb at this point.

I did read two engine building articles last night that suggest the too rich condition on initial start-up may have doomed the seating process.

 

14-15 inches of vacuum is not a good sign IMHO for a new engine. Something is wrong. A mild cam, from what I recall the one you used is, you should be in the 18-21 range. Same for your compression results...low. Are you sure the pushrods are the correct length?

 

Pretty sure. When I bolted the rockers down, I only had to turn each bolt 1-1/4 to 1-5/8 turns after zero lash to achieve proper torque. I think called for preload was at spec at .060"- .090".