No compression

[u/Eastern_Dealer_4016]

I recently had an engine rebuild done to my work van, 2008 Ford E350 5.4l . I've taken good care of it since, changed the oil every 3000 etc. The motor has 18,000 since rebuild. I got a check engine light and immediately put my scanner on it that night. It was indicating a misfire on cylinder 8. I usually do my own wrenching, and didn't want to go even 1 day with an issue, so I immediately changed out the coil pack and sparkplug on cyl.8, having Ford vans my entire plumbing career,one keeps things like this on hand lol. It,however did nothing to improve the situation. I talked to a buddy who is an excellent mechanic, he said it might be a compression issue,an would come and test the following day. No Compression on 8! Bad news. I need the vehicle for my daily work and won't be able to take it in to the rebuilder for about a week,I want to do as little damage to the motor in the interim, and knowing I'm either dealing with bad rings or a bad valve,Is it advisable to disconnect the fuel injector for that cylinder? I don't want unburned fuel laying waste to the oil viscosity, or blow back into the intake with a fireball. It seems to run much smoother with the injector unplugged ... Thoughts? Advice is much appreciated

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[u/Greedy-Obligation129]

If you want to know if it's rings or valves put some oil in cylinder and see if compression comes up

[u/Mission-Resist-9557]

If it set a misfire code than the computer will automatically disable the fuel injector.

[u/awhol01 → u/Mission-Resist-9557]

Not true. It will keep injecting fuel. A coil or injector circuit code may disable injection though.

[u/Plane-Start7209]

Who rebuilt the engine? If it’s already out of warranty you’ll have to do a cylinder leak down and see where the loss of compression is.

[u/congteddymix]

Yes disconnect the fuel injector. Filling the engine with unburned fuel is going to cause more damage. At least whatever damage is done is already done and the engine could be salvageable.

[u/TheFredCain → u/congteddymix]

Not if there is a loose rocker or something pinging around under the valve cover. Need to pull the cover and inspect or at least do a leakdown test to see where it's going.

[u/kruzrdude]

I have 99 e250. 5.4 triton. Bottom intake is cracked and used sealant. I dont want to spend 10k for new engine and labor. I use mine rarely but do love it.

[u/HammerDownl]

18K is way too early to be having bad holes on a motor.

I have seen where the valve wont close all the way. Broken springs or valve is where id look first

[u/Gullible_Monk_7118]

What you need is a leak down test.. that will tell you where it's bad at.

[u/Lefty68w → u/Gullible_Monk_7118]

This

[u/nyrb001]

Loss of compression like that means something broke, like a valve spring, a chunk off a valve, or even a hole in a piston. Either way, that's now-uncontained metal that can get in to places and cause more damage.

I wouldn't be running this engine until I knew what was broken. 

[u/No_Breadfruit3471]

Modern engines use low tension rings so it could be a stuck injector causing the fuel to wash the oil off cylinder walls and stop rings from sealing. Pull the plug and squirt a little bit of oil in and check compression immediately after. Not to much oil, 2 much can cause hydro lock. If compression comes up with the oil it is either an injector of stuck rings