Another cylinder #8 misfire :D

[GoldPanther]

where do I start... will make it simple and short.

about 4 years ago I replaced ALL seals and gaskets, timing chains and components, and fuel pump and fuel screeners and filter, while I had the engine out I also added the rear cooling mod. so car performed good until three months ago.

issue is a missfire in #8, replaced spark plugs, replaced coils with some cheap ass brand, problem didn't solved so I re-replaced them again with motorcraft and the issue persisted, then replaced the fuel injector with motorcraft one and the issue still persists.
Is it possible that I'm having the famous valve seat issue? I am planning to pull a head from an aviator at the yard and send it to get rectified and pretty much all ready to get it replaced but before I do that I'd like to see if anyone has any input or more ideas as to what's causing this? Could the PCM be the issue?

[GoldPanther]

Thought about putting navi heads but in a stock application they will suck lol. Disregarding the idea now.

[musclemerc]

Start with a compression test before you tear anything apart.
You definately covered everything.

[GoldPanther]

Oh man thanks, I completely forgot about it. , I will check on that then I will know for sure. by any chance do you happen to know what are limits of acceptance? I guess I will find out right away when the compression escapes.

Thank you!

[justbob]

In case you’re in need of a head rebuild these guys did me real good on my heads. Super quick turn around and right at average pricing or below. Nice sarcastic smart ass car guys, we got along absolutely great. They REALLY came through when I messed up and forgot to add my cam gear spacer and bent 5 brand new S.S. Valves.. I gave them same day notice I was bringing it in and they had it all re checked and those valves replaced in under an hour and told me to just give their guy lunch money LOL.

Built-Rite engine rebuilders

1 (630) 629 4021

958 N Du Page Ave
Lombard, IL 60148
United States


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[GoldPanther]

Man they really caught my attention, sadly it seems that the shop is permanently closed.
I was thinking to wait for an 05 aviator to arrive at the junk yard so I can he the heads, I'd like to have the latest and revised version with better coolant flow and 9 thread spark plug bore. If anything I know of a small shop in villa Park that can check the heads, maybe while I have the heads put I can have them install new valve seals. I still need to find out if there's no compression. Worse case scenario is a bad piston lol

[8UWITH6]

You need to do a LEAK DOWN test to diagnose a possible burnt exhaust valve. NOT a compression test.

[jaywish]

Why a leak down as opposed to compression?

[musclemerc]

Leak down will tell ya where the loss of compression is.

Not needed in this case since the OP already is on the hunt for used heads and plans to refresh them with new valves anyway.

[GoldPanther]

Update, Did a compression test, cylinder #8 it's at mid 80s when the rest of the cylinders are 150. no wonder why the stalling comes only when idle at red lights with the A/C on. it's a random thing but now I know that one of the valves is letting that precious air thru, knowing how common this is I am sure it's the exhaust valve. car is not worth 2k, not sure to spend another 2k to fix it LOL.

[justbob]

I don’t know man, valve job vs a new to you unknown vehicle? I tend to keep my vehicles a lot longer nowadays.


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