98 scab 4wd 4.6 project truck. I've been troubleshooting a misfire condition/ p0171 code for about 9 months off and on. I finally got around to doing a compression check. I went to pull the plugs today, which I THOUGHT I had changed late last fall.... Tried to remove the #6 plug and couldn't get the socket on it. Started peering down with a flashlight and discovered that the we'll walk half full of gunk. After about an hour of digging with a screwdriver, pick, punch and finally NN pliers and tig wire I finally got the plug out. ( doh- stupid- must have had a few too many beverages ) this is what I found. Guess which one is #6....

 

How do I attach a pic from the app? Anyway the # 6 plug was as black as a coal miners butt.

 

Guess you only changed 7 plugs.


True story
Back in late 90's I bought an 86 arostar xlt with v6 4.0. From the oragnel owner. It came with pappers where it was serviced at ford dealers every year for 12 years. plugs where ghanged 10 times it that time frame. Plugs 1-5 where motorcraft. plug 6 said ford on the side. So the factroy plug in 6 had never been changed. Now I found the only way to get to it was to take the left wheel of and remove the plastic iner finder. But still. The papers where from 4 differnt dealers and not one of them changed that one plug.

 

Once I got the plugs all out, I opened up my brand new "universal" compression tester and shortly discovered the fittings wouldn't fit. So back to harbor freight I shall go....

 

Ok so HF didnt have the correct adapter for the spark plug well so I got a tester from oreillys. When I tried it the adapter would only screw in about 3 full threads. It wont go allthe way to the o ring. When I checked the adapter agains the spark plugs I found the threads aren't the same pitch as the plugs....WTF? Does anyone know what the correct adapter to use is?... I've got all the plugs out...

 

So after figuring out what was wrong with the adapters (plugs are slightly tapered-adapter is straight) and filing down the last couple threads, I got the adapter to thread all the way in by hand. FINALLY got the compression check done...:-< not good results.
Results are (Cyl-Dry/Wet) 1- 150/150; 2-80/100; 3-80/100; 4-80/90; 5-90/130; 6-125/150; 7-80/90; 8-90/100. Pretty sure the motor is toast.
So I put the plugs back in and fired it up. Runs a LOT better (probably because the #6 plug was about as bad as I've ever seen) I'm going to drive it tomorrow and see how it drives. But except for the WAY higher readings on #1 and 6 the rest are close enough...? (Puzzled) update tomorrow after the test drive.

 

top right corner there should be a + press it and that should give you options i think you press reply to thread and from there you can attach pics

 

Best way is to place a mat over the engine, and actually lay on it so you can reach in. 3 threads is all it'll go - that's normal for a 4.6. And you're correct about the pitch of the plugs. Whatever you do, make sure you're using Motorcraft plugs, and not some aftermarket platinum, which get too hot, and wind up screwing up the threads in the head.

 

I replaced the plugs with motor craft and after I got everything hooked back up I noticed there was a tic at the pas side coil. Got to looking and found I had miss wired the spark plugs. Fixed that and the truck runs like a CHAMP! 4wd works and goes into and out of low range but doesn't go back into 2 high. Must have a vac leak because it worked before.... More tomorrow night .

 

You may have pulled one of those little vacuum lines on the passenger side of the engine compartment. Good job on the plugs! Shouldn't have to do again for another 100,000 miles.