Poor performance fe390

Reply Subscribe

Thread Tools

Search this Thread

Oct 5, 2019 | 10:34 AM

#46

Tedster9

Post Fiend

Joined: Apr 2002

Posts: 19,311

Likes: 97

From: Waterloo, Iowa

That sure sounds like it. If your balancer is good, "0" TDC line is accurate, after checking for slop while watching the rotor, another check is to position the #1 cylinder valves exactly right at overlap, #6 cylinder will be at TDC compression. Then see if the "0" mark is past the pointer, and if so, how much.

If there's say for example 6° or 8° chain or timing set slop, and then the camshaft is also installed retarded by 4° or 6°, it adds up and it is going to be a real pooch down low, and down on cranking compression a bit. In fact that was one way hot rodders and DIYers used to install camshafts without degreeing the cam, they'd just move it around until they hit the highest compression. They sell timing sets with adjustable crank gear keyways, to advance or retard the camshaft timing. Since you're up high, and use the truck for hauling or rock crawling 6° or 8° cam advance relative to "straight up" should help a bit.

Oct 5, 2019 | 12:52 PM

#47

niko20

More Turbo

Joined: Feb 2018

Posts: 710

Likes: 3

From: Oregon

Why are you sharing ancient engine tuning articles that are not even for Ford trucks..? Geez it's not that expensive ($30) to get ACTUAL FORD manuals on CD ROM from Amazon, etc. OP I strongly suggest to at least get a set of them for reference.

Oct 5, 2019 | 01:30 PM

#48

Tedster9

Post Fiend

Joined: Apr 2002

Posts: 19,311

Likes: 97

From: Waterloo, Iowa

Your Concern Has Been:

[ X] Noted
[ ] Not Noted

Oct 8, 2019 | 03:57 PM

#49

Horsethief

Thread Starter

Tuned

Joined: Sep 2018

Posts: 364

Likes: 22

From: Eagar, az

Already have the 6 volume factory manuals with 4 foot x 4 foot vac, and electrical schematics. First thing I bought after the truck.
So now I guess it's time to learn the rest of timing besides turning the distributor

Oct 8, 2019 | 04:22 PM

#50

bassmasterdude

Junior User

Joined: May 2019

Posts: 52

Likes: 1

Just a thought. I spent quite a few years working in a machine shop and we had many of these heads come through our shop. Due to the lack of lead in the fuel the cast non-hardened exhaust seats (integral, part of the head) get severely damaged over time and they all deteriorate at the same time which would explain the consistent low compression readings across the board. My thought would be to perform a leak down test. I am not sure what capabilities your bore scope has that you used to inspect the cylinders but if you can position it at the right angle take a look at how low the exhaust valve is pulled down into the seat in each cylinder that would give you an idea of what the exhaust seat condition is.

Oct 8, 2019 | 07:35 PM

#51

Tedster9

Post Fiend

Joined: Apr 2002

Posts: 19,311

Likes: 97

From: Waterloo, Iowa

That makes a lot of sense.

Oct 9, 2019 | 10:55 AM

#52

Horsethief

Thread Starter

Tuned

Joined: Sep 2018

Posts: 364

Likes: 22

From: Eagar, az

Yes that did cross my mind more than once about heads. I know the intake man has been removed because of the aftermarket sealant peeking out, but beyond that I have no clue what's been in this motor, if anything. I have a cheap harbor freight scope that does not bend well, but I am not afraid to break it trying. Every once in a while the exhaust tone develops a thumping drum beat instead of the smooth even tone , like somethings going on with a cylinder. Kind of a bass drum beat that's only heard on medium to hard acceleration

Oct 9, 2019 | 12:38 PM

#53

bassmasterdude

Junior User

Joined: May 2019

Posts: 52

Likes: 1

There is an inexpensive way to check but the seats have to be in pretty bad shape for this to work. You would need to located an 18mm spark plug adapter that has a female 1/4 npt on the other end. I've used these adapters to replaced valve stem seals to pressurize the cylinder and hold the valves in place. Screw in a 1/4" male pipe thread lincoln fitting (the long end of a quick disconnect air fitting) into the adapter. Remove all spark plugs. Start with any particular cylinder you want to. Locate that piston near the bottom of the stroke (you can use a small wooden dowel to determine the piston location). Now install the adapter into that spark plug hole. Stay clear of the fan and if you have a manual transmission be sure it is neutral, now connect your quick disconnect fitting onto the lincoln fitting to charge the cylinder with air, this will locate the piston at BDC due to the air pressure. You really can't use too much pressure so if your compressor runs anywhere from 120 to 150 psi that will be fine. With air pressure in the cylinder go the tail pipe on the side of the truck you are working on ( if it has dual exhaust) and listen for air escaping. This would be air flowing past the exhaust valve. Try this on all the cylinders and see what you come up with.