4.9 compression

Reply Subscribe

Thread Tools

Search this Thread

Oct 14, 2008 | 08:11 PM

va150

Thread Starter

Junior User

Joined: Jan 2007

Posts: 84

Likes: 0

From: Virginia

4.9 compression

What should the compression be on a 1990 4.9. I just check and all cylinders were between 160 and 165 PSI, the engine has 190,000 miles on it. The E4OD tranny just went and I am wondering if it is worth spending the money to fix.

Oct 15, 2008 | 05:43 AM

Motorhead351

Posting Guru

Joined: Sep 2004

Posts: 1,556

Likes: 5

compression is good.

Oct 15, 2008 | 07:04 AM

srercrcr

Postmaster

Joined: May 2004

Posts: 2,854

Likes: 0

Ford doesn't specify specific numbers, only says all should be within 10% of each other.

Oct 16, 2008 | 03:48 PM

F-150battlemaster

Senior User

Joined: Sep 2006

Posts: 107

Likes: 0

Weird. The Book I have states 25% variance. Stupid haynes.

Yeah. Looks good. I run 156-128 psi. #3 cyl obviously being the low one. That cylinder is cursed.

Oct 17, 2008 | 12:42 AM

codejunkie

Senior User

Joined: Jul 2005

Posts: 101

Likes: 0

The compression in my 300 is 165, +-3 (162 lowest, 168 highest). Runs fine.

Oct 28, 2008 | 09:01 PM

05chop

Elder User

Joined: Aug 2007

Posts: 502

Likes: 0

I dont have a compression gauge never did have the need for one.Why? i use an old spark then weld a shop air fitting to it.I put each cly at tdc then slowly add regulated shop air to each cyl.Then if i hear air coming out the tail pipe,air cleaner,valve cover oil fill tube then i have a problem.Still working on how to use spell check too.Its kind of like when you run out of tolet paper you get creative