Compression readings jumping from 120 psi to 90 psi in same cylinder? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
LinkBack Thread Tools
post #1 of 3 (permalink) Old 11-01-2018, 08:03 PM Thread Starter
Registered User
 
Join Date: Nov 2018
Posts: 1
Compression readings jumping from 120 psi to 90 psi in same cylinder?

Hi all.
I have a 66’ Mustang with a 289. Motor was built in the 80’s and now in my 66’. Car that motor was in the 80’s got hit so I pulled motor out and it’s been sitting in garage ever since, till now. Put new seals on motor and upgraded the carb to a Edelbrock AVS 2 and a HEI distributor.
Problem I ran into is when car is warmed up it idles at 1250 rpm. Put C4 auto in gear and idle drops to 350-420rpm.
New gas tank. I checked compression and most cylinders were at 120-125psi. #1 and #8 were at 90psi. So I took another round of compression readings and a few of the 120psi now dropped to 90 psi. My only thoughts are the lifters are failing after sitting in engine 30 years plus.
Any thoughts would be greatly appreciated.
Thank you.
Malibujoel is offline  
Sponsored Links
Advertisement
 
post #2 of 3 (permalink) Old 11-08-2018, 11:40 AM
Registered User
 
Join Date: Aug 2008
Location: Saskatchewan, Canada
Posts: 2,839
Re: Compression readings jumping from 120 psi to 90 psi in same cylinder?

What happens when you do a wet compression test? Have you pulled the valve covers and checked to see if all valves are moving as they should? May want to try a leak down test. Any vacuum leaks?

1970 XL, 351W originally 2V, now 4V
670 Street Avenger, Edlebrock Performer intake, Comp XE262H, Flowtech Headers
70XL is offline  
post #3 of 3 (permalink) Old 11-08-2018, 01:22 PM
Registered User
 
Join Date: Oct 2018
Posts: 60
Re: Compression readings jumping from 120 psi to 90 psi in same cylinder?

Sounds like a few things. And as 70XL suggested, vacuum being one of them. Try spraying carb or brake cleaner around the base of your carb, intake edges, etc. The symptoms of an extremely high idle out of gear, and such a low one under any kind of load leads me to a vacuum leak around carb or intake. I would also do a leakdown test to see how long it takes for cylinder pressure to drop. The 80s were thirty years ago, and that is a LONG time to expect gaskets to holdup and not shrink harden, or retain their seal.
Guitar74 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Muscle Forums : Ford Muscle Cars Tech Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
352 Compression Readings Bill M Galaxie Pages 9 11-18-2015 12:29 PM
Falcon Rear Swap Bar NEW....$120 + Shipping falconwagon62 Chassis and Suspension 1 01-25-2014 09:23 AM
Homebrewed turbo 6.90 @ 105mph 7 psi james302 Drag Racing 8 04-25-2011 08:07 PM
Would you pay 120 grand for this? danv Galaxie Pages 10 08-06-2010 09:49 PM
Ok Ok enough drama, lets talk about my new Galaxie :D - compression readings lgh1157 Galaxie Pages 10 08-11-2006 09:41 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome