Jump to content

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Low compression cylinder 4, help? anyone?

d8rade@yahoo.com
 Share

Recommended Posts

d8rade@yahoo.com Member

d8rade@yahoo.com

Posted
Posted

my '04 anniversary edition 911 misfires on cylinder 4 at idle. above idle it seems to run fine. the compression on the other cylinders is around 240 and is only about 150 on cylinder 4. the car only has 38K miles on it. could it be anything other than burned or bent valves, broken rings,or a bad piston? thanks.

  • Moderators
RFM Member

RFM

Posted
  • Moderators
Posted

What do you think about a bad valve lifter? Do or let do a cylinder leak test to check it out.

d8rade@yahoo.com Member

d8rade@yahoo.com

Posted
  • Author
Posted

i'm going to get a leak down test that should tell more, but i don't see how a collapsed lifter could give low compression. there is no noise except at idle which i believe is just the misfire sound thru the exhaust. thanks for your help i'm really surprised that a $90k car can't make 40k miles without a tear down.

  • Moderators
RFM Member

RFM

Posted
  • Moderators
Posted

Faulty lifters (MY04) do not make noise if the lifter is blocked in the full lift possition.

d8rade@yahoo.com Member

d8rade@yahoo.com

Posted
  • Author
Posted
Faulty lifters (MY04) do not make noise if the lifter is blocked in the full lift possition.

that would be about the best outcome i could hope for. is a blown head gasket possible? no water or steam coming out.

dr914jr Member

dr914jr

Posted
Posted
i'm going to get a leak down test that should tell more, but i don't see how a collapsed lifter could give low compression. there is no noise except at idle which i believe is just the misfire sound thru the exhaust. thanks for your help i'm really surprised that a $90k car can't make 40k miles without a tear down.

If the intake valve is unable to open fully due to a collapsed lifter the compression will be low. I tried to compress a vacuum once, my mom was upset.

Brad Roberts Member

Brad Roberts

Posted
Posted (edited)
If the intake valve is unable to open fully due to a collapsed lifter the compression will be low

Jr :)

You do a compression test with the engine up on TDC for given cylinder. I do compression tests with NO valve train in the engine during assembly :)

A collasped lifter will mean it cannot open the valve all the way.

Matter of fact: I have done compression tests on 3.8 RSR air cooled engines with Ti valves that were bent.. the valve stems are sooo light/weak, that the valves would straighten up as they went back into the seat!!

I'm betting this is a cylinder failure :(

Do the leak down and watch for air bubbles in the expansion tank :( Perform it HOT.

B

Edited by Brad Roberts
dr914jr Member

dr914jr

Posted
Posted

"You do a compression test with the engine up on TDC for given cylinder"

I think you're confusing a leak down test with a compression test. How can you test compression with a stationary piston? :huh:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.