Car Has No Compression On #4, ...can I take the valve cover off without draining oil? |
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Car Has No Compression On #4, ...can I take the valve cover off without draining oil? |
7TPorsh |
Jun 30 2016, 12:30 PM
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#1
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7T Porsh Group: Members Posts: 2,691 Joined: 27-March 06 From: Glendale Ca Member No.: 5,782 Region Association: Southern California |
A problem has recenly developed and I can't figure it out. The car starts up easy and on the first crank. I let it warm up a few minutes and drive....It drives fine as it's warming up.
Then after about 15 or 20 minutes the engine starts developing a shudder. Idles fine but and can run ok under low load but under some load the #4 cylinder starts popping and firing up through the carb. feels like it's running 3 cylinders and wasting gas. It's been suggested I do a compression test but I'm thinking if the engine runs great cold and while warmin up; the compression should be ok. Is there a case where comprression is ok when cold but low when hot? Can't figure out why car runs great when starts f'n up. 1.7 with dual weber 40 IDFs |
JmuRiz |
Jun 30 2016, 01:19 PM
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#2
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914 Guru Group: Members Posts: 5,423 Joined: 30-December 02 From: NoVA Member No.: 50 Region Association: MidAtlantic Region |
Sounds the opposite of a properly setup carb engine...usually they run like crap till they're fully warmed. Maybe it needs to be tuned so it runs best at warmed up temps.
I have no idea how my 356 mechanic does it, but it runs like a top when it's warmed up. |
7TPorsh |
Jun 30 2016, 11:02 PM
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#3
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7T Porsh Group: Members Posts: 2,691 Joined: 27-March 06 From: Glendale Ca Member No.: 5,782 Region Association: Southern California |
Did a compression test tonight.... 105 / 105 / 105 / 0
#4 is dead...what's the next step? take off the valve cover? |
TheCabinetmaker |
Jul 1 2016, 06:43 AM
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#4
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I drive my car everyday Group: Members Posts: 8,300 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
Squirt some oil in the plug hole then retest compression. If it remains at zero look to valves.
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7TPorsh |
Jul 1 2016, 08:24 AM
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#5
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7T Porsh Group: Members Posts: 2,691 Joined: 27-March 06 From: Glendale Ca Member No.: 5,782 Region Association: Southern California |
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rfinegan |
Jul 1 2016, 08:53 AM
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#6
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Senior Member Group: Members Posts: 973 Joined: 8-February 13 From: NC Member No.: 15,499 Region Association: MidAtlantic Region |
Sounds like a tight valve ( held open) adjust and try again. If it gets tight again (stays open) you may have a stretching valve or seat problem
Look at #3 intake as that is the one that is popping through the carb. But its not hard to check them all |
Mark Henry |
Jul 1 2016, 09:26 AM
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#7
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Squirt some oil in the plug hole then retest compression. If it remains at zero look to valves. I'll try this today. How could this help? Stuck valve? Not perfect but an old trick, if it's rings the oil will seal enough to give you a bit of compression during the test. if numbers go up it's rings, if it doesn't likely valves. That said 0 compression I'd suspect a tight valve or dropping valve seat. With a 1.7 I really expect a dropping valve seat....sorry. Head gasket I'd expect a couple of pounds and a hiss/whistle noise. |
BK911 |
Jul 1 2016, 10:44 AM
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#8
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Senior Member Group: Members Posts: 672 Joined: 19-February 04 From: Rocky Top, TN Member No.: 1,674 Region Association: None |
Leakdown
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JmuRiz |
Jul 1 2016, 01:15 PM
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#9
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914 Guru Group: Members Posts: 5,423 Joined: 30-December 02 From: NoVA Member No.: 50 Region Association: MidAtlantic Region |
(IMG:style_emoticons/default/agree.gif)
Leakdown will tell where the issue is, rings, intake, or exhaust. |
7TPorsh |
Jul 8 2016, 09:58 AM
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#10
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7T Porsh Group: Members Posts: 2,691 Joined: 27-March 06 From: Glendale Ca Member No.: 5,782 Region Association: Southern California |
Sounds like a tight valve ( held open) adjust and try again. If it gets tight again (stays open) you may have a stretching valve or seat problem Look at #3 intake as that is the one that is popping through the carb. But its not hard to check them all Off work today and in the garage. I suspect an issue with the #3 valve as described so going to take the valve cover off and have a look. Can i jack up one side of the car and not have to drain the oil? |
era vulgaris |
Jul 8 2016, 11:45 AM
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#11
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J is for Genius Group: Members Posts: 982 Joined: 10-November 13 From: Raleigh, NC Member No.: 16,629 Region Association: South East States |
You don't need to drain the oil to remove the valve covers.
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ThePaintedMan |
Jul 8 2016, 12:15 PM
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#12
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Advanced Member Group: Members Posts: 3,885 Joined: 6-September 11 From: St. Petersburg, FL Member No.: 13,527 Region Association: South East States |
? you do not have to drain the oil to take a valve cover off.
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stugray |
Jul 8 2016, 12:25 PM
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#13
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Leakdown test only works if you have SOME compression.
Waiting for 0 to leakdown to 0 isnt very useful. |
HAM Inc |
Jul 8 2016, 12:42 PM
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#14
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Senior Member Group: Members Posts: 846 Joined: 24-July 06 From: Watkinsville,GA Member No.: 6,499 Region Association: None |
Do a leakdown test. It will tell you where the leak is. Air goes in the cylinder, air comes out of the cylinder. You just have to find where.
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Jetsetsurfshop |
Jul 8 2016, 02:01 PM
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#15
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Senior Member Group: Members Posts: 814 Joined: 7-April 11 From: Marco Island Florida Member No.: 12,907 Region Association: South East States |
You don't need to drain the oil to remove the valve covers. +2 I've run my car on a lift before with the valve covers off looking for a valve train problem, but thats a different story. (IMG:style_emoticons/default/biggrin.gif) |
Dave_Darling |
Jul 8 2016, 02:49 PM
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#16
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914 Idiot Group: Members Posts: 14,981 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Look at the valve tips when each cylinder is on TDC. If one of the valves on #3 is sitting with the tip closer to the head, it's a dropped valve seat.
With zero compression, the problem is almost certainly serious enough that to fix it you will need to drop the engine and remove the head. At a minimum. --DD |
jcd914 |
Jul 8 2016, 05:16 PM
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#17
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Advanced Member Group: Members Posts: 2,081 Joined: 7-February 08 From: Sacramento, CA Member No.: 8,684 Region Association: Northern California |
Look at the valve tips when each cylinder is on TDC. If one of the valves on #3 is sitting with the tip closer to the head, it's a dropped valve seat. With zero compression, the problem is almost certainly serious enough that to fix it you will need to drop the engine and remove the head. At a minimum. --DD (IMG:style_emoticons/default/agree.gif) Several things can cause low compression. Not many things will cause NO compression. Worn out rings won't give you 0 compression. A tight valve won't give you 0 compression. Carboned up, poor seating valves won't give you 0 compression. Dropped valve seat will. Badly burned valves will. Hole in a piston will. Leakdown can help you find where the leak is and then you can figure out what happened. Jim |
76-914 |
Jul 8 2016, 05:26 PM
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#18
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,491 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
Look at the valve tips when each cylinder is on TDC. If one of the valves on #3 is sitting with the tip closer to the head, it's a dropped valve seat. With zero compression, the problem is almost certainly serious enough that to fix it you will need to drop the engine and remove the head. At a minimum. --DD (IMG:style_emoticons/default/agree.gif) It needs to come out and anything you do will be easier once it is out. Don't waste your time, just drop the engine. (IMG:style_emoticons/default/beerchug.gif) |
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