compression high reading - Team Camaro Tech
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post #1 of 13 (permalink) Old Jan 5th, 03, 04:12 AM Thread Starter
 
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Location: vacaville
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Don't want to over trouble shoot. Recentley we had a flood here in california that affected my car. Got a little moisture threw air intake so I let the car run for a few hours to burn off. Ran perfect the rest of the day but the next morning it ran like crap! Car has 120,000 on it so i did A compression test and read between 150-190 between each cylinder. Service manual advised to remove heads and decarbonize. Qusestion? Is this nessesary or can I try to use chemical additives to help remove and how is this carbonization going to affect the perfomance of the car. I am going to change the timing chain because of a shift in the timing reading. Computer value is 25 and it flucuates between 16 and 30. (Auto Xray Computer from Kragen)

Thanks mark
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post #2 of 13 (permalink) Old Jan 5th, 03, 05:58 AM
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Are you saying that you just sucked a little water into the motor or was it submerged? If submerged, you'll need to change oil in the engine, transmission, and differential for starters. If the plugs got wet that will cause problems also. Water does a pretty good job of decarbonizing by itself. Do you have any reason to believe that the compression was better than 150-190 before the flood? That is a pretty broad range. What does the plug look like on the 150 cylinder(s)?

-dnult
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post #3 of 13 (permalink) Old Jan 5th, 03, 06:18 AM Thread Starter
 
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Did not get submeged! Just sucked up some water becuase of k & l filter which sits lower to the ground than stock intake.

Compression readings were 1-150, 2-146, 3-170, 4-160, 5-180, 6-170. Yes , the close to 150 plugs 1 and 2 looked normal, light tan,
where the others were full carbon and black looking. Tested hot and cold with air intake fulled open. Hot just a few pounds higher than cold.

Checked oil anyway just too be safe and found nothing abnormal.

Car ran perfectley fine so uncertain of compression prior to this compression test.
Manual rates compression at 100 but it is a cheap manual so I do not believe to be correct.
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post #4 of 13 (permalink) Old Jan 5th, 03, 08:19 AM
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Any chance it went air filter, intake manifold, vacume advance tube, distributor?
If it's EFI maybe the O2 sensor didn't like the water since some of the special coatings are picky about exposure.
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post #5 of 13 (permalink) Old Jan 5th, 03, 08:36 AM
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Did the water reach the ECM ?
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post #6 of 13 (permalink) Old Jan 5th, 03, 11:23 AM Thread Starter
 
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water did not get that high, just some got sucked into the intake, ecm stayed dry aswell.


mark
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post #7 of 13 (permalink) Old Jan 5th, 03, 04:47 PM
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i don't think the water really affected anything, but an oil change is cheap insurance.

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post #8 of 13 (permalink) Old Jan 5th, 03, 05:19 PM
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The manual should have meant "no cylinder should be 100 or less" which is really bad.
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post #9 of 13 (permalink) Old Jan 5th, 03, 06:58 PM
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Since you say the 150 cylinders look good and the high cylinders are sooty, I wonder if the cylinder has oil or water in it that is making the compression read higher? Things that make you go hmmmm. Perhaps compression and plug condition are coincidental. Might try swapping O2 sensors to see if plug readings change. That would require new or buffed plugs though.

-dnult
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post #10 of 13 (permalink) Old Jan 6th, 03, 06:59 AM
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I see two problems here - one is the timing varying that much and the other is the compression varying that much.

I'd measure the base timing at idle and total timing at 3 or 4000 RPM. You should get a steady reading for both, if not something is whacked out with the computer (if you have a computer) or points or HEI module. Maybe some sensor got wet and went out. Any fault codes? It could be a timing chain, but a little moisture wouldn't have had anything to do with that.

The compression thing is weird. Make sure you have the ignition disconnected and the throttle held wide open when you do the test. Crank the engine the same number of times (like 4 or 5 revolutions) for each cylinder. Your readings should all be within 10% or roughly 15 psi of each other. A blown head gasket could be making #1 and #2 read low (especially if this is an Inline 6 engine and the gasket blew between the #1 and #2 cylinders).

What kind of car and engine?
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post #11 of 13 (permalink) Old Jan 6th, 03, 08:01 AM Thread Starter
 
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Did find some play in timing chain. Will install soon. Also this year 1994, 3.4 liter has a distibuterless ignition and I am sure it got alot of water sprayed on it. Also it is equiped with cam senor and crank sensor and I am sure that got suberged(crank). Going to install new chain, senors, and ICM, and other tune up stuff.
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post #12 of 13 (permalink) Old Jan 6th, 03, 11:00 AM
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Eric
 
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OK - distributorless - that makes sense.

I bet if you fix the ignition and electrical system the compression prob will fix itself. If a cylinder(s) isn't firing right or missing, the unburned fuel can wash down the cylinder walls and make the compression test read low.

I don't think the timing chain will help with the ignition system though. If its worn out it might make the compression in all the cylinders read a little on the low side (since a stretched chain retards cam timing a little) but I doubt it would hurt your ignition. If I remember correctly, the timing chain just turns the camshaft which turns a dummy distributor that is connected to the oil pump.

Eric
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post #13 of 13 (permalink) Old Jan 6th, 03, 11:14 AM Thread Starter
 
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Thanks for tips Eric, Having an older car has its rewards. Newer ones with the electronics can be more sensitve in some cases. Before I pulled the heads I wanted to make sure I was not missing something. Now I can proceed without pulling the top end apart. I kind of miss the old days of a timing light where I can see errors in system better. Even with the scan tool I purchased the information given is lacking in its details. Overall my 94 camaro has been running close to perfect since 1994 and with 120,000 miles one can't complain. I have been using synthitic oil and pleased with results. My last car went 280,000 before it engine went.


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