Terrible pinging at operating temperature
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Well, I swapped out the PCM's. It runs rougher at cold start-up, but settles the pinging down. It doesn't completely kill it off though. She starts up again and the knock sensor kicks in with the oil temps up around 230. Also, the oil temp is 230 while the coolant is still 200-ish. That seems like a pretty big disparity.
I'm going to do a compression test on her in a little bit. Will report back the readings.
-DM
I'm going to do a compression test on her in a little bit. Will report back the readings.
-DM
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
And what are they meant to be?? A 4 psi difference doesnt seem all that important to me.
EDIT: I just looked in my service manual, it says none should be under 100psi, and the lowest should be within 70% of the highest. So just so i know why youre
about yours, what sort of pressure are you expecting??
EDIT: I just looked in my service manual, it says none should be under 100psi, and the lowest should be within 70% of the highest. So just so i know why youre
about yours, what sort of pressure are you expecting??
Last edited by Casethecorvetteman; Sep 14, 2006 at 09:14 AM.
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
From memory, the rule of thumb is the difference between the highest reading and the lowest reading shouldn't exceed 10%.
The actual readings (numbers) depend on several variables, such as camshaft overlap, compression ratio, ring seal, etc.
Jake
The actual readings (numbers) depend on several variables, such as camshaft overlap, compression ratio, ring seal, etc.
Jake
Melting Slicks
Joined: Jul 2006
Posts: 3,356
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From: Chesapeake Va
OK. Did the math. With a 58cc head,.064compression height and a -12cc piston, you should have 10.21:1 compression. If the heads are SMALLER by 5cc youd get 10.92:1. Either way it aint too high on comp. BTW, do we have a scanner on this thing yet? We cant tell nuthin without some scan data. Get a scanner on that thing before you aint got no pistons left. Stop messin with it till you do.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by Casethecorvetteman
And what are they meant to be?? A 4 psi difference doesnt seem all that important to me.
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Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Originally Posted by CFI-EFI
Within 4 pounds is great. That is WAAAY less than 10%, but the readings are about 30 psi too high. My best guess is that the cam isn't installed properly.
RACE ON!!!
RACE ON!!!
Jake
Le Mans Master
Joined: May 2005
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From: Queensland, AUSTRALIA
Originally Posted by CFI-EFI
Within 4 pounds is great. That is WAAAY less than 10%, but the readings are about 30 psi too high. My best guess is that the cam isn't installed properly.
RACE ON!!!
RACE ON!!!
Race Director
Joined: Jan 2002
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From: O'Fallon Missouri
Originally Posted by CFI-EFI
Within 4 pounds is great. That is WAAAY less than 10%, but the readings are about 30 psi too high. My best guess is that the cam isn't installed properly.
RACE ON!!!
RACE ON!!!
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by STL94LT1
Hmmm, too kigh? That's about the same readings I'm getting from my stock short block heads/cam LT1.
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Thats normally what we see. 225-230
Race Director
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From: The Top of Utah
Originally Posted by Casethecorvetteman
I think he means his short block is stock, and the heads and cam upgraded parts.
Originally Posted by STL94LT1
Hmmm, too kigh? That's about the same readings I'm getting from my stock short block heads/cam LT1.
I have to admit to not taking compression reading from many fresh engines. Leak down tests, yes, but not compression tests. Still 215 psi cranking pressure, and up, sounds like a way too high dynamic compression ratio. I still think if it isn't a poorly selected camshaft, it is poorly installed.
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Melting Slicks
Joined: Jul 2006
Posts: 3,356
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From: Chesapeake Va
I've seen 9:1 motors with baby cams have 230 psi cranking. I've also seen 12.5:1 motors with racing cams have 175 psi cranking. We dont place too much value in the actual #s, more in that they're all the same. For diagnostic purposes its more about HOW it makes compression, usually first pulse amount. Leak down testing is also very valuable info, but not really pertinent (typo?) here. I think we're on the wrong path here. I'd definately like to see some scan data. Whats the fuel trim #s? if it pings on 100 octane, its got serious problems. I could see the quench area being an issue, but its definately not too much comp.
Race Director
Joined: Jan 2002
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From: O'Fallon Missouri
Originally Posted by CFI-EFI
215 psi? A stock LT1? Maybe your cam needs to be degreed, too, or maybe it's time to buy a new compression gauge.
RACE ON!!!
RACE ON!!!
To be a little more clear: Stock short block, CNC ported heads, Imp. SS head gaskets, 224/230 605/622 112+2 camshaft. Normally when people say heads/cam, they mean the heads have been ported and the camshaft was changed. At least that's my understanding of the term.
-Mike
Last edited by STL94LT1; Sep 15, 2006 at 04:47 PM.
Safety Car
Joined: Sep 2003
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From: Orange County NY
St. Jude Donor '10-'11-'12-'13
What have your spark plugs been looking like through all of this? Are they all the same, bone white? Do any of them look very different from the others? Have you seen any "pepper" specks on them? Are you using a plug with the stock heat range?
I don't know very much beyond tuning for an L98, but it sounds like it needs to be tweaked, especially if you are seeing a difference when you install the stock PCM.
Does it continue to do this only when the engine is hot?
I don't know very much beyond tuning for an L98, but it sounds like it needs to be tweaked, especially if you are seeing a difference when you install the stock PCM.
Does it continue to do this only when the engine is hot?
Race Director
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From: The Top of Utah
Originally Posted by STL94LT1
Normally when people say heads/cam, they mean the heads have been ported and the camshaft was changed. At least that's my understanding of the term.
-Mike
-Mike
Originally Posted by STL94LT1
from my stock short block heads/cam LT1.
edcmat-l1 I've seen 9:1 motors with baby cams have 230 psi cranking. I've also seen 12.5:1 motors with racing cams have 175 psi cranking.
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Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Originally Posted by CFI-EFI
I agree,but when someone says:With no commas or clarifying words, like "with", it appears that "stock" refers to the short block, the heads and the cam.
I said it first, that the compression ratio is the lesser factor in the cranking pressure, but I have a 9:1 engine with a baby cam that has 170# cranking pressure. Admittedly with little experience checking the compression on fresh engines, it seems like 215# and up indicates too high a dynamic compression ratio for regular street use on pump gas. Too many people think that is wrong, so I will withdraw the point.
RACE ON!!!
I said it first, that the compression ratio is the lesser factor in the cranking pressure, but I have a 9:1 engine with a baby cam that has 170# cranking pressure. Admittedly with little experience checking the compression on fresh engines, it seems like 215# and up indicates too high a dynamic compression ratio for regular street use on pump gas. Too many people think that is wrong, so I will withdraw the point.
RACE ON!!!
Jake