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Join Date: Apr 2008
Posts: 61
Effect of cam timing on ITB's?

The reason for me posting it here, is because a lot of you guys have installed ITBs. I had installed on a 993. We got different afr readings on both banks. We thought it was the o2 sensors so we ordered new ones, and still the afr's are off by 1.7. We synchronized the itb's and get the same flow at 2k rpm and tried again at 3k.

We also checked for the flow of each injector and they are ok.

We noticed that at the start its ok, then after 5 dyno pulls, the afr's on the banks are off. Some tuners suggest checking out the cam timing again. Which we will do.

What is your opinion?
Old 07-11-2011, 06:40 PM
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Walt Fricke's Avatar
 
Join Date: May 2004
Location: Boulder, Colorado
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If just one cylinder was off on one side, could that account for this?

You might isolate the off cylinder or cylinders with a boresocpe, looking at carbon patterns? Plugs show anything?

Is it twin plug? Mixing up a pair of lowers not hard to do by mistake.

No doubt you have ruled out vacuum leaks on either side.

If it seems to be one cylinder, you might see if the cam lobes for that one are in the right place. I have heard of cams being off in their grind registration.
Old 07-12-2011, 11:24 AM
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Quote:
Originally Posted by Walt Fricke View Post
If just one cylinder was off on one side, could that account for this?

You might isolate the off cylinder or cylinders with a boresocpe, looking at carbon patterns? Plugs show anything?

Is it twin plug? Mixing up a pair of lowers not hard to do by mistake.

No doubt you have ruled out vacuum leaks on either side.

If it seems to be one cylinder, you might see if the cam lobes for that one are in the right place. I have heard of cams being off in their grind registration.
The exhaust temps were not a big variance and seemed acceptable. It is twin plug but Ill have them check on the lower plug terminals. Thanks for your inputs.
Old 07-12-2011, 01:42 PM
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