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68 TT · 09-01-2009, 11:30 AM

You really need to data log what is going on to know what the ECM is seeing that makes it run poorly when cold then clean up when the engine gets up to temp.

It sounds like an open loop vs. closed loop issue to me. The CTS is a possible source giving the ECM faulty info but there could be several other causes.

Data logging is a good place to start. It helped me diagnose a vacuum leak that two mechanic friends thought was a fuel system issue. It will also let you see where you can fine tune the programming to suite your particular setup.

09-01-2009, 11:30 AM	#274
68 TT Still plays with trucks Join Date: Jul 2009 Location: Spokane, WA Posts: 3,556	Re: Tbi swap build thread You really need to data log what is going on to know what the ECM is seeing that makes it run poorly when cold then clean up when the engine gets up to temp. It sounds like an open loop vs. closed loop issue to me. The CTS is a possible source giving the ECM faulty info but there could be several other causes. Data logging is a good place to start. It helped me diagnose a vacuum leak that two mechanic friends thought was a fuel system issue. It will also let you see where you can fine tune the programming to suite your particular setup.