Engine Controls - Basic Testing - 2.5L/151 TBI In-Line 4 VIN [U]: Testing

When performing tune-up procedures described in this article, the following notes and precautions should be followed:

• The 2.5L "Iron Duke" VIN U was used from 1985-1991, exclusively on "N" body vehicles. A few changes occurred in the 1987 model year: the engine went distributor-less, and the TBI was upgraded from model 300 TBI to model 700 TBI.
• A timing gear set drove the camshaft from 1985 until 1989. From 1990 to 1991, a timing chain was used.
• To see what other makes and models this engine applies to, go to the top of the article.
• When doing computer system diagnosis, ALWAYS start with the Diagnostic Circuit Check. This procedure is found under the COMPUTERIZED ENGINE CONTROL SYSTEM header.
• The Diagnostic Trouble Codes (DTC) Charts, A-charts, B-charts, and C-charts are not contained in this article. They can be found in the appropriate article in the ENGINE PERFORMANCE section. Therefore, if a procedure in this article direct you to one of these charts, proceed to the ENGINE PERFORMANCE section.
• Specifications and/or procedures shown on the Vehicle Emission Control Information label (in the engine compartment) supersedes all data in this article in the event of a conflict. In other words, if the information in this article and the label differ, use the label information.