1 channel CPA RCT test for A26 or CV 6.6L - diagnostic steps

Sep 2, 2026

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Provides step-by-step instructions for performing a simple relative compression test (RCT) using only one channel of the CPA box on an A26 or CV 6.6L engine. Covers setup and safety actions such as warming the engine, disconnecting the battery charger, and preventing starting by unplugging ECM injector connections or sensors. Guides operation through the CPA application (BEAM > RCT), test execution with repeated cranking, and interpretation of battery voltage patterns in Test Data.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

CHANGE LOG

DESCRIPTION

SYMPTOM(s)

SPECIAL TOOL(s)/SOFTWARE

DIAGNOSTIC STEP(s)

Test setup and execution

Test data interpretation

Countries: CANADA,UNITED STATES,MEXICO Document ID:IK1201444 Availability: Revision: 2 ENGINES Major System: Created: 11/26/2019 Last Modified:1/20/2021 Current Language:English Other Languages:NONE Author: Mark Ehlers Viewed: 191 Less Info Hide Details Coding Information | Copy Link | Copy Relative Link | Bookmark | Add to Favorites | Print | Provide Feedback | Helpful | Not Helpful | | --- | --- | --- | --- | --- | --- | --- | --- | Title:1 channel CPA RCT test for A26 or CV 6.6L Applies To:A26 or CV 6.6L # CHANGE LOG Please refer to the change log text box below for recent changes to this article: 1 10 i ■■■ ■■■■ ■■■■ ■■ ■■■■■■■■■■ i11/26/2019-Initial Article Release ■■■■■■■■■■■■■■ ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ # DESCRIPTION This article shows how to perform a simple RCT (relative compression test)using only 1 channelof the CPA box.It equires no special harnessesor breakout box. # SYMPTOM(s) Perform this test whenever you need to quickly determine if all cylinders have about the same cranking compression. # SPECIAL TOOL(s)/SOFTWARE CPA box and CPA cables to connect to the battery +and- # DIAGNOSTIC STEP(s) 1.Connect CPA box as shown below(A26 example shown) 2.Engine should be warm (if possible) 3.Disconnect battery charger from truck 4.Disconnect injector connector from ECM (to prevent engine from starting)or disconnect camshaft position sensor 5.Open CPA application and select BEAM&then select RCT(see below) 1.Note that CPA can be launched without NEDs.If doing this then manually select the engine type.For CV6.6L select a diferent V8engine. 6.Start test.Ignore any error messages and crank the engine for about 5 seconds pause then repeat the 5 second cranking session. 7.Select Stop Test 8.Ignore the error messages and navigate to Test Data view 9.Focus on the "Battery"graph 10.Use the zoom buttons and zoom in on a segment of the last half of the recording(see below) 11.Compare the voltage pattern the the examples below 12.Repeat test if needed 13If the pattern shows a weak cylinder then ID the cylinder(if needed) 1.A26-Use NEDs testing or fault codes or CPA RCT with cam &crank signals added.See IK1201429 2.CV6.6L-Use fault codes or other GDS tests or repeat this test but add the CAM sensor to CPA and move B+signal to "crank"channel. 1.Open casefile for assistance interpreting the results 14.Reconnect engine connectors that were unplugged(related to this test) 15.Clear faults that were set by preventing the engine from starting https://evalue.internationaldelivers.com/service_kb/DocTool/ArticleViewer.aspx?ControllD.. 2/1/2021 IK1201444-1 channel CPA RCT test for A26 or CV 6.6L IK1201444-1 channel CPA RCT test for A26 or CV 6.6L IK1201444-1 channel CPA RCT test for A26 or CV 6.6L OTHER RESOURCES Master Service Information Site Feedback Information Hide Details | Viewed: 190
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FAQs

What is the purpose of the 1 channel CPA RCT test for A26 or CV 6.6L?

It quickly determines whether the engine cylinders have about the same cranking compression by using a relative compression test based on battery voltage patterns.

What setup steps are required before starting the RCT?

Warm the engine if possible, disconnect the battery charger, and disconnect the injector connector from the ECM (or disconnect a camshaft position sensor) to prevent the engine from starting.

How should the CPA application be used to run the test?

Launch CPA, select BEAM, then select RCT. Start the test, crank for about 5 seconds, pause, repeat the 5-second session, then select Stop Test.

How do you interpret the results from the battery graph?

Navigate to Test Data view, focus on the Battery graph, zoom into the last half of the recording, and compare the voltage pattern to the provided examples. If a weak cylinder is indicated, identify the cylinder as needed.

Sep 2, 2026

Upload by Dozel