For DIY mechanics and car enthusiasts working on GM vehicles, understanding engine parameters is crucial for maintenance and performance tuning. One such parameter, CMP Retard, often comes up in discussions, especially when dealing with distributor adjustments and engine diagnostics. If you’re wondering how Gm.cmpret To Run With Torque Pro Obd2 App Android, you’ve come to the right place. This guide will explain what CMP Retard is, how to check it, and how it relates to your GM engine’s performance, particularly when using the Torque Pro app with an OBD2 adapter on your Android device.
Finding Top Dead Center (TDC) on Cylinder 1
Before diving into CMP Retard, let’s address a fundamental step in many engine procedures: finding Top Dead Center (TDC) on cylinder 1’s compression stroke. This is often the starting point for distributor installation and timing checks. Here’s how you can do it:
- Disable Ignition: First, disconnect the primary coil wires. This prevents the engine from starting during the process.
- Remove Spark Plug: Next, remove the spark plug from cylinder #1. This allows you to feel the compression.
- Check for Compression: Have an assistant briefly tap the starter while you place your finger over the spark plug hole. You should feel air being pushed out as the piston comes up on the compression stroke.
- Locate Timing Marks: On the harmonic balancer, you’ll find timing marks. There are typically two marks. You’ll also see a timing mark on the timing cover.
- Align Timing Marks: Initially, one mark on the balancer should be roughly pointing downwards, and the other should be close to aligning with the timing mark on the timing cover.
- Fine-Tune TDC: Using a socket wrench on the balancer bolt, manually turn the engine clockwise. Continue turning until the timing marks are precisely aligned. This alignment indicates TDC for cylinder #1.
Alt text: Aligning timing marks on the harmonic balancer of a GM engine to find Top Dead Center (TDC).
Crankshaft Relearn: When Is It Necessary?
Another common question among GM vehicle owners is whether a crankshaft relearn is absolutely necessary after certain repairs. Generally, a crankshaft relearn procedure is not required unless you have disturbed or replaced the crankshaft position sensor itself. The crankshaft position sensor is crucial for the engine control module (PCM) to accurately monitor crankshaft speed and position.
Understanding CMP Retard: It’s About Distributor Alignment, Not Ignition Timing
Now, let’s get to the core of the topic: CMP Retard. CMP Retard is often misunderstood as an ignition timing adjustment, but this is incorrect. In GM Vortec engines with distributors, CMP Retard is the setting that ensures the distributor rotor is correctly aligned with the distributor cap terminal when the spark is transferred to the spark plug wire.
Ignition timing on these engines is exclusively controlled by the crankshaft sensor and the PCM, and it is not adjustable through distributor manipulation.
Ideally, the CMP Retard value should be around 0 degrees, perhaps within a couple of degrees if checked with a scan tool. Factors like timing chain stretch or distributor gear wear can cause the CMP Retard value to become negative.
Distributor Installation and CMP Retard
To install the distributor correctly on a GM Vortec engine, follow these steps:
- Set Engine to TDC #1: Ensure the engine is set at Top Dead Center on cylinder #1’s compression stroke, as described earlier.
- Distributor Rotor Position: Drop the distributor into its housing, aiming the rotor to point approximately towards the #6 marking on the distributor housing (note that the distributor housing is not factory adjustable).
- Engine Rotation Check: Rotate the engine manually by hand for two full revolutions to ensure the distributor is fully seated in its position.
- Verify Rotor Position Again: Check the rotor’s final pointing position. If it’s off by a full tooth on the distributor gear, it could cause issues.
- Initial Startup and Code Check: Start the engine. If the distributor is significantly misaligned (off by a tooth), the computer will usually detect this through the camshaft position sensor and set a trouble code, potentially causing poor engine performance.
- No Code, No Immediate Problem: If no Service Engine Soon (SES) light or code is triggered, the distributor installation is generally considered functional. However, optimal performance might still be achievable with fine-tuning.
Alt text: Installing a distributor on a GM Vortec engine, highlighting rotor alignment for proper CMP Retard.
Fine-Tuning CMP Retard for Optimal Performance
While a basic distributor installation might get your engine running, achieving the best possible performance and efficiency can involve fine-tuning the CMP Retard to as close to zero degrees as possible. This often requires an adjustable distributor clamp modification, as the factory clamp is fixed.
To adjust CMP Retard, you’ll need an OBD2 scanner capable of reading this specific GM parameter. This is where tools like Torque Pro OBD2 app for Android come into play.
Using Torque Pro App to Monitor GM CMP Retard
Yes, you can use Torque Pro with a compatible OBD2 adapter to read and monitor CMP Retard on many GM vehicles. However, it’s important to note that CMP Retard is a manufacturer-specific PID (Parameter ID), meaning it’s not a standard OBD2 parameter.
To read CMP Retard with Torque Pro, you will likely need to manually enter the custom PID for GM CMP Retard. The specific PID can vary slightly depending on the exact year and model of your GM vehicle. You can typically find these custom PIDs on online forums and communities dedicated to Torque Pro and OBD2 diagnostics, or resources specializing in GM specific PIDs.
Once you have the correct PID entered into Torque Pro, you can add it to your dashboard and monitor the CMP Retard value while the engine is running. This allows you to see if your distributor is properly aligned and if adjustments are needed.
For more advanced adjustments and diagnosis, professional-grade scan tools like Scan XL Pro or HP Tuners VCM Scanner offer more robust capabilities, including bidirectional communication with the PCM, crankshaft relearn procedures, injector balance tests, and more. HP Tuners, for example, gives extensive control over PCM functions for tuning and diagnostics.
Parts Recommendation
When replacing distributor-related components, it’s generally recommended to use AC Delco parts for the cap, rotor, and spark plug wires. For the distributor itself, while AC Delco is a reliable choice, there are other reputable brands available. However, before replacing the entire distributor, consider inspecting and repairing your existing unit, as it’s a relatively simple device on many older GM vehicles.
Conclusion
Understanding GM CMP Retard and how to monitor it is a valuable skill for anyone working on GM engines. While basic distributor installation can get your vehicle running, using tools like Torque Pro with a compatible OBD2 adapter allows for finer adjustments and diagnostics to optimize engine performance and efficiency. By correctly setting TDC, understanding CMP Retard’s role in distributor alignment, and utilizing OBD2 tools, you can ensure your GM engine runs smoothly and efficiently. Remember to consult repair manuals and online resources specific to your vehicle model for precise procedures and PID information for Torque Pro.
