Owner's Problem Description
The owner has a 1987 Honda Accord with a carbureted engine that started misfiring occasionally while driving. This issue progressed to misfiring even when stopped. Two months ago, the vehicle died and wouldn’t restart, backfiring and spitting fuel out of the carburetor. The owner had the timing checked, which was confirmed to be good. After replacing the distributor with a used one, the engine initially ran well but failed to start again after reassembly.
Professional Technical Analysis
This 1987 Honda Accord is equipped with a carbureted engine, likely a 2.0L engine, with an automatic transmission and approximately 150,000 miles on the odometer. The symptoms started with intermittent misfires, escalating to a complete failure to start. The misfire and backfire symptoms indicate potential issues with the fuel delivery system or air intake system. Given that the timing has been confirmed as correct, we must look into other areas such as the carburetor function, ignition system integrity, and possible vacuum leaks. A backfire accompanied by fuel spitting from the carburetor suggests an overly rich fuel mixture, which could result from a stuck float, faulty needle and seat, or an improperly adjusted carburetor. The intake manifold may also have vacuum leaks affecting the air-fuel mixture. It's essential to assess the integrity of the ignition components, such as spark plug wires and the ignition coil, while also checking for proper fuel pressure from the fuel pump, which should typically be around 5-7 PSI for carbureted systems. Current vehicle conditions show that while the engine may run initially after replacement parts, it fails to maintain operation, necessitating a thorough diagnostic approach to identify underlying issues.
Possible Causes
Most common causes (ordered by frequency):
- Carburetor Float Sticking: A common issue in carbureted engines where the float becomes stuck, causing excessive fuel to enter the carburetor, leading to rich mixture and backfiring. Check the float's movement and clean the carburetor to ensure proper function. - Fuel spitting out of carburetor, backfire upon attempting to start the engine
- Ignition System Malfunction: Weak spark due to faulty ignition components like the ignition coil or worn spark plug wires. Inspect all ignition components for wear, and check spark plug firing order to ensure proper operation. - Engine misfiring, checking the spark plug connections shows potential wear
- Vacuum Leak: A vacuum leak in the intake manifold or associated hoses can lead to an unmetered air entering the engine, causing a lean condition that can contribute to misfires. Use a vacuum gauge to check for leaks. - Unstable idle, possible hissing sound from the intake area
- Fuel Supply Issue: Insufficient fuel pressure from the fuel pump can lead to lean mixture conditions. Check fuel pressure with a gauge to ensure it is within the 5-7 PSI range. - Fuel pressure test shows values below 5 PSI
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Visual Inspection: Begin with a thorough inspection of the engine bay for any obvious signs of wear, loose connections, or fuel leaks. Check all vacuum lines for integrity and ensure they are firmly connected. Look at the carburetor for any fuel leaks or signs of damage.
- STEP 2 - Vacuum Leak Testing: Use a vacuum gauge connected to the intake manifold to measure vacuum levels. A normal reading should be around 18-22 inHg at idle. Additionally, spray carb cleaner around suspect areas while the engine runs to identify leaks by observing changes in idle speed.
- STEP 3 - Carburetor Function Check: Remove the carburetor and check the float and needle valve for proper operation. Clean the carburetor thoroughly and reassemble. Ensure that the float height is set correctly according to the manufacturer's specifications.
- STEP 4 - Ignition System Evaluation: Test ignition coil output using a spark tester and check spark plug wires for resistance (should be around 3-12 kOhms). Ensure all plugs are firing in the correct order and inspect for any carbon tracking or damage.
