In this article you will find a detail guidance on Fuel Systems Diagnostics Tech Tips.
Palivová nádrž
As fuel is used from the fuel tank it must be replaced with air to prevent a vacuum from occurring that could collapse the fuel tank and starve the fuel pump of fuel. Also as the fuel temperature increases, air must be released from the fuel tank in order to prevent excessive pressure from building and ballooning the fuel tank. It is the job of the EVAP system to vent the fuel tank.
ECM/PCM
The ECM/PCM calculates fuel injector pulse-width based on engine speed and load. Pulse-width is further modified to compensate for changes from multiple inputs, including engine temperature, throttle angle, fuel trim, and battery voltage. The ECM/PCM relies on the fuel delivery system to provide enough fuel for all possible engine operating conditions. Fuel pressure and volume are considered “known good” values from the perspective of the ECM/PCM and are not directly monitored. Low pressure or volume conditions can cause changes in the operation and performance of the powertrain that may set codes as a symptom of improper fuel delivery. Low fuel pump pressure or volume can cause a lean mixture and fuel starvation at high speeds that may induce lean-related DTCs. Excessive pressure can result in poor fuel economy, rich mixtures and can cause rich-related DTCs to be stored in memory.
Kontrolovat
Visually inspect the fuel system components for bent or kinked hoses and pipes, damaged electrical connectors, and dented or collapsed fuel tank which may be preventing the fuel pump module from operating properly.
One of the easiest ways to determine if the lack of fuel may be the cause of a non-starting engine is to spray some aerosol carburetor cleaner directly into the throttle while the engine is being cranked. If the engine starts, runs a few seconds and dies, it has spark and compression but is not getting any fuel.
Nedostatek paliva
If a lack of fuel has been determined to be the cause of a non-starting engine, then next it must be determined if that lack of fuel is caused by an electrical problem, the fuel pump, a plugged fuel filter, a faulty fuel regulator, or the fuel injectors. Be sure to check that an injector pulse is present at the injector harness and the vehicle battery is fully charged.
Dodávka paliva
Fuel delivery testing will ensure that the proper fuel pressure and volume are available under all possible operating conditions. Testing can be categorized into two areas:
- No-start diagnostics
- Performance-related diagnostics
All fuel delivery procedures are basically the same. They measure both the pressure and volume of fuel being delivered through the system under standard testing conditions. In addition to testing for pressure and volume, measuring the amperage of the fuel pump circuit can help determine the cause of a malfunction.
Replacing a Fuel Pump
Replacing a fuel pump can become a costly mistake if it is not the true cause of the fuel related problem. A fuel system should be carefully tested for pressure, volume, and electrical integrity before condemning the fuel pump.
Poslouchat
Often the first step in diagnosing a faulty fuel system is to simply listen. Turn the ignition key to the run position and carefully listen for a slight humming sound coming from the fuel tank. This humming sound should immediately follow turning the key to the run position and continue for approximately 2 seconds before stopping. When this humming sound is heard, it can usually be assumed that the fuel pump electrical circuit is functioning and that the fuel pump is running, which means that the next diagnostic steps should include determining if there is an adequate amount of fuel in the fuel tank and then testing for fuel pressure and volume. If the humming sound was not heard then the next diagnostic steps should include verifying the lack of any fuel pressure with a fuel gauge or scan tool and then checking the fuel pump electrical circuit.
Before Inspection
A fuel pump must deliver the correct amount of fuel in order to keep the fuel volume and pressure within specifications. Too little pressure can starve the engine of fuel, causing it to run lean, misfire, hesitate or stall. Too much fuel pressure can cause the engine to run rough, waste fuel and pollute.
Before performing any diagnostic tests on the fuel delivery system, it is important to understand the type of fuel system that is being worked on. Fuel return and returnless fuel systems both contain similar components but it’s the location of these components that determines how the fuel delivery system operates and consequently the tests used for diagnosing it.
Before beginning, ensure that the battery is fully charged (minimum of 12.6vDC). A supplemental power supply may be necessary to maintain battery voltage at the required level. If cranking the vehicle, do not exceed cranking times greater than 10 seconds to avoid overheating the starter circuit and/or other components.
The carburetor is designed to prepare a fuel and air mixture to be sent to the engine. Once there, the mixture can be combusted to produce power and make your vehicle move. Unfortunately, none of that is possible if there’s no fuel getting from the carb to the engine.
The lack of fuel between the carburetor and the engine could be caused by a lack of incoming fuel. That means a failed fuel pump or clog before the carb could be starving it of fuel. As a result, it has no fuel to send to the engine in the first place. Besides that, a stuck float and clogged fuel lines can also cause the same issue.
A lack of fuel from the carb to the engine will keep your vehicle immobilized. So, read through this guide to understand the most likely causes and what you can do to troubleshoot each one.
Why Isn’t Fuel Getting From The Carburetor To The Engine?
Fuel should have no problem flowing from a carburetor to an engine. So, if the engine isn’t getting the fuel it needs, here are the likely causes and how you can troubleshoot them:
1. No Incoming Fuel
O tom: Although this might seem like something obvious, you must always begin the troubleshooting process with the easiest thing to rule out. In this case, you have to ensure that the carburetor is receiving incoming fuel in the first place.
Remember: the carb’s purpose is to mix fuel and air together in the correct amounts and supply that mixture to the engine.
So, if the engine is only getting air and not fuel, check to ensure the carb is getting fuel to begin with.
What’s gone wrong: There are several possibilities as to why your carb isn’t getting any incoming fuel. The most basic is that there is none in the fuel tank. However, a clog in the fuel line can also prevent any from flowing in, which is also why none flows from the carburetor to the engine.
Jak to opravit: The solution here will depend on the root cause. For example, if there’s no fuel in the tank, you’ll have to refill it first before starting the engine.
A clogged fuel line will need to be cleaned or replaced if the clog is too severe to resolve.
2. Selhalo palivové čerpadlo
O tom: One of the most crucial components in any fuel system is the fuel pump. As the name suggests, that’s the part responsible for pushing fuel out of the tank and through the fuel lines towards the carburetor.
Besides that, the pump also maintains pressure in the line to ensure that the fuel can flow all the way into the engine.
What’s gone wrong: Unfortunately, the lack of fuel between the carb and the engine can be explained by a partially or totally failed fuel pump. When that occurs, there won’t be enough pressure in the system to drive the fuel through the carburetor and into the engine.
The pump could be suffering from a clog or an electrical malfunction, or it could have just worn out. Whatever the case, the failed pump prevents fuel from flowing out of the tank and feeding the system.
Jak to opravit: Fuel pumps aren’t the kind of components that fail often. So, if yours has been in use for several years and can no longer deliver fuel to the carb and engine, you’ll most likely have to replace it with a new one.
Getting a high-quality replacement can be pricey, depending on your vehicle’s make and model. However, it’s a crucial investment that will keep the engine running, and that’s well worth the money.
3. Clogged Fuel Lines
O tom: Fuel travels through lines that connect the fuel tank to other parts of the system. They consist of hoses and tubes attached to various fuel system components, through which fuel will flow when driven by the pump.
Fuel lines are flexible and durable, typically made from rubber and other materials that give them those properties.
Ultimately, fuel is supposed to travel from the carb to the engine through one of those fuel lines.
What’s gone wrong: When fuel doesn’t travel from the carb to the engine, there’s a strong possibility that one or more parts of the fuel line are clogged. More specifically, you’ll want to inspect the portion of the fuel line between the carb and the engine.
Fuel line clogs occur because dust or other debris has found its way into the fuel system. That most likely happens through the fuel tank, as it’s the only part of the system with an opening to the outside world.
Clogs typically build up over an extended period, so you won’t notice them at first. Unfortunately, they only become apparent when they’re severe enough to restrict the fuel flow to the engine completely.
Jak to opravit: A clogged fuel line can be cleaned by flushing it from both ends. But, of course, the system must be drained of any fuel before you can do that, and you’ll have to detach the affected fuel line.
This approach can be challenging. However, it’s the most direct approach, allowing you to get to the heart of the problem and deal with it head-on.
You can also prevent this from happening by using a fuel system cleaner. These products are poured in through the fuel tank and will help remove build-ups inside your fuel lines.
4. Stuck Carburetor Float
O tom: Fuel enters the carburetor through a float chamber. When that chamber is empty, the float will be at a low position, allowing fuel to flow inwards. The float will rise and pause the fuel inflow whenever the chamber is full.
The float must always be able to flow freely, as this process of letting fuel in happens continuously.
What’s gone wrong: Unfortunately, a dirty float can get stuck in the up position. When that happens, it will stop any fuel from entering the carburetor, even though it needs that to happen.
When that happens, the carb won’t have any fuel inside. So, therefore, it can’t send any fuel to the engine.
Jak to opravit: You’ll have to remove and open the carburetor to access the float. That way, you can clean away the debris or other impurities preventing the float from moving freely.
If you discover that the float is damaged in any way, you can purchase a replacement for it. Getting rid of a damaged float will ensure your carb works optimally for a long time.
Once you’re confident that the float can move freely, reinstall the carburetor. It’ll no longer have any problems delivering fuel to the engine.
Závěrečné myšlenky
Remember that when troubleshooting a carb that’s not sending fuel to the engine, the problem may or may not be at the carburetor itself. So, your troubleshooting process should begin from the start of the fuel system: at the fuel tank.
Make sure there’s fuel in that tank and that the pump is working correctly. Then, check that the fuel lines are free from clogs.
Once you rule out those basic causes, then you can inspect the carburetor itself for problems. The most likely issue causing this problem is that the float is stuck, and thankfully, that’s a quick and easy fix.
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