Modern fuel injectors are pretty bulletproof for the most part, and even if one of them fails, chances are almost non-existent that all others will fail at the same time. So, if you are not getting any power to the injectors when cranking, for now, we can at least tell you that the injectors are good. So, what can be the cause?
If you get no injector pulse while cranking, it could be a faulty camshaft position sensor, broken wiring, bad ground connections, a faulty ECU, or even blown injector fuses, but not that many cars have those. Of course, fixing any of these problems is different, so stick around to see how you can diagnose and fix them.
Fuel Injectors Explained
The fuel system in most modern cars with electronic fuel injection is pretty simple. There is a fuel pump in the gas tank that moves fuel to the engine, where it enters a simple metal fuel rail. Then, injectors are plugged into that fuel rail on one end and into the intake manifold on the other.
So, how do injectors work? Well, injectors are nothing more than electromagnetic valves or plungers controlled by the ECU (engine control unit). The ECU picks up relevant information from other sensors and decides when to open each injector.
When it’s time for an injector to open, the ECU closes its ground circuit, thus activating the electromagnetic valve, and the pressurized fuel shoots through the injector into the intake manifold. And once it’s time to close the injector, the ECU opens the ground connection, after which the injector has completed one pulse.
Now, what we have explained is a standard EFI (electronic fuel injection) system that’s been the most popular fuel system ever since the 80s and even today. In such systems, the engine has one fuel injector for each cylinder. But, of course, there are some variations on the subject.
First and foremost, the early fuel injection systems, starting with the 1954 Mercedes Benz 300 SL, were mechanical. The injectors in mechanic fuel systems were usually opened and closed by the camshaft or by other mechanical systems like metal rods that were synchronized with the crankshaft. But those systems are long gone and pretty much irrelevant today for the problem we are discussing.
However, it’s worth mentioning SPI (single point injection) and direct fuel injection (GDI) systems. The SPI system is exactly the same as the previously mentioned EFI, with the only difference being that it has one fuel injector for all cylinders. That system is less efficient but cheaper. However, SPI systems were rarely ever used.
GDI systems, on the other hand, are becoming increasingly popular in the past decade. A GDI system is very similar to EFI; however, in a GDI system, the fuel injectors deliver fuel directly into the combustion chambers/cylinders instead of the intake manifold.
The GDI system is much more efficient than EFI but also slightly more complicated and expensive. A GDI system requires a secondary high-pressure fuel pump, plus the injectors are often ten times more expensive than the EFI ones. But at the end of the day, I would say that 80% of cars on the road today use an EFI system, also called MPI (multi-point injection).
What Causes No Injector Pulse While Cranking
Several things can cause no injector pulse while cranking. Unfortunately, if it’s not one of the more obvious ones, like a faulty sensor, diagnosing the problem can be extremely time-consuming. But before we go into fixing the problems, let’s see what can cause them, and who knows, maybe that will be enough to figure out what the problem in your case might be. So, here is what causes no injector pulse.
Faulty Camshaft Position Sensor
There are several sensors that the ECU uses to determine how the injectors should operate, but what sensor controls injector pulse? You guessed it, it’s the camshaft position sensor. The camshaft position sensor sends pulses to the ECU, which are almost directly translated into injector pulses.
So, without a properly functioning camshaft sensor, there will be no injector pulses either, and the engine won’t start. However, the camshaft position sensor usually starts shutting down randomly before it fails. Going by that, if your car has been stalling recently and now there are no injector pulses, it’s most likely the camshaft sensor.
Damaged Wiring
Although the wiring is rarely damaged, especially in cars that are no more than 20 years old, it can still happen. Damaged wiring means pinched wires, broken insulation, or corroded connectors. The wiring that affects fuel injectors is the injector loom and connectors and the camshaft position sensor wiring plug connector.
Bad Ground Connections
As we already mentioned, the ECU closes the injector circuit ground when it wants to open the injector. So, without a proper injector ground, the injectors won’t work. Moreover, the ground connection on one injector affects all of them, which is why none of them work with a bad ground connection.
Faulty ECU
After everything is said and done, the ECU is what sends power to fuel injectors. Now, the ECU doesn’t fail too often, but there are vehicles where it’s a common problem. However, ECUs have been starting to fail more and more frequently on vehicles since the nineties because 30 years of service isn’t neglectable, even for a microchip.
Unfortunately, a faulty ECU either doesn’t show any symptoms other than the problem you are trying to solve or it triggers almost every dashboard warning light. If the latter is the case, the ECU should be your main focus.
Blown Injector Fuses
In most cases, cars don’t have injector fuses or relays. Fuel pump relays and fuses, yes, but not for injectors. Still, it’s worth checking if your car is one of the few with injector fuses. That will take no more than a couple of minutes of swiping through your owner’s manual. And who knows, maybe a ¢10 fuse is all you need.
How Do You Fix No Injector Pulse While Cranking
How you fix unresponsive fuel injectors depends on what’s causing the problem in the first place. So, as the answer explains how to fix each case, the order in which the list below goes is the order in which you should inspect the fuel system. That’s unless you already have an idea of what could be the problem in your car.
Fuel Injector Fuses – Fixes
Fixing the fuel injector fuses is pretty straightforward; you replace them with new ones that have the correct amperage. But again, you will find a fuse box diagram in your owner’s manual, so first, check if your car has injector fuses or not.
If it does, there will be one fuse for each cylinder bank. That means if your car is a four-cylinder, one fuse for all four injectors. If it’s a V6, one fuse for three injectors and another for the other three. And if this turns out to be the problem, it’s not a cause for concern unless the fuses fail again in the next year or so.
Damaged Wiring – Fixes
To check the wiring relevant to the fuel injectors, start with the camshaft position sensor. First, check all three or four wires for broken insulation, hard bends, and if they are scraping on some metal piece. Then, unplug the connector and see if it’s clean inside.
The connector should be as clean as new around the pins and terminal, and if it’s not, clean it with electric contact cleaner spray. Then, do the same with the fuel injectors. Inspect all the wires for each injector and their connectors.
And if you find any broken wires or insulation, it’s best to solder them and put some heat shrink tube over the spot. Since these wires are important, it’s best to leave the soldering and repair to a professional if you don’t have much experience.
Bad Ground Connections – Fixes
First and foremost, it doesn’t hurt to check all the ground connections you can find in the engine bay because each can potentially affect the injectors. But the first ground you should inspect is that of fuel injectors. Now, in most cars, the fuel injectors are grounded directly through the ECU.
However, in some cases, you will find a ground wire bolted to the engine or going to some type of control module. So, if you can’t find the fuel injector ground, inspect the control module or the ECU ground. If you see some broken insulation or visible damage, it’s best to replace the wire. Otherwise, clean the connections with a steel wire brush and contact cleaner spray.
Faulty ECU – Fixes
Since the ECU can be extremely expensive to test, and even more so to buy new, if you don’t find any of the earlier problems, the best solution is to find a used one. Or better yet, borrow an ECU and see if the car fires up. You can find ECUs at breaker yards, or a local repair shop might have one lying around for you to try.
But if that’s not an option, then buy a used ECU and see if that helps. While that could be wasteful, used ECUs typically aren’t that expensive. Plus, the chances of getting a broken ECU are extremely low, especially if you find one from a crashed vehicle.
How Do You Test the Flow Of an Injector
To test fuel injector flow, you need a special bench test machine specially designed for fuel injectors. Unfortunately, those machines rarely cost less than $300, so it makes much more sense to have them tested by a professional, which usually costs about $15 per injector.
Still, the test is pretty simple. The machine fires each injector at the same time, with the same frequency and the same duration. The injectors squirt fluid into measuring test tubes, and whichever fuel injector doesn’t fill up the tubes to a desired level is faulty or clogged up.
Now, there are ways you can make your own fuel injector flow test machine, but I can’t say how accurate that will be or how much time and money it will take. Still, the video below demonstrates how to make one, and explains everything you should know, so it’s up to you to decide if it’s worth it.
FAQs:
Q: What controls the fuel injector?
The ECU (engine control unit) controls the fuel injectors. In some cases, there are fuel injector modules between the ECU and injectors, but even in those cases, the ECU makes the final call. The ECU, on the other hand, uses inputs from certain sensors to decide when to fire a fuel injector.
Q: What sensor tells injectors to fire?
The ECU tells the injectors to fire, but the ECU uses the camshaft position sensor to know when and for how long to fire a certain injector. The ECU also uses the O2 and MAF sensor inputs to decide how long an injector pulse should be.
Q: Does the crankshaft position sensor control the injector pulse?
No, the crankshaft position sensor doesn’t control the injector pulse, nor does the ECU use it to decide when to fire injectors. The crankshaft position sensor controls the ignition timing, while the camshaft position sensor correlates with injector pulses.
Q: What component controls fuel injectors?
The ECU (engine control unit) controls the fuel injectors. The ECU closes the injector ground circuit when it needs to open, but the ECU uses inputs from different sensors to decide when and how long to open an injector. Specifically the camshaft position sensor, O2, and MAF sensors, among others.
Q: How do I know if my fuel injectors are pulsing?
The best way to know if your fuel injectors are pulsing is by using a fuel injector noid light. The noid light connects to the fuel injector harness, and each time the injector pulses so does the noid light. Alternatively, you can use a standard test light or a multimeter.
Final Words
In the end, unless the camshaft position sensor is faulty, solving the problem of fuel injectors not pulsing can be a nightmare. But that’s not always the case, and to minimize the chances of that happening, here is what you should check. First, check if your car has fuel injector fuses, and if the answer is positive, inspect them. After that, inspect all the wiring and ground connections related to fuel injectors, and if everything checks out, the only thing left is to replace the ECU.
