Solving Automotive No-Start Problems
This is where it gets fun. To restate what a crank/no start is, it’s when you turn the key and you can hear the engine moving but it’s just not catching and running. You can first eliminate all the above causes in this article because you have confirmed that your starter, cables, and battery connections are likely good. If they weren’t, you wouldn’t hear the engine turning over when you turn the key.
There are several causes of this type of no-start, but I’ll cover the basics here. An engine needs three things to run:
- A fuel supply; without fuel, the engine won’t run.
- A spark (for gasoline-powered engines). The spark is delivered to the combustion chamber via the ignition system. If you have a fault here, the engine won’t start.
- Mechanical integrity.
There are actually quite a few mechanical issues that can cause a no-start condition with an engine. This video covers the basics of dealing with a crank/no start condition to get you started.
If an engine doesn’t have fuel, it won’t run. Modern vehicles use a pressurized fuel system to deliver fuel to the fuel injectors. If there is a failure of this system, your engine won’t start. I can’t cover every manufacturer here, but I will cover the basics of how to check for fuel if you have a no-start condition.
The first thing to check for is fuel pressure. You can actually do this quickly on many systems. When you turn the key to the ON position, the fuel pump should run for about three to five seconds and then shut off. You need to know this for your testing so you don’t get fooled into thinking the fuel pump should run all the time with the key in the ON position. If the computer doesn’t see a crank signal after the ignition is turned on for three to five seconds, it turns the fuel pump off. During this time, fuel pressure should build up in the system and remain for some time after the fuel pump is shut off. The information about the crank sensor can be helpful here. If you have a start/die scenario, you might want to check the operation of the crank sensor. If the computer doesn’t see a crank signal it shuts off the fuel pump. If the fuel pump turns off, your engine won’t run.
Some engines have a Schrader valve in the fuel rail that you can depress to check for fuel pressure. Mind you, this is a quick check for fuel pressure and should not be taken as anything other than a verification that there is some pressure in the system, although it might not be enough to run the engine. Some engines won’t start unless they have an exact fuel pressure; if it’s low by just a couple PSI, the engine won’t start. So by no means should you consider this test anything other than a verification that the fuel pump can or can not turn on and move fuel. If you don’t see any fuel spray at all when you open the fuel system, then you can start looking into the fuel pump circuit to see what the issue is. Here’s a video illustrating what I’m talking about using a Honda vehicle that does not have a Schrader valve on the fuel rail.
For checking the fuel pump circuit, first start by checking the fuel pump fuse. Fuses are often overlooked and they shouldn’t be, as they are probably the most common cause of electrical faults. Next, there is likely a relay that controls fuel pump operation that should also be checked. Instead of going into lengthy explanations of how to do this stuff, this video explains the process.
A special note on Hondas here. A very common and well-known problem with 90s Hondas is a failure of the main relay. The main relay sends power to the fuel pump and other systems on most Hondas of this vintage. If the main relay fails, it often causes a no-fuel-pressure condition, which leads to a no-start. I’m posting this in all caps because you need to burn this into your brain. HONDA FUEL PUMPS HARDLY EVER FAIL. Toyota is pretty much in the same boat. In 20 years of working on Hondas, I’ve replaced four fuel pumps, and two were aftermarket. That should tell you something. So if you have a Honda that doesn’t have fuel pressure, look to the main relay and forget about the fuel pump. This video shows how to repair a main relay. This fix works and can save you the expense of purchasing a new one. Oh, don’t beat me up over my solder technique either. I’ve fixed my fair share of these relays and I have yet to have one come back. That’s not to say I couldn’t do a better job at soldering.
I’m not saying Honda fuel pumps never go bad, but if you suspect a bad fuel pump in a Honda, be sure to check for power on the yellow wire and ground at the black wire at the connector to the fuel pump itself when you turn the key on. If you have power and ground when you cycle the key and the pump doesn’t run, by all means, replace the fuel pump. But if you don’t have power and ground at the pump when you cycle the key, keep looking and leave the pump alone.