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mr2greasemonkey · 05-16-2007, 12:20 AM

Ok, now that we've made the engine spin we need the basics to make it run. Let's first start off with fuel. Wether or not you have a stock daily driver or a gas guzzling money pit you still need basic fuel system operation.

Fuel system requirements: Alright, no matter what type of fuel you are using you need volume and pressure. Since we are doing diagnostics and not tuning we are going to skip AFR's for the moment and go to requirements and delivery. A fuel pressure test will be handy, they're relatively inexpensive for what they can tell you so buying one is a good investment. Since there are no schraders you are going to have to get a kit that will allow you to tap into the fuel filter or cold start banjo fitting. The proper place to test for line pressure is before the fuel rail. You are looking for about 40 or more psi when the system is primed and at least 36 with the engine running. Think of the injectors as gates, they dont make the pressure. You need the pressure for a proper spray pattern. Modern day engines run higher pressure but with about 40 psi it should try and run. With the gauge you can also see if you have an excessive drop in fuel pressure with the engine running or if an injector is bleeding off. Volume is a little tricky. You could use a graduated beaker and see how much volume is pumped at a certain interval. A quick test for the DIY'er is to use a bottle and plumb the fuel delivery hose into it. A quick prime or start should fill the bottle quickly. Now would be a good time to tell your smoking buddies to put out their cig's , hehe.

The injectors not only need to fire electronically but mechanically. A quick probe with your test light or meter will tell you if the injectors are powered. A noid light or inductive injector testor will pulse the light when the injectors fired. Even a long extension on the injector body and your ear up to it will make a noise when the injector fires and the pintel contacts its seat. If you have a low amp inductive probe you can actually see the pintel come off it's seat and fire on a graphing meter. They should all react the same. A silent injectors or one that does not pulse has issues. Even though it works electronically dont assume that the injector is delivering fuel correctly. A leaky injector or one that is partially clogged will cause troublesome driveabiltiy issues that will be hard to track down.

Now assuming that the injectors are the suspect problem. You can pull the rail out with the injectors intact and do a quick test fire to check spray pattern. An electronic injector tester has a pigtail connector and is independently powered so you can fire the injector manually. Being able to physically see the injector work connected to the system is sometimes a pain in the ass to do but well worth it when chasing driveability issues. Dont assume that a wet spark plug means the injectors are working properly. When in doubt, take them out and have them tested. It's cheap insurance and in some cases remanufactured ones are cheap enough that it'll save you time instead of chasing all the possiblities.

It's always a good rule of thumb to replace the fuel filter when you replace injectors. If something got by the filter to mess up the injector, then it'll do it again to the new ones. Don't forget to get new o-rings and grommets.

more to come....

05-16-2007, 12:20 AM	#3 (permalink)
mr2greasemonkey Once again....yups Join Date: Sep 2005 Location: Portland, OR Posts: 1,658 Thanks: 4 Thanked 63 Times in 42 Posts iTrader Rating: (0/0% )	Fuel system basics Ok, now that we've made the engine spin we need the basics to make it run. Let's first start off with fuel. Wether or not you have a stock daily driver or a gas guzzling money pit you still need basic fuel system operation. Fuel system requirements: Alright, no matter what type of fuel you are using you need volume and pressure. Since we are doing diagnostics and not tuning we are going to skip AFR's for the moment and go to requirements and delivery. A fuel pressure test will be handy, they're relatively inexpensive for what they can tell you so buying one is a good investment. Since there are no schraders you are going to have to get a kit that will allow you to tap into the fuel filter or cold start banjo fitting. The proper place to test for line pressure is before the fuel rail. You are looking for about 40 or more psi when the system is primed and at least 36 with the engine running. Think of the injectors as gates, they dont make the pressure. You need the pressure for a proper spray pattern. Modern day engines run higher pressure but with about 40 psi it should try and run. With the gauge you can also see if you have an excessive drop in fuel pressure with the engine running or if an injector is bleeding off. Volume is a little tricky. You could use a graduated beaker and see how much volume is pumped at a certain interval. A quick test for the DIY'er is to use a bottle and plumb the fuel delivery hose into it. A quick prime or start should fill the bottle quickly. Now would be a good time to tell your smoking buddies to put out their cig's , hehe. The injectors not only need to fire electronically but mechanically. A quick probe with your test light or meter will tell you if the injectors are powered. A noid light or inductive injector testor will pulse the light when the injectors fired. Even a long extension on the injector body and your ear up to it will make a noise when the injector fires and the pintel contacts its seat. If you have a low amp inductive probe you can actually see the pintel come off it's seat and fire on a graphing meter. They should all react the same. A silent injectors or one that does not pulse has issues. Even though it works electronically dont assume that the injector is delivering fuel correctly. A leaky injector or one that is partially clogged will cause troublesome driveabiltiy issues that will be hard to track down. Now assuming that the injectors are the suspect problem. You can pull the rail out with the injectors intact and do a quick test fire to check spray pattern. An electronic injector tester has a pigtail connector and is independently powered so you can fire the injector manually. Being able to physically see the injector work connected to the system is sometimes a pain in the ass to do but well worth it when chasing driveability issues. Dont assume that a wet spark plug means the injectors are working properly. When in doubt, take them out and have them tested. It's cheap insurance and in some cases remanufactured ones are cheap enough that it'll save you time instead of chasing all the possiblities. It's always a good rule of thumb to replace the fuel filter when you replace injectors. If something got by the filter to mess up the injector, then it'll do it again to the new ones. Don't forget to get new o-rings and grommets. more to come....