Fuel Delivery Problem 1999 Bravada

[PaintedStallions]

Hi,
I bought my wife a Bravada and I thought I had a fuel pump problem after about 6 months. Now I am not sure and maybe a little sceptical! I guess what I am trying to say is, is that one day it wouldn't start. To go back aways, it was always was an easy starter in the morning. But when you drove it for a while and it got warm and then shut her down like at a store or something, and went to start it again, you had to step on the pedal a bit to get it to crank. No biggey I thought. Now its dead! I changed the fuel filter, pulled the tank, yanked the pump out thinkin that was the problem. When I plugged up the fuel pump to the wiring harness, "out of the tank", and turned on the ignition, it ran for about 3 or so seconds and cut off. I turned off the ignition and it did the same thing. Cool I thought from reading past posts and rendered it to be normal. So I reinstalled the pump and tank and tried to fire it up. Nothing! I don't even here the pump run like I use to! I checked and replaced both the fuse and relay and still nothing! There is no fuel pressure at all! So what do you think? An actual bad fuel pump? Fuel pressure regulator? I am also aware that certain devices will stop the fuel pump from activating. Can anyone give me a run down as to what they are, where that particular component is located? What I am asking is, is what will stop the fuel pump from running other the the fuel pump itself?

Montana!

[Chris Stewart]

Your fuel injection requires 60-65psi to work, here's where you check it,




The fuel pressure test kits are available at most chain type auto parts stores and Harbor Freight.

[PaintedStallions]

I know where and how to check the fuel pressure! As I stated in my post, there is no fuel pressure at all! Something is stopping the pump from being turned on. Its not a bad fuse or relay. I replaced both. I replaced the inline fuel filter under the driver door near the tank. The only thing left is the fuel pump regulator! But would that stop the fuel pump from working and at least building some kind of pressure if it were bad? I don't see how since the fuel pump has to work first to send fuel to the regulator to be regulated! I am just trying to find out what components are capable of turning the fuel pump on or off so I can do some sort of process of elimination. Any suggestions will be helpful. Montana!

[old_master]

Running the fuel pump dry may have damaged it. The actual pump itself relys on fuel to lubricate it. The pump motor relys on the fuel to cool the motor. I wouldn't think that just a few seconds of running dry would hurt it too badly, but if it's an aftermarket pump, anything is possible. (Aftermarket pumps have a list as long as your arm of known problems.)

Fuel pressure regulator will not stop the pump from running. There is no fuse between the relay and the pump. The PCM supplies ground to trigger the relay. The relay is supplied voltage through an orange wire. The fuel pump relay supplies power to the pump. There is a known issue with the electrical connector overheating and melting on the fuel pump, which can cause the pump to stop running. Check for battery voltage at the fuel pump connector: The pump should operate for 2 to 3 seconds when the ignition is initially turned to the RUN position, then shut off. The pump should run continuously when in the START position.

[fiserman]

I had a 1998 s10 truck with 4.3 that always started fine, then one day it started to do just about the same thing. Found out that sometimes when I was starting it because the battery was getting older when it was pulling on the battery to start the truck there wasn't enough voltage to ingage the fuel pump. Old Master may be right you may not be getting enough voltage to pump.
Fiserman

[Chris Stewart]

Sorry for missing the point on lack of fuel pressure.
If the pump runs but produces no pressure, I suspect a worn out pump.
I replaced mine with a genuine AC Delco with years of good service.

[PaintedStallions]

Thanx for the tips guys! The fuel pump was the culprit. And forgive me for I have sinned! I went with an after market pump! I had to have her vehicle running and couldn't wait to come up with the money for the real McCoy! My daughter has to be driven to school. I have good fuel pressure now. But for some odd reason, injector number 5 ain't working. Can an air pocket form from installing a new pump and filter? Does anybody have a step-by-step diagram or instructions on how to replace the injectors? Is there a way that I can test injector number 5 while in the engine?

[old_master]

No possibility of an air pocket. The system is bled by the fuel pressure regulator constantly. To check the injector, either an injector balance test or an injector leakdown test will determine if the injector is working properly, both tests require a bi-directional scan tool.

[PaintedStallions]

Is there anway at all that I can check the injector for voltage while in the engine? It just seems wierd that the truck was running just fine before the pump went! I put in a new pump and filter and all of a sudden injector 5 goes out! Is cylinder no.5 the one closest to the fire wall on the driver side? But just in case I have to pull the injector, does any know of a site that I can go to to get instructions on how to do this. I can do this without this info. It would just be easier to know a little bit more before I jump into it!

Thanx Montana!

[old_master]

What is the 8th character of the VIN? Will be either a "W" or an "X".

[old_master]

#5 is the rear cylinder on the driver side.

The injectors are supplied battery voltage when the ignition in the START or RUN position. The ECM supplies a pulsed ground to open them. If you don't have a bi-directional scan tool, it would be worthwhile to pay a shop to run the injector tests for you rather than spend a bunch of money on a guess, or run the risk of damaging the ECM.

The thread below explains how to replace the injectors however, these injectors rarely fail. What usually happens is the poppet valve gets clogged and won't squirt fuel. You can purchase the injectors separately, (comes with the poppet) for just under $100 each OR, you can upgrade to the MFI system which totally eliminates the poppet valves and relocates the injectors to the intake ports using all new injectors, and fuel pressure regulator, for just under $200. In this thread, this is what's being done:
http://www.automotiveforums.com/vbul...d.php?t=559014

[PaintedStallions]

Thanx old master! That is really going to help. This new stuff requires a professors' degree anymore. But before i go to hacking away at the engine, where is the poppet valve located? What does it look like? And can you clean the poppet valve? I get this feeling that the poppet valve is in the injector somewhere. Do you have a picture of this poppet valve?
Montana!

[old_master]

With the plenum removed, this is what the Central Sequential Fuel Injection system, (CSFI) looks like.








The image below is what each of the 6 injector/poppet assemblies look like for the CSFI system. Each poppet has two tabs that lock it into the lower intake manifold. (You can see the tabs in the image above.) The two prongs at the top of the injector is the electrical connection. All 6 injectors are in the black plastic housing in the center of the lower intake manifold. When an injector is fired, it squirts fuel on the back side of the intake valve. The injectors are individually fired in sequence with the firing order.






This is the Multiport Fuel Injection, (MFI) upgrade. The poppets have been eliminated and the injectors have been relocated to where the poppets used to be. After the upgrade, it's actually Sequential Multiport Fuel Injection, (SMFI). This upgrade essentially changes the 8th character of the VIN from "W" to "X".




On 95 and older 4.3L "W" engines, only one injector with 6 poppets is used. The injector is "batch fired" which means it delivers fuel to each cylinder any time any cylinder is calling for fuel. This system is called Central Multiport Fuel Injection, (CMFI) and is less fuel efficient, that's one of the reasons why the CSFI system replaced it.

[PaintedStallions]

So I take it that the poppet is inside the injector module that you had shown me? Can the poppet be replaced or fixed? Or do you have to replace that module? I noticed that on the long skinny end of the module, with the tabs, that there is a needle like pin inside. Is that the poppet? Those module injector units are about 65 dollars a piece.

[old_master]

In the middle picture, the poppet is in the end of the black plastic nozzle. The actual poppet itself is a ball with a spring behind it to keep it closed. When fuel pressure overcomes the spring pressure, the poppet opens and sprays fuel onto the back side of the intake valve. It can not be serviced separately, (it comes with the injector as pictured).