I bought a Chevy.

Hello,

I bought a 2004 Chevy Silverado Shortbed 4.3 manual shift. 49,000 mi. I've probably done less then 100 miles on it yet . It probably will get less then 5000 miles a year. It might get about 2000 or less if you look at my other trucks. I've been a pre electric , pre ABs , pre tank fuel pump, pre bullshit 80s kinda man. My Good old reliable 82 Suburban heater core is leaking and its got the rusties bad. I'm getting tired of laying in the grass or gravel to work on my junkers. So I'm liking this new vehicle it a lot.

But a few questions .

I never had a Vortec. I didn't want it but I bought used and you don't get to pick. It does run very well. But the vehicle vibrates a bit more then I expected. I suspect its normal. Does it have that spider central injection system buried in the engine. I read about it a while back. Buried under the intake and some little valves leak and flood the engine . People put Mercruiser intake system in . Or did Chevy get the 4.3 in order. There's some type of fuel system on the intake but I don't see any fuel lines or rails anywhere. And I've noticed there's metal lines on top of the left frame rail next to the engine that are rusty pretty good. probably brakes. My thoughts are to clean them up with some sand paper and paint them with rustproof paint. like POR. I've got a couple quarts. Are there any known issues besides those spider fuel injectors with these vehicles. I'm talking things to be addressed before you're left somewhere or trash something. And what happens if the fuel pump trashes. Am I stranded. Do I need to change brake fluid to keep the ABS from malfunctioning.

Other then that I'm thinking this vehicle is pretty damn nice. Its the best truck I had.

Thanks , Diesel

Reply to
DogDiesel
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By JEFF MASTERMAN

Armed with a pressure gauge, a good scope and a working knowledge of its trouble spots, you can purse the demons that plague GM's CPI system.

In 1992, General Motors introduced a very unique fuel injection system on its 4.3-liter Vortec V6 truck engine. Dubbed Central

Port Injection, or CPI, the system looked and functioned much differently than previous designs. The CPI system utilizes one main injector that pressurizes six plastic tubes house in the intake manifold. Each tube terminates in a spring-loaded poppet valve that supplies fuel to its corresponding cylinder. The main injector is pulsed twice per crankshaft revolution, with pressurized fuel opening each poppet as system pressure approaches approximately 48 psi. Most RecentAuto Articles

The main injector and fuel pressure regulator on the CPI system are housed in a molded plastic piece with the six plastic tubes attached. GM dealers service this assembly as a single part number, and it's quite expensive to replace. The good news is that replacement pressure regulators, as well as fully reconditioned assemblies, are available via the aftermarket, which can save your customers substantial dollars on their repair bills.

Common Problems

Leaking pressure regulators are fairly common on the CPI system. Since the regulator is housed in the intake, a ruptured diaphragm often results in fuel being dumped directly into the crankcase or passenger-side cylinders. Fortunately, the manifold tuning valve (MTV) can be removed to allow easy inspection of the regulator if leakage is suspected.

Fuel pressure leak-down with no external signs of leakage is another common problem on the CPI system. Like most injection systems, leak-down can result in long crank times or a stumble ofter restart. A quick way to isolate the cause of weak-down problem on this system is to cycle the key and allow the fuel pump to run for a couple of seconds. Once the pump stops, simply pinch off the supply line. If the pressure holds, the cause is in the tank. If it doesn't, the intake will have to come off for a closer look at the internals.

no-start condition. GM lists the pressure range for the

no-start complaints with pressure readings as high as 56 to 57 psi on a cold engine. This problem is amplified by the fact that many fuel pressure gauges have seen a rough life and can be off by as much as 2 to 5 psi. So always check the accuracy of your gauge before working on a CPI system. Finally, remember that the fuel pressure shouldn't drop during heavy acceleration. If it does, the volume of fuel being delivered needs to be evaluated.

maintenance item, and it's not unusual to see a filter that's racked up 100,000 miles. Running for long periods against a restricted filter can kill even the best of fuel pumps. It can also cause big-time problems for the CPI system.

significant differences in the volume of fuel flowing through the poppet valves.

The result will be a rough idle, often accompanied by a failed emissions test due to high HC levels. These engines use an electronically controlled EGR valve with a built-in position sensor. Scan data can provide a quick check for this type of valve. With the key on and the engine off, just compare the "EGR Desir percentage to "EGR Actual." If the Actual percentage is higher than the Desired, the valve needs to be cleaned or replaced.

occurs, a large amount of fuel will enter the combustion chamber. Fouled spark plugs can be a tip-off to this problem. If you look at the scan data, em. If you look at the scan data, you'll find that the Long Term Fuel Trim number will be negative, as well.

which could result in a rough idle and high HC during an idle emissions test. Performing a cylinder balance test can help you isolate the problem cylinder. Once the cylinder is identified, add propane at the throttle body until the rpm peaks. Then repeat the test. If the weak cylinder now contributes, the poppet valve for that cylinder should be suspect. One caveat: The intake design of the

4.3-liter Vortec V6 can prevent the propane from being evenly distributed among the cylinders. This can result in misleading test results. When in doubt, remove the intake plenum.

flow on a CPI engine. If one is not available, there's an alternative test that can be performed after the plenum is removed. Begin the test by removing the coil wire from the distributor and securely ground it to prevent the engine from starting. Leave the ignition primary connected so the main injector will pulse. With the intake plenum off, the weak cylinder's plastic line can now be pulled out of the intake and the poppet valve placed in a container. Observe the spray pattern while an assistant cranks the engine briefly.

Since the main injector is concealed by the intake, a noid light cannot be used for no-start diagnosis. However, there is a connector behind the alternator that can be used to check the power feed and the PCM-controlled ground side of the injector with your scope. While the scope is not connected "at" the injector, grabbing a waveform at this location tests the whole circuit. Note that GM uses a peak-and-hold driver arrangement on the CPI system, similar to its TBI setups. If the waveform indicates a problem, the intake will have to be removed to check the rest of the wiring. Mo

With a working knowledge of the system and an accurate fuel pressure gauge, you can win the diagnostic battle with GM CPI. Just remember what makes this system so different from the more common ones you see every day and you'll be on your way to having found a cure for the "fuel injector blues."

Masterman, Jeff "Curing the fuel injector blues". Motor. FindArticles.com. 15 Sep, 2010.

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As for the fuel pump. Keep your tank at least a quarter full. The more fuel, the cooler the pump runs. I had a 91 2.8 v6 s-10 for a few years, then upgraded to an automatic 4.3. I drive 88 miles a day, back and forth to work. Its been. a good truck. If the pump keeps giving you trouble, you can always, cut a hole in the bed. Over the pump. Big enough to reach the pump, Screw a cover over it. I was going to do that with my older s-10. So far, I only had to replace one fuel pump. With my 2,001 4.3.

Reply to
4546

I appreciate the reply. I do remember somebody posting here before showing tneir fuel pump access door on their truck. I can grasp that easy enough.

So back to CPI. Right off the bat my truck runs awesome. So its not pressing . The first thing is do I have it. Somebody wrote somewhere in a rant on a forum that GM replaced it in 2002 with something else. I remember the rant being about GM adding a balancer shaft and changing the fuel system. I cant tell what I have. There arent any fuel rails or anything showing like a multiport .

Reply to
DogDiesel

The 4.3 does vibrate a bit. Even with the balance shaft they are not really smooth. Just the design of the engine.

Sort of. The original 4.3s were carbed, then GM came out with the CPI units. These are the ones that gave problems. However in 02 GM changed the design again. Now they use a unit that still has the pressure regulator but it doesn't use poppet valves. Instead it has small solenoid injectors at each port. The new unit is SCFI, it is sequential just like the "normal" injection systems with fuel rails and injectors.

Look at the left rear of the intake and you will see two fuel lines that go into it. One is fuel in the other is the return line.

Probably brake lines.

There are a few known issues. First thing is the oil cooler lines. They redesigned them a couple times but they still have a bad habit of leaking. Wipe them down good and check for leaks.

Water outlet for the heater lines on the pump, the later quick disconnects tend to rot out and fail, not hard to repair but a PIA if it's the middle of winter and COLD...

Intake gaskets. 04 should have the good ones BUT I have seen a few failed ones. Again, if you swap them out before they fail and use the new design Fel-Pro gaskets it's not a bad idea.

In tank pumps are a PIA regardless of who has them. On most of the GM models the easy way to change the pump is to pull the box off. One VERY common reason for pump failure is the connector itself. They heat up and lose tension in the contacts, this causes a loose connection and makes things worse. IF you do replace the pump DON'T shop by price alone. There are a lot of JUNK pumps out there. Either get a factory pump or one of the better ones from NAPA or Carter. Don't even look at the Autozone/Advance type store brands.

Same as any other FI pump, it fails you don't drive.

Not a bad idea, not just for the ABS but to get the crud, moisture, rust out of the system.

Front and rear brakes can be a problem if you're in a salt/rust state. The pins get moisture in them and the calipers don't slide and the brakes bind. My SOP is to pull the caliper pins once a year, clean them relube with silicone grease and put them back on. Sounds like work but it only takes about 10 minutes per corner and allows you to actually check the pads,grease the joints as needed and check for other wear.

Rear parking brake shoes are a PIA on 4 wheel disc equipped models. They don't get used much so they rust and chew up the lining. When I do the rear calipers I like to pull the rotor and check them.

Reply to
Steve W.

I just got the big picture. Without the poppets its probably good.

Ok , will do.

I dont know about quick disconnects yet. Dont figure to have a problem with them.

Ok.

Im in the salt state. Ive had good luck with anti seize compound. Getting me to the brake changes.

They rust here real bad if not used. This ones getting used . Im gonna keep using it.

Reply to
DogDiesel

Much better.

Neither does anyone else, until they rot and leak.

I'm in NY so know about salt.Sounds like you have a handle on it.

Reply to
Steve W.

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