95 GMC Safari / ruff idle, black exhaust residue

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Old 04-11-09, 07:25 AM
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95 GMC Safari / ruff idle, black exhaust residue

I have a 95 GMC Safari that I just replaced the EGR Valve on. It still idles kind of rough, and it also leaves a black residue on the pavement from the exhaust. The exhaust itself is not black, and appears normal, cloudy white when it's cold out. What would be causing this? Could this be from the O2 sensors, the fuel injectors? Need help, as I don't want to just start replacing parts unneccassarily. Thanks
 
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Old 04-11-09, 03:02 PM
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Sounds like a case of "The Crabs".......

!995 uses a 4.3 litre Central Fuel Injection system. Your fuel injectors and Fuel pressure regulator are a single "Unit" with fuel tubes for 6 individual cylinders.....When you see it, you will Understand the "Crab" comment. Underneath the Intake Plenum....Sealed into the chamber....The Fuel pressure regulator , over time and age, begins to leak fuel. This leakage is inside the Intake chamber,Directly in the Airstream, so "Unmetered Fuel" is introduced to your motor, causing a Rich Burn, Poor Idle quality , and Horriffic fuel consumption.

Very common, and a Bit pricey, as the early design must be changed as a Complete assembly. The Later design allows for replacement of the regulator alone.
 
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Old 04-11-09, 03:12 PM
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With pricey costs due to such engine designs meant to maximize fuel economy and reduce pollution- it be interesting to know if the priceyness negates any fuel savings one would have enjoyed, if compared to a less sophisticated fuel injection system. A possible folly of sorts? I guess this might entail some serious math.

What is the reason why larger engines often have individual port injection and smaller engines instead may have throttle body injection? Or do most have ported injection these days? And is there that much better fuel mileage?
 
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Old 04-11-09, 04:36 PM
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The CPI unit is actually a fantastic design. But Just like any other "Better Mousetrap" ,it has its Gremlins.

Years ago, on a cold winter morning, your "Carbureted" Plymouth Fury Ran terribly until you were on the highway for 20 minutes. If it was raining, your car new it before you did, and made no bones about letting you know. The Fuel injection, and Computer Controls were designed for this specific purpose. Your car should run Exactly the same on Thursday as it did on Tuesday, regardless of Temperature, weather, up in the mountains or down by the shore.
In theory, the Carb, and Fuel injection systems are the same. It is nothing more than a fuel delivery system. Simply put, The more control you have over a system, the less likely it is to be overcome by Natural Forces that we cannot control.
 
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Old 04-12-09, 07:33 AM
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One point in favor of carbs, it is a lot easier to unbolt the fuel pump from the side of the engine, than getting into the gas tank to change the pump on injected vehicles.
 
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Old 04-12-09, 11:43 AM
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Originally Posted by Unclediezel View Post
Simply put, The more control you have over a system, the less likely it is to be overcome by Natural Forces that we cannot control.
Which is good.

Except it comes with a price also, due to complexity and affects what the garage charges you to diagnose and even get to some of these parts in our now cluttered up engine compartments.

Looked at my neighbors car. Hardly have a clue how to reasonably get at his belts. I don't even want a car like that.
 
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Old 04-13-09, 08:14 PM
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Thanks for the information, I'll take it in and get it checked out.
 
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