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Old 10-31-2012, 09:25 AM   #1
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Join Date: Oct 2012
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Default The Ultimate 88/98 Toolbox

Copied and pasted this from another site tons of awsome info
I’ve been on the forum long enough to notice the same questions popping up again and again. Although the forum has a search feature, it is often easier to just ask your question. That's what the forum is for. Well to lessen repeat questions, I've attempted to gather together some great discussions on TBI- and Vortec-related performance topics into one big post – perhaps the ultimate post. I have not limited myself to this board and have included very useful discussions/info from other websites. I have used a running FAQ-type commentary to minimize reading through a ton of posts and so that I can share with you my experiences and expertise. Hopefully, this thread will serve as an important resource for those of you who are new to OBS trucks and serve as future reference for the FSC “old timers”. Feel free to offer suggestions or add your own Q/A entries to the appropriately entitled...


What is TBI?
TBI stands for throttle body injection. This was one of the first mass-produced fuel injection systems on GM trucks starting in 1987 for the final year of the square box body style. GM introduced a redesigned body style the following year in 1988, which would last 11 years from 1988 to 1998. TBI-equiped motors included the 4.3L V6, 5.0L, 5.7L and 7.4L engines. The 7.4L version aptly resided in 454SS trucks and production ran from 1990-1993. The 5.7L TBI engines were produced from 1987 to 1995, with power levels that ranged from 185-210hp. These pre-Vortec engines used hydraulic non-roller camshafts.

What’s a Vortec engine?
In 1996, GM introduced the 5.0L and 5.7L Vortec engines were that included several key enhancements: hydraulic roller camshaft, new higher flow Vortec cylinder heads, central sequential fuel injection (CSFI), OBDII, etc. These enhancements allowed the 5.7L Vortec engine to produce 250 hp and 320 lbs-ft of torque. Production of these engines ran until 1998 when GM redesigned the Chevy and GMC trucks for the 1999 model year, ending the smooth body style now referred to as the old body style (OBS).

Are there any cheap ways to make more power and get better fuel economy?
Well it depends on how much of the work you can do yourself. There are free or relatively cheap mods for sure, like the infamous reverse air lid trick on TBI engines, the ultimate TBI mods, and making your own AFPR for your TBI engine. You can also learn how to burn your own PROMs for a small investment that will pay you back huge as you keep upgrading your motor with better fuel economy and power. But unfortunately, more power requires a significant investment in time and money. Speed costs money…How fast do you want to go?

Better fuel economy can come with more power. How? Because it takes less throttle to get going and less pedal to keep you going. On the highway, you’ll especially notice the difference when your engine doesn’t have to downshift in order to get up hills. It is power that you can feel and it will save you money at the pump. The other factor is driving-style. Light throttle saves you money at the pump. Not always easy, but that’s the key to saving money on fuel costs. Let’s be honest here. V8 engines, despite their “advanced” fuel injection, are only capable of about 17-18 miles per gallon on the highway. If you wanted fuel economy, you would have bought a hybrid car instead.

What should be the first thing I do to my TBI/Vortec engine?
The first thing you should do to your engine is to make sure it has a complete tune up and is in proper running condition. This means replacement of the spark plugs and wires along with a new distributor cap, and rotor. The TBI or throttle body unit should also be cleaned thoroughly. This requires taking it off and cleaning all of the small passages that run along the bottom side of it. Cleaning or replacing the PVC valve is also crucial. You will also want to check your serpentine belt and coolant and vacuum hoses. They get old and crack and break down over time and this would be a good time to replace them. Finally, you will want to check your timing. The factory setting for the L05 (TBI) 5.7L engine is 0* but check your engine’s emission sticker under the hood for the factory timing setting for your truck. You can advance the base timing if you want, but timing is mainly controlled by the engine’s computer. A custom chip will add more timing under the curve to improve low RPM torque, so adjusting the base timing is pointless. You may have to run a higher octane fuel though so you will have to consider that. After your truck has received a full tune up you can start to consider your first modifications.

What is involved in a performance tune-up? What are some regular maintenance items to replace?
A complete tune-up includes: new air filter (cleaned reusable filter), new distributor cap/rotor, new spark plugs set at the appropriate gap, test and replace faulty spark plug wires, check timing, check and/or replace PCV valve, check and replace faulty vacuum hoses, check coolant level, oil/oil filter change, check transmission fluid level, check steering pump and brake fluid levels, check windshield washer fluid, check and readjust TV transmission cable (pre-93 trucks), remove slack from throttle linkage, clean terminals on battery.

Some common replacement items in general and preventative maintenance: Fuel filter, O2 sensor(s) (replace after 65,000-80,000 miles), PVC valve, belts, wiper blades.

I want to clean my IAC because I’ve heard that it can affect engine idle. How can I do this?
The quick way: remove the IAC and lightly spray carb cleaner on it and inside the chamber. Wipe the residue off with a shop towel. Reinstall.

The detailed step-by-step, careful approach:
1). Remove the IAC. It can be found on the pass side of the TBI.

2). After you have done so, reconnect the IAC connector and place a bag or towel around the IAC so the pintle doest go flying off. Once this is done, jumper pins 'A' + 'B' in the ALDL connector. Once jumpered, turn the key to the ON position, but don't start the car. The ecm will eject the IAC pintle. Turn off the ignition and remove the IAC and its components.

3). Next step is to clean the parts. I like using lighterfluid or naphtha. Cleans and leaves no unpleasant odor once it evaporates. Use a toothbrush to remove all the carbon deposits from the guide, spring, and the threads on the pintle shaft. Once dry lightly coat the pintle shaft and guide with a light grease or oil.

4). Reassemble. Place the spring over the pintle and place the pintle shaft in the guide slot in the IAC. It wont just go in as there is an armature with gear teeth on it. Screw the IAC pintle in until the guide slots on the pintle shaft just meet up with the guides in the IAC main body. From there gently rock the IAC pintle back and fourth while applying light pressure until the pintle gets partially back into the IAC.

5.) Reinstall the IAC. Screw it in by hand and if you feel any sort of resistance, STOP!!! The pintle has bottomed out. Reconnect the IAC and pull the jumper out of the ALDL if you have not yet done so. Lightly depress the gas pedal and start the car. Let it run for about 30 secs and shut down. Hand tighten the IAC and add about 1/16 additional turn is about all that's necessary. And you’re done. The vehicle is ready for use.

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