Image
| Image Image Image Image Image Image Image Image Image Image Image Image
Members Login
User ID: Password:   Forgot Password  
MODIFYING YOUR 454SS FUEL SYSTEM FOR STREET PERFOR
Published: 2/28/2001  
Author: Paul Romanych a.k.a. RedSS
A topic that seems to resurface every few months is what can be done to the fuel system to extract more power from the big mill, either as stock or lightly modified (to about 390 HP). Your first and foremost consideration should be on the fuel system, bef

A topic that seems to resurface every few months is what can be done to the fuel system to extract more power from the big mill, either as stock or lightly modified (to about 390 HP). Your first and foremost consideration should be on the fuel system, before the intake, before the exhaust, before the nitrous (especially!!) and before just about any other mods. For if you do any mods so as to add more air without adding more fuel while the motor is operating under open loop conditions (like when racing that pesky Stang or frying up a hot burnout), your 454 sitting happily in the engine bay will not be happy for long. Read on to find out why and what can be done to protect your motor and originality of your ride, and give you more power. For the purpose of this article, I used my own 454ss as a test mule to put into practice what I have learned from the experts like Blown SS and others.

I knew that eventually I wanted as close to 450 HP as I could from my truck, through whatever means and still keep it somewhat original looking, not to mention trying to avoid screwing up the fine tune of the computer and EFI controls and/or the motor in the process. I began the way I told you not to, modifying the intake with a K/N filter, flipped lid with a planned all chrome open element cleaner and custom ram-air hood, and exhaust system of 3" muffler-less straight pipes after the cats. I had just added a whole bunch more airflow potential without adding more fuel. Blown SS helped me just in time… And thus he taught me about the SS computer (originally I knew nothing of Chevy EFI controls when I bought the 454ss). This is what he emailed to me:

Let's first look at a bit of SS TBI fuel injection operating theory, To figure out why the O2 sensor reading is important to you, and how it can tell you whether or not your fuel delivery system is healthy.

The SS TBI computer has two basic operating modes 1) Open Loop (O/L) and 2) Closed Loop (C/L). "Closed Loop" operation is in effect during most periods when the engine is up to temperature, and the vehicle is being used in a manner where good fuel economy and emissions control are expected. During C/L operation the computer monitors the O2 sensor, as a measure of the exhaust stream oxygen content. The exhaust gas oxygen content (post combustion) is related to the Air/Fuel (A/F) ratio that was previously delivered to the engine. By monitoring the O2 sensor voltage during C/L operation the computer is able to continually adjust the A/F ratio so as to achieve the perfect mixture known as "Stoich", or about 14.7:1 Air/Fuel ratio. In this manner, the computer is able to compensate for slight engine wear and modifications, and will learn correction factors that must be applied to future C/L fuel commands. However, there are times when C/L fueling is either not possible, or not desir able.

The O2 sensor is only accurate over a small band of A/F ratios near stoich, but there are times when the engine absolutely MUST have an A/F ratio other than stoich. During these periods, the computer defaults to Open Loop (O/L) fueling. During O/L fueling, the computer continues to measure the O2 sensor voltage, but ignores its value for the purposes of fuel delivery calculations. In a sense, the computer will calculate the amount of fuel that it "thinks" it should deliver to the engine, and then delivers it, but it never actually checks whether or not what was delivered was "correct".

The O2 sensor voltage that the computer "sees" is displayed on service scan tools in units of millivolts. 450mv would represent stoich. An O2 sensor reading of less than 450mv indicates a lean condition, or an A/F ratio above 14.7. An O2 sensor reading of greater than 450mv indicates a rich condition, or an A/F ratio below 14.7:1. If you do not have access to a scan tool, you can backprobe the circuit with a high impedance digital multimeter. However, it is important that the meter has a total impedance exceeding 10 Mega Ohms, otherwise the meter will influence the circuit and the voltage values will be incorrect.

During hard WOT acceleration, your engine requires a slightly rich A/F ratio for best power, and cylinder protection. To accomplish this, the computer defaults to O/L fueling, and substitutes an A/F value of roughly 12.5:1 in place of the stoich value. The factory engineers have spent many hours ensuring that the stock fuel calculations will deliver ample fuel during hard WOT use, in a stock SS truck.

However, by removing much of the exhaust flow restriction in your truck you have increased the total airflow potential of your engine during hard WOT acceleration, and in a sense have "leaned out" your engine during hard WOT use. Lean WOT mixtures can cause a loss of power, detonation, overheating, cylinder scoring, burnt/warped exhaust valves, and deformed (tuliped) intake valves. The degree of "leanness" and the duration of lean operation will dictate which of these symptoms you will experience, and the severity.

So what now?................

Install a fuel pressure gage, and establish what your baseline fuel pressure is (refer to the "Fuel Pressure" article on the Discussion page). Borrow a service scanner (any brand will suffice), and become familiar with the data screens. In particular, look for the O2 Sensor voltage reading. Find a willing co-pilot, and a local drag strip (I use an abandoned back-road, but I can't advise you to do that) and make a couple of hard passes while watching the scan tool display. Ideally, you want the O2 sensor reading to immediately rise to 800-850mv and stay at or above this value during the entire run. Make sure that you explore all of the RPM range. If this turns out to be the case, then your fueling is perfect, and no further action is required.

What you will probably notice is that the O2 reading dips to 600 or 700mv, or even less. This is VERY bad! Not only will this cause a loss of power, but it will also eventually hurt your engine. At this point, you must install an adjustable fuel pressure regulator, and begin to increase your fuel pressure until you reach a level which restores the correct WOT O2 sensor voltage readings. Again, refer to the "Fuel Pressure" article found in the Discussion archives, as it details how to accomplish this. Do not venture past 15-16 psi fuel pressure for continuous everyday use.

So I got started on modifying my fuel system. First on the list was a JET pressure regulator (p/n 61500). It is a direct replacement for the stock unit, which GM advises you not to try to disassemble (yeah right). Next was a higher flow filter. Everyone knows the stock filters are poorly suited to our use, so I ordered GM's filter for a medium duty truck (ours of course are "light duty"). Blown SS has flow tested this dealie at 400#/HR (or 60 US Gallons/HR). This will support 450 HP he said, with less than .5 psi pressure drop across the whole assembly. He assured me this would deliver the volume I needed for the upgraded motor. It even comes with grottings to attach the stock SS fuel lines to it, and looks similar to that Fram high flow filter in the Summit catalog. This filter is easy to change the element on; it's all too similar to changing an oil filter. Lastly, came the high flow fuel pump. I was originally going to buy the same pump Whipple included with their kit, but Norm Pearson persuaded me to pick up one from Turbo City, saying it was a more consistent pump that delivered 30-40 psi consistently (P/N 635-212 direct from Turbo City). This one didn't come in yet so, I'll have to update this article later.

The first article to arrive was the fuel filter. Easy modification here! To tie it in, I first removed the old filter (located on the inside of the driver side frame rail right above the tranny crossmember) and trashed it, and spilled the fuel in the lines into a container (watch getting that stuff on the undercoating, it will eat it right off). Then, I looked for a mounting spot. I decided to tuck the top of the filter mount as far up as I could, in approximately the same location as the old pump, hoping to avoid cutting the stock lines. But, due to the tranny crossmember, I had to shift it rearward on the frame rail a little. I placed the filter in this location, marked where the mounting holes were to be drilled, and drilled a 9/32" hole for each side. Then to tap the holes (too squeezed under there to want to get up again to grab the tap set), I removed a screw (it is a self-tapper) from the brake/fuel line plastic tie down on the right of my new mounting holes, and threaded it into my new holes. I grabbed two more of the same from my box of misc. screws and stuff, and proceeded to bolt up the filter assy. I then cut the feed line going to the TBI, as it was too short, installed a section of high pressure FI fuel line between the two ends, and re-attached it to the filter (I flared both ends of the hard line a little so as to hold the high pressure FI rubber hose more securely). Then I had to hook up the tank-side line. The bends were so radical that I could not get them out without kinking. Not only that, but the line was 5" too long. I cut the line 1 ½" behind the grotting, then cut it again before the first bend to eliminate the excess and bends. Finally, I took a 4" piece of 5/16" ID rubber fuel line (the hard steel line to the TBI is all 5/16" OD) and stuffed it onto both the short piece with the grotting on it and then the feed line from the tank, and tightened down a pair of heavy duty hose clamps on the assy, and made the final connection to the filter. I checked for leaks and found none. Lastly I re-sprayed bare metal over with Chassis Black after washing the chassis off.

Next came the pressure gauge. You will find this easier to look around and work with if you remove the whole air cleaner assembly. I cut the line right behind the TBI, on the first bend, and removed a 1 ½" chunk off the side now not connected to the TBI. I unscrewed the tag end off of the TBI, this you will need to clean REAL thorough if you cut it with a hacksaw, which I did as there is no way to get a pipe cutter in there easy. Then replace it. Anyhow, I flared both ends a little so as to hold the high pressure FI rubber hose more securely, and stuffed a 2 foot section of hose on the feed end, while I held a gallon jug under the end of the rubber to catch the fuel when I told my partner to turn the key to the "Accessory-Only-On" position (this will activate the fuel pump, which will pump fuel through the line until the pump senses a preset pressure, and shuts off). This effectively expelled all the bits of metal (from cutting) and other crap that may have fallen into the line to this point. I then took the hose, wrapped a small circle in it so as to leave enough slack in the line in case I needed to shift stuff around later, then cut the excess and stuffed the new end onto the TBI line stub. Then I cut this rubber line in a convenient spot, and spliced a T into the line, to which another 1-ft. section of hose was attached and run to a fuel pressure gauge. I clamped all connections with hose clamps, turned the key to Accessory-Only and checked out to find no leaks. I then got a 1"x5" long section of 1/4" thick piece of aluminum cut off a sheet, (this dissipates the heat better) and machined it to look nice, drilled a hole in one end so the alternator bracket screw would slip right in, bent the bracket up at a 35* angle right after the hole, and downward about ¼" from the opposite end, and bolted it to the rear alt. bracket screwhole. A later mod was to drill 4 holes through the bracket for which to slip wire ties through, to hold the pressure gauge line to the bracket.

You want to establish the base pressure of the truck, for comparison between stock and after the mods. Energizing the fuel system revealed 10 psi. I kept this info handy for later. The truck was running REAL lean on the top end so I knew I would need to jack up the pressure a bit.

Next came the fuel pressure regulator, as that was the 2nd goodie to arrive. Hell of a simple piece of metal with it costing 60 something dollars. Now this installation made spark plug swaps look tough. It is probably one of the easiest mods you can do. First I took off the air filter lid, and air filter element, and disconnected the injector wires. Then I removed the top half of the TBI. There are 8 Torx-head bolts holding it in place, three long and 5 short. I scraped off the old gasket (Blown SS told me that you can reuse the gasket but I didn't want to chance it) from the TBI and vacuumed off the loose particles on top of the TBI butterflies. You probably don't have to be this anal about it but, I don't like to tempt fate. I then LOOSELY clamped the top half and pressure regulator (looks like a small metal canister) in a vise, removed the 4 bolts holding the reg. into the TBI, and gently slackened the vise. This prevents the spring from popping off into some dark corner of your shop. I took the JET reg. and assembled the two pieces (there is only one way they fit at all) and laid the spring in place. I then stuck the other end of the spring into the top TBI half, and squeezed the reg and TBI top together by hand, enough to replace it in the vise (just to hold it long enough to start the screws). It helps more if you have another guy to start the screws as you hold it, and ignore the vise part. Tighten the screws to just past finger tight. IT IS CRITICAL to avoid tightening the screws more than finger tight, it does not take much to seal the gasket. I replaced the top half of the TBI on the lower half, again careful not to over-tighten, using all-new gaskets. I found out, apparently you cannot adjust the reg. without removing the top half again, so guess close the first time. I energized the system, checked again for leaks, and fired up the beast, checked again for leaks (see a pattern here?). COOOOL! Everything worked fine, stable pressure of 13 psi. throughout the RPM range, even when punched, which actually is just a TAD rich, but I feel better about that than too little fuel. Very cool. Now it was time for a drive, after checking everything once again and buttoning up the intake.

I took 'er down RTE 6 at near 120, twice, everything seemed fine, until I started smelling gas and saw the temp shoot up to 200*…odd as it normally stays at 150* … popped open the hood to reveal a half gallon of fuel all over the nice hot areas. Fuel line near the pressure gauge split. Anyhow, got that repaired to limp home, removed the whole pressure gauge ordeal, and stuck a stub between the TBI stub and main line, ran it a few times more with the motor now-no-longer deprived of fuel, with a GM scanner hooked up to the O2 sensor to get a reading of 450 MV at idle and no less than 800 all during a hard-hammering run. Very nice. I am estimating another 25 hp & 20 ft. lb. at least with just the fuel mods. I feel more than 25 HP 20 ft. lb. but I also have done the exhaust very recently before this and have been running with a largely unrestricted air delivery system. Alas three weeks later I am bored already; time for heads, a cam, and a supercharger. One last thing I am having ALL THE FUEL LINES from the tank-up run in flex stainless hose, but my buddy's shop is doing that, as I have not the special tools. Looks nicer and easier to work with. I plan to mount the pressure gauge in the same fashion, but in all honesty if I were to do it again, I would buy a dash-mount gauge.





Printable page