Ford ’87-’96 4.9L (300) EFI Fuel Injector and Pressure Upgrades

By Edward Trethewey
Copyright 2001, All rights reserved
DISCLAIMER:It must be understood that this upgrade should only be performed on 4.9L inline six-cylinder “race trucks” (oxymoron?) which are only used off-highway, as this modification may have a deleterious effect on Federally-mandated exhaust emissions limits and/or state emissions inspections.It must be completely understood that performing this incredibly fun and almost unbelievably effective modification is probably a breach of Federal law and could conceivably result in both author/tinkerer and
the reader/tinkerer spendinglong stretches in Marion County Federal Penitentiary alongside other vicious criminals, i.e., former dictators and/or drug lords, cannibals, mad bombers, and other infamous high-profile bozos.


Implementation of the steps outlined here will almost certainly trigger revocation of our tree-hugger status!

PART I—Fuel Pressure Guage, Building and Mounting Fuel Pressure Gauge Manifold
PART II—Adjustable Fuel Pressure Regulator, Selection and Installation

PART III—Electronic Fuel Injectors, Selection and Installation


Always keep in mind that while no “high-performance” version of this engine was built (even in the Land of Oz), Ford did intend for it to be a highly reliable, high-economy, high-torque, bottom-of-the-line truck engine, and therefore the design compromises made were conservative in nature—want high-torque at low RPMs? Cylinder displacement! Want durability? Seven main bearings and cam gear drive! Want cylinder block stiffness? Thick castings throughout the head (you should see some of the outrageous porting done on these heads--think sewer pipe). Want to make sure your fleet driver can’t deliberately blow up an engine so he can get some paid downtime? Use small, maxed-out fuel injectors on it, and camshaft timing biased toward the low end (the stock cam runs out of breath promptly at 4,000 rpm., but boy does it pull hard 1,800-3,000).

Assumptions, assuredly, but curiosity, observation, deduction, trial-and-error, the various Internet forums, personal interaction, initiative, and blind-melon assumptions are really the keys to effecting performance increases from this engine, and since the engine was overbuilt to begin with and skewed by the factory toward low-rpm torque production, grafting on proven mild 5.0 V-8 hardware can yield astonishing results. The trick is to enhance the stock midrange curves without losing bottom end. Upgrading the fuel injection hardware is one of these, as are virtually any exhaust improvements.


A fuel pressure guage is absolutely mandatory to this project, as is an adjustable fuel pressure regulator and bigger injectors, 19-lb./hr. (or higher). Ford specified white plastic-topped weenie 12-lb./hr. injectors @ 55-60 psig fuel pressure for the 300-EFI (4.9L) engine, whereas the rest of the concurrent V-8, V-6, and I-4 truck engines ran orange plastic-topped 19-lb./hr. injectors @ 30-45psig.


Studly19-lb./hr injector (top)

Needs Viagra:12-lb./hr. injector (bottom)

All of these engines (except the 4.9L) had a crossflow cylinder head design, which places the fuel injectors a cylinder head’s width away from the hot exhaust manifold, enabling those injectors to run much cooler. The 4.9L has exhaust and intake ports all in a row on the same side of the cylinder head with the injectors in a very close proximity to the exhaust manifold, and may be subject to vapor lock when run at a lower fuel pressure, which was one of Ford’s criteria in designing this engine’s fuel system with a higher working pressure. One of our design criteria is the ability of this revised fuel system to pass emissions testing via a turned-down line pressure. The hellish Texas summertime approaches, so we’re sure to learn all about vapor lock.


The higher line pressure may in its turn have influenced the Ford designers to specify a 12-lb./hr. rated fuel injector rather than the other truck engines’ norm of 19-lb./hr., and with that 7-lb./hr. difference lies the crux of this upgrade, because the pathetic 12# units are being replaced with the 19# (or higher) units. There is some speculation that 24-lb./hr. injectors may also be of value because of their additional capacity to supply ultimate fuel quantity for very high horsepower engines, as the later (’95 California/’96 50-state) Mass Air Flow (MAF) 4.9L units are adaptable to higher flow values achievable. Supercharging, for instance.


 The ’87-’95 50-state speed density versions generate error codes (the “check engine” emissions dash light) at a relatively low circa-40 psig, (Ford averages 39 psi across their lineup), but this is still a very worthwhile swap. Apparently, the antiknock sensor allows the engine to run a lot of ignition advance because the rich fuel mixture simply won’t spark knock, which on these horribly lean low-emissions/high-MPG engines makes an incredible difference in their power output and drivability. We are having very good luck with our initial advance increased to 12-degrees BTDC; stock is 10 BTDC, and we’re burning that wonderful 87 octane stuff. We’ve mused aloud about the possibility of using higher octane and cranking the advance way up there and been told sternly to “…not trust…” a knock sensor too far.


PART I: The Guage and its Mounting Manifold




Plastic hose protector, hose routing by heater core box, bracket, screw(s), guage

Schrader valve points toward engine. Copper-colored 1/8 vacuum line above guage is, well, 1/8 ”  copper refrigerator line used to replace 1/8” plastic vacuum lines that just can’t wait to shatter when touched.


End tees orientation, pipe nipples between horizontal-bull tee and end vertical-bull tees, pipe plugs, Schrader valve, hose fitting, flare. Not seen are two shortened 10-32 machine screws threaded upwards through bracket bottom into tapped holes drilled in square wrench areas on two pipe plugs in bulls of end tees..

Summit and Jeg’s both offer numerous fuel pressure gauges, under their own logos as well as others. A 60psig or higher guage face is what counts here. The 1.5-in. diameter underhood gauges have a 1/8” NPT spud; use the horizontal-mount type, as opposed to the vertical-mount type.
If forced induction is in your engine’s future, then you probably want to run an inside-mounted fuel guage. Guage pods are available to make a clean job of mounting additional gauges inside many popular vehicles, as are gasoline-isolating diaphragm fuel guage drives. We highly recommend both items, especially the isolator, which gives direct hydraulic readings but won’t let gasoline in the passenger compartment with us—we really hate being on fire.


We went about guage-mounting the “harder” way (as opposed the “hardest” way, which means interior-mount…cleanly…fooling around under the dashboard…) and built a neato-looking, cheapo engine compartment guage mounting manifold which included a Schrader valve for depressurizing the fuel system (like stock).


These are the parts we used:


  1. Home Depot (HD)--1 ea. joist hanger.. We used this because we had it lying around, and wanted a small 1”x 1” x 6” light gage galvanized length of angle on which to mount our guage manifold and with which to fasten the assembly to the firewall.
  1. HD—2 ea. #10 x 1” self-drilling sheet metal screws, with which to mount our angle to the firewall. These can be longer or shorter, depending on where you mount them and how comfortable you are about not interfering with whatever is behind the bulkhead you mount to.
  1. HD—2ea. stainless steel #10-32 machine screws—we got ours about 2-3” long so we had some screw shank to hold on to when we cut shortened these screws--$0.70 for 3-in. vs. $0.50 for the shortest they had in stock (which had to be shortened anyway, so who cares?)
  1. HD—5 ea. stainless steel flat washers to fit the #10-32 screws.
  1.  HD—1 ea. roll of ½-inch width Teflon Tape—get the smallest quantity available; one wrap of tape on 1/8” NPT pipe just doesn’t use very much tape.
  1. Auto Parts (AP)—1ea. 1/8” NPT-base Schrader valve.
  1. AP--2 ea. 1/8” NPT pipe plugs. Brass if you can get them, square or hex drive, either style, as long at the plug is solid inside, not hollow, and has material enough to support threading deep enough to engage at least four threads of the mounting screws-- Read On!
  1. AP--3 ea. 1/8” x 1/8” x 1/8” NPT brass pipe tee. Some Plumbing 101 for you here: stand that Tee so the single vertical stem is pointing downward, toward the center of the earth, (We always know where we’re at—we’re directly above the center of the Earth… at all times), and the long part of the Tee is horizontal—just like the T in the word “Tee”. The horizontal part, that you can sight through side-to-side, is called the “run”, and the vertical stem is call the “bull” (no bull). Class, learn these definitions because They Are On The Test!
  1. AP—2 ea. 1/8” x 2” NPT brass pipe nipples.
  1. AP—1ea. 1/8’ male NPT by –4 hydraulic flare fitting, stainless steel.
  1. AP— “Red” Threadlocker
  1. AP—1/2-in. size x 16-in., black plastic wiring protector wrap.

View of assembled guage manifold



  1. Jeg’s—0-100 psi guage, P/N 656-103. These gauges all cost around around $20.00, and come under several different manufacturer names. If it’s worth it to you, spend another couple of bucks and get “NOS” “Holley” “Barry Grant”   or whatever—the guage is the same. We debated long and hard: a 0-60 gauge range, or (the next step up), 0-100psi. The best of the in-tank fuel pumps max out around 80 psi, making the capability of the 100 psi guage possibly necessary. The downside of the 1-100 guage is that the gradations are smaller than a 0-60, and harder to see, so accuracy suffers.
  1. Jeg’s—1 ea. 1/16” male NPT x –4 hydraulic/fuel flare fitting, P/N 741-179-45, NOS-brand. We’ve never heard of 1/16 NPT before, but that is the thread size Ford used on the fuel pressure relief Schrader valve on the fuel rail of 4.9L trucks and Mustang 5.0s, and presumably other EFI motors as well. We bought ours from a local dyno/high tech motorsports place under the “NOS”-brand…the counterman there (as well as at “Jeg’s”) was well-familiar with “…that weird fitting Ford uses…”
  1. Jeg’s—1 ea. 16-inch –4 high pressure steel-braided teflon-lined hose with stainless steel female-swivel ends, Aeroquip or Russell are good sources. Jeg’s has a prepackaged 12-inch “Nitrous Works” (P/N 113-24412) which meets this spec, but in our opinion it is a little too short to enable us to make the clean, gentle-radius corners we prefer, en route from the fuel rail takeoff point up and back to the firewall.


--4 Stainless steel hose, 1/16” MNPT x –4 flare adaptor, pressure takeoff port on fuel rail at extreme rear of engine, between firewall and head at #6 ram tube

  1. 1ea. 10-32 tap, and its specified drill bit.
  1. 1ea. Pair straight cut aviation snips1 ea. ¼” dia. drill bit.
Start off by wrapping male threads (NPT only) with ONE WRAP of Teflon tape, beginning ONE THREAD back from the threading where it begins to thread into the female-threaded hole. We’ve heard it said, often enough, that several wraps of tape make for a better seal, as though Teflon tape has some sort of intrinsic, magical sealing power—it doesn’t, all it does is reduce friction, thereby allowing a deeper thread penetration at the same torque load. And by starting back one thread, the chance of a frayed fragment of tape detaching itself and worming its way into the fuel injection system’s ultra-precise works is reduced.
Thread the two nipples into the runs (I told you!) of the tees, such that a tee, bull downward, nipple, tee bull horizontal, nipple, tee bull downward pattern is established, making sure that there is exactly a 90-degree difference in bull orientation between the two end tee’s bulls, which as a finished product will point at six o’clock, the central horizontal bull at 3 o’clock (or 9 o’clock).


Measure the total length of the two pipe plugs, and transfer that measurement LESS 1/16-inch (or so) to the 10-32 drill bit. Wrap a length of tape around that drill bit at this measurement so that maximum depth is marked and easily seen and is achieved without perforating the plug…gasoline under high pressure will be contained within the guage manifold and back behind these not-completely-drilled-through plugs! Tap each pipe plug 10-32, as far as possible. Thread into the bulls of the two tees having a vertical orientation.


Cut a straight length of light-guage metal angle 1” tall, 1” wide, and 6” long. On its back (or vertically-oriented) side, this angle will mount to the firewall, and the bottom (horizontal-orientation) will form a surface to which the fuel guage manifold is anchored.


Measure exactly the mean distance between the pipe plugs, and transfer that measurement to the horizontal mounting “shelf” formed by the angle, so that the fuel guage manifold is centered in both the length and width of the angle. Drill those holes ¼-in. dia.


Shorten the two 10-32 screws so they bottom out in the pipe plugs using one flat washer each, but not the angle. The added thickness of the angle when assembled will ensure proper torque without thread-bind at final assembly time.


Mock-up the fuel guage manifold on the bracket, and mark the back of the bracket for holes for the two #10 sheet-metal screws that that will fasten the assembly to the firewall, keeping in mind that a screwdriver has to be held nearly horizontal to turn the screws, then drill those holes, too.


Countersink all holes, finish all edges, clean in lacquer thinner, and, if galvanized, smear on some cheapo 5% white vinegar, which will etch the surface and enhance paint adhesion, ‘cause it’s time go go blow some paint on the angle, the four screwheads, and the guage manifold (plug the two end holes and center guage hole with toilet paper, masking tape if you’re a high-roller). We used ‘60’s Ford engine blue.


Final-assemble the guage manifold to the angle, using copious amounts of the threadlocker plus one flat washer per screw. Remember how those four ¼-in. dia. holes were bigger than the 10-32 but smaller than the o.d. of the washers? Gee, it all went together easily! (If you can drill same-size accurately-spaced holes, well…)

You’ve been itching to do this one…go ahead and screw that new, chromed and high-perfed-logo guage in—WITH THE CORRECT OPEN-ENDED WRENCH ON THE WRENCH-SQUARE AT THE BACK OF THE GUAGE, not with pliers around the periphery of the guage case! It is only too easy to ruin a delicate guage, so don’t get ham-fisted (drink decaf coffee, not beer); NPT means “National Pipe Taper” meaning the shank of an NPT nipple is gradually tapered, wedge-shaped in profile, and gets progressively tighter as it is screwed inward. The mounting spud of this guage, like most of the rest of the assembly, is 1/8” NPT brass; some judgement , “feel”, is required to get a., enough torque without too much torque on this guage fitting, and b., correct orientation of the guage’s face so that the numbers midpoint of its travel are in the 12 o’clockpoint position; i.e., “50” psi should read at the top of a 0-100 guage; “30” psi likewise in a 0-60 piece.


A vertical-mount guage could be used, but to our mind the assembled guage manifold unit is too tall, and takes up too much firewall room vertically.


Using the correct backup combination of box end and line wrenches and being very careful not to disturb the 90-degree difference in all the tee’s orientation, assemble the Schrader valve to the driver’s side end tee’s run, and the 1/8” x –4 flare to the passenger’s.


Relieve pressure on the engine’s fuel rail via the stock Schrader valve—conveniently located near #6 cylinder, nestled inside the curve formed by the EFI air manifold tubes, close to the firewall. Try not to spew gas everywhere; self-immolation went out with the ‘60’s—try not to reinvent a questionable fad! Catch any pressurized gas with a rag (and then dispose of it, muy pronto!) As always when working on a fuel system, have a fire extinguisher close to hand.


 Unscrew the stock Schrader, and screw in the special Ford-size flare fitting, snugly but not excessively tight—those threads are small! We used no Teflon tape here. Dispose of that Schrader; it won’t fit anything else, anywhere.


Hand-tighten the braided hose so that it will swivel freely without coming off fuel rail fitting, and gently, thoughtfully, route it through the air manifold between runners #5 and 6, then up and backwards outside the heater core box, then curve around so the other end swivel fitting is aligned horizontally at the firewall, pointing toward the spark plug side of the engine.


Loosely screw the hose to the guage manifold, align that puppy so it is horizontal and high enough on the firewall to be easily seen, fasten the bracket-to-firewall screws, and using two wrenches, tighten the swivel fittings, then leak test your work by turning the ignition key to “On” but not “Start” (you can hear the in-tank pumps pressurizing the system). Leaving it “On”, go eyeball your pipe joints, then test with a dry finger, NOT A LIT MATCH!


I betcha that guage reads “55 psi”; if so, turn it down to around 40.


PART II: Adjustable Fuel Pressure Regulator, Selection and Installation

There are a lot of detail similarities between the small-block V-8 engines and the 300-6, which is not too surprising considering they originated during statistically the same timeframe, early-to-mid Sixties, from the same manufacturer, with probably quite a bit of design department interface. There is a high percentage of commonality in small part; volume production with the smallest degree possible of variation from the basic design an economic imperative; look at Ford’s current Modular Engines—that are used across a dozen brand names and in myriad uses, high-winder Eurocar to heavy-duty truck. We rest our case!
Installing a 5.0 Mustang adjustable fuel pressure regulator is nowhere near as complicated as we made the guage installation. Go buy:
  1. HD—3 ea. 10-32 x 1-1/2 machine screws, stainless steel;
  1. HD—3 ea. 10-32 flat washer, stainless steel;
  1. HD—3 ea. 10-32 Nyloc self-locking nuts;
  1. Home Depot—25-ft. (or smallest) roll 1/8” copper refrigerator tubing (optional);
  1. Home Depot—1.5” dia. hole saw and arbor (mandatory);
  1. Home Depot—3.0” dia. hole saw and arbor (optional, but a nice touch);
  1. Ford Dealer—1 ea. Upper/Lower Air Manifold Gasket;
  1. AP—EGR-to-EFI plenum gasket;
  1. AP—High-temp gasket sealant for EGR gasket;
  1. AP—1/8 i.d. vacuum/windshield washer hose;
  1. Jeg’s—“Crane Cams” brand adjustable fuel pressure regulator for Ford speed density EFI, ’86-’93 ; Jeg’s P/N 270-99471-1;
  1. 6-mm Allen wrench;
  1. Your favorite steel supplier.

We suppose it’s possible to change regulators without removing the upper air manifold and appurtenances, but we unlucky enough to be hatched without the eight fingers for each of three or four hands jointed by quadruplicate elbows required, so we pulled the upper manifold. Begin by pulling off the air cleaner tubes, throttle body, EGR from T/B, and that upper air manifold. Clean that mating flange well, and when pulling that upper manifold, pull straight up! There are a couple of easily-broken plastic dowel pins locating gasket and manifold.

Also, the Thermactor (you know: air pump, smog pump, @#$%^&*() pump, etc.) vacuum and pressure connections and numerous other vacuum connections will have to be disconnected.

Ford Motor Company, in its infinite wisdom, has equipped modern vehicles with numerous vacuum-operated emissions devices, fed through 1/8 dia. plastic hoses often bundled together and/or in with wiring harnesses.

These small plastic vacuum pipes embrittle with heat, oily vapor, and time (obviously; they belong in a long-lasting motor vehicle, right?) and therefore, when disturbed, break with only the smallest provocation.  Only seriously disturbed citizens soup up their six-cylinder pickups, so plan on using up some of that copper line and 1/8 i.d. rubber hose you were told to go get.  Or don’t.

Upper manifold off (that last bolt by the firewall was a “challenge”, wasn’t it?), get the that Allen wrench, remove and fling stock regulator and weirdo allen bolts in the trash, where they belong.

Rip your cool new adjustable unit out of its blister packaging with the Crane Cams logo (on the packaging, not the regulator…somebody else makes it, Crane just markets it--cheaply), and plug it into the fuel rail. We’re using the Crane Cams piece because the vacuum reference hose slides down over the pressure adjusting screw, which has a small hole drilled in it. The hose hides the fact that it is adjustable, which to our paranoid mind is a Good Thing come emissions inspection time.(PHOTO 6)This is not such a Good Thing if you want to make adjustments with the engine running and vacuum reference hose connected, and there are other AFRs out there with a separate vacuum nipple.

The good news is, the pressure and return spuds and base gasket all match up perfectly, same-same, which is what really matters.

The bad news is, the new regulator’s base flange is smaller, shaped differently, has a way-different bolt pattern, and the flange is internally-threaded so its hold-down screws thread from the bottom upwards through an unthreaded fuel rail mounting pad, whereas the I-6 fuel rail mounting pad is internally threaded, and the stock regulator’s mounting flange is undrilled, the screws threading downward.

A retroactive review of “Ford Electronic Fuel Injection Systems” confirmed this—all the pictures of different I-4, V-6, and V-8 engines used the bottom-upward bolting system.

We know that you really wanted to know that.

The 4.9L fuel rail regulator base is much larger physically that the 5.0L AFR, so it would be possible to simply drill and tap two new holes (of three required) in the 4.9L fuel rail’s regulator mounting pad. This leaves the third mounting hole in the new regulator hanging off in space, with nothing to secure it to—and since the base is triangular, all three mounting holes have to be used to ensure an equal clamp load. We suppose that we could have devised some sort of clamping strap to pass underneath the fuel rail, but that’s tacky and besides, we’d have to drill and tap two additional holes in that mounting pad--and we really don’t like the idea of drilling holes that closely to the fuel rail inlet; microscopic metal shavings have a way of migrating into fuel injectors!

We elected to do something simpler, cleaner, and far more elegant.

The regulator is barrel-shaped, the two halves crimped together circumferentially at the widest part of the “barrel”, a perfect place for a hold-down flange.

Circumferential crimp ring around body of fuel pressure regulator; large washer illustrating hold-down collar flange principle


Large triangular base of stock regulator showing intake and return spuds, gasket, unthreaded mounting holes


Note different mounting flanges, mounting method, vacuum reference elbow, 1.5” hole in center of 3” dia. flange—the pressure adjusting screw has a small hole drilled through its middle, 19-lb./hr. injectors, all in a line, hold-down flange. Partially obscuring injector #1 is the infamous #1 fuel rail bracket that didn’t get adequately tightened! Look carefully and you’ll note we were living dangerously in this picture and weren’t at that time using Nyloc backup nuts underneath hold-down screws!

The idea is go buy a 4” by 4” hunk of .125” thick mild steel plate. The thickness, material, and size really doesn’t matter as long as it is inflexible and can take a 3-inch outer diameter cut.

The first step is to lay out what is essentially a big, flat, washer with three ¼” dia. holes in it that correspond to the threaded holes in the regulator’s mounting pad on the fuel rail, and drill them.

The second step is to is to holesaw the 1-1/2” central hole which will slide easily but snugly over the new AFPR.

The third step is to make the 3” outer holesaw cut, at which point the rough-in work is done. Go countersink, deburr, and paint your new masterpiece of machine art.

Paint dry, mount the flange using all the #10-32 machine screw hardware mentioned above, with plenty of Loctite. The factory holes probably have metric threading, but the #10-32s screw in there though just a smidge looser than is ideal. The threadlocking compound and the Nyloc backup nuts make that irrelevant.

PART III—Big, Huge, Studly Injectors For Your Six (She’ll Love Ya For It, Too!)

This is a no-brainer; you can’t screw it up (we did, naturally!) All six injectors seat (float, actually) in drilled pockets in the lower air manifold, sealed by thick “O”-rings, tips pointing at the respective intake valve, and are held in place from above by the fuel rail, which in its turn is bolted to the same air manifold by THREE bolts.

Remove the bolts, and gently work the fuel rail off the injectors. There is enough play in the fuel delivery and return lines to make this possible without disconnecting the A/C-type garter fittings back by the firewall, which is a major PITA. Unhook the Weatherpack electrical connectors (oh-so-gently; the plastic clips love to break).

  Pull the old injectors from both air manifold and fuel rail, clean fuel rail and air manifold injector pockets, lightly lube all new “O”-rings and all pockets, and gently work the injectors into their respective manifold pockets and the fuel rail onto them.

Reinstall all three bolts, torque all three bolts to 18-ft./lbs; read that last sentence again.

Take a good look at the fuel rail mounting bracket in the vicinity of injector #1, just beyond the 180-degree curve taken back toward the firewall by the fuel rail. Certain brainless wonders left that bolt loose. Consequently, the slight freeplay allowed between bracket and mounting pad by that oversight enabled gasoline pressurized at 55 psig to spit the upper “O”-ring out after a couple of days, and spew gasoline so hard into the windings of the alternator that it shorted out temporarily, scaring us somewhat.

In fact, down here in Texas, they call that kind of scare a “brown pants special” or “trouser chili”.

Three bolts.

Tighten. You have been warned.

Edward Trethewey

Houston, Texas, USA
December, 2000