Project Review
Let's recall what we were after with this project. We wanted to build up a fairly economical 5.0L EFI, with the requirements that it be reliable, deliver decent gas mileage and driveability, AND yet provide impressive performance for a daily driver. More specifically we published the following criteria:

• Reliability: Daily driver, 100,000 mile capable engine
• Economy: 20 mpg (freeway) or greater
• Performance: 260-275 RWHP, Mid-High 12's on sticky tires, full weight '88LX
• Streetabilty: Near stock "feel and manners", must pass California emissions

We transferred over our low mileage Spec Stage 1 clutch. Good to 300 HP, it should be adequate for this engine.

The rebuilt 5.0L looking like a million bucks between the fenders of our '88 project car. From this point its about a half-days worth of re-assembly of all the peripheral components before we can fire it up.

So what happened?
Well in the last two articles we detailed the buildup. We put together a no-frills budget short-block. To it we added a mild Lunati cam which we had laying around, as well as a set of out of the box Edelbrock RPM heads and an Edelbrock RPM intake with 65mm FMS throttle body. Initially we set the car up with 24lb injectors and a 76mm C&L mass air meter to match. The engine was dropped into the engine bay sometime in early December 2001, and then the frustration began.

When we fired the motor up we immediately noticed a very rough idle. Idle vacuum was around 10", which is uncharacteristically low for an long-runner intake EFI car. Funny thing was for a few minutes it didn't even dawn on us that something was wrong, since our years of flat-tappet experience had conditioned us to waiting through the rough break-in periods associated with those cams. Realizing that this EFI hydraulic cammed motor should be smoother than silk from the get-go, we started the troubleshooting. Fuel pressure was adequate, and their were no detectable vacuum leaks. The EEC was not showing and codes, other than an EGR code 34, which we knew was due to our inadvertent blocking of the crossover passage between the intake and head. Since EGR functions at part throttle, we were confident this was not the problem.

Puzzled, we then turned our efforts to the 24lb injectors. We speculated that the used injectors we bought could be messed up, perhaps a couple weren't firing, so we put the 19lb injectors and stock mass air back on. The idle got a slightly better. We reset the idle speed a few times, and played with fuel pressure. Eventually after a few days of driving the idle seemed to reach a consistent state, or perhaps we just got used to it. Stock idle is between 650-750 rpm, we found with the new cam that idle was best around 850-900 rpm. However as much as we tried to set idle in that range, the engine would, and still does, hunt or "roll" between 800-1000 rpm on occasion. Perhaps a quirk we will have to live with if we want this cam -something we're not quite decided on.

More annoying quirks... The engine now has a very peculiar stumble or bucking when engaging first gear at low speeds, like from a dead stop. If the rpms are not kept above 1500 rpm while letting the clutch out, the engine seems to get bogged down as the clutch grabs and then almost stalls out. This is a far cry from our stock cammed motor which would engage and maintain first gear without the need for any amount of throttle, it would roll along off idle speed alone. This made for very pleasurable driving in heavy stop and go traffic. The current bucking problem, which we are certain is a by product of the more aggressive cam, is a major annoyance in traffic. The only way to drive this car in stop and go is to slip the clutch at 1500 rpm. Not completely convinced that such a mild cam (215/222 .522) could make the computer freak out that bad, we went through and tested EVERY sensor on the motor. We replaced the O2 sensors, the Vehicle Speed Sensor, checked and cleaned the idle speed controller, and verified the ACT and ECT were working.

We temporarily replaced the stock AOD computer in the '88 with a manual "A9L" processor. While it seemed to help the idle and bucking problems, it left us stranded with a no-start condition after running fine for a day. We put the stock AOD computer back in and the engine resumed normal operation. The cause may be due to a difference in input voltage between the two processors on one of the pins. The fact that the A9L seemed to help the driveability and idle quirks, lends to the idea that the mass air voltage-to-air flow maps in the stock AOD computer are simply not matched correctly to the load of the T5 and new induction system. The solution will be to modify the transfer table via a custom chip or EEC tuning software. Incidentally, the AOD computer does have a slightly different timing curve, this enables the computer to keep engine rpm steady between shifts to avoid harshly engaging the AOD. It's little differences like this that are not noticed when you first do a AOD to T5 swap, but may come out as gremlins when you make mods.

We even wondered if the AOD computer was the culprit, not capable of working with a T5 and a bigger cam (remember this car is a T5 conversion.) So we borrowed a A9L (manual computer) and plugged it in. The engine did idle better, but after a day of driving it failed to start, leaving us stranded on the side of the road. We then replaced the coil, TFI module, cap and rotor, and still no start. Finally we put the old AOD computer back in and the motor fired back up. The only good thing to come out that experience was the potential that simply a custom burned chip with modified transfer functions would eliminate the low speed bucking and idle quirks. Something we'll have to look into for a future article....

Finally, and perhaps the biggest disappointment was the loss of low end torque. We pretty much anticipated this risk however when we opted for the RPM intake. In retrospect I'm not even sure why we went with the RPM intake over the Performer. I think our rational was based on our experience with the carbed versions of these intakes. We have seen time and time again that the carbed Performer is simply a dog compared to the Performer RPM. On several engines we've seen the RPM produce just as much low-mid range power, with huge increases in top end over its smaller runner brother. We naturally applied this reasoning to the EFI Performer RPM intake.

Well we were clearly wrong in our intake decision. The RPM intake was just a slushy, torque-less, unsatisfying intake for our 3.55 gears, and mild cam (idle to 5500 rpm). Above 2800rpm the intake simply rocked...the power came on like a nitrous blast, and pulled until the factory rev limiter (even though the engine probably stopped making power beyond 5600.) However having power coming in so late in the curve does not fulfill our expectations for driveability. This car is a daily driver, 60-80 miles per day on the freeway, in traffic, and through town. Torque is not desired, it's a requirement! What we wanted was the familiar 'force you in your seat' feel of the stock 5.0L torque curve. The RPM intake, on this engine, felt too much like the peaky torque curve of a carbed small block.

Fuel System Upgrades
The stock 5.0L Mustang fuel system consists of an 80lph (liter per hour) in-tank fuel pump, nonadjustable pressure regulator, and 19lb. injectors. This is good enough to support 250-275 flywheel horsepower, or basically your typical bolt on modifications without heavy induction mods. Once you get into better breathing heads and a cam, around the 300-350 horse range, the fuel system must be upgraded to 24 or 30lb injectors. This means the fuel pump, injectors,mass air, and an adjustable fuel pressure regulator. You really can't do without all three.

• Injector and AFPR installation
  We installed a set of good used 24lb. injectors (blue tops) and a regulator. Installation is straight forward. Depressurize the fuel rails by depressing the schrader valve. It is not necessary to disconnect the fuel lines from the injector rail.
  
  Next remove the upper intake manifold and associated vacuum lines. Now you can remove the four fuel injector rail screws and slowly pry the rail and injectors out of the manifold ports. Remove the old injectors, making sure not to leave any O-ring behind in the rail or the manifold.
  
  With the injector rail up and off the manifold, remove the three Allen screws which hold the stock regulator to the rail. Then install the new regulator and O-ring and secure with the same Allen screws.
  
  Put a little petroleum jelly or Vaseline on the new injector O-rings and place them into the rail ports. With all eight injectors on the rail, carefully line up the injectors in the manifold ports, and use light pressure to force the rail and injectors into place. Replace the rail retaining screw.
  
  
• Fuel Pump Installation
  While we could get fuel pressure to 38psi. the car seemed sluggish at WOT, as if the stock fuel pump was not keeping up with the demand. So we made the $100 upgrade to a Walbro 190lph replacement pump.
  
  Installation of the pump is straight forward. Drive until the fuel level is at empty. Depressurize the fuel rails at the schrader valve, and disconnect the battery. Jack the rear of the car as high as possible, and remove the tank straps. Lower the tank carefully, disconnecting the electrical connectors and two fuel lines necessary to allow the tank to drop. Eventually you'll need to pull the tank off the filler tube. The pump assembly is accessed from the top of the tank, secured by a circular retaining ring. Use a brass punch to knock the ring loose and then pull the pump out.
  
  Images Right--->
  Third from top, new Walbro 190lph kit includes new connector, filter, hose, and rubber tank seal. The kits are universal fit, meaning there are minor mods to make. For one, don't use the tank seal since it's a square cut and the stock one is round. The square cut will leak. Secondly, the rubber hose needs to be shortened to match the stock hose (shown in lower pic.) Finally the stock connectors are simple spade lug style, they will need to be transferred over to the new pump.

We obtained a good used (and partially polished!) Edelbrock Performer upper intake manifold. The difference between it and the RPM is the Performer features longer runners. Edelbrock rates its range from idle to 5500 rpm, whereas the RPM intake is rated at 1500-7000 rpm. Both models utilize the same lower intake. The runner length influences the resonant tuning effect of the intake charge, which effects the torque characteristics of the engine. The longer the runner the greater the low end torque. The Performer we obtained is an older model, which features a cool ribbed "vintage" style plenum cover. However the older design utilizes a bolt inside the plenum to mount to the lower intake. A little patience and stubby wrench is required to tighten the bolt.

However not wanting to give up so quickly, the other option was to first get the driveability back by obtaining a Performer upper intake. Fortunately we located one locally and in a matter of hours we had the RPM upper removed and the Performer upper in its place. (The nice thing about the two Edelbrock intakes is that they share the same lower intake, making the swap a matter of minutes.)

Bingo! The first 100 yards of driving confirmed our suspicions that the Performer intake, rated at idle to 5000 rpm, is a better match for our engine combination. The off-idle torque was now abundant, and suprisingly we noticed no significant top end loss. The idle and bucking were not improved, lending more support to our theory that the stock mass-air voltage transfer functions in the EEC must be modified to the match the load of the new engine combination. (The EEC processor contains tables which correlate voltage from the mass air sensor to air-flow in kg/hr.

We were stunned with the improvement in driveability. Fifth gear passing on the freeway was now possible, whereas with the RPM intake we found ourselves having to downshift into fourth in order to avoid a spongly, responsless, throttle until the tach hit 3000 rpms.

Lesson learned...the Performer RPM intake is too much for this motor -or any naturally aspirated 5.0L making power below 6000 rpm in our opinion.

So where are we at now?

The Performer intake was hands down the key to the performance puzzle here. The latest track results show a clear gain in power across the board. Without getting the car on the dyno it is hard to say how much power the Performer makes versus the RPM, but we are pretty confident that what we'd see is the RPM making perhaps a few more peak HP at a higher rpm, however the Performer will have a flatter, broader torque curve, which calculates into more average horsepower...and that is what counts in a street car.

The driveability issues are still not completely resolved. In order to live with this cam in a daily driver we must resolve the low speed bucking, and choppy idle, problems. A custom chip, or perhaps playing around with one of several aftermarket EEC tuning software, will make this engine the perfect all around street-strip daily driver. F/M

Previous articles in the Build a 5.0L EFI series

• Part 1: The Shortblock
  
• Part 2: The Longblock