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

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 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.