Marlan Davis Senior Technical Editor
June 29, 2016

Eleven years ago, then 13-year-old Rod Arias inherited a 1989 Mustang LS V8 coupe from his newlywed brother, who could no longer afford to keep the car up. "When I first obtained the car," Arias says, "all it needed was a clutch. Over the years, I've upgraded the rearend, the trans, and the brakes." Currently, the original 5.0L engine (now with more than 100,000 miles on the clock) is exhausted through MAC headers and Flowmaster mufflers. Behind the motor is a Ford Performance Parts (FPP) World Class T5 trans and a 3.73:1-geared 8.8-inch Ford rearend with a Traction-Lok diff that's supported by Roush rear lower control arms. The rearend, out of a 1995 Mustang GT, had five-lug wheels and rear disc brakes, so Arias decided to go to larger discs and five-lug wheels up front, too. "Installing 19941995 Mustang front spindles allowed me to bolt on much bigger 2000 Mustang GT front brake rotors and calipers. My long-term goal is autocrossing and drags, and I keep adding stuff as good used parts become available in the wrecking yard where I work. But this is still a street-driven California car, so it's important to me it remain emissions-legal."

"The 1993 Explorer intake swap is a great econo mod for 5.0L SFI Mustangs, but there are a few things that can trip you up." — Mark Sanchez/AEW

Mira Loma, California's Rod Arias has owned his 1989 Mustang LX since he was 13. Now 24, he's been upgrading it incrementally ever since.
The dark-blue car's 19971998 Mustang five-lug rims clear larger 2000 Mustang GT disc-brake calipers and rotors.

Arias' troubles began when he grabbed the upper and lower intake manifold, injectors, and injector harness off a 1997 Ford Explorer when it passed through the yard. An Explorer intake is virtually identical to the 1993 Mustang 5.0L Cobra production intake and FPP's GT-40 intake retrofit kit, but (since the Explorer intake is commonly available used) it goes for around $200, versus the $600 cost of the now-discontinued FPP package when it was still available new (used Cobra intakes are said to cost more than a grand). Obviously, this makes the Explorer conversion a popular retrofit for savvy Ford 5.0L SFI modders.
After bolting everything on, Arias says, "I started getting a little misfire and surging. The engine was running about 1-percent rich and the check-engine light kept coming on. I asked questions everywhere—mechanics, friends, online forums—but no one could figure it out." Fortunately, Arias is a stone's throw away from our favorite Southern California Ford rescue specialist, Mark Sanchez's Advanced Engineering West (AEW).

After upgrading to a used 1993 Ford Explorer intake, the 5.0L SFI engine had part-throttle driveability issues and began setting codes. Photo credit: Rod Arias

Sanchez quickly confirmed Arias' complaints. The motor was running slightly rich, there was an occasional miss, and the engine control unit (ECU) was setting the exhaust gas recirculation (EGR) valve and air charge temperature (ACT) sensor error codes. "Problems with the EGR can often cause a misfire," Sanchez explains. "With no ACT provisions, the ECU can't compensate for the air temperature entering the motor, so it won't adjust the timing accurately."
Looking further, Sanchez observed not only was the EGR valve electrical connector unplugged, there was also no coolant hose running from the lower intake to the EGR's coolant passage. "Circulating coolant through the EGR housing reduces the exhaust gas temperatures to prevent tar buildup and keep the EGR clean," Sanchez says. As for the ACT sensor, it was connected, but the sensor itself was just dangling in the wind.

The missing EGR coolant hose and the dangling ACT sensor provided a critical clue for Ford specialist Sanchez: On standard 5.0L Mustangs and the 1993 Cobra, the coolant hose nipple for the EGR and the ACT sensor screw into lower intake manifold bosses—but not so on the Explorer (or 19941995 Cobras), where, though present on the casting, these bosses are unfinished.

"It's commonly overlooked on what otherwise is a great econo swap," Sanchez points out. "I pulled the top half [of the intake] and confirmed the missing tapped bosses in the lower half. With the top half out of the way, I pulled the injectors in the lower half and examined them for any problems." It turns out that half of them had damaged pintle shields; the 42-lb/hr nonstock units were also way too large anyway for Arias' existing combo. Deteriorating seals in the stock throttle-body still in use on the car were also causing a slight vacuum leak.

One of SoCal's go-to guys for late-model Ford diagnostic issues, AEW's Mark Sanchez found and fixed all of Arias' driveability problems.

Sanchez removed the lower intake so he could drill and tap the blank bosses. "It's pretty easy—you just need the right drill bit and pipe tap to make everything good," Sanchez says. He then screwed in the EGR coolant nipple and ACT sensor, reinstalled the intake, and added a set of new, correctly sized injectors. For reliability and consistency, Sanchez always replaces injectors as a matched set—in this case, "24-lb/hr FPP units that best match the intake and Arias' other mods. I prefer genuine Ford OE, Motorcraft, or FPP injectors for their quality and consistency."

A larger 70mm Accufab unit replaced the leaky stock throttle-body. "Accufab builds the extreme high-quality throttle-bodies for Ford for use on the GT500 and Cobra-Jet limited-production cars. They're the only billet-aluminum throttle-body that meets Ford's high-quality OE standards."

A remanufactured distributor and new fuel injectors plus intake manifold mods to accept missing sensors cured Arias' main problems.

As received, the Mustang was running way too big 42-lb/hr fuel injectors, at least half of which were also damaged. Yet Sanchez says typical stock Mustang and Explorer 19-lb/hr injectors are way too small to support the larger Cobra-style intake in a performance application. In fact, the rare Cobra Mustangs used 24-lb/hr units. Sanchez still had a set of NOS, original-style (but now discontinued), EV1 Jetronic-type, 24-lb/hr injectors (old FPP PN M-9593-A302) that are a direct bolt in. FPP's current replacement for them is a late-style, slimmer-bodied, EV6 USCAR-type injector, which requires an electrical adapter to connect to old EV1 harnesses. The Parts List on page 98 lists the newer parts and the necessary adapter package.

If you're going the total budget route and shopping the wrecking yards, besides the 19931999 Mustang Cobra (which you'll probably never see in a wrecking yard), Sanchez says the following more available apps also used 24-lb/hr direct bolt-in EV1 injectors:

19891995 Ford F-350 truck with 460 big-block
19941996 Lincoln Continental front-wheel-drive with 4.6L DOHC 32-valve modular motor.

Always thoroughly test and clean used injectors!

Arias' swapped-on 1997 Ford Explorer intake manifold is similar (but lots cheaper) than the vaunted (but rare and expensive) Mustang Cobra intake. Unfortunately, the Explorer unit lacks finished mounting bosses for several critical parts used on the Mustang. This plus a flaky distributor, fuel injectors that were both too large as well as damaged, and a vacuum leak in the throttle-body were the main causes of the 'Stang's driveability issues.

But here's where the domino-effect kicks in. The larger throttle-body works better with a larger mass airflow (MAF) meter that's properly calibrated to "fool" the ECU so it won't set any codes. "We changed the MAF to a Pro-M unit. Pro-M is the only meter, in my opinion, that's calibrated properly for the injector size and throttle-body you are using. Others may set a check-engine over-voltage code. Fortunately, as a 1989 California-emissions stick-shift car, this Mustang had the A9L ECU that has a very wide tolerance for modifications."

Owner Arias threw in the smoothly-curved chrome induction pipes to streamline the induction tract. Of unknown origin, Arias says they're pirated from a car that ran through his wrecking yard sometime in the past. "You never know when some of this oddball stuff will come in handy. I knew I'd find a use for them someday!"

Continues Sanchez, "Once I cleared the codes, modified the intake to accept the missing sensors, upgraded the MAF and throttle-body, and replaced the injectors, the car ran a lot better." But later, Arias complained about one persistent remaining driveability issue.

"After driving the repaired car for awhile," Sanchez says, "the owner reported there was still a surge under certain cruise conditions. However, I could not duplicate it. It took the owner driving (with me along as shotgun) to show me where the surge was occurring. My natural driving style was just different than his." It turns out the problem only occurred intermittently in Third gear between 3,000 and 4,000 rpm at about 50-percent throttle.

01] FPP GT-40 kit and rare 1993 Mustang production Cobra intakes (right) are similar to 19961997 Ford Explorer lower intakes (left), but the Explorer unit is more common. Though present in the casting, the bosses for the EGR coolant passage (A) and ACT fitting (B) on the Explorer versions usually aren't drilled and tapped. For use on 5.0L Mustangs through 1993, "activate" the bosses with a 916-inch drill bit and 38-18 pipe tap. Avoid some late 19971998 Explorer intakes (cast F87E-9K461-BB) that lack the two blank bosses as well as an EGR exhaust passage hole (C).
Half of Arias' fuel injectors had broken, missing, or cracked plastic pintle shields. This degrades the conical spray pattern that's critical for achieving optimum performance and fuel economy. Arias' mysterious "green" 42-lb/hr injectors were way too big for the combo anyway, which can cause an over-rich condition at idle and low rpm.
A standard 5.0L Mustang or Explorer would have used 19-lb/hr injectors (too small); a stock Cobra, 24-lb/hr (just right). Sanchez used a set of "Cobra" 24-lb/hr "blue" injectors that he still had in stock (shown). The EV1 Jetronic-style injector is a direct bolt in physically, but it's been discontinued through Ford Performance.
The current FPP 24-lb/hr injector (PN M-9593-LU24-A) is the newer-style EV6 USCAR slim-bodied unit that's said to have better heat-rejection. This style of injector is used stock on most of today's production Ford MFI systems.Ford Performance Parts (FPP)
The late-style EV6 injector requires an electrical connector adapter package to interface with wiring harnesses designed to use the older EV1 injector. FPP sells a set of adapters under PN M-14464-4A8.
The OE 58mm 1989 Mustang throttle-body (right) had an internal vacuum leak. Sanchez: "At this point, we could have installed a remanufactured stock body, but that's way too small to be a good match for the larger Cobra upper intake. We decided to upgrade to a 70mm Accufab throttle-body and spacer (left), which is, in my opinion, the best fit for the Cobra intake."
The restrictive screen-style 55mm OE MAF meter (left) was replaced with Pro-M's 75mm Chrome Bullet unit (right). Pro-M meters are custom-calibrated for the specific engine combo they'll be used on. Pro-M owner Bob Atwood was one of the Ford engineers who developed Ford's OE MAF-meter design. Sanchez: "Pro-M uses the same equipment that Ford used to calibrate its own meters."
After the induction, sensor, and intake fixes, there was still a slight occasional surge under certain cruise conditions—but the engine no longer set codes. Going back to basics, Sanchez pulled the distributor's "spout connector" so he could check the no-load ignition timing. It was fine; as it turns out, there were other problems lurking in the distributor.
Ignition coil integrity was checked by spraying water around the coil in a darkened shop with the motor running. "It's a quick and dirty shade-tree test, but it's fairly reliable," Sanchez says. "I saw no arcing, so the coil was likely OK. There was no arcing around the spark-plug wires, either."
Ford distributor modules can go bad. Sanchez: "A simple test is to pull the cap, and press down on the orange rubber piece. If your fingernail sinks in and there's a soft spot that feels like you're pressing down into a gummy bear, it's no good." But here the rubber remained firm to the touch, indicating the module was OK.
Although the module checked out, while manipulating the distributor, Sanchez found a different problem: "When I manually turned the shutter wheel, I noticed the magnetic pickup move—and it's not supposed to."
What Ford calls an "octane rod" (circle) is supposed to rigidly hold the magnetic pickup (arrow) in place. Sanchez: "The rod in this car's cheapie remanufactured distributor was plastic. I removed the rod and found its mounting hole had elongated. Not good." Compare the damaged hole in the cheap plastic rod (detail, left) with an original-style, all-steel Ford rod (right).
The rod isn't serviced separately. Sanchez: "The cheapest and most reliable route is to just go ahead and replace the distributor. But carefully inspect any remanufactured parts-store unit before purchase. You want a quality unit with the steel rod. We installed a Cardone unit that definitely comes with the steel rod." The Cardone unit also has the proper steel drive-gear that's compatible with late-model hydraulic-roller cams.

At this point, the engine wasn't throwing codes. The air/fuel ratio was correct. The no-load timing was correct. Sanchez suspected it could be an ignition issue, explaining that Fords sometimes have problems with the coil or the distributor. Sanchez first checked for a possible defective coil or spark-plug wire shorts and found no issues. He then checked the distributor for a defective module, another common problem. Although the module checked out OK, further distributor inspection revealed a magnetic pickup that improperly moved when the shutter-wheel/rotor rotated. For proper rotor phasing, the pickup is supposed to stay locked in place by what Ford calls an "octane rod." In this case, the budget remanufactured distributor's plastic octane rod was worn. Sanchez installed a quality Cardone remanufactured unit that, he says, "Definitely comes with a wear-resistant steel rod."

"Everything now is running fine," Arias says. The Explorer intake is a good shade-tree performance boost on a 5.0L V8-equipped Mustang if you're willing to perform the necessary mods on the intake's lower half. While not strictly necessary, a performance throttle-body and properly calibrated MAF meter will help the Cobra/Explorer-style intake achieve its full potential.

Back on the road again, Arias' future plans include a blower, a fully built engine, and Maximum Motorsports autocross suspension.

Patience and a logical diagnostics approach will solve most problems, but it also helps to have experience in the brand and model's individual idiosyncracies as Sanchez does.

If your car has a gremlin that just won't quit, you could be chosen for HOT ROD to the Rescue. Email us at PITSTOP@HotRod.com and put "Rescue" in the subject line. Include a description of your problem, your location, and a daytime phone number.

Includes the major items needed to fix the problems. Does not include miscellaneous small parts, labor, shipping charges, or taxes. Priced 05/04/2016 and subject to change.
ACCUFAB THROTTLE-BODY ASSY., MFI system, billet aluminum, 70mm bore, standard, w/ EGR spacer and gaskets, 1986-1995 Mustang 5.0L F70K Accufab $299.99
ARMORMARK HOSE, SAE J30R7, "-id, bulk, 1ft length, cut to length (EGR coolant hose) 50057 AutoZone $1.59
AUTOZONE SENSOR, Air Charge Temperature (ACT), Duralast store brand SU203 AutoZone $13.99
CARDONE DISTRIBUTOR, ignition, remanufactured, less module 30-2892 RockAuto $26.89
ADAPTER, " hose clamp-on to 38-18 NPT male, brass (EGR coolant hose) 844640 Summit $2.25
FEL-PRO GASKET SET, intake manifold, lower and upper, 1993-1995 5.0L MFI Cobra VIN-D MS95952 RockAuto $9.68
FORD PERFORMANCE4 ADAPTER, electrical connector, Jetronic/Minitimer harness to EV6 USCAR fuel injector (8/pkg.)5, 6 M-14464-A8 Don Wood $26.76
INJECTOR, fuel, w/ O-ring, 24 lb/hr, 11-18 ohms impedance, EV6/USCAR-style, color-code "black", (8/pkg.)5 M-9593-LU24A Summit $199.99
PRO-M Custom7 Pro-M $299.99
RIDGID TAP, pipe, 38-18 NPT, RH, high-speed steel, black-oxide finish (for Explorer lower intake mods) 35825 Amazon8 $17.34
SEARS CRAFTSMAN 66050 Sears $15.99
NOTES: Alternate PN 65126. Distributor w/ module, Cardone PN 30-2892MA: $45.79 at RockAuto. Or transfer part from old intake. 4Formerly Ford Racing. 5See sidebar on page 106 and photos 04-06 for details. 6There is an error in the current FPP catalog, but the description and PN listed here are correct. 7Custom-calibrated for specific vehicle/engine/drivetrain combination: Fill-out online specsheet or call Pro-M tech-support. 8Hajoca Richmond via Amazon Marketplace. TOTAL $914.46