Written by Marlan Davis on June 29, 2016The 5.0L SFI V8 in Rod Arias’ 1989 Mustang Misses, Surges, and Sets Codes. We’re Gonna Fix It.
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 1994–1995 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
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).
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 1994–1995 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.
THE INITIAL FIXES
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.”
LATE-STYLE FUEL INJECTORS NEED ADAPTERS
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 1993–1999 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:
• 1989–1995 Ford F-350 truck with 460 big-block
• 1994–1996 Lincoln Continental front-wheel-drive with 4.6L DOHC 32-valve modular motor.
Always thoroughly test and clean used injectors!
01] Modify Explorer intake for EGR & ACT fittings
02–05] FPP 24-lb/hr fuel injectors
06] Accufab 70mm throttle-body
07] Pro-M calibrated MAF meter
08] Pull spout connecter to check base timing
09] Check ignition coil with water-spray
10–12] Check distributor module and octane rod
13] Install remanufactured Cardone distributor
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.
THE FINAL FIX
“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.
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.
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.