RICHMOND, Va. — It was a freakish, quirky part failure, but it ruined AJ Allmendinger’s winning chances last Sunday at Kansas Speedway.
Allmendinger started on the pole and led the first 44 laps of the STP 400, but his hopes of winning his first NASCAR Sprint Cup race evaporated when his secondary throttle linkage broke.
The failure of that part is incredibly rare, but it was also the next episode in a series of bizarre issues that have plagued Allmendinger and teammate Brad Keselowski this season.
“I’ve never seen it,” Todd Gordon, Allmendinger’s crew chief, said of the linkage failure. “We’ve managed to find all the things that nobody’s ever seen before.”
What compounded Allmendinger’s problem on Sunday was the difficulty in diagnosing it. The transition to electronic fuel injection in the Cup series has brought a new set of variables and an added layer of complexity to the fuel delivery system.
The carburetor that EFI replaced was a self-contained unit that mixed air and fuel. Where the carburetor was mounted now sits a throttle body, which controls airflow.
The fuel injectors themselves are in the manifold. The process is governed by an electronic control unit.
Three major components in three different places make for a more efficient system, albeit one that also is more complicated.
“With a carburetor, your whole fuel system is in one piece there,” Gordon said. “Now the fuel operation system is an ECU on the dash, injectors in the manifold and the throttle body on top, so those three things are in different places.”
That makes it tougher to pinpoint the cause when something goes wrong. In the case of Allmendinger’s No. 22 Dodge, the car began “spitting and missing,” at race speeds, as Allmendinger put it, but ran without problem in the pit stall. Hence, the crew started looking for an electrical problem.
While the car sat on pit road, the crew replaced the ECU and the coil pack and checked the spark plugs — to no avail.
It wasn’t until the engine tuners downloaded the data from the replaced ECU that they realized where the problem lay.
“Actually, how we found it was looking back through the ECU data,” Gordon told the NASCAR Wire Service. “We could see some things that didn’t line up, and when they started talking about it . . . nobody thinks to change a throttle body on pit road.
“We changed coil packs. We did everything electrical, because the car would run fine in the pit box. So we changed the ECU and the coil packs, and we checked all the spark plugs, and everything was fine there. After changing out the ECU and downloading the data and looking at it, they discovered what they thought it could have been.”
The diagnosis, however, didn’t come quickly enough to help Allmendinger, who finished 32nd, 10 laps down.
Yes, the secondary throttle linkage was broken, but the ECU didn’t read it that way. There are two shafts in the throttle body, each with two butterfly valves. If the butterflies are wide open, the engine gets maximum airflow.
The secondary throttle linkage connects the front shaft to the rear one. When the linkage broke, the throttle position sensor, which is mounted on the front shaft, communicated to the ECU that all four buttterflies were open. In reality, only the front two were.
“The computer sees that we’re wide-open throttle providing all this air,” Gordon said. “We’re only providing half the air. Thus, the fuel usage goes up, because it’s putting more fuel than we need to have in it.”
Given new parts and sensor arrays that have accompanied the transition to EFI, crew chiefs and engine specialists have little experience to draw on as they learn the nuances of the new fuel delivery system.
“I’d say the biggest thing is that it’s an unknown to everybody,” Gordon said. “We all look at the new parts first (when diagnosing a problem), and it can actually be old things or new things. There’s more question marks because we haven’t built a log of confidence in the durability of parts.
“Knock on wood, with some of the things that are in that system, we haven’t had a coil pack failure at the racetrack. We haven’t had an ECU failure. We’ve just got to build confidence in that.”