At first glance, the only thing amiss with Yoelkys Cuba Cardoso’s Ford Expedition was that the windows were tinted too dark.

But when a state trooper pulled him over in Hialeah Gardens, he immediately smelled the overpowering odor of diesel fuel. Hidden inside the cab was a 150-gallon aluminum tank, masked in tan carpeting, rigged with a pump and hose to dispense fuel like some sort of mobile gas station.

Cardoso, 38, didn’t appear too concerned about the combustible cargo. “He was smoking a cigarette when I pulled him over,” said Florida Highway Patrol trooper Alexis Otano.

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And inside a side panel, troopers found 53 gift cards encoded with stolen-credit card numbers, which were suspected of being used to purchase the product for Miami’s thriving gas black market serving shady fuel resale companies and long-haul truckers.

Cardoso, who will be formally charged Thursday, is just one of dozens of men who have been arrested during the past two years in a scam that costs consumers, cheats legitimate fuel companies and poses a safety hazard. Police estimate that there are scores of trucks swollen with gas in unsafe containers traversing South Florida roads on any given day.

Yoelkys Cardoso Miami-Dade Police

“These are potential moving fire bombs,” said Miami-Dade State Attorney Katherine Fernández Rundle. “It’s a miracle that we haven’t had any serious casualties.”

Over the past two years, records show, the State Attorney’s Office has prosecuted at least 31 Miami men in separate cases with possessing a vehicle with an illegal fuel tank. It’s a third-degree felony that can be upgraded if the suspect used stolen credit-card info to buy the gas.

Often, those cases include charges of trafficking in stolen credit cards, a law beefed up last year to include stiffer penalties.

The scheme generally starts with small scanners, devices a small business owner might connect to their smartphone or tablet to ring you up. Only crooks modify the devices to be hidden inside the credit-card readers at fuel pumps.

At gas stations across South Florida, customers pay for gas using their credit cards, unknowingly supplying their account numbers to the thieves, who return later to collect the devices — along with hundreds of card numbers.

Just how many skimmers are operating at any given time is anyone’s guess. In 2017, Florida Department of Agriculture and Consumers Services inspectors discovered 148 skimmers in gas pumps across the state.

For victims, the impact is immediate. Using high-tech software, crooks put the stolen numbers on blank gift cards from businesses such as Walmart, Amazon and Winn-Dixie.

Gift cards found inside the Ford Expedition driven by Yoelyks Cardoso, who was arrested in a suspected “fuel bladder” vehicle in December. The cars are suspected of being encoded with stolen credit-card numbers. Florida Highway Patrol

Prosecutors say one of the biggest culprits in town was Jaime Fernandez del Pino, who is accused of running his illegal operation out of a Hialeah condo that “was capable of producing up to 1,000 counterfeit credit cards a day.”

When investigators raided the home last month, they found thousands of counterfeit credit cards, more than 50,000 blank cards, printers, magnetic strip encoders, computers, gas-pump skimmers and even large metal plates that normally cover pumps at gas stations.

In all, over a dozen people were arrested statewide, almost all of them in Miami. Also seized, according to federal court documents: a Mercedes-Benz, a Range Rover, a BMW — and a “bladder truck used to steal gasoline.”

As in Cardoso’s case, the “fuel bladder” vehicles are sometimes large SUVs. Other times, they are flatbed pickup trucks outfitted with fake tool boxes to hide the illegal tanks, which are painted black to blend in with the cab bottom.

Sometimes, they are ubiquitous white Ford Econoline vans, the seats ripped out, rigged so a switch can toggle between the vehicle’s own gas tank, and the cheap plastic containers hidden inside. But those vehicles lack the proper tanks and safety measures of real tankers regulated under state and federal law.

Rogel Morejon-Soto had his 2004 Econoline van parked outside his apartment in West Kendall early last year. In the back were two 264-gallon “plastic totes,” according to a Miami-Dade Police arrest report.

For some unknown reason, something hot or an “electrical event” came into contact with the fuel. The van exploded into a furious blaze that burned for hours. Whipping flames nearly took out two firefighters. Special teams had to be mobilized, including an airborne fire-fighting plane. The effect was disastrous — even the soil underneath the pavement was contaminated.

A suspected “fuel bladder” van that exploded into flames in January 2017 outside a home in West Kendall. The owner, Rogel Morejon-Soto, is awaiting trial for arson and having an illegal fuel vehicle. State Attorney’s Office

The cost to taxpayers was hundreds of thousands of dollars. Morejon-Soto is now awaiting trial, accused of arson and possessing a vehicle with an illegal fuel tank.

Out on the streets, the vehicles visit gas station after gas station, using the illicit cards to surreptitiously fuel up the bladders, never surpassing $100 — the cutoff for most transactions at gas-station pumps. “They do that 10, 15, 20 times a day,” said Florida Highway Patrol spokesman Joe Sanchez.

Police often bust them by chance. Aventura cops on patrol arrested Nelson Foseca-Diaz and Luis Reyes on Dec. 27 at a Marathon gas station on Biscayne Boulevard. According to the arrest report, they saw the panel to a station gas pump was open — the men were caught in the act of installing a skimmer. In the back of the white van, officers found two fuel bladders capable of holding 1,400 gallons.

Prosecutors and Miami-Dade Police’s organized-crime unit are still trying to build cases on just who is buying the fuel.

Investigators believe much of the fuel goes to companies who own tanker trucks and appear legit but don’t have any permits to sell gas. Still, they sell the ill-gotten gas to construction, car rental and tow truck companies — even back to some gas stations themselves. All for cash.

That cuts into business for wholesale South Florida fuel companies such as Port Consolidated and Tropical Oil, which pay business taxes. “It hurts legitimate fuel guys who are selling fuel, who can’t sell it to people who are buying in on the black market,” said Ned Bowman, the executive director of Florida Petroleum Marketers and Convenience Store Association.

The customers are also long-haul truckers, who count fuel as a primary expense. Cops say the bladder vehicles cruise truck yards, selling fuel at a discounted rate — which amounts to all profit for them anyway.

Miami-Dade police photo of a suspected illegal fuel truck gassing up a tractor-trailer truck. The suspect, Damian Martinez, is awaiting trial. Miami-Dade State Attorney’s Office

Trucker Jesus Medina told police he was approached by two fuel resellers at a truck storage yard in Homestead. The price: $1.50 per gallon, almost half of what it costs at your average gas station.

“I told him that because it is very difficult for these trucks to enter a gas station, I let him and his partner in to put diesel in the trucks,” Medina wrote in a statement to police. “When they were leaving, the police arrived and arrested us and the police explained to us that this was illegal.”

Medina was not arrested, but was instead listed as a witness against Damian Martinez-Valdez, 43, who is facing two separate criminal cases against him.

Martinez-Valdez, prosecutors say, was a street tough who earned a lucrative living by stepping into the sophisticated economic crime.

The 43-year-old Cuban native spent seven years in prison for a home-invasion armed robbery in the mid-1990s. When Miami-Dade economic crimes detectives raided his posh West Kendall house in June 2016, they found 84 counterfeit credit cards, a device to encode gift cards with credit-card numbers, four skimming devices rigged to be hidden in gas pumps and $30,000 in cash.

Damian Martinez-Valdez

“Martinez-Valdez was unable to provide any legitimate source of income,” Miami-Dade detectives Fernando Menoud and Sebastian Monros wrote in a search warrant.

An analysis of his computer revealed more than 20,000 stolen credit-card numbers. While awaiting trial — and free on bond — Miami-Dade police got a tip that Martinez-Valdez was back in business. Detectives began tailing him, but lost his truck when Martinez-Valdez began taking “evasive measures” that included frequent U-turns and stops.

But by chance, another detective with the same unit was doing an unrelated surveillance on a Hialeah Gardens gas station and saw Martinez-Valdez fueling up the illegal tank in the back of his gray Ford pickup truck for over 20 minutes.

A review of receipts revealed Martinez-Valdez used four different credit cards to buy 190 gallons of diesel fuel. His defense lawyer, Simon Steckel, believes he’ll prove his innocence.

“The law involving legal versus illegal fuel bladders is not simplistic,” Steckel said. “It’s our position that any bladders he was involved with in this case were lawful. We’ll have our day in court.”