Abnormal Thirst – Fuel Supply Failure – Car Engine

There are few worse things a car man can experience than when the engine refuses to start or just stops while driving. The error presented below generated just such phenomena, but not in a precisely definable way. The source of the error was made more difficult by the fact that the car in question underwent several service visits, during which many of its parts were replaced again, so the search was disrupted by the ‘since it was replaced, it could not have caused’ siding.

The mounting cover of the petrol pump can be easily removed, the connectors come off the head of the pump housing and the fastening is loose. Photo: Mihály Dombóvári

The first fault was that towards the end of the tank’s emptying, when the red light was already on and “Please refuel” appeared, the engine drowned uphill or at higher acceleration. The telitank solved the problem, then the error did not occur, but later the drowning limit crawled close to the amount of about a quarter. As none of the technicians interviewed said the exact direction of repair and the machine did not give an error signal, the owner used the car with this in mind. The first suggestions pointed in the direction of a dirty tank, a long-replaced fuel filter, and a faulty gas pump, but the latter two were replaced within 15,000 km and a year and a half. 2 months passed like this, and then came the following inconvenience: harder morning cold start. First only every now and then, and after a few weeks, every first start or start in a cooled state became difficult. It helped somewhat if the start started after waiting for the ignition to turn on before starting so that the pump could build up pressure. This is already enough of a fault signal that has led the suspicion to the pump or the fuel system to release the pressure somewhere, somehow, and since there is no flow or over-enrichment, the fuel can get back into the tank.

Lifting the pump housing out of the tank: it is best to let the fuel drip

Due to the complexity of the cars of the last 20-30 years and the variety of design solutions used, it is worth contacting a specialist to correct unambiguously correctable faults or to perform non-periodic maintenance, as well as successful fault detection and troubleshooting. As the final inoperability matured, and the “broad-spectrum” fitters were more likely to guess, we managed to find a type specialist. He did not want to guess, suggested a full diagnosis, but in living conditions. So he connected his laptop to the OBD II port and was then able to go the test drive on the M6 ​​motorway. During the interrogation, the engine was mapped over the full speed range, observing mixture formation, operating pressures, temperatures, and control unit modification reactions. Different values ​​compared to well-functioning engines showed the direction of repair: this will be a fuel pump as there is little gasoline delivered. Not dramatically little, but the engine electronics are very “leaky” to make the machine work – he did it skillfully because under ordinary conditions, with average driving skills, the car didn’t do anything that would have appeared to be a fault.

On the mounting table is the unit

The next day, the car rolled into the service room after the usual grinding morning start. The new Pierburg fuel pump has been waiting to be installed. The specialist has exposed the mounting opening, which, being a pump inside the tank, is deep in the luggage compartment. This is more conveniently achieved from the passenger compartment by folding down the rear seat. He removed the cover plate, tied the wires, then unscrewed the threaded ring that secured the pump. He lifted the entire plastic pump housing, drained the gasoline, and then the structure was placed on the workbench. He highlighted the really novel pump and then the real cause of the fault was revealed. The O-ring under the pump was sheared, and the seal allowed gasoline to pass through here, the fuel level also dropped abnormally from the pump housing, and it was difficult to build up the necessary pressure for morning starts.

Removing the fuel pump from the pump housing

Since the new gasoline pump already existed and represented a better level of quality than the pump that had been working in the car until then, the new one was introduced with new seals. The old one went into the box for backup. After the installation, another laptop test round followed, and based on the observed values, the improvement was immediately visible, and since then the start-up has been almost immediate. Enthusiastic about the successful troubleshooting, based on the mileage and the facts shown by the data, even more non-vital but necessary parts for the reliable operation of the engine arose, which will be reported in the following articles.


From the seals on the bottom of the pump housing, you can see the rupture of the smaller ring (red)

Source: Autó-Motor by www.automotor.hu.

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