Tech Stuff

Got gas? Get ready for fuel delivery diagnostics

Truglia is the owner of Car Clinic, a state-of-the-art repair facility in Mahopac, N.Y. He is ASE certified with a M.A. from Columbia University. In the automotive world he has been trained by Technicians Service Training and Automotive Technician Training Services. Car Clinic’s facility is fully equipped with factory-level equipment and services American, European and Asian vehicles, including diesels and hybrids.

The present-day is an interesting time for the automotive technician. Perhaps now more than ever, the vehicles that are on the road resist breakdown, and with the help of a few repairs can routinely last about 200,000 miles.

This is a far cry from the day when vehicles had carburetors or early versions of fuel injection. While it appears that fuel-saving technologies such as direct fuel injection and the increased use of turbochargers may also break down quicker in the future, many of these vehicles are so new they have not yet reached the point where they have breakdown-related issues.

So, the question service technicians need to ask themselves is whether or not they are prepared to deal with a fuel-related no-start or misfire.

Because the truth is, it has been about 20 years since OBD II technology hit the market and aside from General Motors vehicles, it is not very common to run into one of these issues.

Figure 1: This 1987 Pontiac Grand Am creates a nice and neat amperage waveform when running the fuel pump.
<p>Figure 1: This 1987 Pontiac Grand Am creates a nice and neat amperage waveform when running the fuel pump.</p>

Tip Number One: Give up on current ramping, or don’t even start if you have heard about it.

Back in the day, when 90% of vehicles were made by three American companies, there was not a lot of diversity in what fuel pumps these vehicles had. Not coincidentally, when the amperage of these pumps was ascertained using an amp clamp and a labscope, they produced neat looking waveforms, such as the one seen in Figure 1.

Many technicians think that all fuel pumps can be diagnosed this way. However, if they actually tried the technique on vehicles made after the year 2000, they would see that the fuel pump waveforms don’t lend themselves to such easy interpretation.

Figure 2: A 1998 Chevy Malibu with a driveability problem.
<p>Figure 2: A 1998 Chevy Malibu with a driveability problem.</p>

Figure 3: A fuel pump waveform on a 1998 Chevy Malibu.
<p>Figure 3: A fuel pump waveform on a 1998 Chevy Malibu.</p>

Take a look at Figures 2 and 3. Does this vehicle have a bad fuel pump?

Many current ramping gurus would say “most definitely.” The problem is, the actual answer is no! This fuel pump is fine and this is not even a new vehicle, it is a 1998 model year GM. Further, as one can see in Figure 4, the vehicle’s fuel trim is not highly positive, compensating for a bad fuel pump. It is well within normal range. Quite frankly, the fuel pump is fine.

Further, to effectively current ramp fuel pumps the technician is required to undergo the impossible task of taking specs of every new car he finds. And it is not always easy to access fuel pump relays. Rents and taxes are too high and labor is too expensive to waste time doing this, especially when, quite frankly, it does not work anyway.

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