How To

A repaired gas leak leads to new fuel gauge problem

John Paul, AAA Northeast's Car Doctor, answers a question from a reader who is frustrated by a fuel gauge issue on an older car.

The Car Doctor answers a question from a reader who is frustrated by a fuel gauge issue on an older car. Lincoln

June 5, 2024

Q. My wife has a 2013 Lincoln MKZ Turbo with 140,000 miles. It developed a gas leak that caused a puddle of gas to appear under the gas tank when she started it after a fill up. After replacing a fuel line that only worked in the short term, our repair garage decided to replace the fuel tank and install a Delphi fuel pump and sender. We also replaced the fuel filler neck, fuel lines, vapor lines, fuel pump seal, and locking rings. It was extremely expensive, but the gas leak stopped. However, the gas gauge no longer functions properly. As soon as the gauge needle reaches around the halfway mark, the low-gas message comes on, saying that I can only travel seven more miles before I run out of fuel. But I still have roughly five gallons of gas left in the tank. My garage has not been able to diagnose the problem. We would appreciate your opinion on what is causing this problem. A local Lincoln dealer thinks that the problem may lie with the use of after-market parts, but wants me to bring it in so they can analyze the problem — at a considerable additional expense.

A. There was a time when a fuel gauge was simple – a sender in the tank and a gauge on the dash, power, and ground to make it all work. Even in your 11-year-old car it is complicated. The fuel gauge is a virtual gauge. The IPC (cluster) sends a reference voltage to the fuel level sender(s). As the fuel level changes, a float actuates the variable resistor fuel level sender, raising or lowering the fuel level signal voltage. The IPC monitors the changes in voltage from the sender(s) and commands the fuel gauge with a corresponding movement of the pointer. The IPC uses four different operating modes. One mode is called recovery, this mode is incorporated into the IPC strategy. After a fuel fill up, the time for the fuel gauge to move from empty to full ranges from 2 seconds to 40 minutes, depending on which operating mode the fuel gauge is in. With this level of complexity, it is possible an incorrect signal from an aftermarket sender or poor electrical connection could be the cause of the poor gauge readings.

Q. I have a 1966 Ford Mustang that my wife originally got in 1974. It is a driver that does not get driven enough. I have been lucky over the years to not have massive repair bills, but I have always been concerned about being overcharged and whether the work being done is by capable mechanics and shops. Or maybe I just expect better customer service or better service overall. I prefer to have someone close, since when something must be done it always needs overnight or multiple days in the shop. Again, is that normal or can the service be better?

A. This is a great car, relatively simple to repair with easily available parts. The problem, as you found, is that good shops are busy. Back when shops had plenty of help, classic cars were great fill-in work, especially in winter. Today, with fewer quality shops and the challenges of finding qualified staff, almost no one has time for this kind of work. I was recently at a cars-and-coffee, and the most common question was where to get a car fixed. And like those great fishing spots, no one wants to let others know their secrets, because they may not be able to get their own car fixed. As warm weather comes around go to car shows (look for Ford owners) and ask around, you may find some leads. AAA has Approved Auto Repair shops, go to aaa.com/repair for a shop near you. The AAA shop may not have the time to work on your car, but may be able to offer a recommendation.

Q. My 2018 Subaru Outback info screen has been beeping and changing stations on its own. Sometimes the screen freezes and I cannot do anything. There is no rhyme or reason to when it happens. I have searched several YouTube videos and so far, everything I tried is temporary. Help!

A. Unfortunately, the issue is the screen itself and the fix is to replace it. The screen delaminates and causes the phantom changes. There was a class action lawsuit, but as far as I know it did not go anywhere.

Q. I am working on my 2005 Buick and am having trouble finding the information I need. I priced out GM shop manuals and even on eBay, they are costly. I have tried the local library but did not find what I needed. Any suggestions?

A. I tend to use AllData as a technical database and they do have a DIY version for single make of vehicles which is pretty cost effective. In the “too good to be true” category, I found Operation Charm-free, service manuals for everyone. The manuals go up to 2013, cover most vehicles, are pretty complete, and free.

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your Car Doctor question to [email protected]. Listen to the Car Doctor podcast at johnfpaul.podbean.com.