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Dear Tom and Ray:

I'm a busy, poor veterinary student with an old, 1989 Volvo 240 DL. I have a wannabe boyfriend/mechanic who likes to tear into things and see what's inside, then put things back together the best he can. I appreciate his efforts very much, but there are times when I hesitate to risk mistakes. I am wondering what you think about an inexperienced home mechanic changing a fuel pre-pump on my car? The engine light code and physical symptoms all say the pre-pump is bad. I am so poor that I would love to buy a pump on eBay and have this guy put it in for me. However, the Volvo mechanics say pre-pumps are a very tricky business, and even new ones might go bad. Should I listen to them and pay them the big bucks to fix it? Or can I save some money and let my guy try it? What do you think?

-- Janel

TOM: Well, let's look at the upsides and downsides of each approach, Janel. If you go to the Volvo dealer, the upside is that the car will be fixed correctly. And presumably, they'll even guarantee the work for a while.

RAY: And you'll get to drink all the free, lousy coffee you want in their waiting room.

TOM: The downside is that you're going to pay quite a bit for that privilege. You'll pay a markup on the part, and you'll pay in the neighborhood of $100 an hour for labor.

RAY: The advantage of having your mechanically inclined would-be boyfriend do it is that it'll cost you a fraction of that price.

TOM: The downside is that he might leave your car in pieces. Or in a smoldering heap.

RAY: And if he DOES manage to fix it, it may take a restraining order to get rid of him after that.

TOM: But if you think you can handle the interpersonal expectations that may come from this, I'd definitely let the would-be boyfriend try it.

RAY: But first, have him confirm the diagnosis. The most common symptom of a bad pre-pump is that the car doesn't run well when the gas tank is near empty. But since I don't know of any computer code for a bad pre-pump, you want to do a little more diagnostic work before digging in.

TOM: Start by unplugging the power to the main pump. Then turn the ignition key to the "run" position. If the pre-pump is working at all, you should hear it groaning from the back of the car.

RAY: Then, to see if it's actually pumping anything, unplug the fuel line where it goes into the main pump, and see if a steady flow of gasoline comes out. Did I mention he should extinguish any cigars before doing this?

TOM: If no fuel comes out, then the pre-pump is bad and your adventure begins.

RAY: The pre-pump on this car is located inside the fuel tank. If memory serves, it's accessible from above (fortunately, it's been a while since I've had to do one of these). There's a plate on the floor of the trunk that you remove, and that gives you access to the tank so you can reach down and make the swap.

TOM: But rather than just buying a used pre-pump on eBay, I'd get a new Bosch pre-pump, just like the one that's in there. You may find one online for less than the local dealer sells it for. The advantage of using the original pre-pump is that it fits easily, without requiring any "improvisation."

RAY: If you have the right pre-pump, it should snap in there pretty easily. It's not a terribly difficult job. Just be sure to test it before you close everything up.

TOM: Just like you would in veterinary medicine, Janel. Good luck!

Dear Tom and Ray:

Everyone knows it is illegal to change an odometer reading, and I wouldn't do it even if I knew how. My 1999 Chevy Malibu (the best car I've ever owned) has an electronic display. I am curious as to why the odometer data is not lost when the car battery is removed. On the electronic clocks I have, if the power is disconnected, you have to reset the clock when power is restored. I'm sure many of your readers are wondering about this also. An "expert" told me there is a small battery backup in the circuit. But what if the car were put in storage for months and this battery eventually failed? Thanks.

-- John

TOM: Great question, John. Electronic odometers are not the same as electronic clocks. If they were, every used car you ever bought would have an odometer flashing 12:00!

RAY: They actually work like computer drives, which store data magnetically. If you turn off your computer and put it in your basement for years, when you start it up again, all of the stuff on your hard drive will still be there.

TOM: So guys, remember that! Anything you don't want discovered after you're dead, be sure to delete before shutting down your old computer!

RAY: Yeah. It took my brother a day and a half just to delete all of his "GMCs Gone Wild" videos.

TOM: The advantage of magnetic media is that they store data without power. The data are "imprinted" on the drive as a series of magnetic flux patterns.

RAY: And as long as you don't park next to Bernie's Dry Cleaning and Industrial De-Magnetizing Emporium, that data will remain there indefinitely.

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