You should buy a tool for that job
Dear Mike: I’m trying to replace the engine in my car with a used one, because I can’t afford to have the old one rebuilt. I have the new engine in my garage, and it still has all the fuel-injection hoses and stuff.
This is probably easy, but how do you take apart the fuel lines? The new engine’s hoses just end in a steel fitting, and I can’t figure out how to get apart the ones still in my car. It looks like they just plug in.
— T.P., Baltimore, Md.
A: You could simply saw off the old lines and splice in more tubing with hose clamps — but you’d have real problems, such as gas leaking all over your engine compartment and fires and, well, I’d rather you did it right.
•Go to the auto-parts store and get a fuel-injection hose-fitting tool. The fuel line’s female fitting has a spring inside it that clips over the flange on the male end. You need to depress the spring by clipping the tool over the line and stuffing it into the fitting until the spring releases.
•But before you disconnect the fuel lines, release the pressure in the system. You can do this at the Schrader valve on the fuel rail or by cracking open a fitting somewhere.
•Some car manufacturers suggest that you release pressure by pulling the fuel-pump fuse and trying to start the engine for a few seconds to let the fuel injectors bleed off the pressure, pumping the gas into the intake ports. I simply use a rag and try not to set the shop on fire until it dries off.
•Pop the tool into the fitting until the spring releases, and then wrap the fitting in a rag, to catch any gasoline, before you pull the fitting very far apart. While the fittings are apart, be careful not to mar the surface of the steel line between the end of the fitting and the flange, or to let it rust. This smooth surface seals against the O-ring in the female end, and any imperfections may scratch the O-ring as it’s inserted, causing a leak.
•By the way, some vehicles use this same type of connector for the air-conditioning refrigerant. Don’t take apart the wrong one, or you’ll get a giant surprise as the car vents a couple of pounds of icy refrigerant. But, if you are looking to reuse the a/c compressor from your old engine with the replacement, you might be able to do it without opening up the lines and spilling the refrigerant. If not, it’s probably best to have an a/c technician remove the refrigerant for recycling first.
Dear Mike: As an electronics technician for over 25 years, my curiosity got the best of me. I just purchased a Chrysler Pacifica with digital readouts for instantaneous and average miles per gallon.
What is the source of information for this data? Is it flow rate vs. torque? Fuel volume remaining?
I understand the basic math used to compute mileage from tank to tank. But when the vehicle is in motion, this display is updated every few seconds, and reflects driving style and even the terrain. How does it do that?
— J., Temecula, Calif.
A: It’s even more basic than you think: A sensor connected to the engine-management computer provides instantaneous vehicle velocity and distance traveled.
The computer also sets the width of the electronic pulses that open the fuel injectors. The amount of fuel injected is proportional to the width and frequency of these pulses, which means that totaling the area under the pulses during that same period gives an accurate representation of the volume of fuel used by the engine during the measured time. The computer then divides that number by the number of miles traveled, and translates the result into units that make sense.
Simple as pi, at least if you’re a computer and do math really fast. For the average mileage per gallon, the only difference is that the numbers are cumulative since the last time you reset the computer.
Dear Mike: The water pump on my 1990 Geo Storm GSi seized and tore some teeth off the timing belt.
I installed a new water pump and a new timing belt. I aligned the marks on the cam sprocket with the deck of the cam box, like I was supposed to. The engine cranks over fine, and has good spark and fuel, but it makes no attempt to actually start.
Where’d I go wrong?
— J.B., via e-mail
A: I’m going to assume that, since you knew enough to align the timing marks on the cam, you knew enough to align the No. 1 cylinder top dead center (TDC) mark on the crankshaft at the same time. If that’s the case, then I’m afraid you have bent valves.
When the cam stopped, some of the valves were still open. When the pistons came up to TDC, bingo, your valves got bent. Confirm this with a compression test, but basically, if that’s the case, you’re out of luck. You’ll need to remove and replace the head and get new valves installed.
If you didn’t bring the crank to TDC before installing the new belt, you’ve probably bent more valves trying to start it. Your Geo engine is what’s called an “interference” engine, one in which the valves open far enough that — if the camshaft timing is wacky enough — they can interfere with the top of the piston. Other engines, called “noninterference engines” for obvious reasons, leave enough room between the piston crown and the valves to prevent any contact.
One further caveat: Any time a valve hits a piston, I get nervous about the possibility of a bent rod, cracked piston or bent crankshaft. If the engine was zinging along when this happened, you may have further issues beyond the simple bent valves.