In the event of an accidental downshift, safeguards are in place to protect the transmission of the Jeep Wranger Unlimited.
Question: I have a brand new Jeep Wrangler Sahara Unlimited with just under 1,000 kilometres on it. A couple of days ago when making a turn in a 50 km/h zone, I accidently tipped the gearshift to Tiptronic manual mode. It had shifted from fouth to third gear and as I approached a set of traffic lights, I tried to shift back to drive but in my panic, I shifted down further instead. My speed was less than 60 km/h and I immediately went back into a higher gear. I did not notice a high r.p.m. on the tachometer, as it all occurred in just a couple seconds, but it is a new vehicle and I am trying to be very careful about everything. The Jeep drives fine, but my mind needs to know that I have not damaged my childhood dream vehicle. Can you please advise?
Answer: You can rest easy. Your Jeep was not damaged by accidently moving the shift lever to a lower gear while moving. Modern electronically controlled automatic transmissions have many safeguards built into the control system and one of them is that the computer will not downshift the transmission to a lower gear that would cause damage to the engine. Even though you moved the shifter, the computer would only shift the transmission down if it wouldn’t over-speed the engine, regardless of how fast you were driving.
It may have even downshifted to first gear if you were driving slowly enough and you could feel a harsh downshift and a bit of a jerk when the shift occurred, but again, this wouldn’t cause damage to the vehicle. You can sleep easy knowing your new dream vehicle is just fine.
Answer: Most vehicles newer than your classic Nash didn’t have a rebuildable fuel pump, so replacement was the only solution. A mechanical fuel pump is a relatively simple device. The engine moves an arm which lifts a rubber diaphragm in the pump. A spring pushes the diaphragm back down. This works in conjunction with check valves. The movement of the diaphragm creates a vacuum to draw fuel from the tank and then pressure to force it to the carburetor.
Two one-way check valves inside the pump control the fuel flow. When the diaphragm lifts, fuel flows past one check valve into the body of the pump. As the diaphragm returns down, that check valve closes and the fuel is forced out of the other one-way check valve. With the symptoms you describe, I would think one or both of the check valves are not sealing and this causes the pump not to work. If you operate the pump by hand, you should be able to feel suction on the inlet port to the pump and a slight pressure on the outlet port. If this doesn’t happen, disassemble the pump and make sure the check valves are installed correctly. That should fix your fuel delivery problem.
Another solution would be to install an electric fuel pump on your car. Many classic vehicles have had electric pumps installed, but be sure to get one with the correct fuel pressure rating. Most carburetted vehicles require between four and seven PSI fuel pressure, while a pump for a throttle body fuel injection system will provide perhaps up to 90 PSI and a port fuel injection pump may deliver 120 PSI or more. Installing an electric pump with too high a pressure will cause a massive fuel leak at the carburetor because the float system in the carburetor can’t handle the higher pressure.