Q: I have a 1997 Ford F-350 pickup with a 351 engine. One problem I have is I have replaced both exhaust manifolds four times — once on the driver’s side and three times on the passenger side — and this one cracked again. The converter is about a year old. The other problem is I keep having power loss. The truck will run fine, then it’s almost like I lose a few cylinders. This lasts a minute or 10 to 15 minutes, hot or cold, and lately it’s a lot worse when it’s wet out. I’ve checked codes — none. I’ve replaced the mass air flow sensor on the fire wall, cap, wires, plugs, rotor, fuel filter, throttle position sensor and coil. The truck has about 130,000 miles. It’s in good shape but has had a hard life. Any suggestions?
A: Everything you tell me leads to a lean mixture problem. Scanning the computer will show you have a lean condition when monitoring the long- and short-term fuel trim. The excess heat caused by the lean condition is the reason you are going through exhaust manifolds. A few things that could cause the lean condition are low fuel pressure and volume, an erroneous reading by the oxygen sensor that may be setting the fuel lean, a clogged fuel filter, a failing fuel pump, an in-tank fuel filter that is getting clogged, or even an old fuel filter that is reducing the fuel flow.
Q: I have a 2006, four-wheel-drive Chevy Trailblazer LT. It has about 50,000 miles on it. It is no longer under warranty. I have recently begun having problems with the gas gauge and the digital display of mileage left before gas is needed. Both read empty (0 miles left — low fuel) when the tank has just been filled. In fact, the gauge reads empty for several miles after fill-up. Then it will sporadically jump around between empty and full while I am driving around. It goes up and down all day long. I have no way of knowing when I actually need gas except to set the trip meter and fill up when I reach 200 miles. Any idea of what is causing this?
A: It sounds as though your fuel sending unit has gone bad or the ground wire has lost continuity. The ALLDATA information system describes the testing procedures for the tank sending unit, that is if you are using a General Motors scanner. Basically, all it does is assimilate the signal sent to the computer by the sending unit. Giving the computer a certain predetermined voltage will make the gas gauge read at a different position. The diagnostics should not cost that much, however, if you need a new sending unit, you could expect to spend more than $600 installed.
Car Care Tip: Studded snow tires must be off the car by April 30, according to state law.
Larry Rubenstein is a master technician who owns a North Shore service station. His column appears every Saturday. Write to Larry at The Salem News, c/o Auto Scanner, 32 Dunham Road, Beverly, MA 01915, or send an email to firstname.lastname@example.org.