Replacing valve core in RV tires
Iwas changing the tire pressure sensor caps onmymotor home and found that one of the rear tire valves had become bent and doesn’t interact with the sensor. Can I simply remove the valve without jacking up the back wheels? Are they all the same or is there a special type? — Ray
It sounds like you have an aftermarket TPMS system which employs tiny sensors integrated into the valve stem caps. These are a great idea as about 50 percent of RVs are running on one or more tires that are underinflated, per the NHTSA. I believe you’re referring to the valve core within the stem that’s bent. If damage to the valve stem occurs, tire removal and demounting is needed to replace it.
Yes, since you have dual rear wheels you can deflate one rear tire safely to renew the core with the RV stationary, but if you have levelers, why not put them down for an added element of safety? Valve cores come in a long (older style) and short version and are interchangeable. You likely have a brass/rubber stem, so a typical brass (yellow/gold) core is fine. On vehicles with original equipment TPMS sensors with an aluminum valve stem, a nickel plated (silver colored) core should be used to prevent galvanic corrosion, which could lead to the core seizing to the stem. When removing the core, keep in mind there is perhaps 100 PSI behind it and it can shoot like a tiny missile when it finishes unthreading. Wear eye protection! Can you explain again howfuel trimswork? I took your advice and bought an OBD-II scanner and have been learning what various things are. — Chad R. Fuel trims are among the two dozen or so engine parameters that can be viewed using an inexpensive OBD-II scan tool. Let’s use a four cylinder (single cylinder bank) as an example. Fuel trim is the correction needed to the the base operating calculation in order to satisfy the exhaust oxygen or air-fuel sensor with an appropriate airfuelmixture. Let’s say an engine has a really dirty air filter and is being driven at 35MPH. The base calculation, derived from engine speed. load, and temperature says we should injectX amount of fuel. The oxygen or air-fuel sensor says HEY! I’mreading something different down here! The system will add or subtract fuel from the base calculation to bring the sensor to a correct value.
Fuel trims are typically expressed as a percentage, either positive (more fuel is added) or negative (fuel is removed) from a neutral (zero) value on a short term and long term basis. Short term fuel trim is quick on its feet, responding to instantaneous situations, while long term handles issues of amore consistent or permanent basis that have been learned. Our engine above would have likely learned to adjust for the dirty air filter so a negative reading (a lean correction) would be seen in the long term fuel trim during various driving conditions. Short termtrim may look fairly normal (plus/minus 5 percent) unless long term can’t handle the problem fully (20-30 percent is typically themaximum correction). It’s important to look at fuel trims under all driving conditions. For example a dirty fuel or air filter will show up mainly at high engine load/airflow, while a vacuum leak may appearmostly at idle. Multi-bank (V6, V8) engines typically have bank one and bank two fuel trims (a total of four). Low fuel pressure would be seen in the trims for both banks, while a faulty injector would appear in just one bank’s trims.
Email Brad Bergholdt at bradberg holdt@gmail.com; he cannot make personal replies.