Ford Tailpipe Louver Mysteries
Q. I just bought a used F-250 with the 6.4L Powerstroke diesel. I am really happy with the truck, but one thing really bugs me. The tailpipe tip has some funny louvers punched into it that extend into the tip. Just what are these for? No one at the dealership can tell me anything.
Santa Barbara, CA
A. They do look strange, don't they? But they do have a purpose, strange as it seems. Your truck has a particulate filter on it to catch what some people call diesel soot. Every once in a while, the computer says it's time to clean out the filter, so an extra amount of fuel is dumped into the filter and actually burns out the soot that it has caught. This causes the tailpipes to get extremely hot, and the louvers in the tip are designed to draw outside air into the tailpipe to cool off the exhaust and to prevent damaging the paint or anything that comes close to the exhaust. Unfortunately, this system also plays havoc with fuel mileage. (Just another measure that the EPA required truck manufacturers to add.) And to your next question, no, it cannot be removed.
Revisiting GM's Beloved Insta-Trac
Q. I bought a '90 Chevy 1/2-ton pickup from my uncle. Believe it or not, it has been stored in a barn for the last 10 years or so, and only has 56,000 miles on it. He got mad at it one day because he got stuck in a snowbank, and when he tried to put it in four-wheel drive, the front axle would not engage even though the transfer case was shifted. So he parked it. I've got it running and have replaced the tires and changed all the fluids, but I am finding that some days it will go into four-wheel drive, and some days it will not. I have been stuck enough times to the point where I'm about ready to again park it in the barn for another 10 years. I did notice that there appears to be some kind of a device on the axlehousing with some wires going to it. I did some asking around, and a mechanic told me the truck had a two-piece front axle on this side, and that this "motor" (that's what he called it) with wires coming out of it locks the two axle shafts together. Okay, but if this is the case, then why doesn't the other tire have traction? Can you help me out? I really like this truck but without four-wheel traction here in upper Michigan, the truck is worthless.
A. It has been along time since I have received a question about the '88-'97 trucks not going into four-wheel drive. The first vacuum-shift four-wheel drive system that Chevy used was not the brightest idea, especially for a manufacturer building trucks in Michigan.
They use what they called a Thermal Linear Actuator. That "motor" is nothing more than a cylinder holding some special gas, a piston, and a heating element. When you shift into four-wheel drive, an electrical switch closes, allowing current to flow to this actuator. The current goes to a heating element that heats the gas, which then expands and pushes the piston down the cylinder. The piston is connected to linkage that engages a coupler that in turn connects the axle shafts together. In very cold weather, or when packed with snow, the thermal actuator does not get warm enough to heat the gas sufficiently to cause the piston to move.
The aftermarket, including companies like Warn, tried to solve the problem early on with an electric motor but ended up with strange RF signals that were picked up by the ECM, which in turn confused it, so they dropped the project. Then a guy whose name memory fails me at this time came up with a cable-operated manual engagement system and marketed it under the name "Posi-Lok." He has sold it to a company in Coldwater, Michigan, and you can read more about it at www.4x4posi-lok.com. For those who drive Dodge trucks, Jeeps, S-10s and even a couple of Ford models with vacuum shifters, there are also Posi-Loks available.
It took Chevy until 1998 to solve the problem. A September, 1998 Technical Service Bulletin # 76-43-01A addresses the problem with a new-style front axle actuator including a new wiring harness kit. To get the proper one from your Chevy dealer, you need the three-letter axle code that starts with a "Z," as there are four different kits. Hopefully, the small metal tag is still attached to the axle by one of the cover bolts.
Between you and me, I think that the Posi-Lok is the better way to go.