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Automania/Repair & Maintenance
AUTO QUESTIONS AND ANSWERS FOR WEEK 33
by Bob Hagin
Q. We have a 1996 Toyota Previa LE with the supercharged four-cylinder engine, all-wheel-drive and the All-Trac option. We bought it second-hand from a Toyota dealer with around 75,000 miles on it and it is in very good condition. We bought it because we have four children ranging from pre-teen to just graduating from high-school and all of us are involved in outdoor sports. We wanted the all-wheel-drive system because we do a lot of skiing in the winter. One evening recently we were driving for several miles up a mountain highway coming back from an overnight excursion. When we reached a four-lane section of the highway, another driver pulled alongside and frantically waved us over to the side of the road. When we stopped she told us that our van had been spitting sparks and flames out of the tail pipe for a mile or more but she couldn't get alongside to warn us. We could find nothing amiss under the van and when I had my wife double back and then drive by me, there were no flames or sparks evident. What could have caused the problem?
A. When you made that long uphill run, your Previa was probably close to full throttle which creates a lot of power and dumps a lot of fuel into the system. In addition, the supercharger was no doubt working hard at cramming additional fuel and air into the combustion chambers and creating a lot of heat. I suspect that this combination was very hard on the catalytic converter that's in your exhaust system and caused it to overheat. This can cause it to begin to break down and spit its overheated reactive innards out the tail pipe. I'd guess that the converter itself was glowing red-hot while it was all going on. It might be a good idea to have your fuel delivery system and catalytic converter checked to see they're still operating correctly.
Q. I have an '85 Jeep Grand Wagoneer with the 360 CID V8 engine and 134,000 miles. When the engine is cold, the oil pressure is 60 PSI and slowly drops to 40 at speed but when it idles, the oil pressure goes to zero. The problem seems heat-related so I had the radiator cleaned out. It has had several new oil pressure switches and a rebuild kit put into the oil pump. I tried 50-weight oil for a while but with no increase in pressure. I had the rear crankshaft seal and the valve cover gaskets replaced some time ago because it was leaking oil. One mechanic says that a part in the timing chain cover is worn out and causing the problem but this doesn't sound logical. Should I put in another engine? I've already spend $1000 trying to cure the problem.
A. First have to a mechanic install a test hydromechanical gauge in place of the electric gauge to make sure that the electrics aren't at fault. It's possible that an malfunctioning oil pressure operated timing chain tensioner is causing the problem but it's expensive to get to just on a hunch. It could also be caused by a faulty oil pressure relief valve or worn camshaft or main crankshaft bearings. Years ago I worked at a shop that had a external pump that would pump up the lubrication system with the oil pan removed. It was terribly messy but it always found the problem. I've seen engines run thousands of miles with low oil pressure at idle as long as the pressure was OK at running speeds.
Q. I have a '91 Chevy 1500 V6 truck with an automatic transmission. I bought it new in '91 and at 60,000 miles, the paint is peeling off the roof and the tops of the doors. Now it's starting on the hood. Who can I call for some answers?
A. General Motors experimented with paint techniques back then and some didn't work. I've had lots of letters on G.M.paint peeling but unless the vehicle had very low mileage, the company turned a deaf ear. Try the Hot Line in your owner's manual but don't get your hopes up.
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