Truck Trend Garage: Expert Advice July/ August Edition

Getting the Good Gas
Q: I recently bought a 2006 Jeep Grand Cherokee, and the base where I'm stationed in Yokosuka, Japan, only has 93-octane gasoline. The Jeep owner's manual recommends 87- or 89-grade gasoline for optimum performance. Will 93 grade hurt the engine?   |   expert Advice A: Higher-than-recommended-octane fuel typically gives two results: a small or negligible gain in power and/or fuel economy, and a significant waste of cash at the pump. I don't know of any official studies, but I've heard talk about higher octane than necessary producing extra carbon buildup within the combustion chamber--that takes up space, raises compression, and may cause the engine to really need a higher-octane fuel. Again, there's no proof. Don't worry. Use the 93 octane and add a gas treatment periodically to keep the combustion chamber clean--just in case. Ford Diesel Troubleshooting
Q: My 2003 Ford F-250 turbodiesel won't start in the morning unless I hold a gas-soaked rag over the air duct. Once I do that, it starts with a bad knocking noise for about five minutes and is okay for the rest of the day. A: The more ignitable gasoline vapor from the rag (just like starting fluid) is treating the symptom, not the cold-start problem. The induced startup is followed by some nasty knocking as the high-compression diesel engine wolfs down the wrong fuel for breakfast. Don't mess with this one. Get it to a qualified independent diesel technician, or better yet, a local Ford service department. Diesel problems can be even more difficult to identify than those of their gasoline-powered counterparts. A technician will plug in a scan tool to check for related trouble codes, while analyzing pertinent data. Depending on what's found, there may be a long list of areas to cover after that. The 2003 model-year 6.0-liter Power Strokes had a number of driveability issues that may include a hard- or no-start condition while cold. Fuel pressure, fuel contamination, and fuel-injector problems are high on the list, along with glow plugs not working correctly. Unlike a gasoline engine that uses a spark to ignite the air/fuel mixture within the combustion chamber, a diesel uses much higher combustion-chamber pressures to initiate the explosion. It just needs warming up by the electrically powered glow plugs that protrude into each cylinder. There's a known problem with poor connections at the glow-plug control module. The fuel-injection control module, or shorted wiring thereof, also can cause trouble. And it's always important to keep the entire system up to date with the latest software calibrations. A good technician will read through all of Ford's TSBs related to the condition. He'll probably even have a few memorized. Binging Ram Needs a Purge
Q: My 1996 Dodge Ram 1500's engine wants to die when I'm driving, but only when I let off the gas to apply the brake or to go around a curve. The check-engine light is on, but the only code that's coming up is "Purge Solenoid." A: Which engine's under the hood? Also, which purge solenoid trouble code was stored in the PCM's memory? There are about five related codes. There are a high number of potential causes of a stall condition while letting off the gas in a high-mileage Ram: vacuum leaks, idle air-control valve problems, and carbon buildup in the throttle body, to name a few. Dodge emissions recalls #7631 and #7632 pertain to all gasoline-burning 1994 to 1996 Rams. The problem was a defective evaporative vapor canister, which allowed its internal charcoal to be sucked up through the purge solenoid and into the engine. The charcoal within the canister absorbs vaporized fuel emissions from the gas tank, and at the appropriate time, the purge solenoid opens up and allows vacuum to pull the vapors from the canister into the engine, where it can be safely burned up. The bits of charcoal leaving the canister may allow fuel vapors to escape into the atmosphere. These little guys can also plug up the purge solenoid resulting in stalling and a check-engine light (trouble codes). It's possible that the recall wasn't performed, or there may be an unrelated failure with the vapor purge system. Sierra Pickup in Alaska
Q: Every time I start my 5.3-liter 1999 GMC 4x4 half-ton Sierra, it doesn't achieve full throttle potential until I run it about a quarter mile. Then it regains power and speed and responds normally. It'll run fine until it's turned off again. The situation recurs each time it's started, whether the engine's cold or hot. No warning lights appear. The lack of throttle response at startup has been present for about two years. The fuel pump bit the dust about a year ago, but replacing it didn't alter the annoying problem. I can't take it to a GM service center as I live in Nome, Alaska, where I had to ship the vehicle in by barge due to the region's isolation. A: After reading your description, I'm not sure what the symptoms actually are. Hopefully, Nome has a local mechanic. It may be worthwhile to have him drive the truck and experience the condition. If not, perhaps your local shop can call a GMC service department long distance and explain the problem to a top technician on staff. I'm sure they'll be glad to help. With a little luck, your local guy has a scan tool. Be sure he's in the truck with the scanner in his hands when he makes the call, so he can relay trouble codes and data to the far-off technician. There are a lot of potential causes: a fuel-related issue, the PCM acting up, a mass-airflow sensor struggling, or even a glitch in the transmission. There've been problems with the automatic transmission starting in second or third gear instead of first, which can feel just like an engine with no power. The cause is a lack of voltage to the shift solenoids (electronically controlled transmission), caused by either a bad ignition switch or the inappropriate installation of an aftermarket remote-start system. How To Reach Alex
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.

Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage--visit Alex Steele at www.RealWorldAutomotive.com.