Q: My wife's 2005 Dodge Grand Caravan will not let us add gas to it. At best, I need to fill it painfully slowly. I have a feeling it has to do with the EVAP system. The dealer said it would be $400 to fix. It sounds like the vapor venting is restricted. Is it possible to damage the charcoal filter by putting in too much gas?

A: It is possible to fill the charcoal canister with fuel by regularly overfilling the tank. It's called "fuel packing" and involves continuing to add fuel after the automatic shutoff has clicked on the nozzle. Doing this at a half-dozen fill-ups or so can eventually fill the vapor separator and force liquid fuel into the canister, which is designed to capture and store fuel vapors until the engine is started and they are drawn into the induction system and burned.

The problem with difficult refueling is a different issue. My ALLDATA automotive database pulled up Chrysler service bulletin 14-001-09 REV.A dated September 2009, outlining the possible causes and repairs for this issue. In brief, on certain models fitted with a "saddle"-style fuel tank, it recommends idling the engine for a minute or so to allow the fuel transfer pump to move fuel to the left side of the tank, opening space for refilling the right side.

The specific components to test are the vapor recirculating tube, fuel filler tube, fuel tank or components related to the evap control valve or the canister itself.

Q: If I do a fast takeoff from a stop in my 2005 Buick LeSabre, the transmission clunks hard shifting through all gears. If I stop and shut the car off and do a normal takeoff, it is fine and won't do it again until I do a quick takeoff. What do you think?

A: Has the "Service engine soon" light ever come on in relationship to the hard shifting? If not, I suspect debris in the valve body is the issue. Under hard acceleration, the TCM — transmission control module — will command higher hydraulic pressure to ensure solid, non-slipping shifts. As this occurs, debris in the valve body may be causing a valve or accumulator to stick. Try adding a half-can of SeaFoam Trans-Tune to the transmission fluid and drive the vehicle for a week or so to see if it helps clean the valve body.

I'd also suggest stopping by a parts store that offers free DTC code scanning to see if any specific fault codes are stored in memory.

Q: I purchased a 2001 Jeep Cherokee Sport 4.0 with 77,000 miles for my newly licensed son. The "Check engine" light is constantly blinking due to a misfire in the No. 5 cylinder. I replaced the coil pack, installed new plugs, installed rebuilt fuel injectors, sprayed SeaFoam into the air intake and "drove it like I stole it" to attempt to blow out any carbon build-up. I've heard other possibilities such as the fuel filter, crankshaft position sensor, camshaft position sensor or a stuck valve. Any suggestions would be greatly appreciated.

A: Since the misfire is specific to the No. 5 cylinder, at this point I'd focus on the mechanical health of that cylinder. Low compression due to worn/broken rings, burned/bent/stuck valves, worn cam lobes or an intake manifold vacuum leak could cause this misfire.

Start with a simple compression test. If it shows normal compression, then do a cylinder leakdown test. If leakdown is normal, try a running compression test. This involves removing the Schrader valve from the compression tester before installing it in the No. 5 cylinder, then starting the engine and monitoring the compression. If it begins to drop as the engine runs, not enough air is entering the cylinder, which could be caused by a worn cam lobe or a valve that's not properly opening.