QUESTION: I have an enigma that even the auto dealer can't fix. My 1999 Jeep Grand Cherokee goes out with no problem at all. Then if I stop somewhere for 15-20 minutes, it won't start. Sometimes it will start if I really give it a lot of gas, but it won't run well, like a misfire.
I had a diagnostic check but the mechanics at different Chrysler dealerships haven't found the problem. The body and interior are in great shape; I would like to fix it. I am afraid to go too far from home. Whatever you could suggest would be greatly appreciated.
Q: I hope you might have some suggestions for the following mystery. My 2004 Dodge Dakota, a 3.7-liter automatic with 80,000 miles, won't idle smoothly in park or in drive with foot on the brake.
This occurs in dry weather (low humidity) only. Thank you for your informative assistance.
ANSWER: Both of these intermittent problems are certainly frustrating but solvable. It's imperative that both owners pin down the precise conditions when the vehicles act up, and practice baiting the conditions so that they can be duplicated/presented at the time of inspection. The Jeep suffers from a hot-soak condition, possibly affecting under-hood electronic or electric components or connections. And in the case of the Dakota, it's a very odd one - I'm leaning toward a circuit connection fault.
In both cases it's likely the on-board diagnostics system, or OBD-II, has set a trouble code, which could be hugely helpful in determining the cause. Additionally, a scan-tool snapshot of engine parameters can be taken during the no-start or a runs-rough episode, providing sensor inputs, output commands, fuel and idle system correction percentages, and a host of other pertinent information. The list can be compared to a previous snapshot taken when the vehicle was running fine. Scan data is great, but one needs to remember the listed values are what the engine computer believes is happening, which isn't always the same as the actual conditions occurring beneath the hood.
Sometimes even with great diagnostic information, you still need to resort to old-school tests and observations.
Adding fuel (propane into the air intake), verifying the strength of ignition spark, attaching and interpreting a vacuum gauge, listening for odd sounds and odors, checking exhaust emissions, killing cylinders to check for power contribution, pinching vacuum hoses, spraying water around gasket areas, wiggling connections, checking power and ground voltage quantity and stability - the list goes on and on.
It sounds like a new course of action is needed in finding a repair shop. I'd insist on a five-minute pre-write-up consultation with the technician to be assigned, and inquire what diagnostic strategies are recommended. Problems like these require a top-notch tech with the patience and skills to disassemble the haystack in a timely and efficient manner.
BRAD BERGHOLDT is an automotive technology instructor at Evergreen Valley College in San Jose, Calif.