Stalling vehicle needs good tech to diagnose

I have a 2008 Chrysler Pacifica with 140,000 miles. I have made many trips to the dealership about one thing or another. They keep charging me but can’t find anything the matter with the vehicle. Sometimes when I’m driving, not fast, it will just stop running. I stop and place it in park and it starts right up. No problem then. I have had the spark plugs and coils changed just recently. It still runs like it’s missing. The problem continues. I amthinking of having a new fuel pump installed, which would also give me a new fuel filter. What do you think? — Linda S.

This must be incredibly frustrating and scary as you don’t know when it might happen next! I need to ask quite a few questions, so please don’t be offended if I take some of your statements apart.

When the Pacifica quits, does this happen after driving for a while? Cold or hot weather, does it always occur at the same speed? Does it occur when coasting, climbing? At a particular fuel tank level? Is the symptom quick and sudden, as if someone switched off the ignition, or does the engine sputter or jerk beforehand? How difficult might it be for you to take a technician for a ride and demonstrate the symptom? Is it somewhat frequent in occurrence?

When you say “missing,” are you referring to either an occasional or continual shuddering/roughness from the engine, more noticeable under load (climbing/accelerating)? This could be related to the quitting symptom, and possibly not. A faulty ignition coil is a common cause of misfire (missing), as are spark plugs, but far less common. With 140,000 miles on the clock, your fuel pump is on borrowed time and a possible culprit, although when a fuel pump fails it’s usually once and that’s it.

Amisfire typically results in an illuminated check engine light, depending on driving conditions and fault severity. A sharp tech with a scan tool can verify if misfires are occurring as well as in which cylinder (in most cases). The scan tool can also be programmed to record amovie of operating data; if you could duplicate the fault for him or her, a snapshot of the instant the engine quits, and events leading up to this could very likely point to the specific fault.

Let’s say the fuel pump is the fault. The short term fuel trim readings for both cylinder banks would ramp up sharply within the last few seconds prior to engine speed falling to zero. Or if the EGR valve sticks on, causing a stall-out during slowing/stopping, the manifold vacuum would plunge just prior to the stall-out.

One ofmy favorite activities as an automotive technology teacher is replaying a variety of scan tool scenario movies withmy students. They play detective, stitching together the sequence of events, and separating causes from effects.

It seems you need to find a sharp tech. Look for one with an emissions license, ASE advanced engine performance L-1 certification (these are the smartest cookies), and the resourcefulness/desire to work with you to duplicate the fault conditions.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.