Expert: Roland Finston - 9/30/2007

Question
I had a problem with getting some bad gas in my fuel tank.   My car ran rough and would hesitate.  We did clean the fuel injectors.  But I still get a code 43 and when I disconnect the negative cable, soon as I start the engine up I get a check engine light

Answer
The code is based upon the detection of minor missing which causes subtle differences in the rpm as each cylinder fires to produce its rotational input (crankshaft speed sensor is the detector involved). The Chrysler troubleshooting manual lists the possible causes as:
secondary ignition wires, puel pump or fuel filter, injector harness connectors, ignition coil circuit, spark plugs, mechanical engine problem, contaminated fuel, water in fuel, PCM grounds, Injectors, Restricted exhaust, intake restriction, PCM, evap system, EGR system, Air gap at high rpm's, damaged sensor trigger wheel, intake manifold gasket leak. That is quite a list!
The approach suggested is to check all electrical connectors and wiring, then do the tests in the following order:
secondary ignition
fuel delivery
engine vacuum
PCM power and ground connections
engine mechanical
The first one uses an engine analyzer scope to look at the high voltage pattern, then spray water on the cables to see if it changes. The possible repairs: individual spark plugs, coil or cable replacement
The second one involves pressure measurement and from there a variety of possible solutions
The third involves reading the intake manifold vacuum to see if it is steady at between 13 and 22 inches of HG. and if not the suspects depend upon the pattern shown by the gauge.
The PCM involves checking various wires at the PCM plugs
The last involves engine compression testing and a variety of other mechanical checks.
You might want to try spraying very small spurts of starting fluid around the margin of the intake manifold to see if there is a spot where the rpm changes, which would be the site of a manifold leak.
So I guess that beginning with the ignition wires makes sense unless you have a scope and the experience/knowledge at interpreting the patterns. You might try looking at the wires in the dark with the engine idling, then also spray some water mist on them to see in either case if you see arcing which would be a sign that the wires' insulation is breaking down. Then measure the coil resistances. If it passes that, then focus on the fuel filter and pump.
I'm uncertain whether the 'bad gas' was real, or just coincidental to the problem. Do you have any corroboration about the gas itself?
I'd be interested in learning what you find to have been the solution.
Roland