2 scanners have shown no trouble code and that is why parts have been
thrown at the problem. Three mechanics (two certified) have tried to
diagnose the problem so far based upon what their scanners read. Their
scanners say there is no problem but the driver says different.
Well now, you didn't say that before. Could be electrical, but if code reader
didn't show anything, it's most likely mechanical. It could be the fuel pump,
fuel filter, or fuel pickup sock (filter) in tank. If all else fails, drop the
tank & clean it; I had to do that once, to solve the same type of problem.
At this point, I would verify that the fuel pressure is good WHILE THE
CONCERN IS HAPPENING. If this proves good, then we get into diagnosis by
symptom and your tech will need a scan tool with flight recorder
capabilities. This method works but the tech needs to be sharp....
I would start with monitoring short and long term fuel trims, upstream and
downstream O2s, TPS and MAF... what I saw here would indicate which PIDs I
might need to add or ignore during diagnosis.
Other considerations... were any changes made just before the symptoms
appeared.... add-on accessories? Repairs? Gas purchase? Is the speedometer
reading steady or is it jumping all over? Has the charging system been
tested for excessive alternator "ripple"?
Try this... warm the car up. pull over and shut off, disconnect the MAF
harness connector. Drive car to see if the symptom changes for better or
Better = the MAF is dirty or out of calibration
Worse = There is another sensor at fault, possibly BAP
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