QuestionQUESTION: has codes 171, 174, banks too lean. checked intake pipes, cleaned mass air flow with proper cleaner, has no intake leaks. borrowed a scanner, monitored maf, it reads in - lb/min. while at idle reading is at .394 - .435. unplug maf and reading doesnt seem to change any..... i'm confused. by the way, the long terms are at 25 on both banks, freeze frame, and live. short terms live are in the neg. please help i gotta get this thru de. insp.
ANSWER: Hi, Chris. Unfortunately, these codes are difficult to diagnose because the trouble code tells you more about the symptom than the cause. You've started with the right ideas.
I can't look up the air flow readings because I don't know the year and model vehicle, but it bothers me that they don't change when the sensor is unplugged. Ordinarily, this would be enough to set a trouble code for the air flow sensor. Do they change when the engine is revved? Is the bellows between the air flow sensor and throttle body intact and securely attached?
If you haven't done so already, check for vacuum leaks by pinching each of the vacuum lines (EGR, PCV, evap, brake booster and monitoring fuel trims. Also spray a combustible liquid around areas that might leak and monitor the fuel trims. Expect to see a change if you've encountered or blocked a leak.
Compare air flow sensor readings with the proper values. Replace if off by 10% or more.
Check your fuel pressure. Low fuel pressure could cause these DTCs.
Check your fuel. Excessive alcohol content in the fuel could cause these DTCs.
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QUESTION: its an 03 tiburon v6, all data stated that fuel psi should be 50 psi at idle. i checked it, it was at 31 psi, spiked to 40 on full thottle. r&r the fuel pump. no change, rechecked the fuel trims, at idle all trims at or near 0. rev it up and short terms go to around 25 both banks. this vehicle is equipped with a cold air intake. i also monitored the maf with a handheld scanner, the maf read - lb/min - .394 - 435 while at idle
AnswerYour air flow readings appear to be a little low. They convert to 10.7 - 11.9 kg/h. The specification in the repair manual is 11.6 - 15.4 at idle. This is a much larger range than I'd like, but is different enough from your readings to indicate a problem. I had meant to consult my list of known good readings at work, but forgot to check this. If I can remember to do so, I'll add to this answer.
It still bothers me that the readings don't change when you unplug the sensor. Do they change when you rev the engine?
The reasonably possible causes for low air flow sensor readings are as follows:
-- defective air flow sensor
-- air entering engine that isn't measured by the sensor (e.g. vacuum leak or leak in plumbing between sensor and throttle body)
-- poor ground for sensor.
It also bothers me that this car has a cold air intake. If an oiled filter is used, this can cause the oil to be deposited on the sensor. As I suspect you know, oil on the sensor element will significantly affect the readings.
In regard to the fuel pressure, the manual indicates it should be 38 PSI at idle and 47-50 at open throttle (or with vacuum hose disconnected). Since you've already replaced the pump, this leads me to believe the fuel pressure regulator may be defective. It's hard to say whether this difference would be enough to cause the trouble code.
