10-18-2017, 06:21 PM
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#14 (permalink)
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A True Z Fanatic
Join Date: Sep 2010
Location: Albuquerque, NM
Posts: 2,045
Drives: 09 370Z Touring/Sprt
Rep Power: 10091
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Quote:
Originally Posted by Jhill
Well I'll have to disconnect my mafs to make sure the z doesn't do something different than what I'm used to but from what I'm hearing is it's running really well at cruise load but issues at idle (where engine are most sensitive). I've seen engines with moderate leak down (valve train issues) do this but it's usually accompanied by a rougher idle and an intermittent misfire but at 158k on an engine not known to have valvetrain issues I doubt it, vacuum leaks can cause this but I would suspect your fuel trim would be going + not -, mafs acting up (typically accompanied with a dead spot in the powerband) but I'll admit none of the car lines I've worked for had dual intakes but I assume it averages
both. I will say I have had one injector have a poor spray pattern sort of have the same symptoms you describe but again a rough idle and misfire that would smooth out and run fine at cruise with more airflow/turbulence to atomize the fuel (not sure what fuel trims would be doing as it was pre obd) but this is highly unlikely i think. Slightly leaking injector but usually accompanied with a stumbling start.
Do you have a scope with amp clamp? If so scope the amperage for the injectors power wire (before it splits into parallel) and see if all the injector amperage are relitively equal.
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I tested the engine with no mafs connected again after i got home today, results are interesting to say the least. From cold start with both mafs disconnected the rpm’s fluctuated between 1500 and 2500 rpm until the engine coolant temps were up to spec at which point the rpm’s flattened out to about 1100rpm and only once about every 20 to 30 seconds the rpm’s would dip down to about 600 and then clim back up to 1100. Just a note, but i decided to check and see what fuel trims were doing after everything was warmed up. Long terms were pegged at 0 for both banks while short terms were pegged at -25% and would go to 0% when the rpms dipped to 600 and climb back to -25% when rpms came back to 1100. I tried driving the car while the mafs were disconnected, it would not let me go past 2500rpm, but seemed smooth otherwise. I recorded a few minutes of data while the mafs were disconnected that I’ll upload here shortly and see if we can glean anything from that if necessary.
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