Originally Posted by Jhill If you do an ecm reset after warm how quickly and how high (or low I guess) do the short term fuel trim jump? Meaning does
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10-14-2017, 02:48 PM | #31 (permalink) |
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It’s been a while since i did that so i woukdnt be sure about the exact behavior it exhibited. What i can tell you about the last time i did that is that i do remember it struggling and having a rough idle after i performed an ecu reset and performed an idle air relearn, it did finally smooth out after a few minutes though.
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10-16-2017, 08:30 PM | #33 (permalink) | |
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10-16-2017, 09:48 PM | #34 (permalink) | |
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10-16-2017, 10:13 PM | #35 (permalink) | |
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10-17-2017, 05:06 PM | #36 (permalink) | |
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10-17-2017, 06:27 PM | #37 (permalink) | |
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At idle after warming up ltft sits at -10.2% with stft fluctuating between +3% and +20%, usually i see the +20% and above after the engine is heatsoaked and idling. During cruising with rpm at a steady 2500 ltft usually sits at -3 to -5% with stft between 0 to +3% Sent from my iPhone using Tapatalk |
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10-17-2017, 07:11 PM | #38 (permalink) | |
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10-17-2017, 08:01 PM | #39 (permalink) | |
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Just climbing up on 158,000 miles, the only roughness i encounter is when the stft pegs itself at +25% and then the engine stumbles and almost stalls and then that’s when the fuel trim numbers flip and the idle smooths out again, curiously the engine seems to act like it’s choking after this when i go to accelerate and does not really pick up power till after 5,000rpm. Sent from my iPhone using Tapatalk |
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10-17-2017, 09:22 PM | #40 (permalink) | |
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10-17-2017, 09:46 PM | #42 (permalink) | |
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Have you checked the basics like vacuum leak? |
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10-17-2017, 10:08 PM | #43 (permalink) | |
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Triple checked and couldnt find any leaks even trying to hunt one down with soapy water. The only suspicious thing i happened to spot was what looked to be a tear in the outer part of of the intake manifold gasket. Sent from my iPhone using Tapatalk |
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10-17-2017, 10:26 PM | #44 (permalink) |
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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. |
10-18-2017, 01:49 AM | #45 (permalink) | |
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Unfortunately a scope is one tool i dont have in my arsenal, I’ll see if i can put together a graph of what exactly it’s doing at cruise speeds as i do have another data file that i recorded over an 80 mile trip after resetting the ecu that i havent processed yet. Appreciate the help in trying to track down this issue, it has been a pain in my side for the last few months trying different things to find out what’s causing it with what little knowledge i have and every mechanic I’ve tooken it to has said there’s nothing wrong with it that they can see Sent from my iPhone using Tapatalk |
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