Originally Posted by Jhill (Post 3700226)

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 it jump to something like -15 and keep pegging there as long term drops.

Originally Posted by Jhill (Post 3700226)

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 it jump to something like -15 and keep pegging there as long term drops.

Originally Posted by Z_ealot (Post 3700683)

I did the best I could getting a chart of what the fuel trims are doing with what tools I have, keep in mind the blue and gray lines are short term fuel trims for banks 1 and 2 and the orange and red are the long terms, this was taken today with ambient outside temps at 92 degrees while driving normally

http://www.the370z.com/members/z_eal...fuel-trims.jpg

Originally Posted by Jhill (Post 3700691)

Little hard to read, is this idling or driving? I was more just after seeing the short term % pegged - after a reset to idicate if you have an injector leaking or something else causing a large unaccounted increase in fuel. Unsure on the z but I've rarely actually had leaky injectors (maybe I'm just lucky). Your comment of it having a hard/stumbling start after reset would indicate an issue (especially if it says a hot start after reset). May be time to check fuel pressure (typical they fail low but I have on vary rare occasion had overly high pressures). Can check residual pressure at same time.

Originally Posted by Z_ealot (Post 3700697)

The peaks on the blue and gray stft are when it’s pegged at +25%, what might be interesting to you is that before i started recording the ltft was at -8% at a hot start with stft pegged at +25% for a good 10 seconds and then the engine stumbled and the fuel trims reversed with ltft shooting up to +10% and stft dropping to -15%. The graph i posted was recorded after this while i was driving in the city so it was a mix of acceleration and idling

Originally Posted by Jhill (Post 3700903)

So what's stft and ltft after full warm and leveled out, idle and like a steady cruise, no radical acceleration etc.

Originally Posted by Z_ealot (Post 3700913)

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%


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Originally Posted by Jhill (Post 3700919)

Ok so your cruising numbers look good. Idle I would like a lower number but not terrible for ltft but the huge fluctuations in short term don’t look so good (although not a vq expert but that doesn’t seem great to me). How many miles on this engine? No roughness or intermittent misfires at lower RPM/idle?

Originally Posted by Z_ealot (Post 3700945)

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.


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Originally Posted by Jhill (Post 3700960)

How's it drive with both mafs disconnected?

Originally Posted by Z_ealot (Post 3700962)

Acts like it wants to die with both disconnected at idle, rpm’s fluctuate between 1500 and 600rpm, both maf’s are new


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Originally Posted by Jhill (Post 3700963)

That's odd, I haven't tested this on the Z but typically a car will default to safe mode that almost always runs smooth with no MAF reading (usually a good indicator if the MAF is bad if it's smooths out with it disconnected). I'll have to test it on mine.



Have you checked the basics like vacuum leak?

Originally Posted by Jhill (Post 3700979)

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.