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Discussion Starter #1
Heeeelp please. So car has cams, 3071 turbo, full exhaust, 3.5 ic and piping, fuel rail, ets intake, injectors, pump, tuned to 430whp. Above 3000-3300rpm runs flawlessly. Below that giving it gas (any throttle position) it bogs, stutters, backfires, and the AFR maxes out as well as logging some knock (1-3). No boost leak, MAP is fine, MAF seems ok (as per the AP), idles fine at 13.x afr. Worst is getting off the line at lights, just does not want to go. Working with my tuner but would like input from you guys in case there’s something obvious.
 

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Discussion Starter #2
Update: giving it like 10% throttle (just very light) does not trigger the stutter and sputter. Is it the car switching to the open loop map which has too lean fueling down low?
 

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Did it ever run right, and then suddenly started doing this? Or is this a new build?
 

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Discussion Starter #4
Both? It was purchased as an 80% finished project that sat for over a year. New parts added and re-tuned. For a while there was an issue with the MAP sensor, cleaned it and it’s been good after that.

Update on current stutter/sputter issue - tuner changed the “load comp map” and it’s behaving much better. I’m not very well versed in all the intricacies. It’s now not dying out in 1st and barely in 2nd at low rpm but still sputtering and going crazy lean in the higher gears at low rpm (higher load?) the difference now is that you can give it up to like half throttle before it starts the sputter but it will accelerate through it instead of just dying like before. Just to note I’m not normally driving my car under 3k rpm and stomping on it down low, just an issue I noticed and would like fixed for the cars health.
 

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Discussion Starter #5
Another update, changing fueling has made it better but now the car threw a misfire #4 code...... I’m checking plugs tomorrow and hope to god I didn’t destroy anything in there. Runs well though in the boost so I truly hope I didn’t wreck cylinder #4.
 

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oof, those cylinder 4 scares suck. I think it's probably just a spark plug or coil issue, either of which you can diagnose. But if anything is suspicious with the spark plug don't drive it any longer. I had that happen to me. Started misfiring like crazy, sounding like a Subaru. Took out my plugs, cylinder 4 plug was BENT. Stupid me thought, "Oh, that's odd. I'll just replace them!" then drove for 20 miles and blew up piston 4 :)
Hope all is well!
 

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Discussion Starter #7
Update: plug from cylinder 4 had a piece of the ceramic coating missing........ hope it just blew out the exhaust. I drove for about 300km to get home that night with it misfiring and after putting new plugs in it seems ok. Had to change the map back to a more lean one for it to drive ok but now I’m back to square one with the low rpm stutter. Not sure what to do, making it richer only did so much. Fuel pressure is good, the pump is good, maybe injectors? But wouldn’t they be bad across all rpm not just down low? I’ll pull them and see but it’s getting a little desperate here. I mean I guess I never drive it below 3k anyways except in 1st (it’s fine in 1st), still would be nice to not have this issue.
 

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Discussion Starter #11
Not melted just a piece broke off on that side. If I feather the throttle at low rpm I don’t get the stutter, as soon as I put the car under load it starts to stutter until about 3k rpm. So under light load (feathering throttle) the car runs off a closed loop and is ok. But with load it switches to open loop and has too lean of fueling down low? I’m trying to work through this logically because as far as I can tell mechanically all is well.
 

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Did you ever figure out what the issue was? My car started doing this as well after upgrading my fuel system after a failed attempt at the tuner (ran out of fuel at top end)

I upgraded my pump, fuel rail, and return line.

I installed the upgraded fuel rail and that seemed to help a lot, but only for a short period of time.
 

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Discussion Starter #13
I kinda figured it out but it turns out my car was bastardized beyond belief before I got my hands on it. The biggest thing that seemed to help was replacing the o-ring seal on the MAF sensor. The old one was pretty loose and would not seat properly, get pinched when I would bolt the sensor back on. I also put a beefier seal on the turbo inlet elbow. My other problem seemed to be the knock sensor clip on the harness had a broken tab so it would vibrate and partially disengage, this would cause the car to retard itself to the point I could feel it. It’s hard to diagnose when there is so many little things wrong. One by one I got them all sorted, and I still try to drive it at higher rpms as anything below 3k is just pathetic unless you’re just cruising.
 
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