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Copied over from scan and tune, delete if not allowed
So I had my car tuned last week. Here’s the short mod list:
B&B Bullets
Speed Engineering 1-7/8” long tubes
K&N air filter
Powerbond UD Pulley
The car made great power, all things considered. The issue is in those little dips you see on the graphs I’ve attached. Those are misfires. Run 30 was my final one. These misfires happen mainly at higher RPMs at WOT, but can also happen at various other throttle inputs and in different rev ranges. It’ll also sputter and backfire if I’m in 6th at around 1500rpm and I floor the throttle.
My air fuel is fine too. The base map wanted it about 14.0, which is obviously high, but what was weird was that the more fuel he added the more it would miss. So it ended up around 12.8
Basically he would see the misfire, track it down and smooth that area down, and it would just pop right back up again in a different spot.
Prior to about 2 months ago, it never did any of this. It did it before the tune also, although it’s not knocking like it was before the headers and tune.
So my tuner and i are trying to get this figured out.
Our first theory is coil packs. The second is fueling, although that seems less likely given that my injectors have been cleaned and are in good shape, could be the pump though idk
any input? I sincerely hope it’s just the coil packs or something nice and simple like that, but what do y’all think?
have you changed the plugs?... what gap?... you (or the tuner) should find the cause of the issue and not have him tune around it in my opinion
yeah he did the plugs too, NGK iridiums. He just gapped them to the recommended spec, don’t remember it off the top of my head. Early on, some of the symptoms looked like original cats falling apart (car is at 115k), so we figured headers and tune ought to remedy that.
Last edited by DeathMetalAsian; 12-14-2018 at 01:47 AM.
2020 Corvette of the Year Finalist (performance mods)
C5 of Year Winner (performance mods) 2019
take them out and check the gaps, also ohm check the plug wires while checking the plugs... check all the coil harness wiring for obvious damage, especially on the driver side near the back of the intake... there is a bracket that the harness can rub against and over time chafe the wires and cause misfire and fuel issues... the coils are pretty reliable on these cars, that doesn't mean they can't fail but I would check the simpler things first... do you have any way to datalog the car?... that info is helpful in determining exactly what is going on
Without getting some scan data it's basically a crap shoot for you but I can say that almost 50% of misfires are ignition related and the rest is split between fuel and mechanical and other issues...if your tuner doesn't have a scan tool and a scope he's really not going to be of much help in the diagnosis. Save yourself some money in the long run and take it to a good diagnostic shop and pay for diagnostic time and fix it yourself if you're mechanically inclined. As mentioned previously check the wires if you haven't all ready. Yes, it could be fuel pump related but without looking at fuel trims or current draw it's just a guess. You said your injectors are in good shape...how was that verified ??...they can be clean but can be defective electrically...that's where a scope is your friend...I'd do a compression test to rule out anything mechanical and yes, those coils are bullet proof !!
Don't rule out rocker arm issues or even valve springs.. You could be getting float under load. The OEM springs
are usually fine for stock cam, but with the mileage you never know.
12-13-2018, 11:04 PM
Made good power, but misfires!
