Random lean spike during part throttle
Thread Starter
Drifting
Joined: May 2008
Posts: 1,505
Likes: 7
From: Jacksonville FL
Random lean spike during part throttle
So for a while now my car has had random lean spikes during part throttle driving. The shop has taken a few looks at it and it's still doing it... last thing they tried was completely disabling the DFCO.
The car drives normally and has a normal 14.7 AFR during cruise but will randomly jump up to 16-17A AFR and stay there for about 30-45 seconds unless I give it a decent amount of throttle where it finally drops it back down. Sometimes it will only do it once a drive and sometimes it does it back to back to back. WOT pulls are perfect but the car does throw out random cylinder misfire codes every couple of days. It may be due to the cam but you can feel the engine miss every now and again.
It's starting to really get annoying especially during city driving or trying to pull out in traffic when it just kills the power.
Attached is a video of what happens but I would also like to see if I can catch it on my scan tool. It's nothing fancy just a ABS/OBD II scan tool from Advance Auto but it does some data logs. I'll see if I can get it to work as well.
The car drives normally and has a normal 14.7 AFR during cruise but will randomly jump up to 16-17A AFR and stay there for about 30-45 seconds unless I give it a decent amount of throttle where it finally drops it back down. Sometimes it will only do it once a drive and sometimes it does it back to back to back. WOT pulls are perfect but the car does throw out random cylinder misfire codes every couple of days. It may be due to the cam but you can feel the engine miss every now and again.
It's starting to really get annoying especially during city driving or trying to pull out in traffic when it just kills the power.
Attached is a video of what happens but I would also like to see if I can catch it on my scan tool. It's nothing fancy just a ABS/OBD II scan tool from Advance Auto but it does some data logs. I'll see if I can get it to work as well.
Melting Slicks
Joined: Oct 1999
Posts: 2,181
Likes: 421
From: Ponte Vedra Beach FL
You need to take that car to EFI Alchemy in nearby Green Cove Springs. The tuner there, goes by "Doc", can easily solve that problem, as he just did with my 2013 Grand Sport today It's not just fueling, but timing/knock retard settings that are causing you grief. He will have your run the car hard on a nearby back road with him sitting alongside with his laptop taking in data. He'll make a few tweaks during those runs, and then it's onto the dyno for final tuning after he has you drive it for a few days to see if he's found the main "miss" problem. It's amazing how he can "see" what's going on and fix it with a bit of typing on a computer. He will probably have you go one-step cooler on plugs to help with knock issues, he'll change your fan "on" settings, and so forth.
When he was done, I was at 396 RWHP, 388 T. Not bad for a showroom stock Vette.
When he was done, I was at 396 RWHP, 388 T. Not bad for a showroom stock Vette.
Melting Slicks
Joined: Oct 1999
Posts: 2,181
Likes: 421
From: Ponte Vedra Beach FL
When you say you took the car to "the shop", what does that mean? Your local Chebby dealer, or a true tuning shop where they'll run EFI Live or something like that? And on top of that, it's not the tools, but the guy who knows how to use them is what counts.
Again, EFI Alchemy in nearby Green Cove Springs will find the problem and make you happy.
Thread Starter
Drifting
Joined: May 2008
Posts: 1,505
Likes: 7
From: Jacksonville FL
Never actually expected replies on this post. Car has had other engine issues since but the lean condition was never fully figured out. Doesn't matter now since a rebuild has been performed.
The car was tuned by Doc. We had been going over multiple fixes the last month or two. Right now I was hoping the fuel pump was going bad and either never had an actual voltage booster (which would be a miracle considering the car made 664whp) or did have a voltage booster which would basically reset the fuel pump when I went WOT.
I've actually dropped it down to plugs that are two steps colder since it's running fairly high boost. The same tune will go back in with a few tweaks here and there for the pure methanol I'll be running and high flow valve job. Otherwise it's the same as before so if the lean issue is gone it was the old fuel pump.
The car was tuned by Doc. We had been going over multiple fixes the last month or two. Right now I was hoping the fuel pump was going bad and either never had an actual voltage booster (which would be a miracle considering the car made 664whp) or did have a voltage booster which would basically reset the fuel pump when I went WOT.
I've actually dropped it down to plugs that are two steps colder since it's running fairly high boost. The same tune will go back in with a few tweaks here and there for the pure methanol I'll be running and high flow valve job. Otherwise it's the same as before so if the lean issue is gone it was the old fuel pump.
Melting Slicks
Joined: Oct 1999
Posts: 2,181
Likes: 421
From: Ponte Vedra Beach FL
Well, I feel pretty silly for telling you to get a tune at EFI Alchemy, now that I learn that you have a heavily modded car. And I'll feel sillier still if that was your black car in their shop in mid-February in a million pieces, entire drivetrain apart and engine getting a rebuild, blower parts and giant exhaust and the fuel tank with the big pump/lines being installed.....is that yours?
I mean, jeeeeez.....it's hard to give internet advice to John Force about making more horsepower.
I mean, jeeeeez.....it's hard to give internet advice to John Force about making more horsepower.
Thread Starter
Drifting
Joined: May 2008
Posts: 1,505
Likes: 7
From: Jacksonville FL
Yup lol
I'm by no means John Force. Hopefully the pumps take care of things. Been tweaking everything here and there with no luck. They thought the DFCO was an issue but that didn't change anything. I actually may have them turn it back on and leave it on pretty high I miss the exhaust pop it had.
Engine is back and getting ready to be installed so hopefully I'll see how she runs soon enough.
I'm by no means John Force. Hopefully the pumps take care of things. Been tweaking everything here and there with no luck. They thought the DFCO was an issue but that didn't change anything. I actually may have them turn it back on and leave it on pretty high I miss the exhaust pop it had.
Engine is back and getting ready to be installed so hopefully I'll see how she runs soon enough.
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Burning Brakes
Joined: May 2007
Posts: 934
Likes: 0
From: jax fl
afr
had the same problem with my car for about 18 mths periodically it would come and go, brought to many tuners and gm they could not tell me what was wrong, took it upon my self to start checking wire's. and finally found the driver's side precat o2 wire's were melted together and taped up so as nothing was ever visible. made the repair and afr has been perfect since 
just check all wiring good luck joe
just check all wiring good luck joe