Generation IV External Engine - Why does my car go VERY lean from 2-3k then clean up?

This problem is killing me. Ive tried +/- 10* of timing..and have added enough fuel to fill a small pool and it doesnt change a thing. The car runs PERFECT from idle to about 2k...from there the car runs like shit till 3k..sometimes I watch AFR shoot to 19-20 and it sounds like the engine isn't getting any fuel..other times it will be in the 13-14afr range and the more load I put on the engine (MOSTLY at the 24-2800rpm range) the car will break up bad..as soon as it hits 3k..its cleans up completely. Engine is an ERL 434ci 11.8:1 compression with a massive 262/266 .624/.624@113+3 cam and a fast 102. The block was milled once when it was rebuilt the first time and again when it was sleeved.

At first I thought it was my intake because I was seeing mid 80s KPA at idle..so I switched to a stock LS2 intake and the problem stayed the same along with the vacuum (or major lack there of). It happens whether im in MAF, SD or Hybrid mode.

Plugs are NGks gapped at .045, MSD wires, stock coils with new wire harness on coils. I took the plugs and wires off and found a loose plug..so I tightened it up put all the coils and wires back on and the problem seems to be a little more pronounced now.

I did a compression test today so far (leak down tomorow) and saw 182-185psi (cold..maybe 100*) across the board.


Can anyone give me a possible cause for this? No matter what I do..its only in the 2-3k range and completely clears up after 3 every single time...along with it going to 20afr sometimes always at the same load/rpm..no matter how much fuel I add to it.

Overlap, AFR is reading the clean air that goes through?

That cam is far too bit for that intake IMO. As per other thread, drop the duration.

Who spec'd that cam?

It's a vengeance spec'd cam. Im running TFS245s as well. It doesn't do it every time though. It always breaks up in that area but the completely lean condition is random.

Post the tune and a datalog. Maybe you're missing something that another set of eyes will see.

Been having this same problem....its, the o2s freaking out until they get a good strong exhaust pulse then everything clears up

I'm running open loop. I don't have any o2s

Oh hell...keep me posted on this. I guess im lost again lol

whats your fuel pressure at when it goes lean?

Not.the op but i have sane problem.... no drop in pressure stays at 62lbs

Try changing your tune, take it to MAF only, no VE.

Does injector duty cycle remain the same, drop or increase when you are commanding more fuel?

80kpa idle sounds about right with that set up. Post up a log/tune of your OLSD tune or PM/email them to me.

Have you checked valve springs yet? A local guy was having a similar issue with the car breaking up in that range, not necessarily going lean but the outer spring on a dual kit was broken causing a bad surge in that area, then would clean up in the higher rpms.

I'm running open loop. I don't have any o2s

Don't have as in absent, or don't have as in not using?
They would be the first thing I'd look at for an indication
of fueling related problems.

I'd then look at the spark map (main, and on an originally
EGR-equipped car, the EGR adder table which should be
zeroed), and the delivered spark vs the main table when
the misbehavior is going on. Table ought to be smooth
and continuous, no spikes or steps. Delivered ought to
match desired. Discrepancies are clues.

Oddly most of my LS engines experience an odd lean condition from 2-2400rpm. Although it does tune out quite easily. Fuelling in that area ( ie large throttle openings and around those rpm's ) do have injector pulse widths much higher than seems reasonable

That's been with different engine sizes, heads and camshafts.

it might be getting tons of turbulence in the intake and exhaust at those rpms so it cant move the air in or out or just one. are you running a screen in your maf? if not maybe give it a try. idk im prob wrong but im just giving possible ideas

Im running an LS7 maf. Problem is pretty much gone with just a cam swap.

I'd guess that would be a smaller duration cam?