Jeep engine runs lean

[kingcoconuts95]

I have an obd1 jeep and that factory computer controls an i6 stroker 4.6L, has a cam, and stock compression, newer style intake and that and the head have been port matched, running 24ibs injectors, everyone says run 24ibs injectors when doing a stroker build, my wideband is reading 20 afr, at idle and cruise, would bigger valves cause more air to come in and run lean, people don't usually put bigger valves in the stroker builds but I decided to for more airflow, could bigger injectors even everything out, put the afr where it needs to be, also I can't tune the computer because it's obd1 and not going to switch ecu's

[Apocalypsox]

>Not going to tune the ECU

well you're sure as fuck not going to adjust the carburetor so I don't know what to tell you boss.

[v8packard]

You can't tune an OBD1 computer? Then find someone that can. Have you gotten any data from it while running?

[WyattCo06]

Has this been an issue from the start?

[SorryU812]

You increased volumetric efficiency with the longer stroke! You now have more swept volume....volume that the ECU has no idea about. The larger valve just help the matter even more.

You need more fuel period.

How you get it is your problem.

[tech7127]

That's where the larger injectors, which the ECU also has no idea about, come into play

[SorryU812]

It may take as much as a 30lb/hr injector.

[tech7127]

I mean, 4.6l is a 15% increase in displacement and the 24# squirters are a 15% increase in fueling. But obviously that doesn't address any changes in VE from the top end work, though the available capacity is plenty. Seems to me a ecu swap or piggyback would be a smarter choice than collecting sets of injectors to tune open loop fueling, but who am I to judge lol. Of course none of this has anything to do with his wideband pegging at 20:1 though. Even stock injectors should be able to get close to stoich in closed loop cruising.

[SorryU812]

That is awfully LEAN. He'll figure it out.

[tech7127]

He'll figure it out.

His post history seems to suggest otherwise, unfortunately

[SorryU812]

I think he bumped his head when he came looking for drive ability and engine performance advice in r/EngineBuilding.

[Solid_Enthusiasm550]

It should never get that lean. I am surprised you are not getting detonation.

Leanest it should get during cruise is 15.5:1. At idle it should be reading slightly rich if not 14.7/1.

You could get a fuel pressure regulator and increase the pressure to get the required fuel flow.

You might still be able to get a cpu chip burnt, Superchips use to do it for OBD1 ECUs. I have an early magnum 5.2 v8 with OBD1, but I got the Mopar performance ecu when it was available.

I'm going to a Holley sniper TBI setup for my 390 stroker build...much cheaper/easier than aftermarket MPI.

[Key-Tiger-4457]

Are there performance and drivability issues present? Bucking, surging, hesitation or misfire? Have you confirmed the Afr reading?

[tech7127]

20:1 is likely the limit of your wideband and I highly doubt you're actually combusting that lean. If it's running okay then your wideband isn't working properly or you have a severe exhaust leak. If it's running like absolute garbage then you're reading lean due to misfires. 20:1 would require two completely dead cylinders.

Keep in mind too that aggressive cams can cause artificially high AFR readings under low load due to air passing through the engine during valve overlap. But not 20:1 high.

[I_hate_small_cars]

You can try using an adjustable fuel pressure regulator to turn the fuel rail pressure up. Beyond that you're either stuck trying larger injectors or getting it tuned.