I just finished putting this in the car.

95 Camaro Z29 Complete Rebuild And First Startup.

383 Stroker - LE2 Heads - LE2 Billet Cam - Pacesetter Mid Tubes - Flowmaster 80 Series Catback

11.8:1 SCR
9.1:1 DCR
93 Octaine Pump Gas

SLP cold air intake
Aluminum elbow
Twin 58MM Profesional Products Throttle Body
Loyd Ellot Ported Intake Manifold
LE2 Heads - Comp beehive springs
LE2 billet cam
Comp Chromoly pushrods
Comp 1.6 NSA RR 7/16" Stud
LS7 Lifters
Eagle Cast Crank
Eagle Forged I Beam 5.7" Rods W/ARP Capscrews
Speed Pro Hyper -12CC Dish Forged Pistons
Stage III Clutch
Widebad O2 Sensor - AFR Gauage



I deleted air injection and EGR. So before I even put the motor I removed air and EGR (as well as skip shift) from the PCM. I also changed the injector flow rate to 42#/HR to match my injectors, and I changed the cylinder volume to 780ml/cl. (but I just did the math and I belive it should be 783.848 ml/cl for my 383). So that is all I changed in the PCM.

First start up was fine but a bit lean according to my Wideband. Driving it a bit I noticed some misfires at low rpm once it went into closed look and it was even more lean that before. it was in the 15-16:1 AFR. I changed the min coolant temp for closed loop to 150C so it would stay in open loop and now the AFR stays in the 13-14:1 area under throttle and the misfire went away (with the exception of quick bursts of throttle, just reving.. It will pop before it starts reving up)


So thats where I sit. im sure i dont want to use a speed density tune do I?.. what would you recommend?. Is there anything wrong with what I changed, is that the proper way to keep it in open loop?.



Once i get my laptop running I will get a scan and post it.

 

Bump for the good question. My similar engine (LE3 cam though, similar DCR, about 12.5 SCR) runs GREAT in open loop, and worse in closed loop - it's a bit sluggish at part throttle below 3k rpm, and pops/stumbles sometimes. I'd love to have it drive like it does for the first few minutes, all the time.

I've been pondering doing exactly what you did, but am worried about how far off the fueling might become without the feedback from the O2 sensors. My logs show quite a bit of enrichment (higher BLMs) but they change quite a bit and I don't trust the O2s in lower revs, as overlap is a factor. It runs pretty good with fresh ones, for a few hundred miles, but I'm awfully sick of replacing sensors every time it degrades. My WOT is dyno tuned, but my part throttle-tuning is DIY (timing mostly) and thus obviously not perfect. Do we need the O2 feedback for engine protection at part throttle?

One key consideration in my opinion is how the car runs right after a PCM reset, before the BLMs have re-learned. My car runs much better in closed loop AFTER the PCM relearns. Does yours? I think that says the O2's are actually helping, and I should keep them active. I think it would be required to get the BLMs corrected in the tune somehow first, before forcing open loop all the time. But so far I have been unable to do this. I'd pay pretty well if I could find a tuner that could dial in the BLMs consistently for me, but I don't know how possible that even is with the cam.

How are your BLMs?

 

Some searching reminded me of a couple of things.

1) VEmaster can help dial in the tables for a better tune in open loop.
2) Any changes to the car would not be adapted by fueling (but the MAF would still be active, so I'm not sure I believe this entirely, but it's from Injuneer so 99.99% likely correct!). If that's true, opening my cutout would throw thing out of whack.

I also realized that every time I drag race, the car is in open loop - not enough time to go closed from staging lane to launch. But that's mostly WOT anyway, which is open loop as I understand.

 

If you are running MAF mode open loop then you are using you LT BLM's not the VE tables. If you run better after a PM reset then your O2 readings are messing you up. There are 4 modes MAF open loop, MAF closed loop, SD open loop and SD closed loop. Vemaster requires SD closed loop to gather O2 feedback then corrects the VE tables based on that feedback. If you have O2 feedback problems then VEmaster will mess up your VE tables.

 

Unless I see datalogs and tune files I'm going to avoid the wild speculation present here.

Sometimes what people think is the o2 sensors screwing up is in fact the lt1 intake becoming heat soaked. These engines are terribly sensitive to that. It could also be timing there is a table for timing vs coolant temp too. Unless you guys post logs and files though its all just going to be wags.

Just flopping over into open loop isnt fixing the problem at all rather just avoiding it instead of putting in any real effort to determine the cause.

 

Bobdec thanks for shedding light on tuning modes available and under what conditions VEmaster is applicable.

Wild speculation? Is that what you think of describing a problem situation, and then sharing ideas and questions about what to look into and what to try? It's not like I said 'do this and it will fix your car'.

Believe me, in my case I have 2 years of mechanical diagnoses, dozens of logs, and a few dozen tunes worth of putting 'real effort' into trying to figure this out. It has not completely worked, so I'm hoping to learn more about the pros and cons of alternative tuning methods such as the idea raised by ENRKyle20.

It seems to me running a big cam with overlap, at low RPMs, does not work very well with O2 sensors - as I understand they mess thing up due to overlap letting unburned mixture (thus extra O2) into the exhaust. That seems to be possibly supported by my car and ENRKyle20 both running better when not using said sensors. So, it seems reasonable to investigate the issue, and the pros, cons, and methods available for not using the O2 sensors. And your contribution is to say it's foolish to discuss that without log files?

ENRKyle20, I am sorry to waist space here scolding, but I was interested to discuss your question and I don't appreciate the thread being dismissed as some kind of foolishness.

 

I didnt say it was foolishness. I said if you guys will post logs and tunes I will take a look.

My 24x/24x cammed 355 drives like stock with the o2's working. There are tricks to it but I cant give advice until I see what you are getting and why you are getting it.

The wild speculation bit is talking about wideband readings from open loop to closed loop and then talking about maf and speed density one right after the other. That isnt going to solve anything. You have to isolate the problem determine the cause and fix it, one bit at a time.

Maybe I will help him and you work on your issues if you post what I asked for, perhaps its because I dont want to spend all kinds of time talking about things that arent applicable. Or you can just get your feelings hurt and 'scold' me because that accomplishes alot.