Closed loop fuel on my 3400 s/c

[john_V63400]

My engine is alive again. But I just noticed that I am running in closed loop on my fuel . Is this good or bad? I tried to change it on a scanner but it wouldn't let me. What should I do.

[sil]

closed loop is when the o2 and other sensors become "active" to the ecm, the ecm uses the sensors to adjust fuel n stuff

when you start the car it will run in open loop for a set amount of time, and untill the o2 is warm enough to provide quick cross counts and reliable readings

[john_V63400]

when I set it on open loops I notice my fuel air mix is right where it needs to be. So I was thinking i should just leave it open. But I changed it and it always move back to closed. would it br a good idea to run open loope or is that bad. Has anyone done it bfore

[SappySE107]

If you don't know what something is doing, its probably not a good idea to change it.

In open loop, the computer doesn't change fueling. If it doesn't change fueling, your fuel trims will stay at 0. This does not mean its perfect.

[john_V63400]

Ok nice. I will just leave it at closed then untill I tune it. I was curious cause soon as I changed it to open loop my fuel/air mixture went to rich. Fiquef that's a better place then lean.

[sil]

your prolly looking at the blms?
yea its gonna look 128 128 in open loops because the ecm isnt doin nothing to change the fueling.

then when it goes into closed loop you see the blm drop(rich, ecu trying to lean)

so in effect your running it richer in open loop than you would be in closed loop (going by what your telling us)

now if you drive like that and you have a lean spot in your VE the ecu wont correct in open loops and you risk ping, detonation, damage, loss of power due to spark retard(knock) ect.. ect..

and if your boosting its a really bad idea, unless your pro and run a wbo2 and tune everything dead on.

but downside to that is if atmosphere changes(gets cold or hot, rainy ect..) you lose your tune and you dont have the ecu to make those small adjustments for you

[zofo61]

John,

Are you running the RSM settup and did they "Program" and I use that term loosley, your PCM? If that is the case I suggest you get a spare PCM to tune with.

[john_V63400]

I finally scanned my pcm that rsm sent with the supercharger and it is almost identicale to the stock bin file. The only changes were in the fan settings. The were chaged to go on earlier. Thas it. And it wasnt locked. I am chaging the flow rate to 28#'s it id still set at 21.3. J have the injectors from
the trail blazer.

[sprucegagt]

I believe we told you the RSM PCM was junk some time ago for just the reason you found out. Why are you still using it?

[john_V63400]

cause it unlocked and its stock, and I'm tuning as we speak.

[zofo61]

....but you are still running without a MAF............you really need to put it back in line and get the MAF tables right before you tune anymore without it.