radz282003

iTrader: (1)

Good day all.

My understanding is " open loop " is when the PCM refers to preestablished tables, and does not refer to the O2s for input, to make adjustments. First, is this understanding correct, and second, is if the vehicle is tuned in this mode ( or " closed loop " if I am wrong ), will the vehicle refer to the other sensors for input? For example, will it still refer to the air temp sensor? I mean, if the vehicle was tuned in low temperatures, will it still know when it' s 100* outside, and pull timing if necessary? Will it know if it was tuned at sea level, that it is now a 7000', and adjsut the A/F ratio correctly?

Thanks for your input

Chuck

MeentSS02

iTrader: (11)

Open loop refers to the feedback system... i.e. your O2 sensors. It still uses all other sensors that it would normally use in its airflow and other calculations, it just won't use the O2 sensors to see if it is on the right track or not.

dhdenney

iTrader: (53)

About the last part of the question, your MAF should be able to compensate for the density of the air, ie: it should be able to adjust your engine's parameters for the thinner air of 7000'. I drove mine around in speed density this summer (no MAF) and it was ok during the day but when the sun went down and it cooled off, boy I knew the MAF was gone then. It drove like ***. I plugged it back up and reflashed the PCM real quick. I personally think open loop is fine. I drove mine like that a while in open loop. I went back to the O2's and seemed to run a little richer. I will probably be going back to OL since my O2's are burning down from race gas. Someone said the VE has to be tuned properly for a proper OL mode which mine have been scaled by VE Master. Someone also told me that PE doesn't use O2's so theoretically WOT would be unaffected.

Bombguy99z28

There are a host of sensors that the vehicle uses, all open loop means is that it is not using feedback and correction. Closed loop is for fuel economy and emmissions. Everything will work fine.

The second part of your question, I believe when you first start your car the MAP sensor takes a reading of actual atmospheric barometric pressure to use as a baseline correlation of the VE table, which would compensate for altitude. How well it works in actuality, I don't know, I very rarely leave San Diego.

radz282003

iTrader: (1)

Thanks all, for your input. I appreciate it. I was just curious, because when it was tuned, I remembered hearing my car was being a bear to tune, it was jsut better to put it into open loop. After trying some research, I started to get a little scared about the PCM not compansating for atmospheric variables and for elevation changes, and what not.

Thanks everyone

itchygomey98

iTrader: (2)

Not quite, but you have the right idea - The PCM will use actual manifold pressure. For example: 4000 RPMs with 40% Throttle position at sea level will provide manifold pressure of X and land you in the appropriate VE cell.

At higher elevation, there is less atmospheric pressure so the same 4000 RPMs with 40% Throttle position will provide a different manifold pressure which will put you in a different VE cell.

I tuned my car open loop here (15ft above sea level) and drove it to North Dakota and back with my wideband commander and had NO A/F problems.

Bombguy99z28

Yeah, I guess thats what manifold ABSOLUTE pressure means.. I get mixed up sometimes, I've been reading some aftermarket efi stuff and it takes a baseline of preignition MAP as a correlation factor.