Fbody1

why would my car run so smothly when it is in open loop, and as soon as it goes to closed loop it runs a little rougher, I have just replaced both 02 sens, plugs /wiers ? it is'nt really bad ,but I would like it to run as smooth as it does in open loop.

Honda Hunter

Hook it up to a datalogger and see what the o2's are reading. Could be getting a false lean or something. It runs good because in open loop it's running on a base set of numbers. Once in closed loop it's reading the o2's etc and compensating to reach stoich.

transAMdriv3r

i hear ya, i feel like i can take on the world but as soon as it hit 210 i feel like a stationwagon can outrun me

i heard that madz28 tune eliminates the o2 sensors

EVERESTZ28

what kind of mpg can loose if you program your pcm to be open loop always?

Fbody1

I have a data log that I done last weekend , what should the 02 be , just crusing, I see that they are jumping from high to low , but what is ideal?

transAMdriv3r

i am aleast happy this isnt anything mechanical because i recently just rebuild my engine compleatly, but i started to run out of money and need it to get on the road pronto so i put the original intake manifold, o2 sensors, fuel injectors, and all the excessories including opti and plug wires.some of the vacuum hoses are new. I bought bosch split fire plugs and when i took them out for a plug check, they were all carboned up so im thinking that this mabe a combination of needing new 02 sensors, new spark plugs and plug wires that are recomended for this vehicle, with new fuel injectors and fuel pressure regulater, egr, fuel pump and mostly everything on the outside of this motor.

Injuneer

Interpreting scanner data - read the section on air/fuel management:

http://members.aol.com/InjuneerZZ/ScanMast.htm

Just to clarify... when you start the engine in open loop, it is not "running on a base set of numbers". Its functioning exactly the way it normally does, using the long term fuel corrections that are stored in Cells 16, 17 and 18. The main difference is that "learning" is disabled, and the short term fuel corrections are not used. And its not using Cells 01-15. That tends to indicate its a problem with the PCM getting bad data from the O2 sensors and assuming the engine is running very rich or very lean. It can only correct in open loop by +25% and -15% using the stored long terms. It can't continue to correct using the short terms like it can in closed loop. The false data is causing it to totally over-correct in closed loop using the short terms.... assuming the temperature reading gets high enough to kick the PCM into closed loop.

Look also at the coolant temp sensor. IF its showing an incorrect low temperature, its causing the PCM to add fuel for cold start enrichment, and keep adding that fuel even if the coolant is warmed up.

If you have a data log, you can post it on ".csv" format and people can take a look at it for problems.


does not suddenly run on

Fbody1

do I need to copy all the values or the ones like bpw-L-R, 02 L-R, rpm, tps, ? it is alot of information . thanks

Injuneer

You data logging software should have an option to export the complete file in ".csv" format. You shouldn't have to "copy" anything.