tonytmorgan

Could I gt a brief explanation of open loop/closed loop. I know a little (I think) but want to be sure I have a good understanding. I am also wondering at what temp it switches?
Thanks

Dale1990

Quick and dirty explanation...

Open Loop: Engine runs on only pre-programmed values using the MAF/MAP sensor, Coolant Temp, TPS, RPM and Knock sensor to adjust the Fuel/Timing values.

Closed Loop: Engine uses the O2 sensor to "trim" the pre-programmed fueling values to match the desired Air-Fuel ratio (14.7:1 or so).

The switching temp is somewhere around 150* I think. The value can be changed in the chip. I lowered mine but I can't remember what it was.

93-383

I would have to pull out the book to look up the inital conditions required for closed loop operation. But the simple explanation is under open loop varous sensors (depending on design) feed input to the ECU to determine pulse output to the injectors these typicaly include MAP, MAF, coolant temp, intake air temp, throttle possition sensor. In closed loop only one sensor provides the input for operation the O2 sensor. closed loop is used when the engine is fairly stable in an rpm for a given time (constant speed). Open loop is in operation during idle, start, acceleration/ deceleration or major load change (hill).

tonytmorgan

Thanks. That helps. I have been struggling to get an 88 running. Long story...two seperate threads. It exhibits symptoms of a leaking injector/s. At cold start it runs terrible and rich so I pull the FP fuse and it idles smooth running off of residual fuel in system. When temp gets to about 155 degrees I can put fuse back in and it runs pretty good (sometimes). Working with FI, ECM and all these sensors is new to me.

CFI-EFI

There is a lot of wrong, and bad information in the post, above, by 93-383.

Without going into all the details of how and why, a simple analogy for open/closed loop would be to picture a circle, or a simple electrical circuit. A whole circle is a closed "loop", or a complete circuit with a light on. If you break that circle, or turn off the switch to shut off the light, you have an open circle, an open circuit, or an open loop.

You have some serious wiring problems, at a minimum, with that car. The engine shouldn't run but a few seconds, not until warmed up, with the fuel pump fuse pulled. The fuel pump is receiving power from somewhere it shouldn't.

When you pull the fuel pump fuse, it SHOULD open the fuel pump circuit and shut off the fuel pump.

RACE ON!!

tonytmorgan

I believe that when I pull the fuse the pump stops and car continues to idle a few minutes from residual fuel and pressure in the fuel rails. My FP gauge does drop to zero and after a few minutes the car will stall. The car will not run on and on w/out the FP fuse in place.

redrose

cold start = open loop.
warmed up (typ 2-3 min run time) = closed loop.
warm w/ throttle 75% or + open ( aka W.O.T.) = open loop.

check your coolant temp sensor, resistance (ohms) cold engine/ warm engine and compare with Service Manual values (post em up here if you don't have a SM and i/someone will check)...prolly just that simple.

tonytmorgan

I just put a new CTS in it about a week ago. As I said earlier it's kind of a long story. I just got this car about a month ago, towed it home after it had sat for 3 yrs. Acts like a leaking FI but when I checked them I found none leaking but noticed two of them don't match the other six. I'm thinking of putting in all new FI's. Everything else I have looked at checks out. No codes, etc.

redrose

check the new CTS just to be sure its ''on calibration'', have seen several new ones that were silly.

old injectors may ''gum up'', esp after 3 yr nap...unplug injectors one at a time while idling and see if any change.

did you pump the old gas out and put in fresh ??

tonytmorgan

I will work on checking the new CTS. Yes I drained gas and installed new filter. When this car runs it runs good. But after I shut it off it fuel pressure leaks down (sometimes) and then upon restart it is flooded. Pulled fuel rail and found no leaking injectors.

redrose

fuel pressure ideally would hold forever after shut-down, most don't...slow decay of press is normal, should still hold 10 psi after 12 hr ''key-off'', rapid drop to ''o'' may be due to leaking injector or bad diaphram in pressure regulator (several other causes for press drop that do not cause flooding) which can bleed thru vacuum line to press reg and into manifold...pull the little hose that runs from the press reg to the plenum and smell for gasoline odor, should not be any.

tonytmorgan

I have checked that also. No fuel smell and it hlds vacuum. I believe the FPR is OK. I have talked to several people on and off of this forum and I think it is time to replace the injectors. The car is 19 yrs old and sta for the last 3.

redrose

new squirters certainly won't hurt (other than your beer money)...another check of the press reg, please do this outdoors and with a helper in the car: with that ''little hose'' to the prees reg unhooked from the plenum, start the car and see if gas sprays all over from it (have phone number of raincoat guys at hand).

your symptoms of ''poor operation in open loop'' and ''runs good when it runs'' do strongly indicate too much fuel is being delivered...in closed loop the ecm is likely seeing the ''rich'' condition and compensating (dammed things can do something right once in a while) and a rich mixture revs good (altho not max power)

rickneworleansla

http://www.customefis.com/GMEFI.html

http://www.themotorbookstore.com/cor...injection.html

http://www.themotorbookstore.com/che...injection.html

arieswebb

Open Loop

Open loop simply means there is no feedback of the result to the ECU. In our case, it means there is no sensing or measuring of the exhaust gas to see how the bike is running. The fuel injected is determined by the RPM and throttle position, derived from fuel injector pulse width numbers stored in the fuel maps, and is trimmed for environmental conditions due to air temperature, air pressure and engine temperature.

Closed Loop

Closed loop means there is feedback of the result to the ECU. In our case, it means there is sensing or measuring of the exhaust gas to see how the bike is running. This sensing is done by a probe (a galvanic cell) which generates a voltage based on the gas around it. These probes are referred to as Oxygen sensors, Lambda sensors, O2 sensors, Exhaust Gas sensors and probably a few other names as well.

I Hope This Helps !
Bob M.