Hey Guys,

So, is running in open loop all the time going to hurt anything? I am pretty sure I need to change over to heated o2 sensors to solve this, as i have coated longtubes and put the single wire o2s back on, but for the time being am i alright to drive as normal? Also, would constant open loop cause both fans to run all the time? 93 LT1 6sp. Thanks.

 

Why do you think it isn't going into closed loop?

 

I actually have no way to tell it isnt going closed loop right now, i am trying to make an appointment to verify for sure. But, the car is running rich and my gas mileage is pretty poor. But, since i am unsure what loop i'm in i just wanted to make sure that either way i wasnt going to hurt anything.

Any idea on why both fans are running from startup to shutdown?

 

Get a scanner on it, find out if you are in closed loop or not, and check to see if the O2s are working correctly. Check the fuel trim numbers.

It could be in closed loop but if the O2s are not working, that will kill your mileage as the ECM will default to a rich mixture.

But before you pay someone and get it scanned, pull the codes and see if there are any. It might give you some major clues especially if the oxygen sensors come up.

If you have codes and some other things happening, the ECM may go into limp home mode and run the fans for safety. But you have to find out what is the problems first.

 

Check the ECT (engine coolant temp sensor) on the front of the water pump. Also, if your digital temp gauge isn't working that indicates the ECT has a problem. The analog gauge gets it's info from a different switch on the right head, so if the analog work it has nothing to do with the digital or the ECT.

 

Rather than paying someone to scan the car, buy yourself a scanner (they aren't that expensive) and you will be able to check all your sensors and monitor open-closed loop.

 

I believe some auto part stores will scan for free...

 

Usually indicates a problem with the computer.

In open loop fans will still operate at the programmed temp .Car is in open loop on cold startup
and when everything is working correctly they don't turn on until the programmed engine temp is reached
independent of closed loop operation

Have you pulled the engine codes to see if anything showing?

 

Yeah, on a 96 or later ODBII car.

If a fault code exists in the ECM it will go into open loop, both fans will run. You do not need heated 02's. Your ECM is not setup for these. IF the engine is mostly stock the single wires are fine and what the ECM expects.

IS the CEL on?

FYI, on the scan tool, I have a entry level professional grade OTC Nemisys that does GM 81-07, Ford 8X to 07, Chryler 87-07.
Asian 8X-06. I got it on Ebay for $400, only used like 20 times. They are over $1200 new.

I get all kinds of Engine Data/Codes, ABS/ASR, Air Bag, CCM for my 93.
If your working on a modern car and do not have a scan tool....for many issues your kidding yourself. That is reality. Paper clip codes only go so far. You need to see the data the ECM is seeing. That or throw parts at it, your choice.

 

This $60 cable ,
http://www.aldlcable.com/
some free software and any old laptop will let you do the same and datalog ( record ) the engine running
for later playback and fault diagnosis

 

This is a good idea.

I got my scan tool for more than just my Corvette, however.

 

I ran the codes as i did have get the check engine light...Code 26; but this is due to the fact i removed my EGR/AIR. I did not know if the computer throws a code of any kind the fans will run regardless.

 

That should be enough to force an open loop situation.

 

There is no feedback to the PCM for AIR operation ( or not from it being deleted )
and EGR removal gets you a DTC 32

ECM CODES 1992 TO 1993:

Code #12: Normal No Codes.
Code #13: Left Oxygen Sensor Circuit.
Code #14: Coolant Temperature Sensor Circuit High.
Code #15: Coolant Temperature Sensor Circuit Low.
Code #16: Opti-Spark Ignition Timing System.( Low Pulse)
Code #21: Throttle Position Sensor Circuit High.
Code #22: Throttle Position Sensor Circuit Low.
Code #23: Intake Air Temperature Sensor Circuit Low.
Code #24: Vehicle Speed Sensor Circuit.
Code #25: Intake Temperature Sensor Circuit High.
Code #26: Quad-Driver Module #1 Circuit.
Code #27: Quad-Driver Module #2 Circuit.
Code #28: Quad-Driver Module #3 Circuit.
Code #32: Exhaust Gas Recirclation Circuit.

Some sites state DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit. ( as it is for 94/95 LT1 )

 

So, my next question, is it bad for the car to drive around like this?

 

For your wallet maybe given fuel economy out the window

 

On my car (1986) the SES light will flash at different rates for open or closed loop when terminals A & B on the ALDL connector are jumpered together.

The later cars probably also have a way to show open/closed loop status on the dashboard. Somebody else will have to supply this information, as I don't know how to get in that mode or what you will see.

 

My 95 vette has run open loop for 40 000 miles , it was imported with 02 delete as we did not have unleaded gas in 1995 in South Africa.
I use TTS datamaster and CATS tuner to get it running as well as it can under these conditions. I'm not really worried about gas mileage as if you buy a vette that should be low down on the totem pole , you want POWER!!! The o2 sensors in my car have been replaced by some sort of system that always shows .525volts or something like that.
I might be wrong , but fans on all the time might be a limp home mode rather than open loop.. ?

 

Sure about all that? Any C4 with headers might need heated O2s. Retrofitting 3 wires is common.

 

for the short term...no.
But long term running around rich and "out of tune" will casue a multitude of issues to appear at some point.
\Fouling of plugs and carbon build-up. Detonation from that build up. Oil contamination from excessive fuel or hydrocarbons. And worst of all...the washing of the cylinder walls from a constant rich mixture...which is NOT a good thing. Rich mix washes the micro-thin oil film off the cyl walls with each stroke. This is reduced lubrication of the top end, valve guides, rings. This is not a huge issue unless the mix is extremely rich or a little rich for a long time. Bottom line, running the engine for a long time with it unable to tune itself accellerates wear and ruins the oil faster. If it cannot maintain the 14.7:1 air/fuel ratio then its out of tune. Not an emergency but certainly worth fixing it.

This computer engine mngt and its precision is the ONLY reason why we get 250,000 miles and MORE out of high performance engines (any gas engine) these days. Back in the 60s and 70s the old school threw away a motor (whole car) at 100,000 miles because it was worn out....why? running rich because thats as good as it got with that technology. Now the same engines go 3 or 4 times longer because of the precise engine mngt,. and controls.

IMO there is no need to mess with the o2 sensors...they'll heat up to the min temps with long tube headers.....it just takes longer. You can sometimes move the bung closer. O2 sensors are just small generators...the hotter they get the more the voltage varies...the ECM reads that as a guide or reference to see what the oxy levels are...The sensor has to get to a certain point before it even starts to produce a signal, so being farther downstream just keeps it cold for a bit longer. There were some "kits" that provided a false o2 sensor signal that you could adjust for max performance(rich) or lean it out (econ) back to factory spec. Those never really went anywhere but some folks did use them to experiment with the ability to change the ECM parameters while in motion on OBD-I cars...The little package contained a battery to provide the false voltage signal with a **** to adjust it to full rich or full lean.

Sooner or later as the engine runs and acellerates the exhaust will increase and the temps spread to the sensor. Just takes longer to heat up being 2.5 ft away instead of 12" like it was... If you have a SES on then you are likely in LHM or stuck in open loop. Closed loop simply means the o2 sensor has completed the circle of sensor inputs. Open loop is the o2 sensor breaking that circle...or not able to provide input yet.
If you smell rich exhaust then you are looking for some other possible problems..like a dead cat,. injector issues, the need for a proper "tune" so the ECM isn;t getting confused by attempting to compensate for a lean exhaust by adding fuel with the injector band width. Thats a very likely scenario. Headers often create lean exhaust because they make the flow more efficient. ECM tries to compensate thinking the mix is wrong so it adds fuel when its not necessasy....and you get a rich smell. <---best bet for cash & prizes !