Open or Closed Loop

[John Robinson]

Is there a way to know if you are in Open or Closed Loop while driving. I have heard that you can get a reading on the CIC screen while driving. If so how do I do that? I just recently took a trip and my gas mileage on the road was only 18 MPG down from a normal 26 MPG. The mileage drop leads me to wonder if it is not going into closed loop on the road. The other possibility I can think of would be a problem with the EGR.

 

[Hib Halverson]

If the engine is not going into closed loop there's likely be a fault code and the engine light on but, even if it did run in open loop during highway driving, if all else is working right, the difference would not be as large as that between 18 and 26 mph.

If there was an EGR issue, the engine light would, also, likely be on.

I'd look for a problem that won't usually turn the light on.

Leaking injectors?
Restricted intake air flow?
Oxygen sensors "lazy" or starting to fail?
Restricted exhaust flow?

 

[Schrade]

If it IS staying in closed loop, your cats will foul in short order. Get a scan printed out, and post up here...

 

[John Robinson]

If it IS staying in closed loop, your cats will foul in short order. Get a scan printed out, and post up here...

I am working on getting a computer hook up to my obd1 that will record what the engine is doing as I am driving it. I will post the results if I can do that. It may be a few days before I can accomplish this. Stay tuned for an update when I have one.

 

[89Z51]

Open vs. closed

Is there a way to know if you are in Open or Closed Loop while driving. I have heard that you can get a reading on the CIC screen while driving. If so how do I do that? I just recently took a trip and my gas mileage on the road was only 18 MPG down from a normal 26 MPG. The mileage drop leads me to wonder if it is not going into closed loop on the road. The other possibility I can think of would be a problem with the EGR.

I agree with previous comments about "open loop" engine management being the norm under limited circumstances only (during warmup in particular). Normally, if the engine were to go into open loop management during normal driving, it would be the result of an "out of normal range" sensor input or similar and would be accompanied by a CEL. The only exception "might" be in the event that the ECM thought the engine never warmed up, thus persistent "open loop". As far as what might cause abnormal fuel economy, (very) excessive exhaust gas recirculation, excessive exhaust restriction, a sensor "going goofy", but yet not so far out of whack as to trigger a CEL, etc. Also, perhaps something is dragging in the drive train somewhere. The engine is relatively powerful, so driveability might not suffer with extra "drag", but it might manifest itself in poor fuel economy.

 

[John Robinson]

Hi guys I wont be able to follow up on your suggestions for awhile as l am getting my own tune up at the hospital.

 

[roger longman]

Hi John, You'll be back in no time. Good as new........Roger..

 

[John Robinson]

Well I am home again. I salvaged the air hose they had me hooked up to while in the hospital and have used it to replace some vacuum lines. That may not be good for the long term but I now have the instant mileage showing 28 to 31 on cruise before it was 18 to 22. I will have to get the right kind of hose but this makes me think I had a vacuum leak in the EGR system. I think my next vacuum hose to replace is the one to the vacuum can.

 

[WhalePirot]

I fixed an open loop issue, evidenced by the O/D cycling on/off at steady speed on an open, level road by changing the (then stock, but old) plug wires.

There were no codes indicated and the wire change was the ONLY change.

 

[John Robinson]

I replaced the fuel pressure regulator that was bad. It was so bad that the engine was hydro locked with the crank being full of oil and gas. I suspect this is what was causing my excessive fuel consumption.

 

[vetteoz]

If it IS staying in closed loop, your cats will foul in short order..

Other way around
Closed loop is when the ECM has control of the fueling and adjusts it to engine requirements
OPEN loop is when it is fueled direct from the fixed tables in the tune

 

[Hib Halverson]

If it IS staying in closed loop, your cats will foul in short order.

Catalytic converters do not "foul" when the engine stays in closed loop. In fact, for the cats to work best, the engine needs to run in closed loop. Cats won't foul in open loop, either, as long as the engine is running properly.

When will the cat's "foul"?

If the engine is running overly rich or lean, they will be damaged. If the engine is burning a lot of oil, they'll be fouled. If the engine burns leaded gas, they'll be fouled.

 

[xfirez51]

This thread is full of inaccurate info regarding Open and Closed Loop. :eyerole:ugh

 

[LLC5]

This thread is full of inaccurate info regarding Open and Closed Loop. :eyerole:ugh

Very true, but vetteoz has it correct. Coolant will also disable a catalytic converter.

 

[vigman]

And carb cleaner

( ask me how I know ) .. it was on a FORD though