What is open loop-drive and is it normal?

Trevlaw

Trevlaw

Sketchy Machinist
Supporting Member
Ride of the Month Winner
Joined
Jan 8, 2021
Messages
678
Location
Corvallis, OR
So I've searched around a bit and found some info on jaguar forums, but nothing TJ specific. It seems like Open Loop-Drive is a mode the computer may switch to during heavy acceleration where it sets fuel output to max. I'd like to get a bit more clarification on that.

This is all on a 2002 TJ with the 4.0 and 32rh. Basically a stock motor, no tunes or add ons. Several months ago I had to replace my cats, used the flowmaster kit and redid my exhaust setup at the same time. Had to fiddle with how rigid my mounting was and I may have caused a new manifold leak in the process, but I have several small leaks at the head.

A month or so goes by and my mileage seemed to be getting worse, went ahead and did new plugs (autolite iridiums) and NGK O2 sensors. Didn't seem to help, kept driving it. Then it threw a code, scanned it and it was a cam sensor code. Replaced that and still no change. Kept using my coworkers scan tool to monitor O2 sensor voltages while driving and they all seemed to be normal.

That's when I noticed the computer would start in OL when first started and switch to CL in about 15-30 seconds. It remained in closed loop while driving except when I'm cruising on the highway. I'm geared with 4.56's on 33's so my RPM's are a touch above stock. I turn about 3200rpm at about 65mph. If I cruise at 3k it stay on CL, but if I need more gas for an incline or just go faster, when I hit 3200rpm or about 45% load on the scanner it will switch to OL-Drive and stay there until my RPM's drop again.

Does anyone know if this is normal behavior? I'm not finding any mention of it anywhere regarding a stock motor, seen a bit with regards to custom tunes on different motors. I'm wondering if this might be a cause of my mileage, but idk how long it has done this. The motor seems to run the same as always and that cam sensor code is the first code I've ever thrown in 100k miles. Probably put a couple thousand on it since I discovered this and it's been fine
 
It is normal for the computer to be in open loop when you first start the engine it will transition into closed loop when the engine reaches around 170-180 degrees and it is also normal to switch to open loop after short delay when increasing to full throttle as you experienced.
 
1515art said:
It is normal for the computer to be in open loop when you first start the engine it will transition into closed loop when the engine reaches around 170-180 degrees and it is also normal to switch to open loop after short delay when increasing to full throttle as you experienced.
Click to expand...
But I'm not at full throttle, I could sit on the highway at 65mph, 3200rpm and 45% load for hours and it would be in OL-Drive the entire time. That doesn't seem normal to me
 
Trevlaw said:
But I'm not at full throttle, I could sit on the highway at 65mph, 3200rpm and 45% load for hours and it would be in OL-Drive the entire time. That doesn't seem normal to me
Click to expand...
Somethings not right could also be throttle position sensor? At any rate if it’s in open loop at 45% throttle you are running much too rich and would account for poorer than usual fuel economy. You mentioned possibly some vacuum leaks this can throw off the readings to the O2 sensors too if you are rich are you getting any indication of unburned fuel building up in the crankcase oil?
 
1515art said:
Somethings not right could also be throttle position sensor? At any rate if it’s in open loop at 45% throttle you are running much too rich and would account for poorer than usual fuel economy. You mentioned possibly some vacuum leaks this can throw off the readings to the O2 sensors too if you are rich are you getting any indication of unburned fuel building up in the crankcase oil?
Click to expand...
What are indicators of having unburned fuel in the oil? I don't know of any way to check that.

Yes there are some leaks at the exhaust manifold gasket, I've been meaning to replace it, just haven't found the time yet. I'm sure that's not helping my cause, but not sure if it's entirely related. I used to pretty much always get 13mpg, no matter how I drove it, now I'm closer to 11ish lately. I probably wouldn't even have bothered to check it out if I hadn't noticed the OL-Drive thing. Kinda figure of that was caused just by the exhaust leaks there'd be a lot more mention of it it online from guys with leaks lol
 
Might be normal. Calculated load on scan tools is BS. Very normally they never go from 0-100%. What is the TPS percentage and voltage as well as the MAP sensor pressure and voltage? That will give you a better idea of the actual load the engine is at. I can tell you before I went turbo I did several logs and it was going open loop while cruising on the freeway quite frequently.
 
  • USA Proud
Reactions: CharlesHS
As previous posted... there could be a vacuum leak around the throttle body base or throttle shaft. The MAP sensor could be sending bad voltages to the ECU or the IAT sensor could be reading incorrectly at higher RPMs throwing the Fuel Management into OL.
 
Jezza said:
Might be normal. Calculated load on scan tools is BS. Very normally they never go from 0-100%. What is the TPS percentage and voltage as well as the MAP sensor pressure and voltage? That will give you a better idea of the actual load the engine is at. I can tell you before I went turbo I did several logs and it was going open loop while cruising on the freeway quite frequently.
Click to expand...
Hmm ok, I'll have to borrow the scanner again from my friend this week, then I'll try and get some of that data.
 
CharlesHS said:
As previous posted... there could be a vacuum leak around the throttle body base or throttle shaft. The MAP sensor could be sending bad voltages to the ECU or the IAT sensor could be reading incorrectly at higher RPMs throwing the Fuel Management into OL.
Click to expand...
Ok, I'll try and get those things checked out soon and see if I find anything
 
I checked mine with an older simple live data/code scanner tool. When I drive on the freeway at @65 mph I can stay in CL unless I’m on a steeper hill and trying to keep up 65 mph. At 70 mph it will cruise in CL but most any common uphill grade on the rolling terrain around here puts it in OL if I try to keep up the pace. i average 14-ish when I cruise at 65+ ish. Keeping 70 or up for any significant time drops that to 12.5 - 13 average for the tank.
I’ve got the 4.0l, 32 trans, 4.11, and 35” KO2s. It’s not a good combo but I can keep up in town and still cruise the highway at decent speed. Mountain passes out west are its biggest challenge. I’ll likely go to 33’s someday.
 
  • Like
Reactions: Blondie70
TeeJohn said:
I checked mine with an older simple live data/code scanner tool. When I drive on the freeway at @65 mph I can stay in CL unless I’m on a steeper hill and trying to keep up 65 mph. At 70 mph it will cruise in CL but most any common uphill grade on the rolling terrain around here puts it in OL if I try to keep up the pace. i average 14-ish when I cruise at 65+ ish. Keeping 70 or up for any significant time drops that to 12.5 - 13 average for the tank.
I’ve got the 4.0l, 32 trans, 4.11, and 35” KO2s. It’s not a good combo but I can keep up in town and still cruise the highway at decent speed. Mountain passes out west are its biggest challenge. I’ll likely go to 33’s someday.
Click to expand...
Interesting, that's good to know. Does your scanner just say OL or OL-Drive? Mine says the OL-Drive, idk if there's any significance to that or not though.

I was able to borrow my coworkers scanner today, but it's not as in depth as I thought it was. The jeep is still acting the same way. I can get to about 3200 rpm in CL then after that it switches to OL-Drive. It doesn't give me any voltages besides O2's. The "absolute throttle position" was about 28-30% cruising in OL, and didn't seem to have any weird fluctuations. Was pulling about 19-20 inches of vacuum from the MAP cruising in OL, drops to around 12 if I let off the gas some and about 8-10 at idle.

All of the O2 voltages seemed to be fluctuating between low and high like they should right up into OL-Drive, then they all peg at .840v. Not sure if any of this info is helpful, I don't know much about this stuff. I have a friend with a lot more in depth scanner I could probably use sometime, almost positive that would get me all of the voltage readings and stuff
 
After starting the engine and the initial switch to closed loop, the pcm switches to OL for two reasons.

The first is Power Enrichment mode where in an effort to make power the PCM reverts to preset tables rather than the feedback from the 02s to determine the AFR so it can target closer to 12.6 rather than stoich.

The second reason is catalytic converter protection. At higher loads and subsequent exhaust temps, the pcm switches to open loop to add fuel and cool the converter.
 
  • Like
Reactions: Blondie70
Trevlaw said:
Interesting, that's good to know. Does your scanner just say OL or OL-Drive? Mine says the OL-Drive, idk if there's any significance to that or not though.

I was able to borrow my coworkers scanner today, but it's not as in depth as I thought it was. The jeep is still acting the same way. I can get to about 3200 rpm in CL then after that it switches to OL-Drive. It doesn't give me any voltages besides O2's. The "absolute throttle position" was about 28-30% cruising in OL, and didn't seem to have any weird fluctuations. Was pulling about 19-20 inches of vacuum from the MAP cruising in OL, drops to around 12 if I let off the gas some and about 8-10 at idle.

All of the O2 voltages seemed to be fluctuating between low and high like they should right up into OL-Drive, then they all peg at .840v. Not sure if any of this info is helpful, I don't know much about this stuff. I have a friend with a lot more in depth scanner I could probably use sometime, almost positive that would get me all of the voltage readings and stuff
Click to expand...
My scanner did say OL and drive but they were separated by something. The scanner doesn’t really seem to give real-time data for some of the info and I hate to fiddle it much while driving.
I would guess that even though I’m not at WOT the demand is considered as much with the low manifold vacuum vs rpm. It takes a lot of HP to push these bricks at 70 mph. Not one single thing is aimed at fuel savings or aerodynamics. I don’t even have an overdrive. I could probably tow it on a trailer behind my diesel pickup and get better mileage.
 
You’re Jeep should go into closed loop when the o2 sensors reach operating temp. Open loop is for the ecu to adjust fuel mix like at full throttle or over a certain load percentage. Closed loop is more for emissions and fuel mileage. If you have a chip or some sort of performance tune it could be deleting the after cat o2. They usually just set them or the one in your case to a specific voltage that influences the tune from the front sensors. Or you could just simply have a bad o2 sensor.
 
Juggernaut said:
After starting the engine and the initial switch to closed loop, the pcm switches to OL for two reasons.

The first is Power Enrichment mode where in an effort to make power the PCM reverts to preset tables rather than the feedback from the 02s to determine the AFR so it can target closer to 12.6 rather than stoich.

The second reason is catalytic converter protection. At higher loads and subsequent exhaust temps, the pcm switches to open loop to add fuel and cool the converter.
Click to expand...
Interesting, I wasn't aware of that. It hadn't occured to me that going to OL would produce more power than CL, that makes sense that it would switch at the higher loads I see on the highway. It's sounding like mine maybe just switching a bit earlier due to it being geared for 35's and only running 33's.
 
Top Bottom
Back