Open/ closed loop fuel operation

[jdenning002]

I have been having some issues with my car lately... (There are several posts...)

It has been running rough, and I noticed that on the highway the car goes into "open loop" mode when I let off the throttle (I have a scanguge) and the fuel pressure goes up to 50, 60, 70 or 80 PSI! The RPMs drop when the fuel pressure goes up... This happens almost all the time and will go up and down until I tough the gas pedal again...

I have no idea why it would kick into open loop...

I have done a bunch of research and it looks like open loop is only for warm-up or WOT...The ECT reads 180 and up when this occurs... and well into the drive.

I also have the Check Engine Light on, codes 2195 and 2197= engine running lean....??? WTF?? it seems to be running rich. Cleared the codes and they came back.

In closed loop mode the fuel pressure needle is always moving/fluttering around... but fairly steady.

I have data logged, and I dont see anythign crazy, except STFT values off a bit...

I have searched and searched for a vacuum leak, but everything looks okay...

Car has 125K on it, novi 1200 s/c kit has been on for 50K...

Could it be a tune issue, bad sensor somewhere or bad ECM???

2 other items,

My A/C is also intermittent, the compressor itself is not kicking on, the computer is commanding it on, but it does not kick on... I would think it is un-related to the other stuff... but I wanted to mention it.

The trans shifts seem hard/ off at lower throttle, and the first shift is weird, the RPMS drop sharply right when the shift occurs...


ANY IDEAS?? THANKS!

[Paul]

I am just guessing, but perhaps the fuel rail pressure sensor (frps) or oxygen sensor(s) are failing?

ok, just read other thread and those are all new. How about electrical grounds? Is one missing or bad? (another WAG)

[ctrlraven]

Only very few times when I am coasting down a long hill with my foot off the gas will my ScanGauge tell me the fuel loop is open, as soon as I touch the throttle it goes closed again.

[Paul T. Casey]

Going down hill with your foot off the pedal, the computer is shutting off fuel injectors sporatically (not sure of the sequence or duration). This may account for the pressure going up.

Lean codes would cause the engine to run rich, as it is telling the computer to add fuel to compensate for the problem. Could be bad O2 sensors, or clogged cats (my first 2 guesses).

Hope it helps a little.

[Krytin]

It does sound like a sensor - O2's or maybe the TPS?

Good luck and let us know how you make out!

[Marauderjack]

Mine has always shown a fuel pressure spike when I let off the accelerator (ScanGauge).....depending on temperature it spikes from 55 PSI to 90+ PSI for as long as I stay off the throttle!!:cool:

I have never looked at the "closed or open loop" while coasting but I'll check it today!!:confused:

I have 202,600 miles with almost 120K of those miles with the ProCharger and it has always done it even when I had the AutoMeter analog FP gauge that only read "Net" pressure!!:beer:

I'll report back on the "Loop" thing??

[jdenning002]

Thanks for all the replies...

The O2 sensors are new, the TPS is new, FRPS is new, I have NO CATS...

I will check on the grounds, I doubt it... I have a few upgraded grounds from when I replaced my alternator...

I guess I am going to have to take it to a shop...

[Stranger in the Black Sedan]

the open loop may be just a normal decel fuel enleanment/cutoff routine, a lot of cars do that. The jump to open loop under closed throttle decel, alone, may not be an indicator of a problem

[dohc324ci]

Thanks for all the replies...

The O2 sensors are new, the TPS is new, FRPS is new, I have NO CATS...

I will check on the grounds, I doubt it... I have a few upgraded grounds from when I replaced my alternator...

I guess I am going to have to take it to a shop...

You have no cats? how did you pass smog in cali?

[MM_BKK]

There are 3 basic conditions that the engine will go open-loop:

1-Initial start up when cool.

2-Wide Open Throttle or throttle position more than 70% opened.

3-Closed Throttle deceleration.

On condition #3, the injectors will also shut off and that is why the fuel pressure will spike up during this time. With the injectors shutting off also helps on suppressing the backfire on decel which would be more noticable without cats on some cars.
These are all normal conditions and there's nothing to worry about.

With codes 2195 & 2197, that sounds like both front O2 sensors not putting out voltage (they put out voltage when sense unburn fuel) and the PCM keeps adding fuel but the O2s are not sensing that it's getting richer and eventually the PCM see a "false" lean condition and threw the codes and it probably smells really rich in reality.

You'll need an OBDII reader with live data reading capabilty and check the two front O2S1 Bank 1 & 2 and see if the voltage are fluctuating or just sitting still. They should be fluctuating over and then under .480 Volts rapidly. If not then your new O2s may be dead and that will tell the PCM to add more fuel because it thinks the engine is lean.

As far as the AC, you'll need to hook up manifold gauge set and see what the pressure readings are. There are protection sensors. If you are low on freon, the compressor won't engage.

[-Matt-]

There are 3 basic conditions that the engine will go open-loop:

1-Initial start up when cool.

2-Wide Open Throttle or throttle position more than 70% opened.

3-Closed Throttle deceleration.

On condition #3, the injectors will also shut off and that is why the fuel pressure will spike up during this time. With the injectors shutting off also helps on suppressing the backfire on decel which would be more noticable without cats on some cars.
These are all normal conditions and there's nothing to worry about.

With codes 2195 & 2197, that sounds like both front O2 sensors not putting out voltage (they put out voltage when sense unburn fuel) and the PCM keeps adding fuel but the O2s are not sensing that it's getting richer and eventually the PCM see a "false" lean condition and threw the codes and it probably smells really rich in reality.

You'll need an OBDII reader with live data reading capabilty and check the two front O2S1 Bank 1 & 2 and see if the voltage are fluctuating or just sitting still. They should be fluctuating over and then under .480 Volts rapidly. If not then your new O2s may be dead and that will tell the PCM to add more fuel because it thinks the engine is lean.

As far as the AC, you'll need to hook up manifold gauge set and see what the pressure readings are. There are protection sensors. If you are low on freon, the compressor won't engage.



Good info! I just learned some new stuff :2thumbs:

[Marauderjack]

Good info! I just learned some new stuff :2thumbs:


^^+1^^:beer:

I meant to check mine with the ScanGauge yesterday but forgot......:alone:

CRS!!:cool:

[Marauderjack]

I just checked it and it goes into "open loop" when coasting but mine stays in "closed loop" at WOT.....tried it twice 6300 RPM's, 9.5 PSI and SPINNING LIKE CRAZY!!!!:burnout::beer::banan a2:

[Dennis Reinhart]

I have been having some issues with my car lately... (There are several posts...)

It has been running rough, and I noticed that on the highway the car goes into "open loop" mode when I let off the throttle (I have a scanguge) and the fuel pressure goes up to 50, 60, 70 or 80 PSI! The RPMs drop when the fuel pressure goes up... This happens almost all the time and will go up and down until I tough the gas pedal again...

I have no idea why it would kick into open loop...

I have done a bunch of research and it looks like open loop is only for warm-up or WOT...The ECT reads 180 and up when this occurs... and well into the drive.

I also have the Check Engine Light on, codes 2195 and 2197= engine running lean....??? WTF?? it seems to be running rich. Cleared the codes and they came back.

In closed loop mode the fuel pressure needle is always moving/fluttering around... but fairly steady.

I have data logged, and I dont see anythign crazy, except STFT values off a bit...

I have searched and searched for a vacuum leak, but everything looks okay...

Car has 125K on it, novi 1200 s/c kit has been on for 50K...

Could it be a tune issue, bad sensor somewhere or bad ECM???

2 other items,

My A/C is also intermittent, the compressor itself is not kicking on, the computer is commanding it on, but it does not kick on... I would think it is un-related to the other stuff... but I wanted to mention it.

The trans shifts seem hard/ off at lower throttle, and the first shift is weird, the RPMS drop sharply right when the shift occurs...


ANY IDEAS?? THANKS!

John the AC is one of the wires that did have to be switched, so now this may be that the pins have pulled back in the conector, again the AC worked perfect when it left here?? none of this started till the blower swap, but any thing is possible. I will find out out what four wires we changed, but I still do not see how this will cause the issue, with the tune the four wires only relate to AC and Trans, data log the car for STFT Maf count and load and RPM and send me the data.

[MM_BKK]

I just checked it and it goes into "open loop" when coasting but mine stays in "closed loop" at WOT.....tried it twice 6300 RPM's, 9.5 PSI and SPINNING LIKE CRAZY!!!!:burnout::beer::banan a2:

How many seconds were you at WOT?
There is a scaler in the tune for 'WOT open loop delay time'.
I would suggest you have it set to "0" so that your A/F will get commanded immediately instead of working through close loop for WOT which could be hazard to your motor.
This is not something you can adjust with your flasher device unless you have SCT PRP or similiar software. You'll have to ask your tuner to check your tune file.

[Marauderjack]

WOT all the way through 1-2 shift and deep into 2nd gear....75 MPH or so??

I can have my tuner guy look into it but I've been doing this for almost 120K miles and hundreds of WOT "Blower Runs" without incident...I guess??:cool:

The ScanGauge has a sample rate of a second or two and it could be it just never displayed it.......:confused:

[MM_BKK]

Yes the ScanGuage has about 1-2 seconds lag. If you're spinning 1st & 2nd, you could be at 75 mph in like 3 seconds? There could be as much as 5 seconds delay in the tune.

Can you honestly say that you were looking at the scanguage for a solid 5 seconds while at WOT? I know it's kind of dangerous while trying to counter steer. You might want to have a co-pilot look at it.

[jdenning002]

I do agree that the open loop for decel is normal, however I am getting up and down fuel pressure and rpms... I have always noticed the open loop in decel, but it has always been steady...

The system is staying in open loop until I touch the gas, but the rpms drop from wherever they are at, like 2400 in decel at 70 MPH to like 1100 or 1200 rpm and then up and down until I touch the gas and it goes back into closed loop....

[jdenning002]

John the AC is one of the wires that did have to be switched, so now this may be that the pins have pulled back in the conector, again the AC worked perfect when it left here?? none of this started till the blower swap, but any thing is possible. I will find out out what four wires we changed, but I still do not see how this will cause the issue, with the tune the four wires only relate to AC and Trans, data log the car for STFT Maf count and load and RPM and send me the data.


I will do another data-log and send it to you Dennis...

No argument here, the car ran great when it left your shop, this just came up... but I am going crazy trying to figure it out...

The rear O2s are off right? I just replaced the front O2s and when I look at the voltage for them they drop well below .50 volts, could they be bad out of the box or could it be something else??

Please do let me know about the 4 wires, thanks.