How to Force Closed Loop at ALL Times?

[ferocity02]

Interesting problem I have. My fuel pump (or other fuel component) is causing a fuel pressure of about 25psi. The result is that it will run lean if the vehicle is in open loop. When in closed loop (commanded EQR=1.0) the fuel trims are able to compensate.

I am running COS 5 and have set the commanded EQR vs. RPM (B3647) to 1.0 for all MAP/RPM cells. When the PCM is commanding EQR=1.0 it uses the STFT's to trim and it will run perfectly fine.

However, I'm worried about startup where its normally commanding a rich mixture. With the low fuel pressure it will be very lean during startup even when commanding rich. What do I need to change to force closed loop (EQR=1.0) during startup and warmup?

I need to do this temporarily so I can limp the truck to my shop to change the pump.

Thanks.

[picnic_george]

Should be under closed loop temp enable...

[swingtan]

Surely the correct fix here is to fix the fuel pressure to prevent the lean condition?

That being said.... When the STFT's are active, the LTFT's are also corrected. Even on OL mode, the LTFT's are active and should help correct the fueling during start up and in PE mode. So if you are expecting the STFT's to "fix" the issue, also expect the LTFT's to keep drifting around. Also, the O2 sensors need to heat up before they will start being used to correct the fueling. The ECM will look for O2 sensor activity before enabling CL mode, even if the other enablers are set. Unless you ecpect to sit in the car for 5 min with the ignition on, waiting for the O2's to get hot before you start the car, this is not going to work.

Yet more.... If the fuel pressure is low, then you can correct for this in the MAF / VE tables. If you correct the fueling tables, then there is no need to rely on the O2 sensors to make adjustments. Of course this assumes that the low fuel pressure is constant and does not vary.

Finally, the "rich" startup is meant to achieve a couple of things...

• Help the car idle when cold.
• Shorten the CAT converter heat up time.

If the car still runs, then running a bit lean won't really hurt it. it all depends on how lean it runs and for that, you will need a WB O2.

Simon.

[darcy]

Quickest bandwidth fix would be to adjust the injector flow rate down by Sqrt(25/58)=0.65 since that's what has changed mechanically.

[joecar]

Swingtan has some good points regarding when trims can become active... so I would edit the IFR table as darcy said...

but either way (edit IFR, or edit VE/MAF), at 25 psi, injector flowrate will not be sufficient for anything other than light load cruising.

[ferocity02]

Thanks guys! I have a wideband which is how I first noticed the issue. With COS 5, the LTFT's are not used, they are 0.0 100% of the time. Only the STFT's are used to trim when commanded EQR=1.0.

In fact, I do not know if it's ever goes into "closed-loop" with COS 5, I've never checked. Do you know Joe? I believe the technical term for what I have setup is semi-open-loop.

Reducing the IFR table by sqrt(25/58) sounds like a simple temporary solution. This should get it close enough to warm up, at which point the STFT's will keep everything level enough to limp it to the shop.

[joecar]

With COS5, the LTFT's are not used only if they are disabled... check tables B3801 and B4205.

you will see SOL on the cells in B3647 that are EQR 1.00.



remember, COS5 is fully capable of CL/LTFT operation (not to mention MAF also).

[ferocity02]

I have LTFT's disabled and closed loop disabled. The STFT's alone do a decent job keeping it trimmed to stoich.

[joecar]

STFT's are perfectly fine

( I was pointing out for the casual reader that COS5 supports all modes )

[ferocity02]

Actually, I might enable LTFT's. The STFT's are pretty good for steady state, but can be slow to react to sudden changes in throttle. Does closed loop need to be enabled to use the LTFT's? Or do they work similar to the STFT's where they are enabled when ERQ=1.0?