$OD how to turn off closed loop at idle?

[Kitch]

Hi, my 94 G20 van with a TBI 350 has just started idling rough once the motor warms up.
It's normally quite smooth when in open loop but has always had a slight fluctuation in manifold vacuum when idling in closed loop of about .5".
Just in the last couple of days the van has started to drop 1" of vacuum at idle and then occasionally stall, the van seems fine driving around, at this stage the problem appears to be just at idle and only once it's warmed up and in closed loop.

For testing purposes what's the quickest way to disable closed loop at idle within a $OD bin?

[Fast355]

Hi, my 94 G20 van with a TBI 350 has just started idling rough once the motor warms up.
It's normally quite smooth when in open loop but has always had a slight fluctuation in manifold vacuum when idling in closed loop of about .5".
Just in the last couple of days the van has started to drop 1" of vacuum at idle and then occasionally stall, the van seems fine driving around, at this stage the problem appears to be just at idle and only once it's warmed up and in closed loop.

For testing purposes what's the quickest way to disable closed loop at idle within a $OD bin?

Sounds like an EGR issue to me.

[Kitch]

It could be a mechanical failure with the EGR system, in software I have EGR disabled until I reach 58MPH.
EGR aside, if I can find a way to disable closed loop at idle I can then see if the problem persists or goes away.

[1project2many]

Reach around the top of the EGR to put your fingers on the "inside" of the valve. Tap throttle slightly. If valve lifts the problem is in the vacuum solenoid.

Disable CL by disconnecting O2.

[lionelhutz]

Look for a minimum temperature for closed loop and crank the value. It should go to 255*. I don't think you can just disable it at idle only.

[Kitch]

Thanks for that, I'll give it a go.

Found the problem, aftermarket coil that had only done about 1000 Miles from new started failing after about 25 minutes of heat soak.
Replaced the coil and problem gone (lucky I had a new spare).

[sturgillbd]

If you ever wish to try open loop idle for any reason, here are the directions: http://www.gearhead-efi.com/Fuel-Injection/showthread.php?2149-Setting-up-0D-Open-Loop-Idle-only-Closed-Loop-Off-Idle The Scorp1us link has some good info in it but open loop idle can be set up with one the two Parameters that EagleMark had listed. You just need to increase the Open Loop Idle Temperature Threshold up to 255 degC and it will go open loop when idle qualifiers (tps% and vehicle speed) are met.

Hope this helps
Brian

[lionelhutz]

Well there you go, there is an open loop in idle only minimum temperature value in that calibration.

[myburb]

I have been fooling with those selections in OE. If you have closed loop enabled via temp, you can control open/ closed loop idle via temp and enable box. If you have closed loop blocked via temp. It won't matter what idle selections you make, it will stay in open.

[Kitch]

I can confirm changing the "Open loop idle Temperature threshold" to 151°C has forced my idle to operate in open loop and it then changes into closed loop as soon as I'm off idle (and closed loop parameters are met) :-)
I haven't spent much time testing but idle seems better a steady 19.5" out of gear and 17" in gear, where as before it would fluctuate between 17" and 16.5" when in gear.
Any reason why I shouldn't leave it in open loop at idle as opposed to using closed loop?
Given that it's a near stock TBI 350 with headers is it generaly possible to tune closed loop idle to be as smooth as open loop?

[sturgillbd]

You are right about 151C. I remembered the name but not the value at max. The only thing I noticed about open loop idle was the exhaust smell was stronger (very rich smell) in open loop idle. My idle was smoother in open loop. I played with my INT delay vs airflow and got a decent idle in closed loop. I only used open loop idle for a couple of weeks and set it back to closed loop. Now that the temp is a lot lower outside, I may play with it again just to see how it reacts to the colder temps. I have also installed a MAT sensor and enabled it in the calibration. I have changed careers recently and haven't had much time to play with my tune.

Brian

[Kitch]

Can't say I've noticed a richer smell since I've changed to open loop for idle. Vacuum gauge neadle sits nice and steady now as does the wideband O2 sensor.
I was surprised to see that the engine when fully warmed up after a run was getting around 15.0-15.1 for the Air fuel ratio at idle in gear.