ebl surging idle thread
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From: Chasing Electrons
Car: check
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Re: ebl surging idle thread
SA - Idle Low Compensation
SA - Idle High Compensation
Surging is typically caused by a lean area of the VE table.
RBob.
Joined: Jan 2008
Posts: 329
Likes: 14
From: Grand Rapids MI
Car: 88 IROC-Z
Engine: 6.9L TPI(FIRST) 421ci
Transmission: T56
Axle/Gears: Ford 9" Eaton truetrac 3.50
Re: ebl surging idle thread
Thank you. I hope timing sets still so I can get the VE correct. I see it going lean after it starts the roll but its tough to pull a VE learn at that time.
Joined: Jan 2008
Posts: 329
Likes: 14
From: Grand Rapids MI
Car: 88 IROC-Z
Engine: 6.9L TPI(FIRST) 421ci
Transmission: T56
Axle/Gears: Ford 9" Eaton truetrac 3.50
Re: ebl surging idle thread
Well it wasn't the timing. its dead steady now. I am about to start over and get another set of injectors to see if I can get control of these things. I am running Bosch III 24# that were opened up to 42#. Rob has hated the idea of these since day one so I am getting injectors I can set up right. Am I on the big side for a 421 @ 42# stock pressure?
Re: ebl surging idle thread
Also my SA - idle state SA is at 20 but its jumping from 21 to 13
I suspect lean condition off idle. If you have a WB you could verify that. I would add more IAC fueling post idle.
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Joined: Dec 2001
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From: Bartlett, IL
Car: 92 ZR-1
Engine: LT-5
Transmission: ZF-6
Axle/Gears: SuperDana 44 4.10
Re: ebl surging idle thread
A lot of the ideas that are being kicked around I covered in my first port (#3 of thread). It would be helpful to reread that post.
As far a tuning in the proportional gains tables, I go by exhaust sound and the INT. But first, I rough them in by changing them by the same amount of change in injector flow rate. If a larger displacement engine is in place, say a 383, that too needs to be taken into account.
It is all about ratios. Double the injector flow and need to halve one of the two proportional gains tables. The two tables get multiplied together, hence the need to only halve one of them.
If at a steady state cruising speed the exhaust sounds like there is a bad u-joint, too much proportional gain. Look at a data log and look at the airflow at that time (gms/sec). Go into the proportional gain vs airflow table and reduce it at and around that air flow.
Flash and re-test.
As for using the INT, if the INT is rapidly increasing and decreasing there is too much gain. Would likely see this in the bad u-joint example.
A slowly increasing and decreasing INT means that there isn't enough gain. This forces the ECM to use the INT to create cross counts (O2 signal). This causes an overshoot of the AFR. Which can be heard in the exhaust an oscillation. Can also cause the engine RPM to follow the AFR change.
RBob.
As far a tuning in the proportional gains tables, I go by exhaust sound and the INT. But first, I rough them in by changing them by the same amount of change in injector flow rate. If a larger displacement engine is in place, say a 383, that too needs to be taken into account.
It is all about ratios. Double the injector flow and need to halve one of the two proportional gains tables. The two tables get multiplied together, hence the need to only halve one of them.
If at a steady state cruising speed the exhaust sounds like there is a bad u-joint, too much proportional gain. Look at a data log and look at the airflow at that time (gms/sec). Go into the proportional gain vs airflow table and reduce it at and around that air flow.
Flash and re-test.
As for using the INT, if the INT is rapidly increasing and decreasing there is too much gain. Would likely see this in the bad u-joint example.
A slowly increasing and decreasing INT means that there isn't enough gain. This forces the ECM to use the INT to create cross counts (O2 signal). This causes an overshoot of the AFR. Which can be heard in the exhaust an oscillation. Can also cause the engine RPM to follow the AFR change.
RBob.
RBob,
Odd though that after you looked at my logs, I began to increase the prop gains from
where I had them. They're just about back to stock. And that was to tame the INT being used for x-counts. As an example, I went from 2 count at 0gms to 9.
I did note a bit of a "heavy breathing" at idle if I went further. A bit of an up and down, but motor is cammed and idle varied 875-930rpm. At cruise, motor is monotone. Just a consistent engine note and the INT/BLMs are much steadier. This also allowed me to tune the IAT COMPENSATION so the BLMS remain steady even as IAT temps change.
Joined: Jan 2008
Posts: 329
Likes: 14
From: Grand Rapids MI
Car: 88 IROC-Z
Engine: 6.9L TPI(FIRST) 421ci
Transmission: T56
Axle/Gears: Ford 9" Eaton truetrac 3.50
Re: ebl surging idle thread
Switching to 42# bosch greens fixed my surging problems.
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