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Old 12-30-2016, 05:18 PM   #1
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Default EVO Duty Cycle

Quick:
I checked the Duty Cycle of the EVO on my mp3 Transmission 1998 SC2's P/S pump and it never goes below 68% per my EASE Diagnostics laptop.
My understanding is Duty Cycle should go to zero above 70mph.
Any ideas what's going on?

Background:
Here's where I checked EVO Duty Cycle today:


I checked the 1998 SC2 EVO in 2012:
http://i995.photobucket.com/albums/a...4-22-2012b.jpg

In Post #23, FDryer links a pdf (Document ID # 874534) indicating the 2002 EVO Dyty Cycle = 100% above 70mph. Is this only for model year 2002?
http://www.saturnfans.com/forums/sho...=217896&page=2

The pdf Document ID # 874534 mentions the 2002 model year EVO will be based on engine RPM if the PCM does not get a speed signal. My 1998 SC2's speedometer works fine, so the signal is getting to the PCM.
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Old 12-30-2016, 07:42 PM   #2
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Default Re: EVO Duty Cycle

Wondering if the EVO Duty Cycle is a parameter that could be adjusted at a GM dealer....
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Old 12-30-2016, 08:26 PM   #3
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Default Re: EVO Duty Cycle

I haven't compared service manual info but here's the file for your '99 SC2. The pcm controls the pwm signal and cannot be altered as its part of the programmed parameters. GM's Tech II scantool is the only GM authorized tool to make changes in software as directed by GM whenever an update or version change is necessary. As you are well aware of, no one has ever cracked S-series pcm's so its moot, discussing anyone considering any programs changes to pcm's.

Briefly put, full hydraulic pressure is used in parking and slow speed steering, decreasing as speed increases until surpassing 70 mph where hydraulic pressure ceases for direct steering control. High pressure/assist for low speed steering, variable assist between low and 70 mph, no assist above 70 mph.
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Old 12-30-2016, 09:44 PM   #4
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Default Re: EVO Duty Cycle

Not tweakable by any means. Wonder if you are looking at a bad connector or failing EVO solenoid.
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Old 12-30-2016, 09:53 PM   #5
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Default Re: EVO Duty Cycle

Thank you.
It seems that either my EASE is wrong or my PCM is wrong.
My SC2 does feel flighty in the steering and I never drive with the bottom of my wrist handsomely placed on top of the wheel at the 12:00 position. Both hands on the wheel.

I will have to check the EVO on another '98-'99 DOHC and note the Duty Cycle over 70mph.
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Old 12-30-2016, 09:59 PM   #6
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Default Re: EVO Duty Cycle

Quote:
Originally Posted by OldNuc View Post
Not tweakable by any means. Wonder if you are looking at a bad connector or failing EVO solenoid.
I linked an EVO check I did in 2012 and the one I did today. Those are two different EVO solenoids and they seem to be acting the same. The EASE checks for high/low current.
I would have to drive another SC2 and compare highway feel of the steering wheel.

EDIT:
The EASE I did in 2012 shows 63% Duty at 64mph.
The EASE I did Today shows 68% Duty at 64mph (I get that reading by playing back the recording on the 380ED ThinkPad running Win95)
...if that means anything.

Last edited by bumpdraft; 12-30-2016 at 10:12 PM.
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Old 12-30-2016, 10:33 PM   #7
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Default Re: EVO Duty Cycle

If it is the same EVO then something has changed. How all of these parameters are derived and subsequently presented by the software could be an issue as well. A zero toe setting makes the steering very twitchy.
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Old 12-30-2016, 11:25 PM   #8
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Default Re: EVO Duty Cycle

Quote:
Originally Posted by OldNuc View Post
If it is the same EVO then something has changed. How all of these parameters are derived and subsequently presented by the software could be an issue as well. A zero toe setting makes the steering very twitchy.
They are two different EVOs.
I know the toe setting affects the feel. The toe is near FSM minimum...or so...per my toe gauges.
Over all, I am very happy with the way the car drives. This started out as an experiment to see if Duty Cycle goes to 100% above 70mph...I will eventually check another DOHC.
100% Duty = better gas mileage.
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Old 12-31-2016, 12:07 AM   #9
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Default Re: EVO Duty Cycle

The issue is that 68% may actually be 100% open. I would put a scope on the power to the EVO if I was interested in what it was doing.

FSM
Test 3 - EVO (DOHC and RHD) Subsystem Test

1. Disconnect high pressure line at the power steering pump and install SA9134C Power Steering System Tester SST (or equivalent).
2. Install scan tool to the data link connector (DLC).
3. Open the gate valve on Power Steering System Tester.
4. Run engine until it has reached normal operating temperature. Replace any power steering fluid lost during power steering tester installation. Bleed system if necessary. (Refer to "Power Steering System Bleed" procedure in this service manual).
5. Using the Scan tool, select EVO subsystem in the special test menu.
6. With the Scan tool, command the EVO actuator to provide full assist (0% duty cycle). Increase engine speed to 1500 rpm and maintain this speed while observing flow rate. Record power steering fluid flow rate as indicated on power steering system tester. The flow rate should be between 8.88-10.77 LPM (2.35-2.85 GPM). If not within this range, replace EVO actuator.
7. With the Scan tool, command the EVO actuator to provide no assist . Increase engine speed to 1500 rpm and maintain this speed while observing flow rate. Record power steering fluid flow rate, as indicated on power steering system tester. The flow rate should be between 1.51-3.40 LPM (0.40-0.90 GPM). If not within this range, replace EVO actuator.
8. After completing flow test, stop engine and remove power steering reservoir cap to release system pressure prior to removing analyzer.





Unlike the constant flow power steering system, the electronic variable orifice (EVO) feature (found on vehicle with the DOHC [LL0] engine) as well as RHD postal vehicles adjusts the amount of steering assist to the speed of the vehicle. Vehicle speed is monitored by a vehicle speed sensor (VSS). This information is read electronically by the powertrain control module (PCM), which commands the EVO actuator to control the power steering pump output flow. At low speeds, where high levels of assist are desired, the EVO actuator is opened more, providing more flow to the steering gear and greater assist. At higher speeds, the actuator is closed more, providing less pump flow and therefore less steering assist and improved road feel. All of the additional flow of the pump not needed by the gear is allowed to return to the reservoir.


Pull the connector and see how it feels at speed.
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Old 12-31-2016, 09:07 AM   #10
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Default Re: EVO Duty Cycle

SA9134C was for sale on eb_y awhile back. You know it was tempting ...but without the Scan Tool mentioned in Test 3, Step 5 it would be useless.

The amount I've $pent on the P/S has already passed the crazy mark. If pulling the connector blew the seals out in the middle of winter ...

I had one EVO apart and they seem relatively simple.
Not my proudest accomplishment

Thank you everyone for the help.
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Old 12-31-2016, 10:04 AM   #11
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Default Re: EVO Duty Cycle

Quote:
Originally Posted by bumpdraft View Post
100% Duty = better gas mileage.
Be careful, some members might think if they go fast enough MPG will increase!

Seems like a PITA to pin down without the tester. I would think it would be easier to just take control of the actuator for the cost of the tester.
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Old 12-31-2016, 10:30 AM   #12
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Default Re: EVO Duty Cycle

The queston is, how would someone take control of the actuator?
Maybe get an EVO from a salvage yard and try to get it to click with a 1.5V, 3V, 9V or 12Volt battery and hold it there without overheating the solenoid windings.

All rather achedemic**except people want to know if the steering system is functioning as planned, after 20 years of service and maybe 300k miles.

**Edit: I could not spell "ac·a·dem·ic" and had to look it up
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Old 12-31-2016, 10:56 AM   #13
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Default Re: EVO Duty Cycle

Loss of power closes the EVO.

Quote:
At low speeds, where high levels of assist are desired, the EVO actuator is opened more, providing more flow to the steering gear and greater assist.
The tester is a pressure gauge and flow meter, not real tough to build your own.
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Old 12-31-2016, 11:21 AM   #14
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Default Re: EVO Duty Cycle

Quote:
Originally Posted by bumpdraft View Post
The queston is, how would someone take control of the actuator?
Maybe get an EVO from a salvage yard and try to get it to click with a 1.5V, 3V, 9V or 12Volt battery and hold it there without overheating the solenoid windings.

All rather achedemic**except people want to know if the steering system is functioning as planned, after 20 years of service and maybe 300k miles.

**Edit: I could not spell "ac·a·dem·ic" and had to look it up
From what I've seen, you could hijack the signal with resistance and induce the change that would be commanded through the PCM and PWM signal outputs. In reality not even remotely worth the effort for most since flow is controlled and the pump pressures are roughly the same.

With flow rates at almost triple at low speeds, you might be able to rig up a way to just cheat the VSS and observe flow, though finding a reservoir/catch basin/method to keep the pump fed would be an issue unless you want to dump gallons of fluid.

Most of the systems adjust flow rather than pressure, so any MPG changes would be down the tubes.
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Old 12-31-2016, 12:22 PM   #15
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Default Re: EVO Duty Cycle

Both good info.

More open = more flow = greater assist
No power = closed = less assist

Thanks
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Old 12-31-2016, 12:37 PM   #16
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Default Re: EVO Duty Cycle

As the PS pump is a positive displacement pump with an internal high pressure bypass. There is a hard direct relationship between pressure, flow, and pump RPM.
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Old 12-31-2016, 01:19 PM   #17
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Default Re: EVO Duty Cycle

Quote:
Originally Posted by bumpdraft View Post
Both good info.

More open = more flow = greater assist
No power = closed = less assist

Thanks
IIRC you will find full assist if you remove power. Most systems are designed that way so a loss of assist doesn't happen if the electrical portion of the system fails. I'm not sure about the S Series, but many cars use simple stepper motors similar to IAC function.

I've heard of a few models of Ford/Lincoln that would default to no (or least) assist when the electronics failed, but have never experienced such a setup first hand.

Quite a few systems never remove all assist. With the light weight of these cars, it might happen. But I also tend to think that no manufacturer is going to spend much time on a completely unique system for any given car. The bean counter almost always win.
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Old 12-31-2016, 01:43 PM   #18
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Default Re: EVO Duty Cycle

Search answers the question: http://www.saturnfans.com/forums/showthread.php?t=43512

Disconnected is full assist. apply 12v and there will be no assist.
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