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Mahler9th's Avatar
 
Join Date: Oct 2005
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3.6 Conversions... Engine Diagnostics with factory ECU's??

For some reason, I have been speaking with a few Varioram engine owners lately. In each case, these engines are in, or likely going in earlier cars.

I am curious about the use of stock Varioram engines, with factory ECU's (chipped or not) from the standpoint of diagnostics.

I presume that many folks with "3.6 conversions" using factory ECU's are running closed loop mixture control with oxygen sensors.

My question is... how do you know that the oxygen sensor(s) are working properly? Do folks leverage OBD 1 or OBD 2 set ups and rig up check engine lights?
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Old 03-12-2018, 11:38 AM
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Mine seems to be working fine. I ahve the stock diag port hooked up to check for codes etc (ODBI). I have also rolled it on a dyno a few times to watch the AFR, while chasing issues. Car runs amazingly now, Steve Wong chip and all. The factory ODBI diag was not the greatest, but it would throw codes for things like O2 sensors.

What issues are you having?
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Chris -
1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion
1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C
2001 996 Turbo - ~42k miles
Old 03-12-2018, 12:29 PM
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No issues. I don't run this set up.

I have a '75 race car with a 3.6 and aftermarket ECU. CA Smog exempt.

Sounds like in your case you can access the OBD system.

So in theory you can just connect a generic code scanner now and then to check for codes.
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Old 03-12-2018, 12:42 PM
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i have a 95 3.6 in my sc- how would I go about checking codes or how are you guys checking?
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Old 03-12-2018, 01:07 PM
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I used a Patrick Motorsports wiring harness to put a '90 3.6L in my '74 911. W/that harness, there are wires/provisions for a check engine light and using that light, there is a procedure you can go through to get it to flash codes (long and short flashes), which I have done. The exact procedure and code sheet is in the 964 factory manual... I can't remember exactly how it went, but it was not difficult - something like fully depress the gas pedal for 10 seconds while turning the key to the "on" position or something... There is also an OBD port wired into the harness, but I have not tried it w/a code reader.
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Old 03-12-2018, 01:16 PM
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I have a 3.8l 964 based engine in my 1987 Carrera. I wired a standard OBD2 plug into the ECU harness, of course my 964 ECU provides only OBD1 info. I am using the Bergville cable https://www.bergvillfx.com/index.php/products/obd-diagnostics/t-obd-diagnostics-for-porsche-968-964-and-993.html with a cheap Windows 10 tablet to read the error codes. Works just fine. You can not only read the engine codes but also manually actuate the various magnetic valves including the injectors for testing.
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Last edited by HorstP; 03-12-2018 at 01:46 PM..
Old 03-12-2018, 01:43 PM
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if all you care about is closed loop O sensor, put a digital Voltmeter across terminal 3 & 4 of the 4 wire O sensor connection in the engine compartment. #1 is +12v for sensor heat and #2 is the ground

engine must be warm ~150nV to 900 mV w/ a sinusoidal shape is what you want
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Old 03-12-2018, 02:20 PM
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I installed a conversion harness from PMS as well which has all the leads and a diagnostic port built in. If you don't have that harness, try contacting Ingo (ischmitz). He knows how to DIY your own port.
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Old 03-12-2018, 03:22 PM
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I dont have the PMS harness (yet). I have a cobbled together harness from the PO. I wired in my own code reader through info here onto board. Bought a plug, wired it into the connectors, etc. If you can solder and read a wiring diagram you can do it. Search here for 3.6 conversion ODB.

That said I did it, and still need the PMS harness for other reason. So better bet, in my experience, is buy the PMS harness, spend your time writing it up, have new engine wiring and the plug.
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1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion
1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C
2001 996 Turbo - ~42k miles
Old 03-12-2018, 06:14 PM
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As I said, I don't have any needs in this area. My application is racing, and I don't run a closed loop mixture system. My mixture is set by tuning and is fixed. I run leaded racing gasoline. And again, I have an aftermarket (racing) ECU.

I am just curious about what street car guys do for 3.6 conversions running closed loop.

Still a little murky... I wonder if in a typical application when you have a Varioram engine, a factory harness, a factory ECU (with our without a chip), whether the OBD port is typically present and can be used to scan codes from time to time? Sounds like you can.

If that is true, and there are codes for failed sensors, then I imagine you can just check from time to time. Sounds like some have cobbled/wired in an OBD access connector... I wonder why they didn't just use the factory OBD wiring....

I am not familiar with oxygen sensor failure modes, but I imagine just checking the heater circuit voltage is not a suffiicient diagnostic process.

In my application I do run an aftermarket wideband AFR controller/gauge with a display, and I log the values with my racing data acq. system. I use an AEM. And I need to change sensors pretty often due to the lead (and probably the heat).

If I were gonna run a street car with a 3.6 and I had impunity with respect to smog, I am not sure I'd like the Varioram... adds complexity and weight. I wonder if the current medium displacement ITB street car fad will morph into larger displacement DIY projects.

The improving accessibility of street car grade aftermarket ECU's will no doubt play a role...we'll see.
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Last edited by Mahler9th; 03-12-2018 at 07:30 PM..
Old 03-12-2018, 07:26 PM
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If car needs ECU that appears stock but one does not want any emission stuff, I have made many VEMS PnP ECU's for 911 3.2, 964, 993 as "stealth" meaning VEMS hardware planted inside Bosch DME casing.

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Old 03-13-2018, 07:48 AM
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