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BHP231's Avatar
 
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Oops. Reversed polarity

OK, so as the title suggests I connected the positive and negative terminals the wrong way when putting in a new battery and I have broken something. I feel like a fool and the bills are mounting....
It is a stripped down 1983 944 converted to a race car.
Ignition process when it works: master switch on, electrical switch on, the fuel pump starts and stops after three seconds, press the start button and away we go.
What happens now: master switch on, electrical switch on, the fuel pump comes on and stays on, press the starter button and the engine turns over but does not fire at all.
A car electrician has checked things out and the wiring, fuses and relays seem ok.
He thought the Wolf ECU might be damaged, appears not. The Wolf agent owner thinks the sensor on the crank to start the car may be a problem.
Anyone know exactly what that sensor is?
Thanks!
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2009 997.2 Carrera PDK
1988 Carrera Targa Euro Spec (gone by not forgotten)
1985 944 manual
Old 10-12-2018, 01:57 AM
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Yup, scope output waveforms of crank-sensors.
This tells ECU speed of crank and TDC. If ECU can't tell what speed of crank or where TDC is, it can't do anything, it's blind.
Old 10-12-2018, 12:26 PM
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Crikey (token Aussie comment for you - learned from watching 4WD Action guys Shaun Whale and cohorts). So these two sensors live atop the trans bell housing where it mates to the engine. You'll remember getting these out unless you have incredibly dexterous hands and lots of gadget like tools. Before you start though, its worth someone chiming in if these are vulnerable to polarity damage? I think not as they're just magnetic switches that react each time an iron screw fixture in the flywheel passes. Dunno but I'd ask an electrician to check the wave output as noted above before trying to remove them.
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Old 10-12-2018, 06:03 PM
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Couple of hints to work on, good on ya.
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2009 997.2 Carrera PDK
1988 Carrera Targa Euro Spec (gone by not forgotten)
1985 944 manual
Old 10-12-2018, 07:52 PM
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yeah, they shouldn't be affected... but... due to ground wiring, if you don't have the engine/trans. grounds on, hitting start would fry DME. So I suppose even more-severe case of reverse-polarity might fry ECU.

I guess you can bench-test the ECU with simulator.

Also check each and every fuse. Don't eyeball them, pull them out and measure actual resistance across legs. Look for melted wiring under fusebox.

Last edited by DannoXYZ; 10-12-2018 at 09:29 PM..
Old 10-12-2018, 09:26 PM
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Did you successfully hook up the battery backwards and then try to start it or did sparks fly when connected the second terminal?
Does your tach have bounce when cranking the engine? If no check sensor connections, they are known to crumble. If connections Ok then probably sensor is bad.
The fuel pump now running continuously is curious. Perhaps the reverse jolt damaged the pump and it won't build pressure. Have you tried starter fluid to get it started? If it starts and briefly runs then you have fuel delivery problem.
Try a different ECU/DME if you can first. If you have to pull a sensor make up the tool I posted in this thread.
https://rennlist.com/forums/924-931-944-951-968-forum/1100051-no-start-1988-944-so-i-guess-ftech9-ecu-time.html
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Old 10-13-2018, 08:23 AM
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Pressure is generated by FPR, not fuel-pump. Pump is also DC motor, reversing it will just have it pump in reverse. No damage there.

This is not DME, but aftermarket Wolf3D system. It's most likely fried since it controls fuel-pump. It has old-style prime-the-pump for 3-secs. when key is first turned on. Now it's just turning on pump permanently. Most certainly fried ECU.

Last edited by DannoXYZ; 10-15-2018 at 10:16 PM..
Old 10-15-2018, 10:13 PM
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Thanks all. Confirmed today fried the ECU. Will source an identical unit to install and test if anything else is a problem and then “upgrade” to the Motec ECU and data logger dash. Competition rules are that the ECU is a control unit with only Wolf or Motec allowed.
Have now got red tape wrapped around the positive terminal lead to avoid in the future!
Expensive rookie error.
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2009 997.2 Carrera PDK
1988 Carrera Targa Euro Spec (gone by not forgotten)
1985 944 manual
Old 10-16-2018, 01:47 AM
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Tested with another ECU and she fires up perfectly so looks like everything else is ok. Thanks all for the feedback.
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2009 997.2 Carrera PDK
1988 Carrera Targa Euro Spec (gone by not forgotten)
1985 944 manual
Old 10-19-2018, 05:55 AM
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