DME schematic - injector wiring
01-03-2008, 12:52 AM
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DME schematic - injector wiring
I'm looking at the wiring schematic for my car (87 944 na) out of a Haynes manual and I swear the schematic shows this:
DME grey = injectors 3 and 4
DME grey/w = injectors 1 and 2
the other terminals of the injector connectors are tied together and go to ground.
I have had my car running on Megasquirt since November 2007 and a problem arose which caused me to take a closer look at the injector wiring. The problem is according to the Megasquirt literature- injectors are supplied with a fixed 5V and the ground is switched on/off by the ECU. It appears my Haynes suggests the DME controls the 5V and the injectors are constantly grounded which is opposite of how Megasquirt should be setup. Is Porsche/Bosch controlling their injectors different than Megasquirt?
For my Megasquirt setup I allowed the stock wiring to feed what I thought was a fixed 5V to the injectors and Megasquirt took over grounding the injectors (grey and grey/wht wires). The car ran (ran great by the way, I fully support MS conversions!) for about 500 miles with no problems then it stopped. I'm getting no gas in the combustion chamber but plenty of fuel to the fuel rail so for some reason my injectors are not opening.
Sorry for boring you with all this senseless babble, the question is simple- does the DME supply the 5V to the injectors OR is the 5V constantly fed to the injectors with DME switching the grounds to turn them on/off??
DME grey = injectors 3 and 4
DME grey/w = injectors 1 and 2
the other terminals of the injector connectors are tied together and go to ground.
I have had my car running on Megasquirt since November 2007 and a problem arose which caused me to take a closer look at the injector wiring. The problem is according to the Megasquirt literature- injectors are supplied with a fixed 5V and the ground is switched on/off by the ECU. It appears my Haynes suggests the DME controls the 5V and the injectors are constantly grounded which is opposite of how Megasquirt should be setup. Is Porsche/Bosch controlling their injectors different than Megasquirt?
For my Megasquirt setup I allowed the stock wiring to feed what I thought was a fixed 5V to the injectors and Megasquirt took over grounding the injectors (grey and grey/wht wires). The car ran (ran great by the way, I fully support MS conversions!) for about 500 miles with no problems then it stopped. I'm getting no gas in the combustion chamber but plenty of fuel to the fuel rail so for some reason my injectors are not opening.
Sorry for boring you with all this senseless babble, the question is simple- does the DME supply the 5V to the injectors OR is the 5V constantly fed to the injectors with DME switching the grounds to turn them on/off??
01-03-2008, 11:32 PM
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...haven't solved the mystery yet. A generous gentleman helped me with some schematics. Haynes was WRONG, the injectors are fed 12V and the grounds go to the DME.
However, although I'm getting voltage and the other side of the injector connectors are continuous to Megasquirt AND Megasquirt is giving the right output (tested with stimulator) my injectors aren't opening. Time for new injectors I think.
However, although I'm getting voltage and the other side of the injector connectors are continuous to Megasquirt AND Megasquirt is giving the right output (tested with stimulator) my injectors aren't opening. Time for new injectors I think.
01-04-2008, 09:23 AM
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From Clark's page
Fuel Pressure Too High Disconnect one fuel injector connector and attempt to start car. If the car starts and runs, where it would not before, then the Fuel Pressure Regulator (FPR) is most likely bad and should be replaced. Bascially when the FPR fails causing the fuel rail pressure to go high, the injectors have too high a differential pressure across them, they draw too much current, and the injector driver shuts down. Disconnecting one injector wire reduces the injector current enough to allow the engine to start. Realize that the car will run very rough as it's running on three cylinders
http://clarks-garage.com/phpBB2/view...light=injector
Fuel Pressure Too High Disconnect one fuel injector connector and attempt to start car. If the car starts and runs, where it would not before, then the Fuel Pressure Regulator (FPR) is most likely bad and should be replaced. Bascially when the FPR fails causing the fuel rail pressure to go high, the injectors have too high a differential pressure across them, they draw too much current, and the injector driver shuts down. Disconnecting one injector wire reduces the injector current enough to allow the engine to start. Realize that the car will run very rough as it's running on three cylinders
http://clarks-garage.com/phpBB2/view...light=injector
01-05-2008, 12:06 AM
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Fixed! ... kind of.
I used current limitting 5 ohm, 100 Watt resistors to run my injectors as hi-Z. They melted. I routed thru my wiring to check out the solders and ensure that everything was okay and saw that the plastic covering on the outside of the resistors had partially melted off. I bypassed the resistors and ran with slight PWM and the car started up first time!
Thanks guys! I think I'm gonna use the PWM flyback this time to run as lo-Z.
I used current limitting 5 ohm, 100 Watt resistors to run my injectors as hi-Z. They melted. I routed thru my wiring to check out the solders and ensure that everything was okay and saw that the plastic covering on the outside of the resistors had partially melted off. I bypassed the resistors and ran with slight PWM and the car started up first time!
Thanks guys! I think I'm gonna use the PWM flyback this time to run as lo-Z.
