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Re: Spark No Fuel
Posted by David Prantl (more from David Prantl) on Tue, 20 Aug 2002 22:22:28
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

>  I checked a few junkyards and could get a used one for
>  about 150 bucks.

I would never consider paying $150 for a replacement ECU, especially a 
*used* '89 unit.

>  I'm wondering what your opinions may be for bypassing  the fuel pump 
>relay signal from the ECU to the the  ignition switch.

My first recommendation would be to locate a used '90 ECU (part number 91 19 
447), which I believe is a direct plug-in replacement.  A fair price is $50 
or less.

Another possibility is to obtain a fuel pump relay from an 8-valve car.  8V 
cars used the Bosch CIS mechanical fuel injection system.  They have a 
*smart* fuel pump relay that takes a tach signal as an input.

Paraphrasing the technical description:
'The fuel pump relay is supplied with ignition pulses from ignition pulse 
amplifier 146.  If the signal should stop, the pulses will cease, and the 
relay will then trip, thus interrupting the supply to the fuel system 
components.'

Full wiring diagram can be see here:
http://216.78.172.244/electrical_system_folder/Electrical_900_89-90/056-57.jpg


The ignition signal from pin 7 on component 146 is better displayed here:
http://216.78.172.244/electrical_system_folder/Electrical_900_89-90/084-87.jpg


You might be able to splice into your EZK tach signal that already goes to 
pin 1 of the Jetronic ECU.  The signal could be too weak for the CIS pump 
relay (part number 95 50 948) though, necessitating the use of a pulse 
amplifier (part number 95 18 481).  I've never tried this, but it could be 
worth a try...

>  terminal 86 should now be grounded, and 85 should be the
>  pos 12v trigger to activate the relay.

If you setup your existing fuel pump relay to just come on with +15 switched 
voltage, you'll lose the bad crash fuel shutoff safety feature.  You don't 
have to worry about the 86/85 solenoid wiring convention.  As long as 
positive is on one of them and negative on the other, the relay will 
energize.

David Prantl
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