jamiemiller

ok, does the MS put out ground or 12V on pin 37?

i can be a little thick headed sometimes, thanks for the help.

Joe Perez

iTrader: (8)

Well, it sounds like you're probing the right spots (INJ1 and 2 between the injector and the MS) however if you are probing with a simple voltmeter then it's likely you will see no change at that point. The MS should indeed be pulling those points to ground in order to fire the injectors, but the pulses are very brief- typically 4 to 6 milliseconds while cranking- and a normal voltmeter cannot respond that quickly. In order to accurately measure these points, you need an oscilloscope.

Assuming you've built that part of the circuit to spec, it provides a closure to ground. Note the following:



Pin 37 of the DB-37 is connected to the point called FP1, and the CPU output pin 33 to the point called FP-1. Careful of the difference here.

When the CPU wishes to turn on the pump, it drives its own pin 33 high to +5v. This goes through R16 and biases the base of Q2 positively, which since it is an NPN transistor causes it to turn on. This allows current to flow in from FP1 (DB37 pin 37) and pass through Q2, then through R40, to ground.

R40 and Q19 form an overcurrent protection circuit. As the current passes through R40, it creates a slight voltage differential across it. If the current becomes too great, then the voltage at the top of R40 rises to a level sufficient to turn on Q19, which pulls the base of Q2 to ground, shutting off the circuit.


No, you're asking all the right questions and it seems like you've got a good handle on troubleshooting. We've all been through this phase.

jamiemiller

what would happen if Q19 is not installed? hypothetically..............would the fuel pump output not function?

jamiemiller

its alive, just need to figure out timing.

thank you for all the assistance.

i was missing q19, r40 and d4.

works much better. Does anyone have a slick way of setting base timing? My CAS has been moved.

jamiemiller

New thread created.................