Hi all been away for a bit until now. Ive got a problem with my 1.8 l 2000 mazda protege. It cranks but wont start ,had to get it towed home from work last sunday. I was working on my vent solenoid, as Ive had a few rusty evap lines that Ive had to fix, so I was checking it too, and by the way its new. I wasnt hearing it come on when i turned ignition on. so I tested wires and found I had 12 v but no grd.which I thought so I attached the wire to grd and I could then hear it work. I had the car running around 3pm and all was ok. I came back out at 7pm to go home and the car wouldnt start. I tried a few things and nothing worked so I got it towed home the next day. I decieded to check to see what codes if any I had will I tried 2 scanners that I know work and I cant connect to pcm. I checked all fuses and they are good. So I figured some sensor was maybe pulling down the voltage and caused the computer to shut down so I unplugged them all. I have a engine diagram so I started to check and I noticed that I somehow lost the ground to the main relay. I took apart the engine fuse block to see if something was cracked inside like a copper trace but all is ok. Ive pulled apart the main wiring harness and found some coroded connections that Ive since fixed. I have power to the pcm as per #4 pin to it. Ive checked all grd wires going to it 24,51,76,77,103 and they are all good. So today I put a separate wire to grd for the main relay and it comes on when i turn on key along with fuel pump but I still have no communiction with pcm. Im where I have to check to see if I have power to pcm from main relay at pins 71,97. Ill check to see if I have a broken or open wire. One note that vent solenoid Ive been driving with grd attached for awhile until I looked at drawing and saw that it goes back to pcm like a input to pcm so thats why I disconnected it... and its been fine so all of a sudden my PCM shuts down or is bad? By the way i thought I had a bad wire from connector over gas tank under seat hatch but Ive fixed it and it tests ok. Just wondering if anyone can shed some light on this. Im hoping to pcm is ok since when I got main relay to come on I hear the fuel pump pump gas to injectors. which comes from pcm I beleive as per drawing that I have thanks again.....to be continued..

 

Hi again just wondering if anyone knows what the resistance of the fuel pump relay is as its tests 64 ohms. I've tried to connect up another external relay but it wont pull in due to it being higher resistance. Don't want to buy a new one, as this might not be a issue, as if I connect it to battery it works. It has a small 3 band resistor across terminals which I assume is just for suppression don't want to take it out and damage it. Did a search to find b5b4 relay but cant find specs of coil ...

 

Hi again well I've had my protege down for about a month troubleshooting this problem. Turns out I had part of the computer working and the part that didn't work was the one that didn't turn on the fuel pump relay. I got the master start relay and the fuel pump relay confused while troubleshooting this. I had the wiring pulled apart of the just about the entire car checking for bad connections I did find a few multitap connections that I had to repair including the shock tower grd junction. Turns out it was a bad pcm that probably got shorted as due to me having grded the evap vent solenoid by fuel tank to work and driving with it abt a yr. Oh by the way the resistance of that solenoid coil is only 20ohms somehow I had gotten the wrong replacement on amazon which was 60ohms no wonder it didnt work. Lesson learned u cant grd these sensors as they all go back to pcm.. Had to find another pcm and change it then all ok. Had to go to scrap yard to find another evap vent solenoid removed them and both tested at 20 ohms but wouldn't activate. Took them apart and freed up plunger pin,but couldnt reseal them .I did notice that the new replacement I bought from amazon looked similar turns out i was able to swap coils and reseal it easier due to the bracket being new. Its a old car but i love driving it and don't have to worry about stone chips door dings and getting stolen. She lives another day.