busted ECM????

[Maxximillion]

the problem i'm having with my car seems to coincide with some similar problems that other people have been seeming to have. my car will crank just fine it has spark and the timing is perfect. i get no fuel to the rail upon cranking. i checked the MPI fuse and relay and tested it twice all tests came back perfect. my question is this:

1. the MPI relay serves 3 purposes, fuel pump, ECM, and fuel injectors, my injectors i hear clicking away, but i don't hear my fuel pump with key on or cranking. could it still be the relay? even though i tested it with what the haynes book suggested to do it?

2. if the problem is not the relay, and not the fuel pump (also checked), then what else is there

3. if it is the ECM, how can i test it to rule it out? visually it looks good, but that doesn't mean anything. so far everything works but the fuel pump when its supposed to.

any thoughts???

 

[TT_Stealth]

an easy way to check the ECM or ECU is to connect an analog multimeter to pins 1 and 12 on the diagnostic port, if looking at the connection port, the top right pin that is all by itself is where you hook the negative lead up to, then the pin on the total opposite side and on the bottom is the pin that you connect the positive lead to, then simply turn the ignition on and see what the ECU code is or if there even is one, so top right and bottom left pins, If you have any questions just PM me and I can take pics and email them to you if still confused. hope it helps, if the relay is cheap and the ECU doesnt spit out a code I would just go and purchase another relay and swap them out and then see what happens.

 

[Maxximillion]

hey thanks for the reply and i tried the diagnostic port with pins 1 and 12 but no codes came out just a steady heartbeat. worth a try, and at least i know the ECU isn't fried but i think there could still be a problem with the ECU controlling the fuel pump. you know with our cars there are a whole lot of problems that an engine trouble light isn't going to tell you about. and getting a new relay is exactly what i'm doing tommorow from our local auto wrecker. jeez they even know me by name cuz i've been ripping parts off the 91 awd talon thats there for 2 years now. but thank you very much, any more thoughts i would love to hear them.

 

[Maxximillion]

hey, after much testing i've discovered that cranking the car while jumping the check terminal of the fuel pump to the battery (forcing the fuel pump to run) that the car still wont start. i think the problem lies within the injectors. in my previous posting i said that i could hear my injectors "clicking away" but it wasn't my injectors i was hearing so now i'm going to try to test to see if my injectors are working but first i checked my ECU for signs of corrosion as older DSM's caps will leak.

upon inspection i discovered that i could see the faintest signs corrosion on the heat sink thing below the big cap and as my research on this site has said that if the injectors aren't working, its most likely because of the corrosion from the caps.

there was another thing i noted through my testing. i was using my multi-metre to test for power to the relay and all the things it controls and i discovered that the 12v signal wire from the starter relay (that charges the coil in the relay to close the circuit for the fuel pump) upon cranking will only show 9-10 volts. and the supply power for the fuel pump from the ignition will show 12 volts with key ON but will drop down to 9 volts while cranking. i'm not sure if this is normal but if anybody has had any kind of knowledge about this let me know please.

one more thing. if my injectors are working, and i do in fact have fuel to the rail, but my car still wont start, is there a procedure to get it started if its flooded? or do i need to charge the fuel rail or what? getting kind of desparate to know what the problem is.

Jason.

 

[Jackson]

Have you checked the fuel filter or the fuel pressure regulator?

 

[Maxximillion]

hey yeah i didn't need to check the fuel filter as there is another thing i forgot to mention. so as i said i've figured out that i'm getting no fuel to the rail and no fuel upon cranking the car over. BUT when i bring the key back to the ON position from cranking it, i can hear the fuel pump whirr for 2 or 3 seconds and shuts off. i pulled off the fuel return line and cranked it, no fuel came out of the rail. but again when i returned the key to ON, on came the pump and squirted fuel out the rail for a second to my surprise.

after further testing with the volt meter at the MPI relay i discovered that the 12v signal wire from the starter that charges the coil in the relay and closes the circuit between a 12 volt source wire and the fuel pump,........................breath.................doesn't give me a full 12volts. when i tested the wire without the relay attached, i got 10.33 volts and when i put the relay back on and cranked it the signal wire showed 9 volts. but i could still feel the relay click i just thought it was odd that a starter wire would only show 10 volts. and my batter is fully charged by the way, i have it on a trickle charger after all the testing i've been doing.

another thing to note is the relay is functioning normally. when the relay is tripped from that starter wire, the 12 volt source from the ignition allows the fuel pump to run. BUT - when i tested for that 12 volts going to fuel pump when i was cranking the engine it only showed 9 volts again. so now i have my starter signal wire showing 9 volts to trip the relay and also the 12 volts that is supposed to be going to the fuel pump only shows 9 volts upon cranking.

is there a voltage regulator in our cars or has anybody had these problems before? i think that the fuel pump might not be getting enough juice to run properly even though the battery is defianatly full.

any ideas welcom thank you for the replies so far.

Jason.

 

[karbon]

I really don't THINK it supplies the full 12 volts anyway, which is why a lot of people buy their own relays dedicated to the fuel pump to give it a hardwired 12v connection right from the battery. It's because of the crappy 18 gauge (or whatever it is) wire used to power the stinking thing. I'm 95% sure the relay is performing as it's intended. Will your fuel pump stay on if you supply 12 volts to the test connector on the firewall, rather than just coming on for a second like you can get it to using the ignition?

 

[Maxximillion]

hey man thats kind of a relief to hear and i was thinking that same thing that it might be working as its intended but tomorrow i'm going to be getting a noid light and seeing if my injectors are working. i did use the jump wire to the check harness on the firewall and tried starting but it still won't fire up so i'm almost 100 percent that my injectors are not fireing. therefore it has to be the ECU that controls them. i took out the ECU and i can see corosion around the caps so i'm going to replace them and see where it goes. thank you so much for your reply and i'll let you all know how it goes. as for any other ideas i would love to hear them.

Jason.

 

[steve]

Voltage falls during cranking because the starter uses so much current.
The relay coil has resistance forming a voltage divider. You measured open circuit voltage and then inserted a resistance to ground. The voltage is going to fall with the relay installed.

So, now you know that the relay is triggering during starting but your pump doesn't seem to be running. That's one problem.

If your injectors aren't firing you need to make sure they have power and that the ECU is pulling the other side to ground when they should fire. It also might be a good time to check your Engine Coolant Sensor, since they are know to cause no-starts.

Steve

 

[Maxximillion]

hey guys, i think i'm on the downhill leg of this adventure with the car, and yeah i ordered some new caps and i'll replace those but as for the coolent sensor, i've read the haynes book on how to check it but do you guys know how to check it properly maybe some visuals on which harness and a clear procedure on how to check it. that would be cool. thanks again.

Jason.