90 mustang problem with fuel pump

[cynikal]

ok i have a 90 mustang stock 5.0 and i installed the MS2 v3.0 and i hooked everything up through the stock wire harness where i removed the old EEC. No matter what i do the fuel pump does not prime the only way i can get the pump to run is by jumping the pump. so im assuming the MS is not telling it to turn on is there something wrong with the MS itself or is a problem with the way i have the tuning setup , this is my first run so i have all the tuning set to what the Megamanual instructed me to do any help would be appreciated , thank you

[trakkies]

Assuming you're using the original pump relay, how is it switched? MS provides a ground for this - does the original ECU supply a switched +12V? This was the case with my car, and if trying to keep the original wiring loom standard, you'll need to add a relay or transistor to the MS pump output to change the polarity of its switching signal. This could be mounted in the prototype area, or externally.

[cynikal]

I beleive the original EEC switches ground to enable the pump , but your saying the ms switches 12v so basically I just run another relay? I'm trying to keep my same setup the only reason I say that I beleive the original EEC switches ground is because off the original harness when I hook that particular circuit to ground the pump comes on

[cynikal]

sorry i think i read that wrong in my last post , so MS switches ground? im pretty sure thats how the stock ecu does it as well, so either there is something wrong with the fuel pump circuit in the MS or its not sending the signal for some reason i emailed the guys at dyiautotune so ill see what they have to say

[Matt Cramer]

Right, both MS and the stock ECU switch the ground to the fuel pump relay. Keep in mind Fords also have an inertial switch in this circuit that may be making trouble.

[cynikal]

i dont think it can be the inertia switch though becasuse if i run a ground wire to the original harness that im plugging the MS into the pump runs , it just runs constantly , instead of being switched through MS . im assuming something is wrong with the ms itself but how would i test that circuit?

[trakkies]

sorry i think i read that wrong in my last post , so MS switches ground? im pretty sure thats how the stock ecu does it as well, so either there is something wrong with the fuel pump circuit in the MS or its not sending the signal for some reason i emailed the guys at dyiautotune so ill see what they have to say

Unplug the MS and ground pin 37 of the harness connector? With the ignition on. You should hear the relay click and the pump run.

[cynikal]

Orry that might of been confusing I'm plugging pin 37 from the ms directly to pin 22 (fuel pump relay) on my stock wire harness for my car the same one the old ecu used to control the relay , so if I ground pin 22 with the key on the pump pumps but if I plug pin 37 from ms to pin 22 from the stock harness nothing happens

[trakkies]

Sounds like you've got a simple wiring fault. Is pin 37 on the DB37 actually connected to Pin 22 on your harness? Do a continuity check from DB Pin 37 to the relay coil contact.

Most of these things come down to simple wiring faults. Don't ask why I'm so sure.

As a general point it makes a great deal of sense to draw out your individual circuit diagram, including the actual wiring colours you've used. If anything goes wrong some time down the line it saves having to rely on memory.

[cynikal]

thank you i always draw up wire diagrams before i start a job, the issue im having is for some reason the ms is not sending a ground signal for the fuel pump if i hook up a test light to pin 37 on the MS with one end connected to 12v the test light does not light up when ignition is cycled so the MS is deffinately not sending the signal i just have to find out why

[trakkies]

Since you're just starting tuning, you have set the ECU type in Tuner Studio under Fuel Settings - General?

If so, refer to the MegaSquirt® V3 Main Board Information and Schematics in the manual, and go to the pump driver. With a DVM, check you have an approx 5 volt priming pulse at R16 when you power up MS. If there is, the fault is in the driver circuit. First check for any solder bridges at the transistors Q19 and Q2 with a magnifying glass.

I take it you don't have a stim? This has an LED to indicate pump operation. It also makes testing the basic MS operations so much easier as you can do it on the bench.

[cynikal]

i do actually have a stim , i will try that and i followed the instructions and set everything up the way it told me to i mean the car runs off the ms if i manually control the pump

[trakkies]

i do actually have a stim , i will try that and i followed the instructions and set everything up the way it told me to i mean the car runs off the ms if i manually control the pump

Right - if you try it with the stim that will show if the pump circuit is working correctly, as the pump LED will light when it should be running.

If it does, check the wiring again.

If it doesn't, go through checking the driver circuit as I said earlier.

[cynikal]

its deffinately a drive circuit issue i will check to be sure however, again when i hook one end of a test light to a 12v source and hold it on the pin 37 from the ms and cycle key on and off the test light does not light which means its not sending the ground signal but i will check the board and let you know my results

[trakkies]

its deffinately a drive circuit issue i will check to be sure however, again when i hook one end of a test light to a 12v source and hold it on the pin 37 from the ms and cycle key on and off the test light does not light which means its not sending the ground signal but i will check the board and let you know my results

It might be a software issue - the processor not sending out the command. Hence my suggestion you test the drive circuit as I've said.

[cynikal]

Thanks everyone or the help it was a mistake on my part with the idle circuit everything is fixed now all I need to do is some fine tuning