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Discussion Starter · #1 ·
So the other day, I moved my car from my driveway to the street, left it over night, then in the AM went out to start it up and the fuel pump isn't priming, won't run etc. I checked the relays and fuses under the hood, and the inertia switch is depressed, so now i'm at checking voltages for the fuel pump. I haven't been able to locate a wiring schematic however, and was hoping for some help. Essentially voltage goes in to the fuel pump driver, it modulates it then sends it to the fuel pump correct? So if I was going to test incoming voltages, which wires would I be looking at? And then which wires going out? Usually I would just replace the pump but before I start doing any cutting for access to the pump, I'd like to verify it isn't something else.
Another variable to this problem is that I never had any sputtering, no hard starting, and that right before I tried and failed to start it the first time, I had plugged in an older (but used on other cars) ELM327 OBD2 transmitter. I doubt that OBD2 can cause fuel pumps to not run, but the coincidence is mild alarming.
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They can fail out of the blue with zero warning.
Exact year, some of those wires change up in color. Pump is black for ground and green/orange for 12 volt to pump on at least some of them, disconnect the plug at driver module on pass side and check there.
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They can fail out of the blue with zero warning.
Exact year, some of those wires change up in color. Pump is black for ground and green/orange for 12 volt to pump on at least some of them, disconnect the plug at driver module on pass side and check there.
Just like a optispark on a LT1/4.......
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Discussion Starter · #4 ·
I guess that would have been helpful. 2002 SE wagon. So is the drive not the unit that on mine is bolted to the unibody under the seat maybe a foot from where the fuel pump wiring leaves the vehicle?
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That is the fuel pump driver module yes, but you test the fuel pump without it as that module usually never fails, rather, the pump does. Bear in mind that the pump wiring goes into the driver AND exits as well, you should be looking at TWO of each of those wires and have to figure out which ones goes to pump and which go back to inertia switch.
If you end up needing a pump you CANNOT get pump alone wit6hout the module, you must buy the entire module unless the pump was previously changed in the recall. If the module casing has two sprung steel rods in the top you can buy pump by itself but most are not that way.
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A lot of times the pump will be pretty noisy. Problem is you may not notice until you put in new one like I did. While back '86 Mustang GT running great, no problems. On my way home stopped at McD's and it started for a second then died, towed home.
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I haven't been able to locate a wiring schematic however, and was hoping for some help. Essentially voltage goes in to the fuel pump driver, it modulates it then sends it to the fuel pump correct?
Attached schematic
Fuel pump controlled by fuel pump driver module. Fuel pump driver module is controlled by the PCM.
Paul
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Discussion Starter · #8 ·
So with key on (so position where it would prime, but not cranking the vehicle), my multimeter is only reading at most 6.5V across any two of the terminals of the FPDM plug. My battery voltage is sitting at 12V so is this normal? Or do I have an electricla problem from the sound sof it? I know the FPDM modulates the voltage, but if the plug should be getting 12V and modulating from there I would think?
If i'm losing voltage someplace, I would take it that the inertia switch is the most likely spot? Any tips to taking off the panels to avoid breaking mounting pins?
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Is the plug plugged in? Should be unplugged. That drops out the FPDM as a tilting power source.
You need 12 volt at terminal 9 C731 on the plug (grn/org wire). Not getting it I would be looking at the pump relay and its' plug. Could be inertia switch but pretty rare.
You're asking for it sending voltage into all of the leads there, two go to the PCM and if they are low voltage you just may have fried your computer. It is witless to just start putting power into all wires on a modern electronic car. Not trying to be mean but the truth of it.
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Discussion Starter · #10 ·
I'm confused by how I could have fried it, or I might be describing my test wrong. I unplugged the driver, and took voltage across the plug leads with the ignition on. I tried swapping the low beam and fuel pump relays since they had the same part number under the hood, no change.
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Discussion Starter · #11 ·
Just to confirm again, I didn't jumper or connect any of the plug leads, just took voltage across with a high quality voltmeter. One that I've used to test much more sensitive electronics for boiler and heat pumps.
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Discussion Starter · #12 ·
In case if anyone ever has similar problems and finds this page:
The pump not priming can be related to many things that aren't the pump. So before you go replacing the pump, make sure that besides the fuel pump relay, you check the power hold relay, listed as "Engine Management" in the owners manual. Sit's right beside the fuel pump relay. Once I swapped it with the low beam relay to test, it fired up. Long term prognosis uncertain, but it seems it was the relay. Hopefully this ends up helping someone down the line who's pump dies but you don't know why, and the obvious things don't fix the problem
Cheers
Posted by: michaelthund1973oao.blogspot.com
Source: https://www.focusfanatics.com/threads/fuel-pump-wiring-question.809925/
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