Fuel Pump Not Priming

JBuild

Member
Trying to get the first real start but the fuel pump does not prime. The motor cranks and the fuel pump works without issue if the relay is removed and the terminal 85 is jumped to 87. The car did run and drive before disassembly but the pervious owner definitely has his hand in some "modifications", most I've been able to correct. Just hoping there aren't some hidden gremlins.

I've check all connections, grounds, fuses, replaced the fuel pump relay with two known working relays and all relays appear to be working correctly.

When I test the pins in the fuse box, where the relay goes, I get the following when looking from the back towards the front:
With Key Off:
Top Left-6v
Top Right-Ground
Bottom Left-12v
Bottom Right-0v

With Key On:
Top Left-6v
Top Right-Ground
Bottom Left-12v
Bottom Right-2.45v

2.45 volts seems a bit low to actuate the coil but that's just speculation, some of the other relays tested out at ~6 volts on

Can anyone verify what they get?

Also does anyone have a picture of the fuse box, there is the possibility some of the relays are backwards.
 

Briann1177

Well-Known Member
Check the dark green/white wire that runs from pin 86 to ECM X2/10. When you shorted pins 85 and 87 together, you basically just bypassed pin 86. The dark green/white wire is the control wire that tells the fuel pump relay to close.
 

JBuild

Member
I couldn't seem to figure out how to get the cover off the bcm to probe the connector pin but I'm getting ~2.5v at the ECM pin.

I believe it's pin 6.
 

Briann1177

Well-Known Member
It could very well be pin 6. I'm not sure what year yours is. I got pin 10 from my '09 service manual.

Will the car want to run with the relay jumped?
 

JBuild

Member
Mine is a '10, it fires right up. A bit rough but it hasn't been run in months so I wouldn't say it's out of the norm.
 

Briann1177

Well-Known Member
It has to be something on that dark green control wire circuit then. I wont be able to measure mine until tomorrow.
 

Briann1177

Well-Known Member
With Key Off:
Top Left-0 ohms 0 volts pin 86
Top Right-0 ohms 0 volts pin 85
Bottom left open 14 volts pin 87
Bottom Right-26.54k ohms 0 ohms pin 30

With Key On:
Top Left-0 volts
Top Right-Ground
Bottom Left-12 volts
Bottom Right-2.45 volts
 

Briann1177

Well-Known Member
The only difference is that I don't get 6 volts on the dark green/white (pin 86) relay control wire. That might be because the fuel pump was done priming when I checked the meter.

If yours is reading 6 volts regardless if the fuel pump is priming or not, then I'd go back and verify the pin for that particular wire. It seems strange that the pin location would change between an '09 and '10 model. It's very possible though.
 

JBuild

Member
Went through the wiring diagrams, it is pin 10 on mine as well. When I pull the connector off the ECM and test that pin I don't get voltage. I'm thinking there are other contingent circuits used by that connector that prevent 10 from outputting a voltage with the plug removed.

I'm not positive on this but I believe the pin layout is top left:30, top right:85, bottom left:87, bottom right 86 (like the attached photo). With the signaling voltage at 2.45 the relay won't actuate leaving the power at terminal 87 and not energizing terminal 30, where 30 is the gray power supply to the fuel pump.

This leads me to be believe my ECM isn't sending a pulse to prime the fuel pump, I know the voltage never exceeds 2.45 volts. The question now is why, having voltage on the top left is a bit concerns. Makes me wonder if there is an internal short, either in the ECM for fuse box.
 

Briann1177

Well-Known Member
Yeah, there are a lot of other circuits that are needed for the fuel pump to prime. If you can find that wire by your ECM connector, you can hook up a needle to an alligator clip and pierce the insulation to measure the voltage.
 

Motoracer110

Well-Known Member
My car at first was in no crank condition including the pump not priming after about 40 hrs of diagnosis I found out that the plugs on the relay box were not seated all the way. I had to crank down the bolts that hold all the plugs in (nearly stripping them) and the car came alive. Might be worth trying
10538
 

JBuild

Member
Motoracer110 I have been following your build, one of the first things I tried was to tighten the box down even more.

Also interesting your box is a bit different.


10576


I am suspecting either the ECM or the fuse box is bad. I bought a new ECM and HPTuners but can't seem to get the new ECM to complete the seed key relearn. I've followed this process several times to no avail. When I connect the HPTuners to the original ECM I'm able to read it but not able to with the new one, possibly because I can't get the seed key relearn.

I am getting error P0627, my thought is because of the ECU/fusebox. I've confirmed the dark green/white wire has a ground when not powered on and no ground when the ignition is on. There is no short in the wire.
 

ccannx

Well-Known Member
I had a similar problem I used a circuit tester and found only 1 ground at the fuel pump relay that was coming through the pump brushes back. The other ground for ignition/relay trip was missing. I had no ground on the harness block that the fuel pump was on so I wired one in to a common associated with the relay trip pin.
 

Motoracer110

Well-Known Member
Motoracer110 I have been following your build, one of the first things I tried was to tighten the box down even more.

Also interesting your box is a bit different.


View attachment 10576

I am suspecting either the ECM or the fuse box is bad. I bought a new ECM and HPTuners but can't seem to get the new ECM to complete the seed key relearn. I've followed this process several times to no avail. When I connect the HPTuners to the original ECM I'm able to read it but not able to with the new one, possibly because I can't get the seed key relearn.

I am getting error P0627, my thought is because of the ECU/fusebox. I've confirmed the dark green/white wire has a ground when not powered on and no ground when the ignition is on. There is no short in the wire.
Hmm sounds like the relay is switching the ground when key on. Does the red lock symbol on the dash go away after a few seconds when the key is turned on? Also do you have the little key fob security chip plugged in? It’s located right behind the key slot
 

JBuild

Member
Motoracer, the security light on the dash goes away after a few seconds and the car cranks. I had a similar thought and confirmed the connections and everything looked to be in good shape.

For anyone else having issues the car will not crank with the security light or if the key fob isn't plugged in.

ccannx, interesting suggestion and I am trying to follow along. I confirmed I do lose a ground when the fuel pump is disconnected. My understanding:

pin 85 is the ground - bottom right
pin 86 is the signaling wire, confirmed there are no shorts and can't control this output without swapping the ECM - top right
pin 87 is the 12v supply - bottom left
ping 30 is the supply to the fuel pump - top left

Were you not getting ground at X3:F2, this is the connector/port the wiring diagram shows as the ground, or did you add another ground?
 

ccannx

Well-Known Member
Off the top of my head is you should see two grounds. One from the fuel pump which is actually you seeing ground trough the brushes in the motor and the other ground is the fuse block. When you crank the key the positive comes from the BCM I assume and that along with the ground from the fuse box should trigger the switch sending + Through the relay from the fuse to the terminal that looks like a ground but is really the brushes on the motor completing the fuel pump circuit.

Easy button is go full race car and put a toggle switch on your dash !
 

JBuild

Member
I can't say I haven't thought about a full switch panel. :rolleyes:

I'm at work now but I believe that is what I have. It seems like the ECM isn't sending enough voltage to trigger the relay. Just not sure what that value is supposed to be, guessing ~5-6 volts.
 

JBuild

Member
I only have a single ground, when I disconnect the fuel pump it goes away. Sounds like I need to check my ground.
 

Briann1177

Well-Known Member
When you disconnect your fuel pump, I believe you're going to lose your ground that appears on pin 30. Like ccanx said, that's because of the very low resistance of the fuel pump motor windings. You can verify your ground on that section of wire by going from pin A on the fuel pump connector over to chassis ground. Pin 85 is the only true ground in the fuse box/relay circuit.
 

ccannx

Well-Known Member
When you disconnect your fuel pump, I believe you're going to lose your ground that appears on pin 30. Like ccanx said, that's because of the very low resistance of the fuel pump motor windings. You can verify your ground on that section of wire by going from pin A on the fuel pump connector over to chassis ground. Pin 85 is the only true ground in the fuse box/relay circuit.
This is essentially what I did took pin 85 and ran a ground wire from it and strapped it down to the DF welded on lug right under the fuse box.
 

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