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V1 Solved: First Start - Crank but No Fuel Pump

U

UNFORGIVABLE

Member
U
SOLVED.
ISSUE: BAD WIRING

Hi all! This is my first post on this forum and I'm very excited to be apart of the Goblin Community! Chassis #489 I picked up the frame from podercoat 5 days ago and now we're here! I have an issue during my first start procedure. I have crank but no start.

Donor: 2009 Cobalt LT 2.2l 5 Speed

I've looked up and down and all around about other people having similar issues, but I feel like mine comes from bad wiring in the harness. I'll be brief. I tried to jump the fuel pump to manually prime it. No luck. I made sure that the fuel pump itself was working. It does. I checked that the fuel pump relay and fuel pump fuse were in good condition. I even checked for continuity between all of the pins and the bottom of the fuse box and where the fuel pump fuses and relays connect at the top. All good. ALSO, the fuel pump relay is not switching on with the ignition on. Yes, I checked for continuity between the green/white signal wire from the ECM to the fuse box. It's holding at 2.45 volts with the ignition on. (I'll have to double check that when I get back home)

What I did find was that there was no continuity between the grey wire (fuel pump power) the the connector under the fuse box and the grey wire at the fuel pump connector.

Question 1: Should there be continuity between the fuel pump power relay pin and the power wire going into the fuel pump? Mine does not. It would only make sense if it does.

Question 2: Would this lack in continuity stop the relay from triggering in the first place?

More notes:
With the key in, I got a message saying "Reduced Engine Power", it will crank but the fuel pump will not prime and any point.
I am able to manually trigger the fuel pump buy routing power directly to the power pin (using the ground in the coming from the plug, so I know the ground is good.) So it will start and rev to the moon and the immediately shut off. That sounds like another issue maybe.
The car has 10 codes, mostly evap codes, and one for fuel pump wiring.

Any help would be appreciated. Thanks guys!
 
Last edited:
Markm
You should have power on two pins at the relay if it doesn’t that is one issue. You already figured out you’ll probably either need to dissect the harness or string a new circuit from the fuse block to fuel pump
 
U
Markm said:
You should have power on two pins at the relay if it doesn’t that is one issue. You already figured out you’ll probably either need to dissect the harness or string a new circuit from the fuse block to fuel pump
Click to expand...
I have a 12V at the "always hot" pin and 2.45V at the signal to trigger the relay. Am I supposed to be getting 12V here to trigger the relay?
 
G
I can post the fueling electrical daigram when I get home this evening. I probably have already posted it somewhere but, it won't be easy to find.

There is a decent chance that the "signal" or control wire to close the fuel pump relay is the ground but I don't remember that for certain.

Be careful jumping the fuel pump relay. It's very easy to burn a trace on the circuit board inside the fuse box. But I think that typically causes a no crank situation.
 
Rauq
UNFORGIVABLE said:
What I did find was that there was no continuity between the grey wire (fuel pump power) the the connector under the fuse box and the grey wire at the fuel pump connector.
Click to expand...
If you're saying there's no continuity between two ends of the same wire, that's definitely not right.

Keep in mind, I know this is for LSJ's but I think applies to all Cobalts- the fuel pump will run for a second upon key on, but will not run again until it either sees RPMs (upon crank) or you key off and let it sit for a few minutes. If it runs and then you key off and then back on, it won't do anything.
 
U
Gtstorey said:
I can post the fueling electrical daigram when I get home this evening. I probably have already posted it somewhere but, it won't be easy to find.

There is a decent chance that the "signal" or control wire to close the fuel pump relay is the ground but I don't remember that for certain.

Be careful jumping the fuel pump relay. It's very easy to burn a trace on the circuit board inside the fuse box. But I think that typically causes a no crank situation.
Click to expand...
Thank you! I've been referencing some thing from here:


but anything will help.

Rauq said:
If you're saying there's no continuity between two ends of the same wire, that's definitely not right.

Keep in mind, I know this is for LSJ's but I think applies to all Cobalts- the fuel pump will run for a second upon key on, but will not run again until it either sees RPMs (upon crank) or you key off and let it sit for a few minutes. If it runs and then you key off and then back on, it won't do anything.
Click to expand...

That's very useful info. Do you know what triggers the relay to switch on? Obviously ignition on with the key. Anything else like anti-theft, Data wires, some random sensor, etc??
 
G
The ECM has several things it needs to turn on the fuel pump. Don't worry about that at this point since it sounds like you have more direct problems.

You need to quote pin numbers now that there is a diagram so we can know exactly where you are taking measurements. If you don't have continuity between X2-D4 of the fuse box and pin B of the fuel pump, that is the most obvious problem. If you are getting only 2+v at pin X2-F6 that is probably a problem but sort out the other problem first.
 
U
Gtstorey said:
The ECM has several things it needs to turn on the fuel pump. Don't worry about that at this point since it sounds like you have more direct problems.

You need to quote pin numbers now that there is a diagram so we can know exactly where you are taking measurements. If you don't have continuity between X2-D4 of the fuse box and pin B of the fuel pump, that is the most obvious problem. If you are getting only 2+v at pin X2-F6 that is probably a problem but sort out the other problem first.
Click to expand...

That is correct. When I get home, I'm going cut and solder a new wire connecting X2-D4 to pin B on the fuel pump for continuity and then go from there. Then address the low voltage at X2-F6.
 
G
Make 100% sure you have a good ground when measuring voltage. When in doubt, run a wire from the negative terminal of the battery to use for ground.
 
Markm
You should have power on one post at all times and the other is comes from the ecm at key on
 

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Robinjo
UNFORGIVABLE said:
I'm not sure what happened to my post, But it the grey fuel pump power wire was broken in my harness and so was the ground to trigger the fuel pump relay. I soldered in new wires and the car fired right up.
Click to expand...
Nice, glad you got it worked out. You've now hit a huge milestone.

It's always a good move to post these 'solvings' to the forum so that future builders or people with similar issues get ideas.
 
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